Altran - Umts Overview Book

UMTS OVERVIEW

Contents, Glossary and Abbreviations

I

UMTS Overview July 2001

Contents

CONTENTS ............................................................................................................................................................... I

GLOSSARY .......................................................................................................................................................... VII

ABBREVIATIONS .................................................................................................................................................. X

CHAPTER 1: UMTS, THE DEFINITION OF A NEW ERA ............................................................................. 1

1.1 INTRODUCTION ................................................................................................................................................. 1

1.2 BACKGROUND AND STANDARDISATION ........................................................................................................... 1

1.2.1 Background in Europe ............................................................................................................................. 1

1.2.2 Background in Japan ............................................................................................................................... 3

1.2.3 Background in China ............................................................................................................................... 4

1.2.4 Creation of 3GPP .................................................................................................................................... 4

1.2.5 Creation of 3GPP2 .................................................................................................................................. 5

1.3 IMT-2000 AND UMTS ..................................................................................................................................... 6

1.3.1 IMT-2000 Process in ITU ........................................................................................................................ 6

1.3.2 UMTS ....................................................................................................................................................... 8

1.4 UMTS AS THE 3RD GENERATION SYSTEM ....................................................................................................... 11

1.4.1 Main Service Differences Between 2G and 3G ..................................................................................... 11

1.4.2 New Roles and Relationships for UMTS ............................................................................................... 12

1.4.3 Work Regulations ................................................................................................................................... 13

1.4.4 UMTS Services and Applications .......................................................................................................... 13

1.4.5 UMTS Advanced Concepts .................................................................................................................... 14

1.4.6 Network Operators’ Functions .............................................................................................................. 14

1.4.7 Technological Progress Impact ............................................................................................................. 15

CHAPTER 2: ARCHITECTURE OVERVIEW ................................................................................................ 16

2.1 GENERAL OVERVIEW OF THE SYSTEM ........................................................................................................... 16

2.2 USER EQUIPMENT (UE) .................................................................................................................................. 16

2.2.1 Schematic of the Receiver for UTRAN - Outdoor ................................................................................. 17

2.3 THE ACCESS NETWORK: UTRAN .................................................................................................................. 19

2.3.1 RNS Architecture ................................................................................................................................... 19

2.3.2 UTRAN Architecture .............................................................................................................................. 20

2.4 CORE NETWORK ............................................................................................................................................. 21

2.4.1 Serving Network ..................................................................................................................................... 21


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2.4.2 Home Network ........................................................................................................................................22

2.4.3 Transit Network ......................................................................................................................................22

2.4.4 Interfaces and Their Function ................................................................................................................22

2.5 MOBILITY ........................................................................................................................................................22

CHAPTER 3: CDMA TECHNIQUE ....................................................................................................................25

3.1 INTRODUCTION ................................................................................................................................................25

3.2 ACCESS METHODS FDMA, TDMA, CDMA, FDD VS. TDD .........................................................................25

3.2.1 Frequency Division Multiple Access (FDMA) .......................................................................................25

3.2.2 Time Division Multiple Access (TDMA) ................................................................................................26

3.2.3 Code Division Multiple Access (CDMA) ...............................................................................................27

3.2.4 FDD vs. TDD ..........................................................................................................................................28

3.3 INTRODUCTION TO SPREADING AND MODULATION ........................................................................................28

3.3.1 Orthogonal Codes ...................................................................................................................................30

3.3.2 RAKE Receiver .......................................................................................................................................33

3.3.3 Spread Spectrum Goals ..........................................................................................................................34

3.3.4 Code Properties ......................................................................................................................................35

3.4 SOFT AND HARD HANDOVER ..........................................................................................................................35

3.4.1 Handover ................................................................................................................................................35

3.4.2 Soft Handover .........................................................................................................................................36

3.4.3 Softer Handover ......................................................................................................................................36

3.5 POWER CONTROL ............................................................................................................................................36

3.5.1 Inner Loop Power Control - Uplink .......................................................................................................39

3.5.2 Outer Loop Power Control (SIR target adjustment) -Uplink ................................................................40

3.5.3 Open Loop Power Control - Uplink .......................................................................................................40

3.5.4 Inner Loop Power Control - Downlink ..................................................................................................41

3.5.5 Outer Loop Power Control - Downlink .................................................................................................41

3.5.6 Open Loop Power Control - Downlink ..................................................................................................41

CHAPTER 4: AIR INTERFACE ..........................................................................................................................42

4.1 RADIO TRANSMISSION AND RECEPTION ..........................................................................................................42

4.1.1 Frequency Band ......................................................................................................................................42

4.1.2 Channel Arrangement ............................................................................................................................42

4.1.3 Tx-Rx Frequency Separation ..................................................................................................................42

4.1.4 Terminal Service Classes .......................................................................................................................42

4.1.5 Receiver Requirements ...........................................................................................................................43

4.1.6 Diversity Characteristics ........................................................................................................................43

4.2 LOGICAL, PHYSICAL AND TRANSPORT CHANNELS .........................................................................................43

4.2.1 Transport Channels: ...............................................................................................................................44


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4.2.2 Physical Channels: ................................................................................................................................ 45

4.2.3 Mapping of Transport Channels to Physical Channels ........................................................................ 52

4.3 SPREADING, SCRAMBLING AND MODULATION .............................................................................................. 53

4.3.1 Uplink Spreading, Scrambling and Modulation ................................................................................... 53

4.3.2 Downlink Spreading, Scrambling and Modulation............................................................................... 56

4.4 TRANSPORT CHANNEL CODING AND MULTIPLEXING CHAIN ........................................................................ 57

4.4.1 Channel Coding ..................................................................................................................................... 58

4.4.2 Inner Inter-Frame Interleaving ............................................................................................................. 60

4.4.3 Rate Matching ........................................................................................................................................ 60

4.4.4 Transport-Channel Multiplexing ........................................................................................................... 61

4.4.5 Inner Intra-Frame Interleaving ............................................................................................................. 61

4.5 SERVICE MULTIPLEXING ................................................................................................................................ 61

4.6 TRAFFIC CASES (EXAMPLES).......................................................................................................................... 63

4.6.1 Continuous Transmission in Uplink with Variable Rate ...................................................................... 63

4.6.2 Discontinuous Transmission (DTx) in Downlink with Variable Rate (1) ............................................ 63

4.6.3 Discontinuous Transmission (DTx) in Downlink with Variable Rate (2) ............................................ 64

4.7 INITIAL CELL SEARCH .................................................................................................................................... 64

4.7.1 Step 1: Slot Synchronisation .................................................................................................................. 65

4.7.2 Step 2: Frame Synchronisation and Code Group Identification .......................................................... 65

4.7.3 Step 3: Scrambling Code Identification ................................................................................................ 66

4.7.4 Idle Mode Cell Search ........................................................................................................................... 66

4.7.5 Active Mode Cell Search ....................................................................................................................... 66

4.8 PACKET ACCESS ............................................................................................................................................. 67

4.8.1 Common Channel Packet Access .......................................................................................................... 67

4.8.2 Dedicated Channel Single Packet Transmission .................................................................................. 67

4.8.3 Dedicated Channel Multi-Packet Transmission ................................................................................... 68

CHAPTER 5: RADIO THEORY ......................................................................................................................... 69

5.1 INTRODUCTION ............................................................................................................................................... 69

5.1.1 Radio Waves and Modulations .............................................................................................................. 69

5.1.2 Access Methods ...................................................................................................................................... 71

5.2 RADIO TRANSMISSION PROPERTIES AND PROBLEMS ..................................................................................... 72

5.2.1 Needed vs. Available Capacity .............................................................................................................. 72

5.2.2 Path Loss ................................................................................................................................................ 72

5.2.3 Shadowing .............................................................................................................................................. 73

5.2.4 Multi-Path Propagation ........................................................................................................................ 74

5.2.5 Time Dispersion ..................................................................................................................................... 75

5.3 RADIO TRANSMISSION OPTIMISATIOIN TECHNIQUES ..................................................................................... 75

5.3.1 Access Methods: Capacity vs Interference ........................................................................................... 75


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5.3.2 Diversity ..................................................................................................................................................77

5.3.3 Error Detection and Correction .............................................................................................................78

CHAPTER 6: USER EQUIPMENT (UE) ............................................................................................................81

6.1 TERMINALS IN THE GENERAL UMTS SYSTEM ................................................................................................81

6.1.1 User Equipment Domain ........................................................................................................................82

6.2 APPLICATIONS OF THE UE ...............................................................................................................................83

6.3 MULTIMEDIA USER EQUIPMENT .....................................................................................................................84

6.4 UMTS SUBSCRIBER IDENTITY MODULE (USIM) ...........................................................................................86

6.5 TECHNOLOGY OF THE TERMINALS ..................................................................................................................88

CHAPTER 7: UMTS TERRESTRIAL RADIO ACCES NETWORK (UTRAN) ..........................................90

7.1 INTRODUCTION ................................................................................................................................................90

7.2 UTRAN MAIN ASPECTS .................................................................................................................................90

7.2.1 General Principles ..................................................................................................................................90

7.2.2 Capabilities .............................................................................................................................................90

7.2.3 UTRAN and GSM BSS (GSM Base Station Subsystem) ........................................................................91

7.3 UTRAN SYSTEM ARCHITECTURE ...................................................................................................................92

7.3.1 UMTS General System Architecture ......................................................................................................92

7.3.2 UTRAN Architecture ..............................................................................................................................92

7.4 UTRAN NODES ...............................................................................................................................................93

7.4.1 Node B .....................................................................................................................................................93

7.4.2 The Radio Network Controller (RNC) ...................................................................................................95

7.5 UTRAN INTERFACES ......................................................................................................................................95

7.5.1 General Principles for UTRAN Interfaces .............................................................................................95

7.5.2 Iu Interface ..............................................................................................................................................96

7.5.3 Iur Interface ............................................................................................................................................98

7.5.4 Iub Interface ......................................................................................................................................... 100

7.5.5 UTRAN Internal Bearers ..................................................................................................................... 102

7.6 UTRAN FUNCTIONS .................................................................................................................................... 103

7.6.1 System Access Control ......................................................................................................................... 103

7.6.2 Radio Channel Ciphering / Deciphering ............................................................................................ 104

7.6.3 Mobility ................................................................................................................................................ 104

7.6.4 Radio Resource Management and Control ......................................................................................... 107

7.7 IDENTIFIERS .................................................................................................................................................. 110

7.7.1 UTRAN identifiers ............................................................................................................................... 110

7.7.2 UE Identifiers ....................................................................................................................................... 111

7.8 UMTS QOS AND RAB ................................................................................................................................. 111

7.8.1 Quality of Service (QoS) ...................................................................................................................... 111


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7.8.2 Radio Access Bearers (RAB) ............................................................................................................... 113

CHAPTER 8: CORE NETWORK ..................................................................................................................... 114

8.1 INTRODUCTION ............................................................................................................................................. 114

8.2 GPRS, AN IMPORTANT STEPPING STONE TOWARDS A UMTS CORE NETWORK ......................................... 114

8.3 UPGRADING THE GSM CORE FOR GPRS ..................................................................................................... 116

8.3.1 New Nodes for Packet Data................................................................................................................. 116

8.3.2 Upgrades to Existing GSM Nodes ....................................................................................................... 117

8.4 MOVING TO UMTS IN THE GSM/GPRS CORE ............................................................................................ 117

8.4.1 Cell-Based Transport Network ............................................................................................................ 119

8.5 UMTS CORE NETWORK PHASE 1 (RELEASE 99) REQUIREMENTS ............................................................... 120

CHAPTER 9: HANDOVER (DOWNLINK CASE EXAMPLE) ................................................................... 122

9.1 POSITION 1 .................................................................................................................................................... 122

9.2 POSITION 2 .................................................................................................................................................... 122

9.3 POSITION 3 .................................................................................................................................................... 122

9.4 POSITION 4 .................................................................................................................................................... 122

9.5 POSITION 5 .................................................................................................................................................... 123

9.6 POSITION 6 .................................................................................................................................................... 123

9.7 POSITION 7 .................................................................................................................................................... 123

9.8 POSITION 8 .................................................................................................................................................... 123

9.9 POSITION 9 .................................................................................................................................................... 123

9.10 POSITION 10 ................................................................................................................................................ 124

CHAPTER 10: CELL PLANING ....................................................................................................................... 125

10.1 INTRODUCTION TO CELL PLANNING ........................................................................................................... 125

10.2 DIFFERENT CELL TYPES ............................................................................................................................. 125

10.3 STEPS IN THE CELL PLANNING PROCESS .................................................................................................... 127

10.3.1 System Requirements: ........................................................................................................................ 128

10.3.2 Define Radio Planning Guidelines: .................................................................................................. 128

10.3.3 Initial Cell Plan: ................................................................................................................................ 128

10.3.4 Surveys: .............................................................................................................................................. 128

10.3.5 Individual Site Design and Parameter Setting: ................................................................................ 129

10.3.6 Implementation: ................................................................................................................................. 129

10.3.7 Launch of Commercial Service: ........................................................................................................ 129

10.3.8 On-going Testing, Analyses and Optimisation: ................................................................................ 129

10.3.9 System Growth ................................................................................................................................... 130

10.4 DIFFERENCES WITH 2G TDMA SYSTEMS - DEPLOYMENTS ...................................................................... 130

10.4.1 Exploiting Existing Networks ............................................................................................................ 130

10.4.2 Multi Service ...................................................................................................................................... 130


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10.4.3 New Air Interface ............................................................................................................................... 130

10.5 CALCULATION OF COVERAGE AND CAPACITY ........................................................................................... 130

10.5.1 Needed Input Parameters .................................................................................................................. 131

10.5.2 Uplink Design .................................................................................................................................... 131

10.5.3 Downlink Design ............................................................................................................................... 132

10.5.4 Co-Siting With GSM Case ................................................................................................................. 132

CHAPTER 11: WORLD-WIDE CONSENSUS ON ADDITIONAL SPECTRUM FOR 3RD

GENERATION ..................................................................................................................................................... 133


VII


Glossary Active Set:Set of radio links simultaneously involved in a specific communication service between an MS and a UTRAN. Air Interface: The radio interface between a mobile communications handset and the base station. Bandwidth: The information capacity of a communications resource, usually measured in bits per second. Also see Narrowband, Wideband and Broadband. Broadband: A classification of the information capacity or bandwidth of a communication channel. Broadband is generally taken to mean a bandwidth higher than 2 Mbit/s. CDMA: Code Division Multiple Access. A multiple access technique used for CdmaOne and WCDMA air interfaces. Cell: The basic geographical unit of a cellular communications system. Service coverage of a given area is based on an interlocking network of cells, each with a radio base station (transmitter/receiver) at its centre. The size of each cell is determined by the terrain and the number of users. Geographical area served from one UTRAN Access Point. A cell is defined by a cell identity broadcast from the UTRAN Access Point. Chiprate: Chiprate is the bit rate of the code/codes used for spreading. This is for helping us distinguish between user data or control data which is expressed in bit rate. Coded Composite Transport Channel (CCTrCH): A data stream resulting from encoding and multiplexing of one or several transport channels. Drift RNS: The role an RNS can take with respect to a specific connection between an UE and UTRAN. An RNS that supports the Serving RNS with radio resources when the connection between the UTRAN and the UE need to use cell (s) controlled by this RNS is referred to as Drift RNS. ETSI: European Telecommunications Standards Institute. A body formed by the European Commission in 1988 to take over most of the standardisation work previously undertaken by CEPT. ETSI´s purpose is to define standards that will enable the European market for telecommunications to function as a single market. Fixed Wireless (or Fixed Cellular) Network: This apparent contradiction in terms signifies a cellular network that is set up to support fixed rather than mobile subscribers. Increasingly being used as a fast and economic way to roll out modern telephone services, since it avoids the need for major cable-laying. GPRS: GSM General Packet Radio Services. A data transmission technique that does not set up a continuous channel from a portable terminal for the transmission and reception of data, but transmits and receives data in packets. It makes very efficient use of available radio spectrum, and users may pay only for the volume of data sent and received. GSM: Global System for Mobile Communications. Originally defined as a pan-European standard for a digital cellular telephone network, to support cross-border roaming, GSM is now one of the world’s main digital wireless standards. Uses TDMA air interface. Can be implemented in 900 MHz, 1800 MHz or 1900 MHz frequency bands. IMT-2000: The term used by the International Telecommunications Union for the specification for the projected third-generation wireless services. Intelligent Network (IN): A capability in the public telecom network environment that allows new services such as Free-phone and tele-voting to be developed quickly and introduced on any scale, from a local trial to network-wide. Also implies a suitable network infrastructure. Internet: The name given to the world-wide collection of networks and gateways using the TCP/IP protocol, that functions as a single, virtual network. IP: Internet Protocol. (See also TCP/IP).


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ISDN: Integrated Services Digital Network. A digital public telecommunications network in which multiple services (voice, data, images and video) can be provided via standard terminal interfaces. ITU: International Telecommunications Union. Iu: The interconnection point (interface) between the RNS and the Core Network. It is also considered as a reference point. Iub: Interface between the RNC and the Node B. Iur: Interface between two RNSs. Logical Channel: A logical channel is a radio bearer, or part of it, dedicated for exclusive use of a specific communication process. Different types of logical channel are defined according to the type of information transferred on the radio interface. MexE: Mobile station Execution Environment Narrowband: A classification of the information capacity or bandwidth of a communication channel. Narrowband is generally taken to mean a bandwidth of 64 Kbit/s or lower. Node B: A logical node responsible for radio transmission/reception in one or more cells to/from the UE. Terminates the Iub interface towards the RNC. PCS: Personal Communications Service. A generic term for a mass-market mobile personal communications service, independent of the technology used to provide it. Physical Channel: In FDD mode, a physical channel is defined by code, frequency and, in the uplink, relative phase (I/Q). In TDD mode, code, frequency, and time-slot define a physical channel. Physical Channel Data Stream: In the uplink, a data stream that is transmitted on one physical channel. In the downlink, a data stream that is transmitted on one physical channel in each cell of the active set. PSTN: Public Switched Telephone Network. The ordinary, wired, analogue telephone network. Radio Access Bearer: The service that the access stratum provides to the non-access stratum for transfer of user data between MS and CN. Radio Access Network Application Part: Radio Network Signalling over the Iu. Radio Cell: The area served by a radio base station in a cellular or cordless communications system. This is where the term "cellular" came from. Cell sizes range from a few tens of meters to several kilometres. Radio Frame: A radio frame is a numbered time interval of 10ms duration used for data transmission on the radio physical channel. A radio frame is divided into 16 slots of 0.625 ms duration. The unit of data that is mapped to a radio frame (10ms time interval) may also be referred to as radio frame. Radio Link: A set of (radio) physical channels that link an MS to a UTRAN access point. Radio Link Addition: A [soft handover] procedure whereby a branch through a new [sector of a cell] is added in case some of the already existing branches were using [sectors] of the same cell. Radio Link Removal: A [soft handover] procedure whereby a branch through a new [sector of a cell] is removed in case some of the remaining existing branches use [sectors of] that cell. Radio Network Controller: This equipment in the RNS is in charge of controlling the use and the integrity of the radio resources. Radio Network Subsystem: Either a full network or only the access part of a UMTS network offering the allocation and the release of specific radio resources to establish means of connection in between an UE and the UTRAN. A Radio Network Subsystem is responsible for the resources and transmission/reception in a set of cells. Radio Network Subsystem Application Part: Radio Network Signalling over the Iur. Roaming: Ability of a cordless or mobile phone user to travel from location to location, with complete communications continuity. Supported by a cellular network of radio base stations. RLL/WLL: Radio in the Local Loop/Wireless Local Loop. The use of a radio access technology to link subscribers into the fixed public telecom network. The radio link replaces the traditional wired local loop. RRC Connection: A point-to-point bi-directional connection between RRC peer entities on the UE and the UTRAN sides, respectively. An UE has either zero or one RRC connection.


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Serving RNS: A role an RNS can take with respect to a specific connection between an UE and UTRAN. There is one Serving RNS for each UE that has a connection between a UE and the UTRAN. The serving RNS terminates the Iu for this UE. Signalling Connection: An assured-mode link between the user equipment and the core network to transfer higher layer information between peer entities in the non-access stratum. Signalling Link: Provides an assured-mode link layer to transfer the MS_UTRAN signalling messages as well as MS-Core Network signalling messages (using the signalling connection) TCP/IP: Transmission Control Protocol/Internet Protocol. The data protocol used in the Internet. TDMA: Time Division Multiple Access. A technique used for GSM, D-AMPS (IS-136) and PDC air interfaces. TIA: Telecommunications Industry Association. The US telecom standars body. Transport Channel:The channels that are offered by the physical layer to Layer 2 for data transport between peer L1 entities are denoted as Transport Channels. Different types of transport channels are defined by how and with which characteristics data is transferred on the physical layer, e.g. whether using dedicated or common physical channels are employed. Transport Format: A combination of encoding, interleaving, bit rate and mapping onto physical channels. Transport Format Indicator (TFI): A label for a specific Transport Format within a Transport Format Set. Transport Format Set: A set of Transports Formats. For example, a variable rate DCH has a Transport Format Set (one Transport Format for each rate), whereas a fixed rate DCH has a single Transport Format. UMTS: Universal Mobile Telecommunications System. The European third-generation system, under development, under the auspices of ETSI. UTRAN Access Point: The UTRAN-side end point of a radio link. A UTRAN access point is a cell. User Equipment: A mobile Equipment with one several UMTS Subscriber Identity Module(s). Wideband: A classification of the information capacity or bandwidth of a communication channel. Wideband is generally taken to mean a bandwidth between 64 Kbit/s and 2 Mbit/s. Wideband CDMA (WCDMA): The air interface technology selected by the major Japanese mobile communications operators, and in January 1998 by ETSI, for wideband wireless access to support third-generation services. This technology is optimised to allow very high-speed multimedia services such as full-motion video, Internet access and videoconferencing. World Wide Web (WWW): Name commonly applied to the global Internet for multimedia, graphics, sound, etc...


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Abbreviations ARQ Automatic Repeat Request AAL Application Adaptation Layer ATM Asynchronous Transfer Mode BCCH Broadcast Control Channel BER Bit Error Ratio BLER Block Error Ratio BS Base Station BSS Base Station System BPSK Binary Phase Shift Keying CA Capacity Allocation CAA Capacity Allocation Acknowledgement CBR Constant Bit Rate C- Control-CC Call Control CCCH Common Control Channel CCPCH Common Control Physical Channel CCTrCH Coded Composite Transport Channel CD Capacity De-allocation CDA Capacity De-allocation Acknowledgement CDMA Code Division Multiple Access CN Core Network CTDMA Code Time Division Multiple Access CRC Cyclic Redundancy Check DCA Dynamic Channel Allocation DCH Dedicated Channel DCCH Dedicated Control Channel DC-SAP Dedicated Connection Service Access Point DL Downlink DPCH Dedicated Physical Channel DPCCH Dedicated Physical Control Channel DPDCH Dedicated Physical Data Channel DRNS Drift RNS DRX Discontinuous Reception DTX Discontinuous Transmission DS-CDMA Direct-Sequence Code Division Multiple Access FACH Forward Access Channel FDD Frequency Division Duplex FDMA Frequency Division Multiple Access FEC Forward Error Correction


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FER Frame Error Ratio HCS Hierarchical Cellular Structures HO Handover GMSK Gaussian Minimum Shift Keying GSM Global System for Mobile Communication ITU International Telecommunication Union JD Joint Detection kbps kilo-bits per second L1 Layer 1 (physical layer) L2 Layer 2 (data link layer) L3 Layer 3 (network layer) LAC Link Access Control LLC Logical Link Layer MA Multiple Access MAC Medium Access Control MAHO Mobile Assisted Handover Mcps Mega Chip Per Second ME Mobile Equipment MM Mobility Management MO Mobile Originated MOHO Mobile Originated Handover MS Mobile Station MT Mobile Terminated NRT Non-Real Time ODMA Opportunity Driven Multiple Access OVSF Orthogonal Variable Spreading Factor (codes) PC Power Control PCH Paging Channel PDU Protocol Data Unit PHY Physical layer PhyCH Physical Channel QoS Quality of Service QPSK Quaternary Phase Shift Keying PG Processing Gain PRACH Physical Random Access Channel PUF Power Up Function RACH Random Access Channel RANAP Radio Access Network Application Part RF Radio Frequency RLC Radio Link Control RLCP Radio Link Control Protocol RNC Radio Network Controller RNS Radio Network Subsystem


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RNSAP Radio Network Subsystem Application Part RR Radio Resource RRC Radio Resource Control RRM Radio Resource Management RT Real Time RU Resource Unit RX Receive SAP Service Access Point SCH Synchronisation Channel SDCCH Stand-alone Dedicated Control Channel SDU Service Data Unit SF Spreading Factor SIR Signal-to-Interference Ratio SMS Short message Service SP Switching Point SRNS Serving RNS TCH Traffic Channel TDD Time Division Duplex TDMA ime Division Multiple Access TFI Transport Format Indicator TPC Transmit Power Control TX Transmit U- User-UE User Equipment UL Uplink UMTS Universal Mobile Telecommunications System USIM UMTS Subscriber Identity Module UTRA UMTS Terrestrial Radio Access UTRAN UMTS Terrestrial Radio Access Network VA Voice Activity VBR Variable Bit Rate

Chapter 1: UMTS, the Definition of a New Era

1



1.1 Introduction

In 1992 the International Telecommunication Union (ITU) defined in World Administrative

Radio Conference (WAPC) global frequency bands for Future Public Land Mobile

Telecommunications Systems (FPLMTS). FPLMTS is standardised by the

Telecommunications Standardisation Sector (ITU-T) and the Radio-communications Sector

(ITU-R), formerly known as the CCITT and the CCIR. These FPLMTS bands were identified

as 1885-2025 MHz and 1980- 2010 MHz which included a special band identified for satellite

communication of 2170-2200 MHz.

1.2 Background and Standardisation

1.2.1 Background in Europe

1.2.1.1 ETSI

The European Telecommunications Standards Institute (ETSI) is a non-profit organisation in

charge to determine and produce the telecommunications standards. It is an open forum made

of Administrations, network operators, manufacturers, service providers, and users. In total,

490 members from 34 countries are represented.

The members of ETSI are in charge to fix the work program standards in function of market

needs. ETSI produces voluntary standards; which are requested by those who subsequently

implement them, as the standards remain practical.

ETSIs work program is based upon, and is co-phased with, the activities of international

standardisation bodies, and mainly with ITU.

ETSI consists of a General Assembly, a Board, a Technical Organisation and a Secretariat.

The technical standards are produced and approved by the Technical Organisation. It


2


encompasses ETSI Projects (EPs), Technical Committees (TCs) and Special Committees.

More than 3500 experts, in over 200 groups, are at present working for ETSI.

The central Secretariat of ETSI is located in Sophia Antipolis, a high tech research park in the

south of France.

1.2.1.2 ITU

The ITU is an international organisation (United Nations) within which governments and the

private sector co-ordinate global telecom networks and services. The ITU has its headquarters

in Geneva, Switzerland.

Samuel Morse did the first usher in the communications era on 24 May 1844, by sending the

first public message over a telegraph line between Washington and Baltimore. Barely ten

years later, telegraphy had become available to the general public. However, at this period

telegraph lines did not cross national frontiers because each country used a different system

and what is more, each had its own telegraph code to preserve the secrecy of its military and

political telegraph messages. Therefore, before being retransmitted over the telegraph network

of a neighbouring country, messages had to be transcribed, translated and handed over the

frontiers.

It is not surprising then, that agreements were made between countries to interconnect their

national networks together. But for each link numerous agreements were required. As a

conclusion, 20 European States decided to work together on a framework agreement, deciding

on common rules to standardise equipment to guarantee generalised interconnection. They

adopted a set of uniform operating instructions and came along to common international tariff

and accounting rules, which by the past were different from one country to another.

The first International Telegraph Convention was signed by the 20 participating countries on

the 17 May of 1865 after two and a half months of negotiations, and the International

Telegraph Union was born.

Since that time, the telecommunications progression has continued and advances have been

made.

With the invention in 1896 of wireless it was decided to convene on a preliminary radio

conference. In 1903 the conference would be held to study the question of international

regulations for radiotelegraph communications.


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In 1920 sound was broadcasted at the studios of the Marconi Company. In 1927, the Union

allocated frequency bands to the various radio services existing at the time: fixed, maritime

and aeronautical mobile, broadcasting, amateur and experimental.

At the 1932 Madrid Conference the name was changed to the International

Telecommunication Union to reaffirm the whole scope of its responsibilities: wire, radio,

optical system or other electromagnetic system communications.

In 1959, the ITU set up a Study Group for the study of space radio communication.

In the changing world of telecommunications today new players constantly appear on the

international scene.

In the area of telecommunications, new trends are emerging: globalisation, deregulation,

restructuring, value added network services, convergence (of services as well as

technologies), intelligent networks and regional arrangements. Telecommunications have

become a key ingredient in many non-telecommunication services such as banking, tourism,

transportation and information services of various types.

The traditional role of telecommunications is being transformed every day with new service

dimensions.

1.2.2 Background in Japan

In Japan, the development of internationalisation, the integration of telecommunications and

broadcasting, and the promotion of businesses using radio waves required the need for an

organisation. In response to this need, on May 15, 1995, the Association of Radio Industries

and Businesses (ARIB) was established as a public service corporation with the support of the

Minister of Posts and Telecommunications.

This organisation would proclaim the research & development of new radio systems and the

international standardisation of technical standards in the fields of telecommunications and

broadcasting.


4


1.2.3 Background in China

China Wireless Telecommunication Standard is the standard development organisation

responsible for wireless standardisation in China as approved by the Ministry of Information

Industry.

1.2.4 Creation of 3GPP

In November 1998, the standardisation organisations (ARIB, ETSI, T1, TTA and TTC)

involved in the creation of the 3rd Generation Partnership Project known as 3GPP. They all

agreed to co-operate for the production of technical specifications for a 3rd Generation

Mobile System based on the evolved GSM core networks and the radio access technologies

that they support (both FDD and TDD). In 1999 China Wireless Telecommunication Standard

(CWTS) joined the project.

At a meeting in July 1999, the Third Generation Partnership Project agreed to make standards

for the FDD and TDD modes following the recommendations from ITU IMT-2000.

According to the agreement, 3GPP will cover the technical issues related to the development

of FDD and TDD modes. The work will also include the inter-working between the evolved

ANSI-41 and GSM MAP platforms.

For a global harmonisation, 3GPP changed the chip to rate to 3.84 Mcps and adopted a new

downlink pilot structure. The complete 3G standards will enable global roaming and seamless

provisional.

The 3GPP have established a schedule of annual releases for the development of the

standards. Release 1999 will be completed by 31 December 1999 and will be first deployed in

early 2001 in Japan. Release 2000 will include Internet Protocol based networks and will be

rolled out in 2002. Further enhancements will be included in later releases.

For more information about 3GPP see: www.3GPP.org.

The six standards development organisations are:

ARIB, www.arib.or.jp.

CWTS.

ETSI, www.etsi.org.


5


T1, www.t1.org.

TTA, www.tta.or.kr.

TTC, www.ttc.or.jp.

The tree market representations partners are:

The GSM Association represents 347 members which is comprised of GSM Network

Operators and Regulators with more than 165 million GSM subscribers in 133 countries. See

www.gsmworld.com.

The Global Mobile Suppliers Association, GSA, has a cross industry representation world-

wide of GSM infrastructure, terminals, customer care and billing suppliers. See

www.GSAssociation.org.

UMTS Forum represents 182 members from over 30 countries and content representing

operators, regulators, manufacturers, IT providers. See www.UMTS-Forum.org.

1.2.5 Creation of 3GPP2

Members of the ANSI board were concerned that the ETSI proposal was too limiting, and as a

result, established a 3G ad hoc committee to examine how all standards development

organisations (SDOs) could be involved. In June 1999, a meeting was held between this ANSI

ad hoc group and a delegation from ETSI in Seattle to further discuss how the 3GPP could

accommodate all industry participants.

3GPP 2 is an effort spearheaded by the International Committee of the American National

Standards Institute's (ANSI) board of director to establish a 3G Partnership Project (3GPP) for

evolved ANSI/TIA/EIA-41, "Cellular Radio-telecommunication Intersystem Operations"

networks and related radio transmission technologies (RTTs).

This co-operation may result in either complete specifications or in agreed technical elements,

which the participating SDOs may submit to the ITU through their normal national or

regional processes.

The proposed 3G partnership is structured into two projects:

3GPP 1: Global specifications for GSM/MAP network evolution to 3G and the UTRA RTT.


6


3GPP 2: Global specifications for ANSI/TIA/EIA-41 network evolution to 3G and global

specifications for the RTTs supported by ANSI/TIA/EIA-41.

1.3 IMT-2000 and UMTS

1.3.1 IMT-2000 Process in ITU

In 1986, the ITU began its studies on International Mobile Telecommunications-2000 (IMT-

2000), when the availability of hand-held cellular phones offered the potential for global,

rather than National/Regional, land mobile systems.

IMT-2000 is an initiative of the ITU.

It will provide wireless access to the global telecommunication infrastructure through both

satellite and terrestrial systems, serving fixed and mobile users in public and private networks.

With close to 5 million new mobile users a month, million a month in Japan alone, wireless

access will likely blast fixed access to global telecommunications very early in the 21st

century.

Future public land mobile telecommunication systems (FPLMTS) are aimed at providing

global wireless access around the year 2000, based primarily on the 2 GHz spectrum

identified at the 1992 World Administrative Radio Conference (WARC-92). Standardisation

of FPLMTS is one of the strategic priorities of the ITU.

The acronym FPLMTS where changed to IMT-2000.

The International Mobile Telecommunication vision encompasses complementary satellite

and terrestrial components. Satellite systems have limited capacity due to power and radio

spectrum. Terrestrial macro, micro and pico cells complement global satellite coverage and

provide the frequency reuse necessary to serve a global market estimated to be of the order of

one billion wireless access users early in the 21st century.

IMT-2000 represents the satellite and terrestrial portion of IMT that will be available around

the year 2000 primarily based on the spectrum identified at 2 GHz.


7


The satellite component of IMT-2000, together with earlier global satellite systems in other

bands, will likely provide the first telephone in many rural villages. The terrestrial

infrastructure will then follow as demand increases.

There are two major areas of technological innovation that may impact on future wireless

systems: the first is multimedia, the second is software radio technology. What this really

means is that more and more is being done by software rather than by hardware.

The impact of microprocessors and chip will allow greatly increased flexibility in radio

equipment which is going to have a dramatic effect on what should, and what should not, be

standardised. In the past, radio standards were developed to a certain level of detail based on

channel, modulation and coding structures over the radio path because ¡t was difficult to build

flexible radios.

One of the key benefits of IMT-2000, as a true third generation system, will be its ability to

deal efficiently with audio-visual multimedia communications In the future the users

application will control how the negotiated radio bearer is used, which will require a very

different radio and control infrastructure.

IMT-2000 covers a very wide range of radio operating environments, all the way from the

satellite to indoor pico cells. An adaptive radio interface is envisaged for IMT-2000 to

optimise performance in these widely differing propagation conditions. This adaptation will

be controlled by software using digital signal processing technology.

Multi-mode and multiband mobile terminals will be a common mechanism to link IMT-2000

to earlier systems. The ITU standardisation work on IMT-2000 encourages convergence of

the many diverse satellite and terrestrial mobile systems towards the ITU vision for third

generation global mobile communications, i.e. IMT-2000. However, with the rapid changes in

technology, particularly in the digital processing area, new standards must not be restrictive,

but should enable future telecommunication enhancements. In other words the standardisation

must be in such away that it can be efficiently controlled by future applications that we do not

even dream about today.


8


1.3.2 UMTS

1.3.2.1 ETSIs Projects on GSM and UMTS

The task of SMG, Special Mobile Group, is to develop and maintain the specifications of the

digital cellular telecommunications system operating in the 900 MHz band known as GSM

900 and of its variation in the 1800 MHz band, known as DCS 1800.

Moreover it is responsible for maintaining the integrity of the GSM platform by close co-

operation with ANSI T1P1, who are responsible for the 1900 MHz version, known as PCS

1900.

SMG is also responsible for studying, and defining all aspects of third generation mobile

systems based on the concept of Universal Mobile Telecommunications System (UMTS), in

co-operation with studies by the International Telecommunication Union (ITU) regarding a

global system known as the International Mobile Telecommunications 2000 System (IMT-

2000).

UMTS Terrestrial Radio Access (UTRA) is the ETSI candidate for IMT-2000 Radio

Transmission Technology (RTT).

SMG maintains close-working relations with the UMTS FORUM based on the co-operation

agreement between ETSI and the FORUM.

The scope of the work is focused to the GSM family. It includes the definition of the GSM

services offered and the selection and specification of the most efficient radio techniques and

speech coding algorithms.

SMG is also responsible for the elaboration of the GSM network architecture, signalling-

protocols and conditions of interworking with other networks. In addition SMG is charged

with the application of the Telecommunications Management Network (TMN) concept to the

GSM network entities regarding operation and maintenance.

The goal for the future work in SMG2 is to provide the standard for the radio access network

part of UMTS. In addition, to this goal SMG2 is to provide UTRA as a candidate for IMT-

2000 to ITU.

For the work towards the UMTS standard it proposed that this work should consist of the

following, events and phases:


9


Finalise the SMG2 proposal of the radio access part of IMT-2000 and present this

(submission from SMG to ITU June 30, 1998).

A first phase is to elaborate technical descriptions and evaluate performance of the final

solutions of UTRA. This phase is concluded with a detailed description of UTRA including

the mobile station. This includes all radio protocols terminated in UTRA, the UTRA internal

protocols and the Iu interface as well as descriptions of the functionality's required of the

network nodes and in terminal.

A second phase that could be initiated during phase 1 would be to write the actual

specifications/standards based on the material elaborated in the first phase. It should he the

goal to freeze the specifications/standard in December 1999.

The third phase is the iterative correction phase, where the specification/standard is corrected

based on the experience gained with the standard during development and implementation of

UMTS. This phase in principle never ends, but should considered done in 2001. The fourth

part would further development of UMTS towards the UMTS phase 2 to be introduced 2005.

Figure 1.1. Spectrum Allocation UMTS/IMT-2000.

Spectrum consists of one paired band (1920-1980 MHz + 2110-2170 MHz) and one unpaired

band (1910-1920 MHz + 2010-2025 MHz). Same spectrum allocation in Europe and Japan.

ETSI decision on UTRA in January 1998:

-WCDMA to be used in the paired band

-TD/CDMA to be used in the unpaired band

Sat.IMT-2000

MSSS-PCN(UL)

MSSS-PCN(UL)

MSSS-PCN(DL)

IMT-2000

IMT-2000

UMTS FDD

220021502100205020001950190018501800

IMT-2000Sat.

IMT-2000

IMT-2000MSS

S-PCN(UL)

TDD

PHS

UMTS FDDMSS

S-PCN(UL)

TDD

DECTTDD

GSM 1800(DL)

PCS (DL)MSS

S-PCN(DL)

PCSUn.Lic.

MHz

PCS (UL)USA

Europe

Japan

ITU


10


It is also stated that it should fit into 2*5 MHz spectrum allocations and that the two modes

FDD/TDD should have harmonised parameters.

UTRA FDD UTRA TDD

Multiple-Access scheme W-CDMA W-TDMA/CDMA

Duplex scheme FDD TDD

Chip Rate 3.84 Mcps (7.68 Mcps, 15.36 Mcps)

Carrier spacing (3.84 Mcps) 4.2-5 MHz (200 kHz carrier raster)

Frame length 10 ms

Inter-BS synchronisation Not required Required

Max. Spreading factor 256 16 Table 1.1. UTRA Basic Parameters

1.3.2.2 UMTS Harmonisation Phase

UMTS Phase 1

- GSM GPRS Release 99 with UMTS

UMTS Phase 2

- Higher bitrates (2 Mbit/s)

UMTS Phase 3

-?

1.3.2.3 UMTS Releases

December 1999: Standardisation freezes. First operator licences for UMTS. Release 99

completed by 31 December.

2000 –2001: Vendors development of network elements. Iterative experimental

process that might effect the standards. First launch of UMTS in Japan

2001 based on Release 99.

January 2002: UMTS in Europe. Release 2000 including Internet Protocol based

networks.

2005: Availability of all core bands for UMTS.


11


2008-2010: Additional spectrum for terrestrial and satellite use.

To meet the need of higher bitrates and packet data for the user UMTS will include other

enhancements in the network. In order to reach higher bitrates High Speed Circuit Switched

Data, HSCSD will let the users use more than one timeslot in the TDMA air interface. GSM

Packet Radio Switching will add the ability to send and receive packet data. It will also be the

backbone in the UMTS/GSM network. EDGE will be a complement to UMTS that might give

the operators without UMTS frequencies the possibility to present high bitrates for the

customer.

Figure 1.2. Bit Rate and Coverage

1.4 UMTS as the 3rd Generation System

1.4.1 Main Service Differences Between 2G and 3G

Three main criteria characterise the services in 2G systems :

• A variety standardised services are provided by 2G network operators.

• The system restricts Roaming where provided.

• Designed primarily for speech, 2G mobile networks are usually restricted to relatively low

bit rate services.

GSMHSCSD, GPRS

10 kbps

144 kbps

384 kbps

2 Mbps

EDGE

UMTS

Wide area/High mobilityFixed/Low mobility

User bit rate


12


In contrast, the following main features characterise 3G systems:

Under the conditions of a still growing mass market, 3G system shall meet the individual

communication requirements of a customer with his personalised service profile and user

interface.

Instead of individual services the tools for service creation will be standardised.

Access to and invocation of the users' own personalised services should be possible regardless

of the operating environment and access system, thus supporting intersystem roaming.

3G system can offer spectrum efficient access to multimedia services of higher, flexible

bandwidth to mobile users, in addition to services already offered within 2G system.

The user of today expects a variety of services to be offered by various providers and for these

services to be flexible enough to meet his individual demands.

In pre-3G mobile systems like GSM but also in ISDN, the user has already a broad choice of

services, in particular supplementary services. This variety of services has led to complex

instructions on how to use these services. Ordinary users will not accept an increase in

complexity of service handling. Instead they will prefer a simpler 'personal assistant type'

man-machine interface.

1.4.2 New Roles and Relationships for UMTS

Traditionally, in most models, the following actors play a role:

• Network Operator

• Service Provider

• Subscriber

• User.

However, a new business environment such as Value Added Service Provider, Content

Providers, Service Brokers and others, may create new categories. Between the roles various

relationships can appear. These will be used to identify interfaces that may require

standardisation and make relations more clear.


13


While maintaining a single identity, a user may subscribe to services at different service

providers. In addition, services offered by a provider may be offered to more than one

network.

In consequence, definitions of the home "network" or visited "network" used by second

generation’s system are no longer valid. The term "home environment", is proposed as a

replacement.

1.4.3 Work Regulations

In recent years, we have been seeing the telecommunication services deregulation. Today

service definition is not a matter for regulators, except for emergency services.

Commercial network operators/service providers may agree on some items such as a

minimum set of services and the respective specifications, but the decision is left to the

market demand.

As a consequence, IMT-2000 is expected to exist in various forms and aspects.

In the area of licensing, the position of regulators is also changing, with a tendency to giving

licenses for frequency use rather than to complete systems. As a result it increases the

complexity of interworking or interoperation of networks for global roaming.

1.4.4 UMTS Services and Applications

3G service capabilities for these services should take account of their discontinuous and

asymmetric nature in order to make efficient use of network resources. Basic services

provided in 3G networks are audio, video, facsimile transfer, data communication, Internet

services, e-mail/voice mail, paging, messaging, and combinations of these i.e. multimedia.

They can be divided in several classes.

1.4.4.1 UMTS Service Classes

1.4.4.1.1 Conversational Class

3G must provide the capabilities for high quality speech conversation.


14


1.4.4.1.2 Streaming Class

It is assumed that video communications will become a mass service after ordinary telephony.

1.4.4.1.3 Multimedia Class

3G systems will support multimedia services and provide the necessary service capabilities.

1.4.5 UMTS Advanced Concepts

1.4.5.1 Service Portability

Roaming between different 3G environments shall he possible without limiting the user in his

personal service set and accustomed user-interface.

1.4.5.2 VHE Concept

Virtual home environment (VHE) is a system concept for service portability in the Third

Generation across network borders. In this concept, the serving network emulates for a

particular user the behaviour of his home environment.

1.4.5.3 Relationship Between Mobile and Fixed Networks

Any future system should be designed with the concept of a new type of network. Future

network operators and service providers will have to offer both wired and wireless access for

terminals.

Mobile Fixed Convergence, MFC, is a technological trend in telecommunications. in it

distinction between fixed and mobile networks is continuously blurring through increased

singularities of network functions in both network types.

1.4.6 Network Operators’ Functions

In GSM networks, operators agreed on a set of services to be provided by each operator. This

simplifies the service management considerably but should no longer be sufficient to satisfy

user demand.


15


Service providers may request from the network operator that it enable roaming in other

environments for all or some of his customers. Third generation systems must provide the

necessary tools.

It is proposed that in future the networks should only provide service capabilities, which may

differ slightly or fundamentally between different networks (e.g. cordless, cellular, satellite

networks). These service capabilities are used by other parties to compose services for the

market.

1.4.7 Technological Progress Impact

Latest achievements in modern technologies as information and entertainment technologies,

transparency between fixed and mobile network concepts, multimedia presentation, transfer

of application support software packages (e.g. Java applets), high-capacity chips and

memories, has to be taken into account in the design of any third generation mobile system.

The use of Internet service is already today very common and well accepted by the user. The

3G system should cope with Internet and Intranet services, putting high demands on

bandwidth requirements.

3G systems capabilities need to be built upon standardisation of the following services:

• Definition for flexible service.

• Personal mobility in mobile and fixed networks.

• Support for multi-system terminals.

• Support of multi-mode operation

• Capability for international roaming and inter network roaming

• Flexible charging, including pre-payment and electronic purse systems

• Comprehensive real time charging information to the user.

• Integrated mailbox-service for voice, fax, text and other formats (in mobile and fixed

networks, accessible via both networks).

• Personal Assistant and intelligent agent suppor.

Chapter 2: Architecture Overview

16



2.1 General Overview of the System

Figure 2.1. UMTS Architecture

2.2 User Equipment (UE)

The UMTS behaviour will be much faster than the GSM one. The progressive change from

one system to the other will give us a whole new world of possibilities in terminals for the

user, with all the new technology that it involves.

We have different kinds of equipment, with different technologies as well. We will speak

about the terminal as the UE (user equipment). The idea is that this terminal will be

compatible with the old system, such GSM, and will be able to connect to both networks,

UMTS-GSM. In addition, the user equipment may include a removable smart card that may

be used in every UE. In this card we the user will have all the data and the private passwords.

The terminal is sub-divided into the Mobile Equipment (ME) and the UMTS Subscriber

Identity Module (USIM).

UMTS GSM

Core Network, CN

IWNInter Working

Unit

IWNInter Working

Unit

RNS 2Radio Network

SubsystemRNS 2Iur

Iu Iu

Terminal Terminal

Uu

GSM CN HLR

MSC GMSC MSC

BSSBase StationSubsystem

BSS 2

A A

MSMS

Um


17


Rake Channel decoding

Searcher

Power control

Inputsamples

Decoded bits

PowerControlrequest

The terminal of the user develops the radio connection with different software capabilities.

Furthermore, the ME can be divided into several parts. We have the MT (Mobile

Termination), that performs the transmission and some related capabilities, and we also have

the TE (Terminal Equipment), the part that contains the end-to-end applications. The

references that can be found in the specifications are not clear in this point, leaving the design

to the several providers.

We have the identification properties inside of the USIM, based on several kinds of data and

procedures that will identify the user with no error. The electronic technology of the VLSI

gives us a very high power of integration so that the smart cards can have a lot of capabilities

of identification. The smart card will identify a user in such a way that it does not matter

which kind of ME he is using.

Inside the UMTS terminals Rake reception in used to generate soft decisions that are fed into

the channel decoder. The channel decoding also develops jobs of setting the target for the

power control, as well as the obvious functions of decoding the channels. If the power control

is bad implemented, the capacity of the network will decrease, as it will be seen in some

following chapters.

2.2.1 Schematic of the Receiver for UTRAN - Outdoor

Figure 2.2. Receiver Method


18


2.2.1.1 Rake Receiver:

When the data acquisition has been already made, the RAKE receiver will use the several re-

echoed signals that arrive to the antenna of the UE to improve the final signal quality. This

can be made because of the properties of the codes used in the system, because they are

orthogonal. We can de-spread the signal whether it is received delayed from a initial one or

not. Once we have the several echoes de-spread, we can combine the signals obtained through

different ways to increase the final SNR, the final quality at the end. We will add the signals

coherently. We can find fast fading in some signals, but this fading is independent from one

signal to the other, so combining correctly the signals, the final SNR will be increased. This

process is known as micro-diversity.

We can also find macro-diversity in the SOHO (soft handover), and the rake way to avoid the

problems in this case is basically the same. Now we have just to consider that the signals

come from different Node B, not from several reflections of the same antenna.

2.2.1.2 Searcher:

Sometimes we want to know the offset and the magnitude of the echoes and the power of the

signals coming from different base stations. This can be made with the scrambling codes and

the primary and secondary synchronisation channels.

Although this will be seen much deeper in following chapters, we can say the PSCH (Primary

Synchronisation Channels) are used to identify the power of the signals coming from different

near base stations, in the cell search process. We can identify the one that will be the server

Node B with this channel. The SSCH (Secondary Synchronisation Channel) allows us to

know the specific Node B and the downlink scrambling code group used by this station. Once

we know the scrambling code, the UE, through the searcher, can identify different echoes

from the scrambled pilot symbol. The echo profile is highly correlated from one power

control period to the next. We can use this characteristic to decrease the complexity of the

design of the UE.

2.2.1.3 Power Control:

The interface in the downlink is reduced minimising the transmission power at the base

station for a particular user, in such a way that the characteristics of the link performance


19


(throughput and error rate) are fulfilled. The UE will ask the base station to increase or to

decrease the transmission power every power control period (0.625 ms), trying in every

moment to keep the SIR as close as possible to a reference value. This SIR target is re-

evaluated every 10 ms depending on the status of the channel that is being decoded.

2.2.1.4 Channel Decoding:

As well as supporting a more powerful version of the convolutional channel decoding used in

GSM, UMTS terminals are likely to employ high performance turbo decoders.

2.3 The Access Network: UTRAN

By Access Network it is known the several physical entities that control the resources of the

access network, and gives the user the chance to access to the Core Network.

2.3.1 RNS Architecture

The Radio Network Subsystem basically is made of the RNC and other objects that at the

moment are called Node B. This Node B has the same function as the Base Station in GSM

systems. We have several interfaces, but here we can introduce the Iub, between the RNC and

the Node B.

Figure 2.3. RNS Architecture


20


2.3.1.1 Radio Network Controller, RNC

This part is the responsible of the handover decisions that need signalling to the UE. The

RNC comprises a combining/splitting function to support macro diversity between different

Node B. This part of the UMTS system will need much more intelligence than its partner in

the GSM system. These extra capabilities will increase the speed of the system, and therefore,

the yield.

2.3.1.2 Node B

The Node B will also be more intelligent than the Base Station in GSM. It will develop

functions of combining/splitting to allow macro diversity. The communication among several

Node B will allow the terminal to change from one cell to an adjacent one without losing

connection in the process.

2.3.2 UTRAN Architecture

At the end, the UTRAN is made of an amount of several Radio Network Subsystems that

represent an interface between the UE and the Core Network. For these functions, we have

several interfaces among the different parts that compose the Access Network that allows the

system to work properly.

Figure 2.4. UTRAN Architecture

It is a hierarchical structure, so every RNS will have a certain group of cells to serve, as it can

be seen in the picture.

We can see two different RNS very easily. First, we have the Serving RNS, which is the one

that gives the service at a certain moment. If it is needed, the Drift RNSs can help the Serving


21


RNS to give radio resources. The role of an RNS (Serving or Drift) is on a per connection

basis between a UE and the UTRAN.

Figure 2.5. Serving and Drift RNS

2.4 Core Network

We must have a fixed network in this system to provide support for the different capabilities

and features that we will find. The system cannot be all-wireless. With the Core Network

(CN), we will support the several functionality of the system, as for example the management

of the location of the user, or to provide a mechanism for transferring the signal (switching

and transmission).

The characteristics of the CN should allow it to handle circuit switched data ≤ 64 kbits/s,

packet data ≤ Mbits/s. To have the strictest control of several service parameters (maximum

delay or bandwidth). To support the Virtual Home Environment VHE, that makes the user

think that he is always using the same interface, always "at home".

We can see different parts in the Core. We can find the Serving Network, The Home Network

and the Transit Network. Probably, in later versions of the specification than the release '99 it

will be possible to find different versions and characteristics of the division.

2.4.1 Serving Network

This part of the core is the responsible of giving connection between the access network (to

which the user is connected) and the core itself. The local functions of the CN are represented


22


by this section. It is also responsible for the routing calls and transport user data/information

from source to destination.

2.4.2 Home Network

This part of the network represents all the functions that are related to a fixed location,

regardless of the place that the user made the connection to the network.

The USIM is related by subscription to the home network. The home network therefore

contains at least permanently user specific data and is responsible for management of

subscription information.

2.4.3 Transit Network

This part of the CN is located between the serving network (home network), and the remote

party.

2.4.4 Interfaces and Their Function

The Inter Working Function (IWF) has the role of interconnecting the Access Network to the

Core Networks, mainly through the Iu interface. This IWF is a logical unit (and a virtual one)

that will allow the CN to work with different protocols, due to the number of vendors that will

work on this technology.

2.5 Mobility

Logically, we can see two domains in the Core. We can find a IP domain and a PSTN/ISDN

domain. It shall be possible to connect the UTRAN either to both these CN or to one of the

CN domains.

It shall be possible to interconnect the GSM network and the UMTS one, from the point of

view of roaming and handover. At the beginning of the deployment, the coverage of the

UMTS network won't be absolute at all, and it will be necessary the compatibility between the

two networks. This implies that International Mobile Subscriber Identity, IMSI, shall be used

as the common user identity in the two CN. Common MAP signalling will be applied to both


23


GSM and UMTS. The GSM MAP mobile service operations shall be evolved and re-used as

fast as possible.

The UTRAN will store all the capabilities of the radio connection and all the radio network

parameters.

We have two service domains the Circuit Switched service domain (PSTN/ISDN) and the

Packet Switched service domain (IP). We have one service state machine for each service

domain. A terminal that is supporting both CS and PS services, has a CS service state

machine and a PS service state machine. They work independently to each other, although

associated to the same terminal (or UE). The UE-CN signalling aims to keep the peer entities

synchronised.

The UTRAN will try to offer a unified set of radio bearers, in such a way that they will bi able

to be used for bursty packet traffic and for traditional telephony traffic. The radio resource

handling is UTRAN internal functionality and the CN does not define the type of radio

resource allocated.

Once we decide to connect the UE, an initial connection is already set up, in such a way that

the radio resource has two modes, Connected and Idle mode. The UE will be identified by the

different modes. In Idle mode the UE is identified by a CN associated identity. In Connected

mode the UE is assigned a Radio Network Temporary Identity to be used as UE identity on

common transport channels. When we are transmitting via a dedicated channel, the UE uses

an inherent addressing (code a frequency), provided by these transport channels.

We can see four areas for different concepts, about the mobility functionality. Location Areas

(related to CS services) and Routing Areas (related to PS services) are used in the Core

Network. In the UTRAN the UTRAN Registration Areas and Cell Areas will be used.

Location Area for CS services: The CN manages one Location Area. This means that the

terminal (UE) is registered in the CN node responsible for handling this specific location area.

The 3G_MSC/VLR for paging the terminal use LA.

Routing Area for PS services: They are managed by the CN. In parallel, this means that the

UE is registered in the CN node responsible for handling this specific routing area. The

3G_SGSN for paging the terminal use RA.


24


Registration Areas and Cell Areas in URAN are only visible in the Access Network and

used when the UE is in connected mode. UTRAN internal areas are used when the terminal is

in connected mode. These areas are used at e.g. UTRAN initiated paging. The UTRAN

internal area structure should not be visible from outside the UTRAN, because the internal

area updating is a radio network procedure. In connected mode, the UE position is known on

cell level or on UTRAN Registration Area (URA) level.

For the relation between LA and RA it shall be possible for the operator to have a LA and a

RA equal (same cell) or a RA as part of a LA, or a LA as a part of RA, and LA and RA

independently. A more clear specification shall be defined in this point if an area consists of

both UMTS cells and GSM cells.

An CS-IDLE terminal will initiate Location Update towards the CN when crossing LA

border. In Idle mode it is the broadcasted system information, e. g. information about the

present LA and RA, that determines when the UE initiates a location registration procedure

towards the CN. A PS-IDLE terminal will initiate Routing Area update towards the CN when

crossing RA border.

When the UE is connected, the terminal receives the system information on the established

connection. A UE in CS-IDLE will initiate Location Area update towards the CN when

receiving information about a new LA, in connected mode. A UE in PS-IDLE will initiate

Routing Area update towards the CN when receiving information about new RA in connected

mode. The UE in CS-CONNECTED mode will not initiate Location Area update and a UE in

PS-CONNECTED mode will not initiate Routing Area update towards CN.

If we use separately PS and CS mobility mechanisms within the UE and within the CN we

may not obtain non-optimal usage of the radio resource. The use of combined updated may be

used to avoid this. It should be possible to use combined mechanisms for location

management purposes as well as for attach/detach status purposes. UMTS Phase 1 R99

terminals should support the use of both combined and separate mechanisms.

The radio access network will not co-ordinate mobility management procedures that are

logically between the CN and the UE, as it is seen in the UMTS specifications R99. This

includes several capabilities, as location management, authentication, temporary identity

management and equipment identity check.

Chapter 3: CDMA Technique

25



3.1 Introduction

CDMA (Code Division Multiple Access), is an access system based on spread spectrum

communication in which multiple users share the same frequency band. This part contains the

CDMA concepts.

3.2 Access Methods FDMA, TDMA, CDMA, FDD vs. TDD

3.2.1 Frequency Division Multiple Access (FDMA)

In FDMA system, all the stations use a diffent band, within the available range of frequency,

so in this access technique each user has a continuous access in a given frequency band. It´s

no necesary a co-ordination or synchronisation among stations and each station doesn´t

interfere in the other bands. It´s not possible a station transmits in a bandwidth used by

stations are idle, this can be a problem when the load is high and more resources are needed.

Also, FDMA is not a flexible system because of adding a new user requires some

modifications in the equipment.

Figure 3.1. FDMA

Advantages: FDMA uses a symple technique that has been proved.

Code

Time

Frequency


26


Disadvantages: Reconfiguration of the system in case of capacity variation is difficult, due to

flexibility.

3.2.2 Time Division Multiple Access (TDMA)

In TDMA the resource is the time which is divided into slots. Each station uses a pre-assigned

slot. The station is allowed to transmit freely into its assigned slot, and the entire system

resources are devoted to the station. Slots are repeated periodically in a cycle called frame. A

station could be assigned to one or more time slots during a cycle. Each station knows when

trasmit because all are synchronised.

Figure 3.2.. TDMA

The most important disvantage of TDMA is the fixed time slot allocation, whether or not it

has data to transmit. For applications with bursty transmission requirements a fixed time

allocation could be a bad use of the resources.

Advantages: High transmission throughput for a large number of stations. A single station

occupies all of channel bandwidth at each instant. Digital processing leads to operational

simplicity. It´s no necessary to control the transmitting power of the users. The tuning is

easier because all stations transmit and receive on the same frequency.

Disadvantages: TDMA need synchronisation. A high throughput is needed to dimension the

station transmits. A better channel and hence better throughput can compensate a big cost of

the equipments.

Code

Time

Frequency


27


3.2.3 Code Division Multiple Access (CDMA)

As we have show neither FDMA nor TDMA allow any time overlap of the stations

transmissions. Code Division Multiple Access (CDMA) is a conflict-free protocol that allows

overlap transmission, both in frequency and time.

Using quasi-orthogonal signals in conjunction with matching filters at the receiving stations

CDMA achieves the conflict-free property. The multiple orthogonal signals (information that

does not interfere with each other) increases the bandwidth required for transmission. Several

systems can coexist in the same frequency bands using different signals, but the transmission

of the code requires a much greater radio-frequency bandwidth. This is the reason for calling

it Spread Spectrum transmission. The code, in CDMA, is modulated on the carrier with the

digital data on the top of it and each station is assigned a particular code sequence.

There are different ways: 1) phase-coded in which the carrier is phased-modulated by the

digital data sequence and the code sequence and, 2) frequency-hopped in which according to

some known pattern the frequency is periodically changing.

The ability of the receiver to lock onto packet while all other overlapping packets appear as

noise (capture effect), minimizes the effect of interference when several stations employ the

same code.

Figure 3.3. CDMA

Advantages: Since it does not require any transmission synchronisation between the mobile

stations, it is simple to operate. Against other interference systems it offers protection.

Disadvantages: The low throughput is the main disadvantage.

Code

Time

Frequency


28


3.2.4 FDD vs. TDD

In FDD (Frequency Division Duplex) mode, separate frequencies are used in the uplink and

downlink for the connection between a mobile and a base station. This means that the mobile

will receive on one frequency and then transmit on another frequency. The FDD mode

doesn´t imply any specific accesses method.

In TDD (Time Division Duplex) the uplink and downlink will be on the same frequency. The

TDD mode doesn´t imply any specific accesses method.

Figure 3.4. FDD vs. TDD

3.3 Introduction to Spreading and Modulation

There are two categories in which spread spectrum, generally, falls into: Frequency Hopping

(FH) or Direct Sequence (DS). It is required, in both cases, synchronisation of transmitter and

receiver. It can be considered the use of a pseudo-random carrier in the two forms, but they

generate the carrier in different ways.

Is typically implement a frequency hopping system by rapid switching frequency in a pseudo-

random pattern.

In the technique for spread spectrum DS-CDMA, the total power is spreaded over the entire

transmission bandwidth. Before the modulation and transmission over the air, the base-band

binary data is spread by means of a high speed pseudo-noise (PN) code called chip rate,

creating a composite data.

By means of increasing the frequency of the time signal spectrum spreading can be

accomplished. Consider a waveform with an amplitude of V and frequency f (where f = 1/T

and T is the bit duration), if we increase the frequency by a factor n, T is now reduced by n.

Time

FrequencyFDD

Time

FrequencyTDD


29


Figure 3.5. Power Spectrum for n = 1 and n =2

The total energy remains the same after spreading. The total area under the curve gives the

total energy delivered and if the spreading bandwidth is high the amplitude of the signal will

be reduced. This is called process gain, Gp.

The definition of process gain is Gp = 10 log (transmission bandwidth/bit rate). For example if

the transmission bandwidth is 2,5 MHz and the bit rate is 1 MHz the processing gain would

be 3,98 dB. If we increase the bandwidth to 5 MHz the process gain would be 6,99 dB. This

would provide as with an additional margin of 3 dB to help as suppress interference.

When more and more users enter the system, the margin described above is reduced since

there will be a processing loss for every new user (interferer) that enters the system. For k

users this loss can be described as Process loss = 10 log (k).

The overall system gain is described by CDMA gain = Process gain - Process loss due to k

users. The formula would become:

CDMA gain = 10 log (bandwidth/k * bit rate)

where the bandwidth is as described a function of the chip rate.

After spreading the amplitude of the signal will be reduced, so energy are independent of the

frequency and that the amplitude of the signal will be reduced. If we consider the Gaussian

"white noise" that we always have around us, the bandwidth is enough the amplitude will be

close to the noise level.

In CDMA each user will have its own code, therefore multiple users use the same frequency.

The code is made by means of an m-bit pseudo random, PR, generator that provides 2^(m-1)

different codes.

n=1

n=2

Amplitude

Baseband


30


Figure 3.6. Uplink DS-CDMA

3.3.1 Orthogonal Codes

A pair of codes is said to be orthogonal if the cross-correlation is zero. This means that for

two m-bit codes: x1, x2, ..., xm and y1, y2, ..., ym the sum of all m from 1 to m shall be 0. For

example, the cross-correlation between two 4-bits codes:

X = 0 0 1 1

Y = 0 1 1 0 will be

_________

1-1+1-1=0 (assigning +1 for xm = ym and -1 xm ≠ ym).

In the transmitter, Direct Sequence is multiplication of more conventional communication

waveform by a pseudo noise (PN) ± 1 binary sequence.

Spreading is entirely done in the binary domain and the transmitted signals are carefully band

limited. It takes prior to any modulation,

In the receiver a second multiplication by a replica of the same ± 1 sequence recovers the

original signal.

When the signals reach the detector, the noise and interference, being uncorrelated with the

PN sequence, become noise-like and increase in bandwidth. The most of the interference

M1M2

M3

M1 PN1

M2 PN2

M3 PN3

PN1 SpreadingPN2

PN3


31


power can be rejected with a narrow band filtering that can enhance the signal-to-noise ratio,

SNR.

The data signal (user information) is multiplied by a PN-code in DS-CDMA. The period of a

PN-code is called the period, so the code is a sequence of chips. PN-codes, M-sequences,

Gold-codes and Kasami-codes are different classes of PN-code. In the simplest case a

complete PN-code is multiplied with a single data bit and the signal is now multiplied by a

factor N, the processing gain.

Figure 3.7.. Chips and bits

In the receiver squeme, the signal is multiplied by the same PN-Code which removes the PN-

code and recovers the desired data signal.

At the modulator/demodulator the transmitted signal (data information) is spreaded and de-

spreaded with a binary value sequence seudo random (PR) that a sequence generator

produces. The basic system design parameters are transmitted power and channel bandwidth.

We increase (spread) the bandwidth of the data signal to overcome the problem of

interference, that will lead to a bandwidth expansion factor, process gain, g = W/R where W

is the spread code bandwidth (chip-rate) and R is the data bandwidth (bit-rate).

Figure 3.8. Different PN-Sequences

1 bit period

Data signal

PN-code

1 chip period

Coded signal

User 1

User 2

User N

Spread code 1

Spread code 2

Spread code N

Σ channel receiver

Output 1

Output 2

Output N

.

.

.

.

.

.


32


It is possible to use the same transmission bandwidth for more than one user by means of

using different PR-sequences for each user.

Figure 3.9. Different PN-Sequences for Each User

If the spreading is done by a different PN-sequence for many users then it is called direct

sequence code division multiple access, DS-CDMA.

Figure 3.10. DS-CDMA Principle

DS-CDMA uses PN codes to detect each multipath signal and to pick up the signals from the

desired base station. Orthogonal code is used for spreading and channelisation.

We get a similar signal as thermal noise (white noise) if the random code pattern is nearly

Gaussian distributed. Thus the interference of the other users is noise, and the problem can be

simplified.

PN1

PN2

PN3

M1

M2

M3PN3

PN2

PN1

Data signal

PN-code

Spread datasequence

t


33


DS-CDMA spreads the original information over wide bandwidth by using much higher rate

spreading codes, and makes use of frequency diversity to combat frequency selective deep

fading. The filtering is essential in DS-CDMA to reduce the required bandwidth and FIR

digital filters are usually used for sharp response.

3.3.2 RAKE Receiver

Transmissions arriving causes deep multipath fading at the receiver that have followed

different propagation paths. CDMA is less prone to this effect. In fact, one approach in

common use with CDMA system, the Rake receiver, takes advantages of multipath, normally

a major source of interference and signal degradation in other systems. In a Rake receiver, the

signals of several correlation receivers belonging to the strongest multipath components are

combined to provide an enhanced signal with better quality.

The users in a CDMA cellular environment simultaneously share the same radio frequency

band and can be separated at the receiver end with the knowledge of their unique code using a

Rake receiver.

Figure 3.11. RAKE Receiver

An optimum receiver contains several detection channels with different code delays, which

are adjusted to match the major components of the impulse response. The timing accuracy to

obtain full processing gain is approximately one chip time, i. e. the inverse of the channel

bandwidth. The fingers in the rake collect together the contributions of the total signal energy

from several multipath components. The impulse response is measured continuously in order

τ1

τ2

τ3

Micro diversity

Macrodiversity

PNgenerator

PNgenerator

PNgenerator

τ1

τ2

τ3

3 fingers

adaptivechanneldelay

Σ

Linearcombiner

data


34


to set the delay and phase of the different rake fingers. Thus the output from the channels can

be added coherently giving diversity combining.

Both the right coding and the right timing must be done to be able to despread the wanted

signal in the receiver. An optimum receiver contains several detection channels with different

code delays, which are adjusted to match the major components of the impulse response.

In the Rake receiver the contribution from several multipath components are combined. It is

necessary to measure continuously the impulse response of the propagation channel in order

to set the delay and phase on the different rake branches. The output from the channels can

then be added giving diversity combining.

3.3.3 Spread Spectrum Goals

"Spread" the radio signal over a wide frequency range by modulating it with a code word

unique to the radio.

Techniques known since 1940s and used in military communications system since 1950s.

Receiver's correlator distinguishes sender's signal from other signals by examining the wide

spectrum band with a time-synchronised duplicate of the spreading code word.

A spreading process at the Receiver recovers the sent signal.

Spread spectrum waveform is more resistant to multipath effects and more tolerant of

interference.

Figure 3.12. Interference Averaging

Spread spectrum systems are power rather than bandwidth limited.

f f

Channel Quality Channel Quality


35


With a wider band the interference will have an averaging effect in such a way that all user

will share the problem.With a narrow bandwidth a user channel might receive severe fading

dips.

3.3.4 Code Properties

The code should have good Auto Correlation (Time Relation) and Cross Correlation (suppress

other users) properties.

3.3.4.1 Short Codes:

Code sequence length = bit (bit = 1 bit user data).

Code sequence repeated for each new data bit.

+ Orthogonal codes if perfect synchronisation.

+ Good synchronisation properties.

- Code planning needed since limited number of good short codes.

3.3.4.2 Long Codes:

Code sequence length >> bit

+ No code planning needed since low probability that users might have same code.

- Non orthogonal codes.

- Bad synchronisation properties since long repetition cycle.

3.4 Soft and Hard Handover

3.4.1 Handover

In general the change of physical channels allocated to a call while maintaining this call is

considered as handover. In a hard handover the mobile station will instructed to move from

one channel to another and only be receiving from one base station at a time (break before

make). In a soft handover the mobile belongs to two base stations during the time it moves

between the cells (make before brake).


36


3.4.2 Soft Handover

The mobile station continuously searches for new base stations on the current carrier

frequency when is in active mode. During the search, the mobile station monitors the received

signal level from neighbouring base stations, compares them to a set of thresholds, and reports

them accordingly back to the base station. The active set is defined as the set of base stations

from which the same user information is sent simultaneously. Based on this information the

network orders the mobile station to add or remove base stations links from its active set.

3.4.3 Softer Handover

Conceptually, a softer handover is initiated and executed in the same way as an ordinary soft

handover. Softer handover is the special case of a soft handover between sectors/cells

belonging to the same base station site. The main differences are on the implementation level

within the network.

The inter-frequency handover is always performed as a hard handover.

Intra-frequency handover is an handover between cells using the same (single) radio

frequency whereas inter-frequency handover is a handover between cells using different radio

frequencies.

3.5 Power Control

Since there are several users in the same frequency band the received signal strength will be

different for different mobiles, resulting in a near-far interference problem. Near-far refers to

the ratio of the signal strength from a near mobile to a mobile far away. This problem will

give lower performance and reduce capacity in the system.

Many simultaneous connections share a common transmission channel in an interference-

limited system, like CDMA. While in FDMA each connection has its one frequency and in

TDMA each connection has one time slot, this will permit high isolation between the

connections (orthogonality).


37


Figure 3.13. Near-far Problem

If the mobiles would transmit the same power the ratio of the received signal would be:

RS1/RS2 = (d2/d1)^λ where lambda is the path loss or propagation environment. If d1 is not

equal to d2 then the received signal strength from mobile 1 might be much stronger than the

mobile 2 and the receiver would not be able to detect and recover mobile 2. This means that

the transmitting power of each mobile has to be controlled so that the received power is

constant irrespective of the distance.

Figure 3.14. Controlled Transmitting Power

M1M2

SS1= SS2=

d2

SS2

d1

SS1

M1M2

SS1=SS2=

d2

SS2

d1

SS1


38


A specific code is assigned to each connection in interference limited system. This will help

us to discriminate between the wanted signal C and interference I from all other users.

There will be a point when the C/I becomes to low when the total interference level is

increased (more users). This is called anti-jamming margin, AJ, which is the maximum value

for I/C. This gives us an interference limited system for CDMA compared to FDMA and

TDMA who are channel limited system.

The Gp determines how much the receiver can suppress the interference.

To get an acceptable isolation between the connections a large bandwidth is needed to

increase the AJ. The processing gain, Gp, is a related parameter, also related to the bandwidth.

It is then very important with power regulation so that all signals have the same level at the

receiver input.

Commercially available SS systems typically implement processing gains in the 10-100

range.

Information can be transmitted at power levels below ambient noise for high values of Gp

(>1000),. This means low probability of "intercept/detect" and narrowband jamming or

interference.

To illustrate the problem and advantages with an interference limited system, the

"International Cocktail Party" analogy can be used. Picture a large room with a number of

people, in pairs, who would like to hold conversations.

The people in each pair only want to talk and listen to each other, and have no interest in what

is being said in other pairs. In order for these conversations to keep place, however, it is

necessary to define the environment for each conversation.

Gp is high and it is easier to distinguish individual speakers, if people speak in different

languages. Now if a Band is playing a "random noise" is got and the Gp will be lower, I/C

increases, and it will be more difficult to extract the conversation from the background.

Now imagine that the Band starts playing even louder! Speakers try to talk more loudly,

increasing the noise and if more and more people enter the room each conversation will be

louder and louder to cope with the interferers.


39


The solution is to minimise the interference level at the base station receiver is only effective

for terminals assigned to this base station. Interference from terminals in other cells is still a

problem. To minimise this interference the use of soft handover and careful selection of

which base station shall be involved in macro diversity are needed.

3.5.1 Inner Loop Power Control - Uplink

The uplink inner loop power control adjusts the mobile station transmit power in order to

keep the received uplink Signal-to-Interference Ratio (SIR) at a given SIR target. The base

station should estimate the received uplink power after RAKE combining of the connection to

be power controlled. Simultaneously, the base station should estimate the total uplink

received interference in the current frequency band and generates a SIR estimate. The base

station then generates TPC (Transmit Power Control) commands.

Figure 3.15. Forward and ReverseLink

Upon the reception of TPC command, the mobile station should adjust the transmit power of

the uplink in the given direction with a step of ΔTPC dB. The step size ΔTPC is a parameter

that may differ between different cells, in the region [0.25-1.5] dB.

In case of receiver diversity (e.g., space diversity) or softer handover at the base station, the

TPC command should be generated after diversity combining.

In case of soft handover, the following procedure is considered:

• In the base station a quality measurement is performed on the received signals; in case the

quality measurement indicated a value below a given threshold, an increase command is

Forward Link

Reverse Link


40


sent to the mobile, otherwise a decrease command is transmitted; all the base stations in

the active set send power commands to the mobile;

• The mobile compares the commands received from different base stations and increases

its power only if all the commands indicate an increase value (this means that all the

receivers are below the threshold);

• In case one command indicates a decrease step (that is, at least one receiver is operating in

good conditions), the mobile reduces its power; in case more than one decrease commands

are received by the mobile, the mobile station should adjust the power with the largest

step in the "down" direction ordered by the TPC commands received from each base

station in the active set;

• The quality threshold for the base stations in the active set should be adjusted by the outer

loop power control (to be implemented in the network node were soft handover

combining is performed).

3.5.2 Outer Loop Power Control (SIR target adjustment) -Uplink

The outer loop adjusts the SIR target used by the inner-loop power control. The SIR target is

independently adjusted for each connection based on the estimated quality of the connection.

In addition, the power offset between the uplink may be adjusted.

3.5.3 Open Loop Power Control - Uplink

Open-loop power control is used to adjust the transmit power of the physical access channel.

Before the transmission of the access burst, the mobile station should measure the received

power of the downlink. From the power estimate and knowledge of the transmitted power

from the base station (broadcast from the base station) the downlink path-loss including

shadow fading can be found. From this path loss estimate and knowledge of the uplink

interference level and the required received SIR, the transmit power of the physical access

channel can be determined.

The uplink interference level as well as the required received SIR are broadcast from the base

station.


41


3.5.4 Inner Loop Power Control - Downlink

The downlink inner loop power control adjusts the base station transmit power in order to

keep the received downlink SIR at a given SIR target.

The mobile station should estimate the received downlink power after RAKE combining of

the connection of the connection to be power controlled. Simultaneously, the mobile station

should estimate the total downlink received interference in the current frequency band. The

mobile station then generates TPC commands.

Upon the reception of a TPC command, the base station should adjust the transmit power in

the given direction with a step of ΔTPC dB. The step size ΔTPC is a parameter that may differ

between different cells, in the region [0.25-1.5] dB.

In case of receiver diversity (e.g., space diversity) at the mobile station, the TPC command

should be generated after diversity combining.

3.5.5 Outer Loop Power Control - Downlink

The downlink outer loop power control sets the target quality value for the downlink inner

loop power control. It receives input from quality estimates of the transport channel,

measured in the UE. The downlink outer loop power control is mainly used for a long-term

quality control of the radio channel.

This function is located mainly in the UE, but some control parameters are set by the

UTRAN.

The SRNC, regularly (or under some algorithms), sends the target down link power range

based on the measurement report from UE.

3.5.6 Open Loop Power Control - Downlink

The downlink open loop power control sets the initial power of downlink channels. It receives

downlink measurement reports from the UE.

This function is located in both the UTRAN and the UE.

Chapter 4: Air Interface

42



4.1 Radio Transmission and Reception

4.1.1 Frequency Band

UTRA is designed to operate in the following paired band:

1920-1980 MHz

UP-LINK

Mobile transmit; base receive

2110-2170 MHz

DOWN-LINK

Base transmit; mobile receive

Table 4.1. Proposed Frequency Band for UTRA

4.1.2 Channel Arrangement

The nominal channel spacing is 5 MHz, but this can be adjusted to optimise performance in a

particular deployment scenario. The channel raster is 200 KHz, so the centre frequency must

be a integer multiple of 200 KHz.

4.1.3 Tx-Rx Frequency Separation

The minimum transmit to receive frequency separation is 134.8 MHz and the maximum value

is 245.2 MHz and all UE(s) shall support a Tx-Rx frequency separation of 190 MHz when

operating in the paired band defined in 4.1.1. UTRA can support both fixed and variable

transmit to receive frequency separation.

4.1.4 Terminal Service Classes

Different service classes will be used to define the data rate and code allocation for a

UTRA/FDD terminal. Data rates of 144 kbps, 384 kbps and 2048 kbps are possible service

profile types.


43


Output power dynamics: Both the uplink and the downlink use the following power control

mechanism:

• Fast closed-loop Carrier/Interference based power control.

• Slow quality-based power control.

Uplink (UL) Downlink (DL)

Power control steps Variable 0.25-1.5 dB Variable 0.25-1.5 dB

Minimum transmit power -50 dBm [ ] dBm

Power control cycles per second 1.5 kHz 1.6 kHz

Power control dynamic 80 dB 30 dB Table 4.2. Output Power Dynamics for UL and DL

4.1.5 Receiver Requirements

A suitable receiver structure must use coherent reception in channel impulse response

estimation and in code tracking mechanisms. A Rake receiver satisfies these reception

characteristics.

4.1.6 Diversity Characteristics

The following diversity possibilities are considered to be available in UTRA:

Time diversity Channel coding and interleaving in both uplink and downlink.

Multi-path diversity Rake receiver or other suitable receiver structure with maximum combining. Additional processing elements can increase the delay-spread performance due to increased capture of signal energy.

Antenna diversity Antenna diversity with maximum ratio combining in the base station and optionally in the mobile stations. Possibility for downlink transmit diversity in the base station.

Table 4.3. Diversity Characteristics for UTRA

4.2 Logical, Physical and Transport Channels

Logical Channel: A logical channel is a radio bearer or part of it, dedicated for exclusive use

of a specific communication process. Depending on the type of information transferred on the

radio interface, different types of logical channel are defined.


44


Physical Channel: A physical channel is defined by code, frequency and, in the uplink,

relative phase (I/Q). In TDD mode, code, frequency, and time-slot define a physical channel.

Physical Channel Data Stream: In the uplink, a data stream that is transmitted on one

physical channel.

In the downlink, a data stream that is transmitted on one physical channel in each cell of the

active set.

Active Set: Set of radio links simultaneously involved in a specific communication service

between an MS and a UTRAN.

Transport Channel: Transport Channels are those that are offered by the physical layer for

data transport between peer L1 entities. Different types of transport channels are defined by

how and with which characteristics data is transferred on the physical layer, e.g. whether

using dedicated or common physical channels are employed.

Transport Format: The Transport Format is a combination of encoding, interleaving, bit rate

and mapping onto physical channels.

Transport Format Combination Indicator (TFCI): The TFCI is a label for a specific

Transport Format within a Transport Format Set.

Transport Format Set: A set of Transport Formats. For example, a variable rate DCH

(Dedicated Channel) has a Transport Format Set (one Transport Format for each rate),

whereas a fixed rate DCH (Dedicated Channel) has a single Transport Format.

4.2.1 Transport Channels:

4.2.1.1 Dedicated Transport Channel

DCH - Dedicated Channel: Both user data and control information between the network and

a mobile station is carried in the Dedicated Channel (DCH), which is a downlink or uplink

transport channel transmitted over the entire cell or over only a part of the cell, using lobe-

forming antennas.


45


4.2.1.2 Common Transport Channels

4.2.1.2.1 BCH - Broadcast Channel

A base station uses the Broadcast Channel (BCH) to broadcast system and cell-specific

information. The BCH is a downlink transport channel that is always transmitted over the

entire cell.

4.2.1.2.2 FACH - Forward Access Channel

When the system knows the location cell of the mobile station, the Forward Access Channel

(FACH) is used to carry control information to the mobile. The FACH is a downlink transport

channel that is transmitted over the entire cell or over only a part of the cell using lobe-

forming antennas. The FACH may also carry short user packets.

4.2.1.2.3 PCH - Paging Channel

When the system does not know the location cell of the mobile, the Paging Channel (PCH) is

used to carry control information to a the mobile station. The PCH is a downlink transport

channel that is always transmitted over the entire cell.

4.2.1.2.4 RACH - Random Access Channel

Control information from a mobile station is transmitted into the Random Access Channel

(RACH). The RACH is an uplink transport channel that is always received from the entire

cell. It may also carry short user packets.

4.2.1.2.5 DSCH - Downlink Shared Channel

The downlink shared channel (DSCH) is a downlink transport channel shared by several UEs

carrying dedicated control or traffic data.

4.2.2 Physical Channels:

A physical channel is defined by a specific carrier frequency, code, and relative phase (on the

uplink, 0 or π/2).


46


4.2.2.1 Dedicated Uplink Physical Channels

There are two types of uplink dedicated physical channels, the uplink Dedicated Physical

Data Channel (uplink DPDCH) and the uplink Dedicated Physical Control Channel

(DPCCH).

Dedicated data generated for the dedicated transport channel are transmitted into the uplink

DPDCH. Each connection may support zero, one, or several uplink DPDCHs. Control

information is transmitted into the DPCCH. The control information consists of:

• Pilot bits to allow channel estimation for coherent detection.

• Transmit power control (TPC) commands.

• Optional transport-format indicator (TFI).

The transport-format indicator informs the receiver about the instantaneous parameters of the

different transport channels multiplexed on the uplink DPDCH. There is only one uplink

DPCCH on each connection.

4.2.2.1.1 Frame Structure

Each frame of length 10 ms is divided into 15 slots, each of length Tslot = 0,666 ms,

corresponding to one power-control period (see Figure 4.1). A super frame corresponds to 72

consecutive frames, i.e. the super-frame length is 720 ms.

Figure 4.1. Frame Structure for Uplink DPDCH/DPCCH

PilotN pilot bits

TFI N TFI bits

DataN data bits

Slot #1 Slot #2 Slot # i Slot #15

Frame #1 Frame #2 Frame # i Frame #72

0.666 ms, 10*2 k bits (k=0..6)

T f = 10 ms

T super = 720 ms

DPDCH

DPCCHTPC

N TPC bits


47


The parameter k is related to SF, the spreading factor of the physical channel, as SF = 256/2k.

SF may thus range from 4 up to 256. The parameter k determines the number of bits per

uplink DPDCH/DPCCH slot. But the same connection usually carry an uplink DPDCH and

uplink DPCCH which have different rates, i.e. have different spreading factors and different

values of k.

The exact number of bits of the different uplink DPCCH is yet to be determined.

4.2.2.2 Common Uplink Physical Channel

4.2.2.2.1 Physical Random Access Channel

The RACH is transmitted into the Physical Random Access Channel (PRACH). The access

control is based on a Slotted Aloha approach, which means that a mobile station can start the

transmission of the PRACH at a number of well-defined time offsets, relative to the frame

boundary of the received BCCH of the current cell. The different time slots, the access slots,

are spaced 1.5 ms (see Figure 4.2). The BCCH broadcasts information about available access

slots in the current cell.

Figure 4.2. Access Slot

The random access burst consists of two parts:

• A preamble part (length 1 ms)

• A message part (length 10 ms)

Random-access burstAccess slot #1

Access slot #2

1.5 ms

Offset of access slot #i

Frame boundary

Access slot #i

Access slot #8

Random-access burst

Random-access burst

Random-access burst

Random-access burstRandom-access burstAccess slot #1

Access slot #2

1.5 ms

Offset of access slot #i

Frame boundary

Access slot #i

Access slot #8

Random-access burstRandom-access burst




48


Between the preamble and the message part there is an idle time period of length 1.5 ms

(preliminary value), which allows for detection of the preamble part and subsequent on-line

processing of the message part.

Preamble Part: The preamble part of the random-access burst consists of a signature. There

are a total of 16 different signatures.

Message Part: The structure of the message part of the random-access burst is the same as

the uplink DPH. It has a data part, corresponding to the uplink DPDCH, and a control part,

corresponding to the uplink DPCCH. The data and control parts are transmitted in parallel.

The data part carries the random access request or small user packets, using a channel bit rate

of 16, 32, 64 or 128 kbps, which corresponds to a spreading factor (SF) of 256, 128, 64 and

32, respectively. The control part uses a spreading factor of 256, and carries pilot bits and rate

information. The rate information indicates which channelisation code (or rather the spreading

factor of the channelisation code) is used on the data part.

The random-access burst consists of the fields shown in Figure 4.3 and listed below (the

values in brackets are preliminary values):

• Mobile station identification. The MS ID is chosen at random by the mobile station at the

time of each random-access attempt.

• Required Service. This field informs the base station what type of service is required

(short packet transmission, dedicated-channel setup, etc.)

• An optional user packet

• A CRC to detect errors in the data part of the random-access burst

Figure 4.3. Structure of Random - Access Burst Data Part

4.2.2.3 Downlink Physical Channels

4.2.2.3.1 Dedicated Physical Channels

The Downlink Dedicated Physical Channel (dowlink DPCH) is the only type of downlink

dedicated physical channel. It carries dedicated data for the dedicated transport channel

(DPH) and control information (known pilot bits, TPC commands, and an optional TFCI).

MS ID Req . Serv Optional user packet CRCMS ID Re . Serv Optional user packet CRC


49


4.2.2.3.2 Frame Structure

Figure 4.4 shows the frame structure of the downlink DPCH. Each frame of length 10 ms is

split into 15 slots, each of length Tslot = 0,666 ms, corresponding to one power-control period.

A super frame corresponds to 72 consecutive frames, i.e. the super-frame length is 720 ms.

Figure 4.4. Frame Structure for Downlink DPCH

The parameter k is related to SF, the spreading factor of the physical channel, as SF = 256/2k.

SF may thus range from 4 up to 256. The parameter k determines the number of bits per

downlink DPCH slot. But the same connection usually carry an uplink DPDCH and uplink

DPCCH which have different rates, i.e. have different spreading factors and different values

of k.

The exact number of bits of the different downlink DPCH fields is yet to be determined.

In order to support the use of downlink adaptive antennas, connection-dedicated pilot bits are

transmitted also for the downlink.

Multi-code transmission is employed when the total bit rate to be transmitted on one downlink

connection exceeds the maximum bit rate for a downlink physical channel: several parallel

downlink DPCHs are transmitted for one connection using the same spreading factor.

In this case, the control information is put on only the first downlink DPCH, while the

additional downlink DPCHs belonging to the connection do not transmit any data during the

corresponding time period.

Pilot Datos

Slot #1 Slot #2 Slot #i Slot #15

Frame #1 Frame #2 Frame #i Frame #72

0.666 ms, 20*2 k bits (k=0..6)

T f = 10 ms

T super = 720 ms

TPC TFCI

DPCCH DPDCH


50


4.2.2.4 Common Physical Channels

4.2.2.4.1 Primary Common Control Physical Channel

The Primary CCPCH is a fixed rate (32 kbps, SF=256) downlink physical channel used to

carry the BCCH.

The Figure 4.5 shows the frame structure of the Primary CCPCH. It differs from the downlink

DPCH in that no TPC commands or TFCI is transmitted. The only control information is the

common pilot bits, needed for coherent detection.

Figure 4.5. Frame Structure for Primary Common Control Physical Channel

4.2.2.4.2 Secondary Common Control Physical Channel

The secondary CCPCH is used to carry the FACH and PCH. As the Primary CCPCH, it is of

constant rate, but the difference between them is that in the Secondary CCPCH the rate may

be different for different secondary CCPCHs within one cell and between cells. This is done

in order to be able to allocate different amount of FACH and PCH capacity to a cell (see

Figure 4.6). The BCCH broadcasts the rate and spreading factor of each secondary CCPCH.

The set of possible rates is the same as for the downlink DPCH.

The FACH and PCH are mapped to separate Secondary CCPCHs. A CCPCH is not power

controlled, and this is the main difference between a CCPCH and a downlink dedicated

physical channel. The main difference between the Primary and Secondary CCPCH is that the

Primary CCPCH has a fixed predefined rate while the Secondary CCPCH has a constant rate

Pilot Data



0.666 ms, 20 bits

T f = 10 ms

T super = 720 ms


51


that may be different for different cells, depending on the capacity needed for FACH and

PCH.

Figure 4.6. Frame Structure for Secondary Common Control Physical Channel

Furthermore, a Primary CCPCH is continuously transmitted over the entire cell while a

Secondary CCPCH is only transmitted when there is data available and may be transmitted in

a narrow lobe in the same way as a DPH (only valid for a Secondary CCPCH carrying the

FACH).

4.2.2.4.3 Synchronisation Channel

The Synchronisation Channel (SCH) is a downlink signal used for cell search. It consists of

two sub channels, the Primary and Secondary SCH, as shown in Figure 4.7.

The Primary SCH transmits the Primary Synchronisation Code, which is an unmodulated

orthogonal code of length 256, the same for every base station in the system.

The Secondary SCH repeatedly transmits the Secondary Synchronisation Codes, a sequence

of 16 unmodulated orthogonal codes of length 256 chips. These are transmitted in parallel

with the Primary Synchronisation channel.

The sequence on the Secondary SCH identifies a group of scrambling codes among 32

possibilities. The base station downlink scrambling code belongs to the indicated group. 32

sequences are used to encode the 32 different code groups each containing 16 scrambling

codes. It is used to uniquely determine both the long code group and the frame timing.

Pilot Data



0.666 ms, 20*2k bits (k=0..6)

T f = 10 ms

T super = 720 ms


52


Figure 4.7. Structure of Synchronisation Channel (SCH)

4.2.3 Mapping of Transport Channels to Physical Channels

The Figure 4.8 summarises the mapping of transport channels to physical channels.

Figure 4.8. Transport-Channel to Physical-Channel Mapping

Cp

i

Csi,1

Cp

Csi,2

Cp

Csi,15

Tframe=15*Tslot

Tslot=2560 chips

256 chips

Primary SCH

Secondary SCH

Cp: Primary Synchronisation CodeCsi,k: One of 16 possible Secondary Synchronisation Codes(Csi,1, Csi,2,...,Csi,15) encode cell specific long scrambling code group i

Transport Channels

BCCH

FACH

PCH

RACH

CPCH

DCH

DSCH

Physical Channels

Primary Common Control Physical Channel (Primary CCPCH)

Secondary Common Control Physical Channel (Secondary CCPCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Dedicated Physical Data Channel (DPDCH)

Synchronisation Channel (SCH)

Physical Sownlink Shared Channel (PDSCH)

Transport Channels

BCCH

FACH

PCH

RACH

CPCH

DCH

DSCH

Physical Channels

Primary Common Control Physical Channel (Primary CCPCH)

Secondary Common Control Physical Channel (Secondary CCPCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Dedicated Physical Data Channel (DPDCH)

Synchronisation Channel (SCH)

Physical Sownlink Shared Channel (PDSCH)


53


4.3 Spreading, Scrambling and Modulation

The basic spreading (and scrambling) chip rate is 3.84 Mcps, which can be extended to 7.68

or 15.36 Mcps.

4.3.1 Uplink Spreading, Scrambling and Modulation

4.3.1.1 Modulation

4.3.1.1.1 Uplink Dedicated Physical Channels (Uplink DPDCH/DPCCH)

The uplink DPDCH and DPCCH are mapped to the I and Q branch respectively. Two

different channelisation codes cD and cC are then used to spread both branches to the chip rate,

and subsequently they are coded by a complex scrambling code associated to the mobile

terminal.

In the case of multi-code transmission, both the I and Q branches may be used to transmit a

new uplink DPDCH, which must be assigned its own channelisation code. However, uplink

DPDCHs transmitted on different branches may use the same channelisation code.

4.3.1.2 PRACH

The message part of the random-access channel uses the same coding/modulation procedure

as the uplink dedicated physical channels, described previously. The data part is similar to the

uplink DPDCH and the control part is similar to the uplink DPCCH. In order to guarantee that

two simultaneous random-access attempts using different preamble codes and/or sequences

will not collide during the message part, the selection of the scrambling code for the data part

is based on:

• The randomly chosen preamble sequence,

• The preamble code associated to the base station, and

• The randomly chosen access slot (random-access time-offset).


54


4.3.1.3 Spreading: Channelisation Codes

The uplink uses the same type of channelisation codes as the downlink. In the case of the

uplink, the limitations on the allocation of these codes are only valid within one mobile

station.

Each connection is allocated at least one uplink channelisation code, to be used for the uplink

DPCCH. Usually at least one additional uplink channelisation code is allocated for an

additional uplink DPDCH. If more than one uplink DPDCH is necessary, further uplink

channelisation codes may be allocated.

As different mobile stations use different uplink scrambling codes, the uplink channelisation

codes may be allocated without any co-ordination between different connections. So the

uplink channelisation codes are always allocated in a pre-established order. Once the mobile

station and network reach an agreement on the number and length (spreading factor) of the

uplink channelisation codes, the exact codes to be used are implicitly given.

4.3.1.4 Scrambling: Scrambling Codes

Either short or long scrambling codes should be used on uplink.

4.3.1.4.1 Short Scrambling Code

The short scrambling code is a complex code c scramb = cI + jcQ, where cI and cQ are two

different codes of length 256.

It’s the network who decides the uplink short scrambling code. After an uplink Random

Access Request, the base-station emits a downlink Access Grant message, which tells the

mobile station the short scrambling to use.

The short scrambling code may, only in rare cases, be changed during the duration of a

connection.

4.3.1.4.2 Long Scrambling Codes

The long uplink scrambling code is typically used in cells without multi-user detection in the

base station. The mobile station is informed if a long scrambling code should be used in the

Access Grant Message following a random-access request and in the handover message.


55


4.3.1.5 Random Access Codes (Spreading & Scrambling)

4.3.1.5.1 Preamble Spreading Code

The base station broadcasts the spreading code for the preamble part, which is specific of the

cell. If the traffic load is high, the base station can use more than preamble code.

Since two neighbouring cells must not use the same preamble code, these codes have to be

planned.

The code used is a 256 chip code, and the system uses all 256 codes.

4.3.1.5.2 Preamble Signature

The preamble part carries one of 16 different signatures of length 16, <P0, P1,..., P15>. The

base station broadcasts which signatures are allowed to be used in a cell.

4.3.1.5.3 Channelisation Codes for the Data Part

The signature in the preamble specifies one of the 16 possibilities for the channelisation code.

The control part is always spread with a known channelisation code of length 256, so it can be

detected by the base station. The base station obtains the spreading factor used on the message

part from the rate information field of control part. The base station gets the channelisation

code used in the data part either with the help of the preamble signature and the rate

information.

In this way, simultaneous detection of multiple random access messages arriving in the same

access slot is allowed by the use of different signatures.

4.3.1.5.4 Scrambling Code for the Data Part

In addition to spreading, the message part is also subject to scrambling with a 10 ms complex

code. The scrambling code is cell-specific and has a one-to-one correspondence to the

spreading code used for the preamble part. Note that although the scrambling code is the same

for every access slot, there is no scrambling-code collision problems between different access

slots due to the 1.25 ms time shift between the access slots.


56


4.3.2 Downlink Spreading, Scrambling and Modulation

4.3.2.1 Modulation

The modulation scheme used for the data part is QPSK; each pair of two bits are first

converted from serial to parallel and then mapped to the I and Q branch, respectively. The

channelisation code cch spreads the I and Q branch to the chip rate (real spreading), and

subsequently they are scrambled with cscramb, the cell-specific scrambling code (real

scrambling).

The spread/modulation process must also be applied to every additional downlink DPCH, in

the case of multi-code transmission. Each additional downlink DPCH should be assigned its

own channelisation code.

4.3.2.2 Spreading: Channelisation Codes

The number of available channelisation codes is not fixed but depends on the rate and

spreading factor of each physical channel.

The BCCH uses a predefined channelisation code, which is the same for all the cells within

the system.

The BCCH broadcasts the channelisarion code(s) used in the Secondary Common Control

Physical Channel.

The channelisation codes for the downlink dedicated physical channels are decided by the

network. After an uplink Random Access request, the base station responds with a downlink

Access Grant message, informing the mobile station about the downlink channelisation codes

to receive. If a change of service or an inter-cell handover occurs, the set of channelisation

codes may be changed during the duration of the connection. This change of downlink

channelisarion codes is negotiated over a DCH.

4.3.2.3 Srambling: Scrambling Codes

There are 512 available scrambling codes, grouped into 32 code sets with 16 codes in each

set. The grouping facilitates the process of fast cell search. In the initial deployment a

downlink scrambling code is assigned to every cell, and the mobile knows the scrambling

code in the cell search process.


57


The scrambling codes are repeated for every 20 ms radio frame.

4.3.2.4 Synchronisation Codes

The Primary and Secondary code words, cp and {c1 ,... , c17} respectively, consist of pair wise

mutually orthogonal codes of length 256.

4.4 Transport Channel Coding and Multiplexing Chain

The following steps can be identified in the Figure 4.9, which describes the overall concept of

transport-channel coding and multiplexing:

Figure 4.9. Coding and Multiplexing of Transport Channels

• Channel coding, including optional transport-channel multiplexing

• Static rate matching

• Inter-frame interleaving


58


• Transport-channel multiplexing

• Dynamic rate matching

• Intra-frame interleaving

The different steps are described in detail below.

The output of the inner interleaving block is usually mapped to one DPDCH. In the case of

multi-code transmission, with very high bit rates, the output is split onto several DPDCHs.

Transport channels are coded and multiplexed as described above, i.e. into one data stream

mapped on one or several physical channels.

4.4.1 Channel Coding

Every transport channel is coded before transport-channel multiplexing, i.e. channel coding is

done on a per-transport-channel basis. Figure 4.10 illustrates this concept.

Figure 4.10. Channel Coding in UTRA/FDD

4.4.1.1 Convolutional Coding

If the service requires a BER in the order of 10-3 then is typical to apply convolutional coding.

If the service requires a BER in the order of 10-6 then convolutional coding is applied in

concatenation with RS coding and outer interleaving.


59


Dedicated transport channels (DCHs) in normal (non-slotted) mode typically use a 1/3-rate

convolutional coding, while DCHs in slotted mode are usually coded with a ½-rate

convolutional coding.

4.4.1.2 Turbo Coding

ETSI is currently investigating the use of Turbo coding for high quality services, which

require data rates above 32 kbps (see Figure 4.11). Turbo codes of rate 1/3 and ½ (for the

highest data rates), have been proposed to replace the concatenation of convolutional and

Reed-Solomon codes. ETSI is awaiting further results of simulations illustrating the

performance of Turbo Codes.

Figure 4.11. Block Diagram of a Turbo code encoder

Figure 4.12 shows the basic FEC coding structure for the UTRA, which will be employed in

case Turbo codes give an improved FEC for high quality services, compared to the existing

proposals.

Figure 4.12. FEC Coding for UTRA/FDD When Turbo Codes are Used


60


4.4.1.3 Service Specific Coding

The service-specific-coding option allows supplementary coding schemes, in addition to the

standard coding schemes listed above, increasing in this way the flexibility of the UTRA

Layer 1. One example is the use of unequal-error-protection coding schemes for certain

speech-codecs.

4.4.2 Inner Inter-Frame Interleaving

Those transport-channels that can allow for and require interleaving over more than one radio

frame (10 ms) use inner inter-frame bit interleaving, carried out on a per-transport-channel

basis. The span of the inner inter-frame interleaving can vary in the range 20 ms to 150 ms.

4.4.3 Rate Matching

Rate matching is carried out according to the following procedures:

• Static rate matching: carried out on a slow basis, typically every time a transport channel

is added or removed from the connection.

• Dynamic rate matching: carried out on a frame-by-frame 810 ms) basis

4.4.3.1 Static Rate Matching

Two different reasons lead to the use of static rate matching:

• To adjust the coded transport channel bit rate to a level where minimum transmission

quality requirements of each transport channel is fulfilled with the smallest differences in

channel bit energy

• To adjust the coded transport channel bit rate so that the maximum total bit rate after

transport channel multiplexing is matched to the channel bit rate of the uplink and

downlink dedicated physical channel.

The static rate matching is based on code puncturing and unequal repetition.

It is important to note that the rate matching must be co-ordinated between different transport

channels, although it is carried out prior to transport-channel multiplexing.


61


4.4.3.2 Dynamic Rate Matching

After the multiplexing of the parallel coded transport channels, it is necessary to match the

total instantaneous rate of the multiplexed transport channels to the channel bit rate of the

uplink DPDCH, which is done by the dynamic rate matching. It uses unequal repetition and is

only applied to the uplink. On the downlink, discontinuous transmission (DTX) is used when

the total instantaneous rate of the multiplexed transport channels does not match the channel

bit rate.

4.4.4 Transport-Channel Multiplexing

The coded transport channels are serially multiplexed within one radio frame. The output after

the multiplexer (before the inner interleaving) will thus be according to the .

Figure 4.13. Transport Channel Multiplexing

Another option is transport-channel multiplexing within the channel-coding unit, usually after

outer RS coding but before outer interleaving.

4.4.5 Inner Intra-Frame Interleaving

Inner intra-frame interleaving over one radio frame (10 ms) is applied to the multiplexed set

of transport channels.

4.5 Service Multiplexing

Service multiplexing allows the separate and independent control of QoS. This is done by

treating multiple services in the same connection with separate channel coding/interleaving

and mapping to different basic physical channels (slot/code) (see Figure 4.14).


62


Figure 4.14. Service Multiplexing (a)

Another option is time multiplexing at different points of the channel coding scheme (see

Figure 4.15).

Figure 4.15. Service Multiplexing (b)

After service multiplexing and channel coding, the multi-service data stream is mapped to one

or, if the total rate exceeds the upper limit for single-code transmission, several resource units.

Time Mux

Time Mux

Outer

Coding/interf.Inner

Coding/interf.

Time Mux

Time Mux

Outer

Coding/interf.Inner

Coding/interf.

Time Mux

Service 1

Service 2

...

Service n

Parallel services

Time Mux

Time Mux

Outer

Coding/interf.

Outer

Coding/interf.Inner

Coding/interf.

Inner

Coding/interf.

Time MuxTime Mux

Time Mux

Outer

Coding/interf.Inner

Coding/interf.

Time Mux

Time MuxTime Mux

Outer

Coding/interf.

Outer

Coding/interf.Inner

Coding/interf.

Inner

Coding/interf.

Time MuxTime Mux

Service 1

Service 2

...

Service n

Parallel services

Coding /interleaving



Parallel services

Service 1

Service 2

Service N







Parallel services

Service 1

Service 2

Service N


63


4.6 Traffic Cases (Examples)

4.6.1 Continuous Transmission in Uplink with Variable Rate

Figure 4.16. Uplink Variable Rate (no DTX)

4.6.2 Discontinuous Transmission (DTx) in Downlink with Variable

Rate (1)

Figure 4.17. Downlink Variable Rate (DTX)

0,666 ms

1-rate

¼-rate

½-rate

0-rate

: DPCCH-part (Pilot+TPC+RI)

: DPDCH-part (Data)

0,666 ms

1-rate

¼-rate

½-rate

0-rate

: DPCCH-part (Pilot+TPC+RI)

: DPDCH-part (Data)

10 ms

1 rate

¼- rate

½- rate

0- rate

Variable rate

R = 1 R = 1/2 R = 0 R = 0 R = 1/2

: DPCCH (Pilot+TPC+RI)

: DPDCH (Data)

10 ms

1 rate

¼- rate

½- rate

0- rate

Variable rate

R = 1 R = 1/2 R = 0 R = 0 R = 1/2


: DPDCH (Data)


64


4.6.3 Discontinuous Transmission (DTx) in Downlink with Variable Rate (2)

Figure 4.18. Downlink Variable Rate (DTX)

4.7 Initial Cell Search

The initial cell search is the process of searching for the base station to which the mobile has

the lowest path loss. Subsequently, the mobile determines the downlink scrambling code and

frame synchronisation of that base station. The initial cell search is carried out using the

synchronisation channel (SCH), see Figure 4.19.

Figure 4.19. Structure of Synchronisation Channel (SCH)

This initial cell search is carried out in three steps:

Cp

i

Csi,1

Cp

Csi,2

Cp

Csi,15

Tframe=15*Tslot

Tslot=2560 chips

256 chips

Primary SCH

Secondary SCH

Cp: Primary Synchronisation CodeCsi,k: One of 16 possible Secondary Synchronisation Codes(Csi,1, Csi,2,...,Csi,15) encode cell specific long scrambling code group i

10 ms

1-rate

½-rate

0-rate


: DPDCH (Data)

R = 1 R = 0 R = 1/2 R = 0R = 1

Variable rate

10 ms

1-rate

½-rate

0-rate


: DPDCH (Data)

R = 1 R = 0 R = 1/2 R = 0R = 1

Variable rate


65


4.7.1 Step 1: Slot Synchronisation

During the first step of the initial cell search procedure the mobile station uses the primary

SCH to acquire slot synchronisation to the strongest base station.

This is done with a single matched filter (or any similar device) matched to the primary

synchronisation code cp which is common to all base stations (see Figure 4.20). The output of

the matched filter will have peaks for each ray of each base station within range of the mobile

station. Detecting the position of the strongest peak gives the timing of the strongest base

station modulo the slot length. For better reliability, the matched-filter output should be non-

coherently accumulated over a number of slots.

Figure 4.20. Matched-Filter for Primary Synchronisation Code to Slot Synchronisation

4.7.2 Step 2: Frame Synchronisation and Code Group Identification

During the second step of the initial cell search procedure, the mobile station uses the

secondary SCH to find frame synchronisation and identify the code group of the base station

found in the first step. This is done by correlating the received signal at the positions of the

Secondary Synchronisation Code with all possible (16) Secondary Synchronisation Codes.

Note that the position of the Secondary Synchronisation Code is known after the first step.

The outputs of all the 17 correlators for 16 consecutive secondary SCH locations are used to

form the decision variables.

The decision variables are obtained by non-coherently summing of the correlators outputs

corresponding to each 16 length sequence out of the 32 possible sequences and its 16 cyclic

shifts giving a total of 512 decision variables. Note that the cyclic shifts of the sequences are

unique. Thus, by identifying the sequence/shift pair that gives the maximum correlation

values, the code group as well as the frame synchronisation is determined.


66


4.7.3 Step 3: Scrambling Code Identification

During the third and last step of the initial cell search procedure, the mobile station

determines the exact scrambling code used by the found base station. The scrambling code is

identifies through symbol-by-symbol correlation over the Primary CCPCH with all the

scrambling codes within the code group identified in the second step. Note that, from step 2,

the frame boundary and consequently the start of the scrambling code is known. Correlation

must be carried out symbol-wise, due to the unknown data of the primary CCPCH. Also, in

order to reduce the probability of wrong/false acquisition, due to combat background

noise/interference, averaging the correlator outputs over a sequence of symbols 8diversity)

might be required before using the outputs to determine the exact scrambling code.

After the scrambling code has been identified, the Primary CCPCH can be detected, super-

frame synchronisation can be acquired and the system- and cell specific BCCH information

ca be read.

4.7.4 Idle Mode Cell Search

When in idle mode, the mobile station continuously searches for new base stations on the

current and other carrier frequencies. The cell search is done basically the same way as the

initial cell search. The main difference compared to the initial cell search is that an idle

mobile station has received a priority list from the network. This priority list describes in

which order the downlink scrambling codes should be searched for and does thus significantly

reduce the time and effort needed for the scrambling-code search (step 3). Also the

complexity in the second step may be reduced if the priority list only includes scrambling

codes belonging to a subset of the total set of code groups. The priority list is continuously

updated to reflect the changing neighbourhood of a moving mobile station.

4.7.5 Active Mode Cell Search

When in active mode, the mobile station continuously searches for new base station on the

current carrier frequency. This cell search is carried out in basically the same way as the idle

mode cell search. The mobile station may also search for new base stations on other carrier

frequencies using the slotted mode.


67


4.8 Packet Access

The requirements for packet access are:

• Fast access

• Efficient use of the radio resources

In order to satisfy these requirements, the connection set-up should be fast and closed loop

power control for large packets, and a small overhead for small packets. Moreover, the

possibility of packet scheduling should be included. Small frequently sent packets are sent on

the common channels, while frequently or large packets should use the dedicated channels.

4.8.1 Common Channel Packet Access

The common channel RACH/FACH would be used for transmitting small packets and

medium data rates. During the time there are no packets to transmit there will be no link

maintenance (see Figure 4.21). Open loop power control would be used.

Figure 4.21. Common Channel Packet Access

4.8.2 Dedicated Channel Single Packet Transmission

Each new packet in a single and scheduled packet transmission is preceded with a random

access request, as shows Figure 4.22 During the packet transmission closed-loop power

control is used.

Figure 4.22. Dedicated Channel Single Packet Transmission

Access Request

User Packet

Access Request

User Packet

Arbitrary TimeAccess Request

User Packet

Access Request

User Packet

Access Request

User Packet

Arbitrary Time

Access Request

Access Request

Arbitrary Time

Common Channel (RACH/FACH)

User Packet

User Packet

Dedicated Channel (DTCH)

Access Request

Access Request

Arbitrary Time

Common Channel (RACH/FACH)

User Packet

User Packet



68


4.8.3 Dedicated Channel Multi-Packet Transmission

In the case of scheduled and non-scheduled packet transmission, the link will be maintained,

and closed–loop power control will be used during the transmission (Figure 4.23). The link

will be released after a defined time-out period.

Figure 4.23. Dedicated Channel Multi-Packet Transmissio

Access Request

User Packet

Access Reques

t

User Packet

User Packet


Link maintenance (pilot, TPC)

Scheduled packets

Non-scheduled packets

Access Request

User Packet

Access Reques

t

Access Reques

t

User PacketUser

PacketUser

PacketUser

Packet


Link maintenance (pilot, TPC)

Scheduled packets

Non-scheduled packets

Chapter 5: Radio Theory

69



5.1 Introduction

The content of this chapter deals with some selected radio properties and their effects on a

mobile system. In a mobile network the connection between the mobile phone and the

network is done via the air interface with the help of radio waves. The area in which the

mobile and the network can stay in contact with some acceptable quality is called the

coverage area. This area is served by a transmitter/receiver that will transmit towards the

mobile and receive from the mobile. The serving area is called a cell.

5.1.1 Radio Waves and Modulations

A radio wave is an electromagnetic wave of a frequency lower than 3000 GHz. The

electromagnetic wave is produced by the interaction of time varying electric and magnetic

fields. The number of cycles or events per time unit is the frequency, which is expressed in

Hertz, Hz (see Figure 5.1).

Figure 5.1. Wave Form

There are many different types of electromagnetic waves including radio waves, light,

infrared rays and x-rays. Radio waves are one example of what we refer to as electromagnetic

radiation. They are generally generated by oscillating charges on a transmitting antenna.

To be able to use the radio waves for transfer of information such as speech or data a

modulation technique is used. Modulation is the process where the amplitude, frequency or

phase of a radio wave (or light wave) is changed.

1 cycle

Time

1 cycle

Time


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Figure 5.2. Digital Modulation Techniques

There are different ways to modulate a radio signal. We could change the amplitude, the

frequency, the phase or use pulse modulation (see Figure 5.2).

In Amplitude Modulation the carrier’s amplitude changes in accordance with the modulated

user signal, while the carrier’s frequency is fixed (shown in Figure 5.3).

Figure 5.3. Amplitude Modulation

Frequency modulation occurs when the carrier’s frequency is changed according to the input

signal, while the amplitude is unchanged (see Figure 5.4). FM modulation is more immune to

noise than AM and improves the overall signal-to-noise ratio. The signal-to-noise ratio is the

ratio between the signal maximum peak-to-peak signal and what remains when the signal is

removed, that is, the ratio of the wanted signal to that of the noise.

Phase Modulation is similar to FM but instead of changing the frequency of the carrier wave,

the phase of the carrier changes (see Figure 5.5 and Figure 5.6).

Pulse Modulation is a sample of the waveform taken at regular intervals. There exit a variety

of Pulse Modulation schemes not covered here.

M

θ

M = magnitudeθ = phase

Quadrature componentQ =M sinθ

In-phase componentI =M cos θ

M

θ

M = magnitudeθ = phase

Quadrature componentQ =M sinθ

In-phase componentI =M cos θ

Time

Amplitude

Time

Amplitude


71


Figure 5.4. Frequency Modulation

Figure 5.5. Binary Phase Shift Keying Figure 5.6. Quadrature Phase Shift Keying

To be able to use analogue signals for digital information they have to be processed by an

intermediate stage before transmission. This is done by a modem (modulator/demodulator) in

a process known as a modulation/demodulation.

5.1.2 Access Methods

In a cellular network we have a mobile phone or terminal connected to the network via a base

station that transmits towards the mobile phone and receives signals from the mobile phone.

This connection is wireless, it uses radio waves in the air interface to set up the connection.

The way we utilise these radio waves in the air is called Access Method and there exist a

number of them with different properties.

Commonly use access methods in radio networks are Frequency Division Multiple Access

(FDMA), Time Division Multiple Access (TDMA) y Code Division Multiple Access

(CDMA).

Time

Amplitude

Time

Amplitude

Q

I0 state 1 state

Phases separated by 180º (π radians)

Binary Phase Shift Keying (BPSK)

Q

I0 state 1 state

Phases separated by 180º (π radians)

Binary Phase Shift Keying (BPSK)

Q

I

01 state

Phase of carrier: π/4, 3π/4, 5π/4, 7π/4

2x bandwidth efficiency of BPSK

Quadrature Phase Shift Keying (QPSK)

11 state

00 state 10 state

Q

I

01 state

Phase of carrier: π/4, 3π/4, 5π/4, 7π/4

2x bandwidth efficiency of BPSK

Quadrature Phase Shift Keying (QPSK)

11 state

00 state 10 state


72


FDMA is used for standard analogue mobile telephony. Each user is assigned a discrete part

of the RF spectrum. FDMA permits only one user per channel since it allows the user to use

the channel 100% of the time.

In TDMA the users are still assigned a discrete part of the RF spectrum, but multiple users

now share that RF carrier on a time slot basis. Each of the users alternates their use of the RF

channel. Frequency division is still used, but these carriers are now further sub-divided into

some number of time slots per carrier (3 for TDMA-AMPS, 8 for full rate GSM, 16 for half

rate GSM).

In CDMA there is no time division, and all users use the entire carrier, all of the time. CDMA

is a spread-spectrum communication system in which multiple users have access to the same

frequency band. The allocated frequency segment for that one carrier is considerably larger

than that used in FDMA or TDMA. To distinguish the different users occupying the same

frequency band simultaneously, each user is assigned a binary code.

5.2 Radio Transmission Properties and Problems

5.2.1 Needed vs. Available Capacity

One problem encountered with radio is that the available spectrum is limited. The fewer

spectrums needed per subscriber the more subscribers that can be accommodated on the

network. Since there is no way to create new frequencies we need good modulation

techniques and efficient access methods to use the air interface properly.

Normally, the capacity available is a compromise between needed capacity and the

interference (more interference involve less quality in our connection) that the use of the same

medium by different users produces.

5.2.2 Path Loss

Path loss or attenuation of the signal causes the received signal at the receiver to get weaker

the further away from the transmitter we are (see Figure 5.7).

Path loss can be a problem, making it difficult to get sufficient signal strength levels, but it

results also in a lower interference from non wanted transmitters far away from the receiver.


73


If there would be no path loss the interference from all transmitters around us would be very

high.

Figure 5.7. Path Loss

For a given frequency, path loss depends on the distance between the receiver and the

transmitter. One way to estimate this is to use the free space formula. According to this

formula, the path loss varies proximally in the following way:

Pathloss ≈ distance 2 x frequency 2

This formula assumes a line of sight condition between the transmitting and receiving

antennas. It also assumes that there are no reflections interacting with the direct radio wave.

Also, as indicated buy the formula, the higher the frequency used, the higher the path loss.

Since the pathloss will increase with an increasing frequency it is beneficial if the weakest

part, according to transmitting power, is using the lowest frequency. By this it will gain some

dB.

5.2.3 Shadowing

If the radio path does not have free line of sight between transmitter and receiver, the

obstacles will cause shadowing. Shadowing is also called “log normal fading” or “long term

fading”. Since the mobile phone normally is located in a low position, transmission will most

likely be affected by shadowing objects, e.g. buildings, hills, the user or virtually anything in

the radio path. When the mobile phone moves around, variations in signal strength, due to the

character of the objects, can be measured in tens of meters.

dd


74


5.2.4 Multi-Path Propagation

Another effect that might occur especially in an urban area with a lot of reflections objects

near the transmitter and receiver is multi-path propagation (see Figure 5.8). Since the

transmitter normally is not transmitting directly towards the receiver but rather in a wide area

towards him/here, there will be a lot of rays reflected by obstacles and the received by the

receiver.

Figure 5.8. Multi- Path Propagation

Different reflections would then mean slightly different time delays for the rays and the

reflections also will have different effects on the phase of the radio wave. Normally we would

receive not one, but several reflected radio waves and the resulting wave could be stronger, or

weaker, than the individual waves. If there is no phase difference between the waves, the

resulting wave may have considerably better signal strength, but if the phase difference

between the two signals is close to 180 degrees they may null each other out. This cancelling

out effect may cause very deep fading dips. The phenomenon is called multi-path or Rayleigh

fading. On the other hand a receiver could with the help of some addative procedures capture

a number of different reflected rays and the take “the best” out of this information.

In a GSM system multipath propagation can cause problems in the receiver, multipath fading,

while in another system like UMTS with a RAKE receiver structure this leads to the

possibility of diversity gain turning the multipath channel to its advantage.


75


5.2.5 Time Dispersion

One effect of multipath propagation is time dispersion due to varying propagation delays. The

effect is that the impulse response of the propagation channel is spread out. The amount of

time dispersion is roughly described by the delay spread (see Figure 5.9).

Figure 5.9. Channel Impulse Response (Power) / Time Delay

5.3 Radio Transmission Optimisatioin Techniques

5.3.1 Access Methods: Capacity vs Interference

Interference is the term for a non-wanted signal that the receiver experiences. In e.g. GSM

where we reuse the number of frequencies available this might mean that there is a transmitter

using the same frequency as the wanted signal (see Figure 5.10). Reusing an identical carrier

frequency in different cells is limited by co-channel interference or C/I. Co-channel

interference is the relation between the desired signal C and the undesired re-used signal I,

both using the same carrier frequency.

Radio communication systems often separate users either by frequency channels, timeslots, or

both. This is e.g. true for GSM. Since the number of available frequencies both are limited by

physics and by regulation the frequencies then must be reused (see Figure 5.11).

This might cause an interference problem that will be handled by keeping the reuse

frequencies (same frequencies) as far away from each other as possible. Satisfactory

performance in these systems depends critically on control of the mutual interference arising

from this reuse pattern.

Impulse response

timeτ1 τ2 τ3

Impulse response

timeτ1 τ2 τ3


76


Figure 5.10. Interference

Another approach to this is used in CDMA. Instead of partitioning either spectrum or time

into disjoint “slots” each user is assigned a different instance of the noise carrier. While those

waveforms are nor rigorously orthogonal (they do not interfere with each other), they are

nearly so.

Figure 5.11. Reusing Frequencies in GSM Figure 5.12. In CDMA

The major benefit of noise-like carriers is that the system sensitivity to interference is

fundamentally altered. Traditional time or frequency slotted systems must be designed with a

reuse ratio that satisfies the worst-case interference scenario. Use of noise-like carriers, with

all users occupying the same spectrum, makes the effective noise the sum of all other-user

signals.

The receiver correlates its input with the desired noise carrier, enhancing the signal to noise

ratio at the detector. The enhancement overcomes the summed noise enough to provide an

adequate Signal to Noise Ratio, SNR at the detector. Because the interference is summed, the

system is no longer sensitive to worst-case interference, but rather to average interference.

The reuse pattern is now the same for each (see ).

CI

Carrier, f1 Interferer, f1

CI

Carrier, f1 Interferer, f1

A

A

AA

B

B

B

B

C

C

C

D

D

D

E

FA

A

AA

B

B

B

B

C

C

C

D

D

D

E

F A

A

AA

A

A

A

AA

AA

AA

A

A

AA

A

A

A

AA

AA

AA


77


5.3.2 Diversity

One of the objectives in system optimisation is to reduce or benefit from the multipath and

shadowing effects. Some are applicable to TDMA and FDMA as well as CDMA system.

There are different combinations to diversity.

5.3.2.1 Space Diversity

By using two receiving antennas, chances are that they do not experience the same multipath

propagation at the same time. A certain distance between the antennas could be used (space

diversity) or the antennas element could be polarised (polarisation diversity). The use of

antenna diversity will improve the carrier to interference (C/I) properties of the systems as the

problem with the fading dips is reduced.

5.3.2.2 Frequency Diversity

Another effective way to fight negative effects of multi-path propagation is to change the

frequency, thus changing the positions of the dips. When frequency hopping is applied as in

GSM/DCS, each consecutive burst will be transmitted (and of course received) at a different

frequency.

5.3.2.3 Multi-Path Diversity

Here versions of the signal arrive via separate paths and at different times and are combined

in the receiver.

5.3.2.4 Macro Diversity

Simultaneous use of links between the mobile and two or more fixed transmitters. Can for

example be used to provide a smooth transition as the mobile moves from transmitter to

another (soft handover).

5.3.2.5 Time Diversity

Obtained by using symbol interleaving and error correction coding to introduce time

correlation into the signal (described later in this chapter).


78


5.3.3 Error Detection and Correction

In the first and second generation mobile system like NMT and GSM the main intention and

use of the system have been foe speech communication. The 3rd generation system, like

UMTS, will need to handle more and more of data transmission and multimedia. This, in

contrast to pure speech system, adds high demands on the quality. Typical data services

require very low error rates. Over a radio channel that experiences a lot of problems we need

something to detect errors and correct them.

This could be done with the help of retransmission of information that was faulty and/or by

adding redundant information to the data. Channel coding is a way to add information to the

data so that errors could be detected and corrected. Interleaving is a technique to help the

channel coding procedure.

5.3.3.1 Channel Coding

In an analogue network the loss of some information will only decrease the quality somewhat.

The ear is able to correct the analogue signals that are slightly incorrect. In a digital network,

however, the importance of each bit of information is crucial. The symbol “1” interpreted as a

“o” gives a totally different piece of information. The quality of the received signal is often

measured in Bit Error Rate (BER). The BER represents what percentage of the bits that is not

correctly detected.

Two different methods of channel coding are block coding and convolutional coding. The

philosophy of both of them is basically the same; adding a number of redundant bits to help

detect or correct the errors protects the bits.

5.3.3.1.1 Block coding

When block coding is used, one or several check bits are added to the information block. The

check bits only depend on the bits in that block.

A simple form of block coding is using a parity bit. The parity bit could be set to zero if the

1’s in the block equal an even number. Otherwise the parity bit is set to one, so that the

number of 1’s in the total block are always even (see Figure 5.13).


79


Block coding is mainly used for detecting errors. In the computer world block coding is often

used together with a retransmission command, demanding the transmitting part to resend.

This is not so useful when dealing with a real time application such as speech.

Figure 5.13. The Principle of Block Coding

5.3.3.1.2 Convolutional Coding

The convolutional code consists of a shift register into which one shifts on the information

bits. Doing logical operations on the positions of the bits in the register produces the coded

information bits. This will make several coded bits dependent on one of the information

symbols shifted into the coder. When all the information are shifted through the register we

have produced the coded bits that will be sent (see Figure 5.14).

Convolutional coding is not good for detecting errors, but also for correcting them. The

condition for being able to correct errors is that only few errors appear at a time, with a certain

number of correct bits in between the incorrect ones.

Figure 5.14. The Principle of Convolutional Coding

5.3.3.2 Interleaving

The error detection and correction methods mentioned, work best when the bits lost are

spread out at a certain distance.

If 1 then add 1

If 0 then add 0

Information Parity bits

Received Means

11 1

00 0

01 error

10 error

If 1 then add 1

If 0 then add 0

Information Parity bits

Received Means

11 1

00 0

01 error

10 error

infoBit 3 Bit 2 Bit 1

Output A

Output B

XOR

XOR

infoBit 3 Bit 2 Bit 1

Output A

Output B

XOR

XOR


80


Interleaving is a method of spreading the potential losses, so that they can be taken care of by

“Channel Coding” thus minimising the harm longer sequences lost. An analogy of this is, if

the last 20 pages are torn out of an Agatha Christie novel, it will be more difficult to

reconstruct the plot than if every 10th page, totalling 20 pages is lost. As an example, let us

assume that each message block contains four symbols.

Figure 5.15. If Several Blocks Regroup the Information.

Assume also that it is likely that we loose not only one, but four consecutive symbols in a

block. If we re-arrange them so that all number one symbols are put together in one block, all

the number two symbols in another, etc., we will loose symbols from several blocks, BUT not

one complete block. If only parts of a block are lost, the chance of reconstructing the

information improves dramatically (see Figure 5.15).

T H E YM U S TH E A RT H I S

THEY MUST HEAR THIS

T H ? YM U ? TH E ? RT H ? S

THMT HEUH IASE SRTY

TH?Y MU?T HE?R TH?S



THEY MUST HEAR THIS

T H ? YM U ? TH E ? RT H ? S

THMT HEUH IASE SRTY

TH?Y MU?T HE?R TH?S

Chapter 6: User Equipment (UE)

81



6.1 Terminals in the General UMTS System

The

Figure 6.1 shown below represents the general schematic in the system, as they are explained

in this chapter.

Figure 6.1. UMTS Domains and Reference Points

We can divide basically between the User Equipment or Terminal (UE), and the

infrastructure. This is represented by the interface Uu. So we can have these two big domains:

the User Equipment Domain and the Infrastructure domain.

Home Network Domain

Zu

Yu Iu Uu Cu

USIM Domain

Mobile Equipment Domain

RAN Domain

CN Domain

Serving Network Domain

Transit Network Domain

User Equipment Domain Infrastructure Domain

Cu = Reference point between USIM and ME

Iu = Reference point between Access and Serving Network domains

Uu = Reference point between User Equipment and Infrastructure domains, UMTS radio

interface

Yu = Reference point between Serving and Transit Network domains

Zu = Reference point between Serving and Home Network domain


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User equipment is the terminal that the user employs to access to the UMTS service. This

equipment has a radio interface to the infrastructure.

The infrastructure is made up of the several physical nodes that develop the various functions

required to terminate the radio interface and to support the telecommunication services

requirements to the users. The infrastructure is a shared resource by all the users and it will

provide services to all these users (authorised) within its coverage area. The reference point

between the user equipment domain and the infrastructure domain is called the “Uu”

reference point (UMTS radio interface). As it has been said, it is a very important interface,

because it separates two different worlds.

6.1.1 User Equipment Domain

This part of the system stores a variety of equipment types with different levels of

functionality. These equipment types are referred to as user equipment (terminals), and they

may also be inter-connectable with one or more existing access systems, in such a way that

we can have dual mode UMTS-GSM user equipment.

As it has also been said, the terminal will include a removable smart card that may be used in

different user equipment types, as it happens in GSM. The user equipment is as well sub-

divided in to the Mobile Equipment Domain (ME) and the UMTS Subscriber Identity Module

Domain (USIM). Here we have another interesting interface, the Cu reference point

6.1.1.1 USIM Domain

The USIM, UMTS Subscriber Identity Module, contains data and procedures that

unambiguously and securely identify it. These functions are typically embedded in a stand-

alone smart card. This device is associated to a given user, and as such allows identifying this

user regardless of the ME he uses.

6.1.1.2 Mobile Equipment Domain

The Mobile Equipment contains applications and performs radio transmission. The mobile

equipment may be further sub-divided into several entities, e.g. the one which performs the

radio transmission and related functions, Mobile Termination, MT, and the one which


83


contains the end-to-end application or (e.g. laptop connected to a mobile phone), Terminal

Equipment, TE.

6.2 Applications of the UE

This 3 generation system wants to offer service capabilities that enable the wide variety of

services that the vendors will offer to be implemented. Such services range from simple

services like voice, to complex multimedia services containing several simultaneous media

components that place totally different requirements on the system and on the terminal

equipment.

A wide range of terminal types is likely in the UMTS environment, e.g. speech only

terminals, videophones, data terminals, wideband data terminals, fax terminals, multi-

band/multi-mode terminals and any combination of the aforementioned. By standardising

service capabilities rather than actual services, more flexibility is available for service

providers/network operators to create unique services. The same principle also applies for

UMTS terminals, i.e. the types of terminals are not standardised and are therefore not limited

in any way.

We know that no UMTS Terminal is going to be defined by the specifications, the power

classes need to be determined, for cell planning reasons. The maximum power will affect

User Equipment possibilities to support the upper range of bit services over the UMTS

coverage area. Cell planners will plan for achieving coverage for higher bit rates on the cell

border primarily for power class 1-user equipment's. The following four classes are defined:

• 2 W

• 0.5 W

• 0.25 W

• 0.125 W

We already know that no terminal types are standardised, so user equipment must indicate to

the network a set of terminal capabilities in order to be handled properly by the UTRAN and

the Core Network. The set of terminal capabilities includes radio capabilities, multimedia

capabilities and speech coders/decoders that are supported by the user equipment.


84


The radio parts of a user equipment can support any combination of GSM circuit switched

radio, GSM packet switched radio, UMTS FDD-mode and UMTS TDD-mode, and

additionally other radio access modes, due to the compatibility we have already talked before.

Multimedia capabilities may include which type of display and which coders/decoders that

are supported for video and audio. Finally, GSM and UMTS networks and terminals include a

number of different speech coders:

• GSM Full Rate

• GSM Half Rate

• GSM Enhanced Full Rate

• GSM Full Rate Adaptive Multi-Rate

• GSM Half Rate Adaptive Multi-Rate

• UMTS Adaptive Multi-Rate

The UMTS user equipment has a default speech code, the UMTS Adaptive Multi-Rate

(AMR) code. It generates a variable rate bit-stream of bit-rates between 4.75 – 12.20 kbit/s

depending on the characteristics of input speech signal.

6.3 Multimedia User Equipment

The ITU has developed extensions to the fixed terminal standards to adapt them to mobile

communication characteristics such as higher bit error rates.

The general architecture of a H.324 multimedia terminal in UMTS user equipment is shown

in Figure 6.2.

Mobile multimedia terminals for UMTS are based on existing multimedia terminal standards

for the fixed networks. ITU has produced a number of such standards, the so-called H-series.

Where needed slight modification for the UMTS case is introduced by 3GPP. ITU standards

H.323 and H.324 are used for UMTS multimedia terminals. H.324 is the standard for circuit

switched multimedia over the PSTN while H.323 targets multimedia over packet switched

networks with no support of guaranteed Quality-of-Service.


85


Figure 6.2. UE Multimedia General Architecture.

The Application SW is not part of the standard. It contains the application software, e.g. the

user interface, in the terminal for multimedia application and controls the usage of the other

blocks in the Figure 6.2 which implement the H.324 standard components.

The H.324 components are:

• A video coder/decoder that transfers analogue video into a digital bit-stream (H.263)

• The audio coder/decoder that transfers analogue audio into a digital bit-stream (G.723.1)

• Data protocols for end-to-end retransmissions and flow control for transfer of user data

end-to-end (e.g. LAP-D)

• Control procedures for multimedia session set up and release end-to-end (H.245)

• All the streams generated by the four entities above are finally multiplexed into one single

bit-stream according to the H.324 multiplex standard H.223.

In order to have terminals that work properly the single bit-stream from the multiplexer

requires a bit-rate of at least 32 kbit/s.

The five entities in the H.324 terminal part reside in the Terminal Equipment part of the

UMTS User Equipment. The single bit-stream from the multiplexer is sent to the Mobile

Termination part of the User Equipment for transparent transport over the radio interface an

onwards. (The core network will be aware of the fact that the call is a H324 call in order to

activate specific rate adaptation functions in the so-called Interworking Function in the MSC).

Multiplex

VideoCodec

AudioCodec Data End-to-End

Control

To Mobile Termination

Application SW


86


3GPP has added the ETSI AMR speech coder/decoder to the list of possible audio codecs for

the purpose of mobile-to-mobile multimedia calls. The G.723.1 speech codec has to be

supported by UMTS multimedia terminals for interworking with terminals in the fixed

network. We also have the standard MPEG-4, for video applications, introduced by the

International Standardisation Organisation. It is introduced for every kind of video

applications, i.e. not only videotelephony.

6.4 UMTS Subscriber Identity Module (USIM)

This module of the Terminal must contain information enough to identify the user and service

provider. USIM is a UMTS specific application residing on a removable IC card and is

required for service provision. The application in order to allow more versatile UMTS IC card

functionality such as access to value-added services. Authentication and ciphering

functionality may be part of USIM or some other application on the same or different IC card.

Necessary requirements for IC Cards used for holding USIM application are related to the

need to have one USIM application on the IC card, as well as to the security issues. The

following functionality is required from the IC card holding USIM application:

• The support of at least one USIM application (several USIM applications belonging to

different UMTS service providers may reside on the same IC card).

• Possibility to update USIM specific information over the air, (e.g. such information as

service profile information, algorithms, etc.) in a secure and controlled manner.

• The support of one or more user profile on the USIM

• Physical characteristics same as used for GSM SIM (note that the standard supports

inserting a GSM SIM card into a UMTS user equipment which will enable access to the

GSM set of services, i.e. no UMTS specific service).

• Possibility to update USIM specific information over the air, (e.g. such information as

service profile information, algorithms, etc.) in a secure and controlled manner.

• User authentication.

• The standard should support the following additional functionality for the IC Cards in

UMTS environment:


87


• Security mechanisms to prevent USIM application specific information from unauthorised

access or alteration. Verification of the access privilege shall be performed on the card

itself and not delegated to another entity (for example the terminal).

• The support for more than one simultaneous application (Multiple USIM, Ecash and/or

some other applications).

• An interface allowing highly secure downloading and configuration of new functionality,

new algorithms and new applications into the IC card as well as updating the existing

applications, algorithms and data.

• Possibility for some applications/files to be restricted to one or some of the subscriptions,

under user/SP control, with all applications that are shared, being done so in a secure

manner.

• Possibility to have shared applications/files between multiple subscriptions including

other user and Service Provider controlled files and data, as well as for as yet undefined

applications (including downloadable applications) required by the future services.

Related security issues have to be analysed.

• Inclusion of a payment method (electronic money and/or prepaid and/or subscription

details)

• Support for storing and possibly executing encryption related information, such as keys

and algorithms.

• The ability to accept popular value-adding IC card applications, such as digital signature

applications, EMV credit/debit card, electronic purses such as Mondex and Visacash, etc.

Dynamic addition and deletion of these applications during the lifetime of the card is

envisaged.

• Possibility for one UMTS SP to block multiple subscription on the card the SP has issued.

• In multi application cards a functionality to prevent the unauthorised access and alteration

of USIM specific information by other applications residing on the card.

With all of these shared applications we can include database (e.g. telephone books), service

profiles (e.g. controlling divert information), users preferences (e.g. short dialling codes) and

SP-specific parameters inside a USIM application (e.g. call barring tables).


88


6.5 Technology of the Terminals

The complexity of the equipment of the 2nd generation digital cellular terminals is already

considerable. The first reason for this, cellular systems themselves require a huge amount of

functions to be fulfilled, from channel and speech coding to signalling and data protocols. In

addition to those functions, all terminals have there owned mobile system independent

features, sometimes also called as Value Adding features. Examples of these are memory

databases, speech recognition, messaging features, display functions, and different source

coding methods (e.g., JPEG).

Terminal development trends for today’s terminals are mainly towards higher integration

levels resulting in smaller size. The goal of “four 100´s” has been a rule of thumb target for

handsets, i.e., 100 hour standby, 100 cc size, 100 gram weight and also 100 MIPS

performance. The size targets have already been achieved and any requirement for smaller

terminals is questionable from the usability and physical size limitation perspective. The other

target parameters have no maximum limitations. On the other hand, we can see the following

further trends for near future terminals:

• Increased number of value adding features (graphics, smart messaging, PC connectivity

and compatibility).

• Support of higher number of source codecs (several speech codecs).

• Application specific terminals (smart traffic, vending machine radio, etc.).

• Multi-mode terminals (e.g., GSM/DECT dual-mode terminal).

• Multi-band terminals (e.g., GSM in 900 MHz and DCS1800).

• Dynamic SW configurability.

These trends are more than likely to continue in the future. The users would prefer multi-band

and multi-mode terminals with high integration levels. Technological development of these

terminals relies on new packaging and interconnection technologies, as well as technological

steps like SW-radio. The concept trends of mobile handheld terminals is likely to diverge

from simple speech terminals towards a variety of different types, e.g., communicators, were

able phones, data terminals, etc. These new data- and multimedia-oriented terminals will

challenge the dominant role of speech terminals in the future.


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New radio-interface and system capabilities will enable higher quality multimedia services to

be provided and therefore new terminal concepts to evolve, the variety of terminals in the

UMTS environment will evidently be large. Terminal implementation technologies, such as

digitalisation providing programmability and terminal configurability, VLSI, and display

technologies, have developed a lot recently and will undergo further development in the

future. Processing power, implementation architectures, IC and passive integration, and

memory technologies are developing rapidly and will facilitate an increase in terminal

functionality that will enable higher integration of terminals, as well as the integration of

more functionality into smaller terminals.

It can be clearly seen that the technical development of IC cards in the UMTS context.

Compared to current IC cards (e.g. GSM Phase 2 SIM cards), the amount of memory and

processing power will increase significantly. These development trends will meet the

requirements of UMTS and should be taken into account while defining the features and

functions of UMTS card.

The trend for IC cards (used form the USIM) is similar to those form terminals. The next

generation of IC cards will be multi-application cards capable of supporting several

applications simultaneously. Furthermore, applications could be downloaded to and removed

from these cards, both at the time of issuing and during the card’s lifetime. The advent of

these virtual machine cards, e.g. Java cards and Multi cards, will change the roles of the card

issuers and application providers, and will enable IC cards to be much more flexible in the

future.

Chapter 7: UMTS Terrestrial Radio Acces Network (UTRAN)

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7.1 Introduction

UTRAN (UMTS Radio Access Network) is the radio access network for UMTS, and it

provides the connection between the core network and the user equipment. In UMTS Release

99 UTRAN is considered the only access network. UTRAN will support high bit rate bearer

services with the notion of negotiated QoS characteristics. It will also support asymmetric and

bursty traffic for single- and multi-media IP as well as N-ISDN applications.

UMTS R-99 puts interoperability requirements on both UTRAN and GSM BSS access

networks, in such a way that the evolved GSM network is compatible with UTRAN regarding

roaming and handover. It might however be the case that the advanced bearer capabilities of

UTRAN not are fully supported by the core network.

7.2 UTRAN Main Aspects

7.2.1 General Principles

The general principles for UTRAN:

• Logical separation of signalling and data transport networks.

• A full separation of UTRAN and CN functions from the transports functions.

• Full support for macro diversity in UTRAN-FDD

• The RNC connection and its mobility is fully controlled by the UTRAN.

7.2.2 Capabilities

The radio access bearer (RAB) capabilities for UTRAN are specified in 22.105.


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UTRAN in R-99 shall have the following capabilities:

• One UTRAN is contained in one UMTS network.

• The set-up, re-negotiation and clearing, of connections.

• Negotiation and re-negotiation of QoS.

• Supported bit rates:

At least 144 kbit/s rural outdoor.

At least 384 kbit/s urban outdoor.

At least 2048 kbit/s indoor/low range outdoor.

• Support for broadcast and multicast applications.

• Support for multiple simultaneous RABs.

• Seamless handover within UTRAN.

• Support for dual mode terminals FDD-TDD.

• Support for handover TDD-FDD-GSM.

• Support for positioning within 50 meters.

• Support for Localised Service Area (LSA)

• Optimisation of UTRAN radio interface is based on high bit rates, bursty, asymmetric,

both real time and non-real time capabilities.

• Standardised operation, administration and maintenance protocols co-operating with ETSI

TMN.

• USIM requirements shall be considered.

7.2.3 UTRAN and GSM BSS (GSM Base Station Subsystem)

Since the evolution to UMTS will be gradually, the co-existence of UTRAN and GSM BSS in

a network is essential. This requires the following for UMTS R-99:

• Support of dual mode terminals (UMTS/GSM) that can select cells to camp on from both

systems in idle mode and connected mode.


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• Paging and cell selection procedures shall be designed to handle the combination of GSM

and UTRAN cells.

• Support of handover between UMTS and GSM BSS in both directions.

Note that some traffic flows might be re-negotiated or even released because of the different

radio access bearer capabilities of the different access networks.

7.3 UTRAN System Architecture

7.3.1 UMTS General System Architecture

UTRAN is connected to the CN over the Iu interface, and with UE over the radio interface

Uu. Over these interfaces the protocols are divided in "User plane protocols" (UPP) and

"Control plane protocols (CPP). The UPP implements the actual Radio Access Bearer (RAB)

service that carries the data through the Access Stratum (AS). The CPP controls the RAB, but

can be used to transparently transfer Non-Access Stratum (NAS) messages (i.e. CM, MM

(Mobile Management), GMM and SM messages).

Figure 7.1. UMTS System General Architecture

7.3.2 UTRAN Architecture

The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network

through the Iu. A RNS consists of a Radio Network Controller and one or more Node Bs. A

UTRAN

Iu

UE

Uu

UTRAN UMTS Terrestrial Radio Access NetworkCN Core NetworkUE User Equipment

CN


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Node B is connected to the RNC through the Iub interface. A Node B can support FDD mode,

TDD mode or dual-mode operation.

The RNC is responsible for the Handover decisions that require signalling to the UE. The

RNC comprises a combining/splitting function to support macro diversity between different

Node B. A RNC supporting the FDD mode may include a combining/splitting function to

support macro diversity between different Node B.

Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnected

together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over physical

direct connection between RNCs or via any suitable transport network.

Figure 7.2. UTRAN Architecture

7.4 UTRAN Nodes

7.4.1 Node B

Node B transmits and receives in one or more cells. There are three modes for a Node B:

TDD, FDD or a combination of TDD and FDD. The Node B interfaces the UE over the Uu

interface, and the RNC over the Iub interface. One Node B consists of the following blocks:

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu Iu

Iur

Iub IubIub Iub


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7.4.1.1 Control

The control function is responsible for the signalling towards the RNC and the O&M

functions. It also monitors the radio quality in the cells, and insert data in the system

information.

7.4.1.2 Signal Processing

The processing of the signal has different requirements in UL and DL:

• Uplink:

SC/CC generation

Despreading

Rake receiver

Deinterleaving

Channel decoding

Combining (in softer handover)

• Downlink:

Splitting (in softer handover)

Channel coding

Interleaving

CC/SC generation

Spreading

7.4.1.3 Transmitter / Receiver

The transmission/reception part handles the carrier generation and is responsible for the

output power. Here is the modulation/demodulation performed. The modulation is QPSK.


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7.4.2 The Radio Network Controller (RNC)

The RNC is in control of one or several Node B:s. It interfaces the MSC or SGSN in the core

network over the Iu interface, and the Node B over the Iub interface. An interface between

RNC:s is specified, and known as the Iur interface. The RNC consists of the following:

7.4.2.1 Radio Network Management

Signalling both to CN and UE is handled by radio network management functions. This

function is also responsible for the (re-)negotiation with an UE in a cell and the CN for the

QoS for a call/session. This function is also responsible for the control of system information

from CN and UTRAN.

7.4.2.2 Radio Access Bearer Management

The radio access bearer management functions is responsible for the establishment,

supervision and release of radio bearers.

• Establishment: assigns and activates channels in Node B, and assigns channels to the UE

• Supervision: monitors QoS, handover decisions

• Release: deactivates channels

7.4.2.3 Signal Processing

The signal processing functions handles flow control and retransmissions, as well as the

SOHO procedures combining (UL) and splitting (DL). It also handles the

ciphering/deciphering.

7.5 UTRAN Interfaces

UTRAN contain two internal interfaces (Iub, Iur) and interfaces to the UE (Uu) and the core

network (Iu).

7.5.1 General Principles for UTRAN Interfaces

• As few options as possible for the functional division across the interfaces.


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• Interfaces should be based on a logical model of the entity controlled through this

interface.

Transport Network Control Plane is a functional plane in the interface protocol structure that

is used for the transport bearer management. The actual signalling protocol that is in use

within the Transport Network Control Plane depends on the underlying transport layer

technology. The intention is not to specify a new UTRAN specific Application Part for the

Transport Network Control Plane but to use signalling protocols standardised in other groups

(if needed) for the applied transport layer technology.

7.5.2 Iu Interface

7.5.2.1 Access Network Triggered Streamlining

One Access Network triggered function needed over the Iu interface is the function for SRNS

Relocation. SRNS Relocation needs support from the Core Network to be executed.

Figure 7.3. Serving RNS Relocation

SRNS

Core Network

Iu

DRNSIur

UE

RNS

Core Network

Iu

SRNS

UE

After SRNS RelocationBefore SRNS Relocation

Cells


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7.5.2.2 Iu Interface Protocol

The Radio Network signalling over Iu consists of the Radio Access Network Application Part

(RANAP). The RANAP consists of mechanisms to handle all procedures between the CN and

UTRAN. It is also capable of conveying messages transparently between the CN and the UE

without interpretation or processing by the UTRAN.

Over the Iu interface the RANAP protocol is, e.g. used for:

• Facilitate a set of general UTRAN procedures from the Core Network such as paging -

notification as defined by the general SAP.

• Separate each User Equipment (UE) on the protocol level for mobile specific signalling

management as defined by the dedicated SAP.

• Transfer of transparent non-access signalling as defined in the dedicated SAP.

• Request of various types of UTRAN Radio Access Bearers through the dedicated SAP.

• Perform the streamlining function.

The Access Stratum provides the Radio Access Bearers.

Various transmission possibilities exist to convey the bearers over the Iu to the Core Network.

It is therefore proposed to separate the Data Transport Resource and traffic handling from the

RANAP (Figure 7.4). This resource and traffic handling is controlled by the Transport

Signalling. A Signalling Bearer carries the Transport Signalling over the Iu interface.

Figure 7.4. Separation of RANAP and Transport over Iu


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The RANAP is terminated in the SRNS.

7.5.3 Iur Interface

The Iur interface connects a SRNS and a DRNS. This interface should be open. The

information exchanged across the Iur is categorised as below:

• One or more Iur Data stream which comprises:

Radio frames

Simple, commonly agreed Quality estimate

Synchronisation information

• Signalling:

Addition of Cells in the DRNS which may lead or not to the addition of an new Iur

Data stream

Removal of Cells in the DRNS

Modify Radio bearer characteristics

From a logical stand point, the Iur interface is a point to point interface between the SRNS

and all the DRNS, i.e. there is no deeper hierarchy of RNSs than the SRNS and DRNS.

However, this point to point logical interface should be feasible even in the absence of a

physical direct connection between the two RNSs.

7.5.3.1 Functional Split over Iur Interface

7.5.3.1.1 Macro Diversity Combining/Splitting

DRNS may perform macro-diversity combining/splitting of data streams communicated via

its cells. SRNS performs macro-diversity combining/splitting of Iur data streams received

from/sent to DRNS(s), and data streams communicated via its own cells.

The internal DRNS handling of the macro-diversity combining/splitting of radio frames is

controlled by the DRNS.


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7.5.3.1.2 Control of Macro Diversity Combining/Splitting Topology

When requesting the addition of a new cell for a UE-UTRAN connection, the SRNS can

explicitly request to the DRNS a new Iur data stream, in which case the macro-diversity

combining and splitting function within the DRNS is not used for that cell. Otherwise, the

DRNS takes the decision whether macro-diversity combining and splitting function is used

inside the DRNS for that cell i.e. whether a new Iur data stream shall be added or not.

7.5.3.1.3 Handling of DRNS Hardware Resources

Allocation and control of DRNS hardware resources, used for Iur data streams and radio

interface transmission/reception in DRNS, is performed by DRNS.

7.5.3.1.4 Allocation of Downlink Channelisation Codes

Allocation of downlink channelisation codes of cells belonging to DRNS is performed in

DRNS.

Note that this does not imply that the signalling of the code allocation to the UE must be done

from the DRNS.

7.5.3.2 Iur Interface Protocol

The signalling information across Iur interface as identified in previous section is called

Radio Network Subsystem Application Part (RNSAP).

Figure 7.5. Separation of RNSAP and Transport Over Iur


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The RNSAP is terminated in the SRNS and in the DRNS.

As already stated in previous section a clear separation shall exist between the Radio Network

Layer and the Transport Layer. It is therefore proposed to separate the Data Transport

resource and traffic handling from the RNSAP (Figure 7.5). This resource and traffic handling

is controlled by the Transport Signalling. A Signalling Bearer carries the Transport Signalling

over the Iur interface.

7.5.4 Iub Interface

The Iub interface connects a RNC and a Node B.

The information transferred over the Iub reference point can be categorised as follows:

1. Radio Application Related Signalling:The Iub interface allows RNC and Node B to

negotiate about radio resources, for example to add and delete cells controlled by the

Node B to support communication of the dedicated connection between UE and SRNS.

2. Radio Frame Data Blocks:The Iub interface provides means for transport of uplink and

downlink radio frame data blocks between RNC and Node B. This transport can use pre-

defined transmission links or switched connections.

3. Quality Estimations of Uplink Radio Frames and Synchronisation Data:The macro-

diversity combining function of the RNC uses Node B quality estimations of the uplink

radio frame data blocks. There is also a need for accurate time synchronisation between

the soft handover branches.

The information in category 3 is tightly coupled to the radio frame data blocks in category 2.

Therefore, category 2 and 3 information is multiplexed on the same underlying transport

mechanism (e.g. switched connection), and is together referred to as an Iub data stream.

The Iub data stream shall follow the same specification as the Iur data stream.

Over the Iub interface between the RNC and one Node B, one or more Iub data streams are

established, each corresponding to one or more cells belonging to the Node B.


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7.5.4.1 Functional Split Over Iub

7.5.4.1.1 Macro-diversity Combining of Radio Frame Data Blocks

Node B may perform macro-diversity combining/splitting of data streams communicated via

its cells. RNC performs macro-diversity combining/splitting of Iub data streams received

from/sent to several Node B(s).

7.5.4.1.2 Control of Macro Diversity Combining/Splitting Topology

When requesting the addition of a new cell for a UE to UTRAN connection, the RNC can

explicitly request to the Node B a new Iub data stream, in which case the macro-diversity

combining and splitting function within the Node B is not used for that cell. Otherwise, the

Node B takes the decision whether macro-diversity combining and splitting function is used

inside the Node B for that cell i.e. whether a new Iub data stream shall be added or not.

The Node B controls the internal Node B handling of the macro-diversity combining/splitting.

7.5.4.1.3 Soft Handover Decision

To support mobility of the UE to UTRAN connection between cells, UTRAN uses

measurement reports from the MS (Mobile Station) and detectors at the cells.

The RNC takes the decision to add or delete cells from the connection.

7.5.4.1.4 Handling of Node B Hardware Resources

Mapping of Node B logical resources onto Node B hardware resources, used for Iub data

streams and radio interface transmission/reception, is performed by Node B.

7.5.4.1.5 Allocation of Downlink Channelisation Codes

Allocation of downlink channelisation codes of cells belonging to Node B is performed in

Node B.

Note that this does not imply that the signalling of the code allocation to the UE must be done

from Node B.


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7.5.5 UTRAN Internal Bearers

For all open interfaces, one mandatory set of protocols must be specified. However, a clear

separation between the Radio Network functions and the Transport functions should allow

this Transport layer to be exchanged to another one with minimum impact on the Radio

Network functions.

7.5.5.1 User Data Bearers

ATM and AAL type 2 (ITU-T recommendations I.363.2 and I.366.1) is used as the standard

transport layer for Soft Handover data stream across the Iur interface.

7.5.5.2 Signalling Bearers

7.5.5.2.1 Signalling Bearer Requirements for Iu Interface

Over the Iu interface the RANAP protocol requires:

• A connectionless transport of RANAP messages to facilitate e.g. paging.

• A connection oriented transport of RANAP messages e.g. to facilitate messages belonging

to a specific User equipment (UE) during a call.

• A reliable connection to make the RANAP simpler.

• Support of signalling inactivity testing of a specific UE connection.

7.5.5.2.2 Signalling Bearer Requirements for Iur Interface

There exist at least two major types of soft handover over the Iur interface:

1. The case when a new physical transmission (Iur data stream) is set up over the Iur

interface to provide an additional cell.

2. The case when existing transmission (Iur data stream) is used over the Iur interface when

an additional cell is added in the DRNS. In this case the DRNS must be able to identify

the UE in order to perform the adding of the cell. Consequently a UE context must exist in

the DRNS.

Over the Iur interface the RNSAP protocol requires:


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• A connection oriented transport of RNSAP messages, i.e. one signalling bearer connection

for each DRNS for a particular UE.

• A reliable connection to make the RNSAP simpler.

• Support of signalling inactivity testing of a specific UE connection.

7.6 UTRAN Functions

The functions of UTRAN are divided in functions for overall system control, radio channel

ciphering, mobility and radio resource handling.

7.6.1 System Access Control

System access is the means by which a UMTS user is connected to the UMTS in order to use

UMTS services and/or facilities. User system access may be initiated from either the mobile

side, e.g. a mobile originated call, or the network side, e.g. a mobile terminated call.

• Admission Control.

• Congestion Control.

• System information broadcasting: This function provides the mobile station with the

information that is needed to camp on a cell and to set up a connection in idle mode and to

perform handover or route packets in communication mode. The tasks may include:

Access rights

Frequency bands used

Configuration of transport channels, PCH, FACH and RACH channel structure of the

cell, etc.

Network and cell identities

Information for location registration purposes

UE idle mode cell selection and cell re-selection criteria

UE transmission power control information

UE access and admission control information


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Because of its close relation to the basic radio transmission and the radio channel structure,

the basic control and synchronisation of this function should be located in UTRAN.

7.6.2 Radio Channel Ciphering / Deciphering

7.6.2.1 Radio Channel Ciphering

This function is a pure computation function whereby the radio transmitted data can be

protected against an non-authorised third party. Ciphering may be based on the usage of a

session-dependent key, derived through signalling and/or session dependent information. This

function is located in the UE and in the UTRAN.

7.6.2.1.1 Radio Channel Deciphering

This function is a pure computation function that is used to restore the original information

from the ciphered information. The deciphering function is the complement function of the

ciphering function, based on the same ciphering key. This function is located in the UE and in

the UTRAN.

7.6.3 Mobility

7.6.3.1 Radio Environment Survey

This function performs measurements on radio channels (current and surrounding cells) and

translates these measurements into radio channel quality estimates. Measurements may

include:

• Received signal strengths (current and surrounding cells),

• Estimated bit error ratios, (current and surrounding cells),

• Estimation of propagation environments (e.g. high-speed, low-speed, satellite, etc.),

• Transmission range (e.g. through timing information),

• Doppler shift,

• Synchronisation status,


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• Received interference level.

In order for these measurements and the subsequent analysis to be meaningful, some

association between the measurements and the channels to which they relate should be made

in the analysis. Such association may include the use of identifiers for the network, the base

station, the cell (base station sector) and/or the radio channel. This function is located in the

UE and in the UTRAN.

7.6.3.2 Handover Decision

This function consists of gathering estimates of the quality of the radio channels (including

estimates from surrounding cells) from the measuring entities and to assess the overall quality

of service of the call. The overall quality of service is compared with requested limits and

with estimates from surrounding cells. Depending on the outcome of this comparison, the

macro-diversity control function or the handover control function may be activated.

This function may also include functionality to assess traffic loading distribution among radio

cells and to decide on handing over traffic between cells for traffic reasons. The location of

this function is depending on the handover principle chosen:

• If network only initiated handover, this function is located in the UTRAN;

• If mobile only initiated handover, this function is located in the UE;

• If both the mobile and the network can initiate handover, this function will be located in

both the UTRAN and the UE.

7.6.3.3 Macro Diversity Control

Upon request of the handover decision function, this function control the duplication/

replication of information streams to receive/ transmit the same information through multiple

physical channels (possibly in different cells) from/ towards a single mobile terminal. This

function also controls the combining of information streams generated by a single source

(diversity link), but conveyed via several parallel physical channels (diversity sub-links).

Macro diversity control should interact with channel coding control in order to reduce the bit

error ratio when combining the different information streams. This function controls macro-

diversity execution which is located at the two endpoints of the connection element on which


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macro-diversity is applied (diversity link), that is at the access point and also at the mobile

termination.

In some cases, depending on physical network configuration, there may be several entities

which combine the different information streams, e.g. one entity combines information

streams on radio signal basis, another combines information streams on wire-line signal basis.

This function is typically located in the UTRAN. However, depending on the physical

network architecture, some bit stream combining function within the CN may have to be

included in the control.

7.6.3.4 Handover Control

In the case of switched handover, this function is responsible for the overall control of the

handover execution process. It initiates the handover execution process in the entities required

and receives indications regarding the results. Due to the close relationship with the radio

access and the Handover Decision function, this function should be located in the UTRAN.

7.6.3.5 Handover Execution

This function is in control of the actual handing over of the communication path. It comprises

two sub-processes: handover resource reservation and handover path new radio and wire-line

resources that are required for the handover.

When the new resources are successfully reserved and activated, the handover path switching

process will perform the final switching from the old to the new resources, including any

intermediate path combination required, e.g. handover branch addition and handover branch

deletion in the soft handover case. This function is located in the UTRAN for UTRAN

internal path switching and in the CN for CN path switching.

7.6.3.6 Handover Completion

This function will free up any resources that are no longer needed. A re-routing of the call

may also be triggered in order to optimise the new connection. This function is located both in

the UTRAN and in the CN.


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7.6.3.7 SRNS Relocation

The SRNS Relocation function co-ordinates the activities when the SRNS role is to be taken

over by another RNS. SRNS relocation implies that the Iu interface connection point is

moved to the new RNS. This function is located in the UTRAN and the CN.

7.6.3.8 Inter-System Handover

The Inter-system handover function enables handover to and from e.g. GSM BSS. This

function is located in the UTRAN, the UE and the CN.

7.6.4 Radio Resource Management and Control

Radio Resource Management is concerned with the allocation and maintenance of radio

communication resources. UMTS radio resources must be shared between circuit mode (voice

and data) services and other modes of service (e.g. packet data transfer mode and

connectionless services).

7.6.4.1 Radio Bearer Connection Set-Up and Release (Radio Bearer Control)

This function is responsible for the control of connection element set-up and release in the

radio access sub network. The purpose of this function is

• To participate in the processing of the end-to-end connection set-up and release.

• And to manage and maintain the element of the end-to-end connection, which is located in

the radio access sub network.

In the former case, this function will be activated by request from other functional entities at

call set-up/release. In the latter case, i.e. when the end-to-end connection has already been

established, this function may also be invoked to cater for in-call service modification or at

handover execution. This function interacts with the reservation and release of physical

(radio) channels function. This function is located both in the UE and in the UTRAN.

7.6.4.2 Reservation and Release of Physical Radio Channels

This function consists of translating the connection element set-up or release requests into

physical radio channel requests, reserving or releasing the corresponding physical radio


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channels and acknowledging this reservation/release to the requesting entity. This function

may also perform physical channel reservation and release in the case of a handover.

Moreover, the amount of radio resource required may change during a call, due to service

requests from the user or macro-diversity requests. Therefore, this function must also be

capable of dynamically assigning physical channels during a call.

This function may or may not be identical to the function reservation and release of physical

radio channels. The distinction between the two functions is required e.g. to take into account

sharing a physical radio channel by multiple users in a packet data transfer mode. This

function is located in the UTRAN.

7.6.4.3 Allocation and De-Allocation of Physical Radio Channels

This function is responsible, once physical radio channels have been reserved, for actual

physical radio channel usage, allocating or de-allocating the corresponding physical radio

channels for data transfer.

This function may or may not be identical to the function reservation and release of physical

radio channels. The distinction between the two functions is required e.g. to take into account

sharing a physical radio channel by multiple users in a packet data transfer mode. This

function is located in the UTRAN.

7.6.4.4 Packet Data Transfer Over Radio Function

This function provides packet data transfer capability across the UMTS radio interface. This

function includes procedures which:

• Provide packet access control over radio channels.

• Provide packet multiplexing over common physical radio channels.

• Provide packet discrimination within the mobile terminal.

• Provide error detection and correction.

• Provide flow control procedures.

This function is located in both the UE and in the UTRAN.


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7.6.4.5 RF Power Control

In order to minimise the level of interference (and thereby maximise the re-use of radio

spectrum), it is important that the radio transmission power is not higher than what is required

for the requested service quality. Based on assessments of radio channel quality, this function

controls the level of the transmitted power from the mobile station as well as the base station.

This function is located in both the UE and in the UTRAN.

7.6.4.6 RF Power Setting

This function adjusts the output power of a radio transmitter according to control information

from the RF power control function. The function forms an inherent part of any power control

scheme, whether closed or open loop. This function is located in both the UE and in the

UTRAN.

7.6.4.7 Radio Channel Coding

This function introduces redundancy into the source data flow, increasing its rate by adding

information calculated from the source data, in order to allow the detection or correction of

signal errors introduced by the transmission medium. The channel coding algorithm(s) used

and the amount of redundancy introduced may be different for the different types of transport

channels and different types of data. This function is located in both the UE and in the

UTRAN.

7.6.4.8 Radio Channel Decoding

This function tries to reconstruct the source information using the redundancy added by the

channel coding function to detect or correct possible errors in the received data flow. The

channel decoding function may also employ a priori error likelihood information generated by

the demodulation function to increase the efficiency of the decoding operation. The channel

decoding function is the complement function to the channel coding function. This function is

located in both the UE and in the UTRAN.


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7.6.4.9 Channel Coding Control

This function generates control information required by the channel coding/ decoding

execution functions. This may include channel coding scheme, code rate, etc. This function is

located in both the UE and in the UTRAN.

7.6.4.10 Initial (Random) Access Detection and Handling

This function will have the ability to detect an initial access attempt from a mobile station and

will respond appropriately. The handling of the initial access may include procedures for a

possible resolution of colliding attempts, etc. The successful result will be the request for

allocation of appropriate resources for the requesting mobile station. This function is located

in the UTRAN.

7.6.4.11 Other Funtions:

• Radio resource configuration and operation

• [TDD - Dynamic Channel Allocation (DCA)]

• Radio protocols function

• [TDD - Timing Advance]

• CN Distribution function for Non Access Stratum messages.

7.7 Identifiers

The following identifiers are used within UTRAN

7.7.1 UTRAN identifiers

PLMN Identifier: PLMN-Id = MCC + MNC

CN Domain Identifier: CN CS Domain-Id = PLMN-Id + LAC

CN PS Domain-Id = PLMN-Id + LAC + RAC

RNC Identifier: Global RNC-Id = PLMN-Id + RNC-Id

Service Area Identifier: SAI = PLMN-Id + LAC + SAC


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Cell Identifier: UC-Id = RNC-Id + C-Id

7.7.2 UE Identifiers

When the UE is known to UTRAN is given an identity, called the Radio Network Temporary

Identity. There are four different RNTIs:

1. s-RNTI: Serving RNC RNTI

2. d-RNTI: Drift RNC RNTI

3. c-RNTI: Cell RNTI

4. u-RNTI: UTRAN RNTI

7.8 UMTS QoS and RAB

7.8.1 Quality of Service (QoS)

The general QoS approach for UMTS is that only the QoS perceived by end-user matter, that

is from one terminal equipment to another terminal equipment. To realise a certain network

QoS a Bearer Service with clearly defined characteristics and functionality is to be set up

from the source to the destination of a service.

A bearer service includes all aspects to enable the provision of a contracted QoS. These

aspects are among others the control signalling, user plane transport and QoS management

functionality. The UMTS QoS concept is describes in the specification 23.107

The QoS negotiation is a trace off between bit error rate (BER) delay and bit rate. There are

four QoS classes defined for UMTS (the same as for GPRS) responding to different

requirements for delay.

When negotiating QoS a number of service attributes are agreed (Traffic class, maximum and

guaranteed bit rate, delay and BER, etc.)


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Traffic class Conversational

class

Conversational RT

Streaming class

Streaming RT

Interactive class

Interactive best effort

Background

Background best effort

Fundamental characteristics

Preserve time relation (variation) between information entities of stream

Conversational pattern (stringent and low delay)

Preserve time relation (variation) between information entities of stream

Request response pattern

Preserve payload content

Destination is not expecting the data within a certain time

Preserve payload content

Example of application Voice Streaming video Web browsing

Background download of emails

Table 7.1. UMTS QoS Classes

Traffic class Conversational class

Streaming class

Interactive class

Background class

Maximum bitrate (kbps) <2000 <2000 <2000 –

overhead <2000 – overhead

Delivery order Yes/No Yes/No Yes/No Yes/No

Maximum SDU size (octets) <1500 <1500 <1500 <1500

Delivery of erroneous SDUs Yes/No/- Yes/No/- Yes/No/- Yes/No/-

Residual VER 5·10-2, 10-2, 10-

3, 10-4 5·10-2, 10-2, 10-

3, 10-4 10-5, 10-64·10-3, 10-5,

6·10-8 4·10-3, 10-5,

6·10-8

SDU error ratio 10-2, 10-3, 10-4, 10-5

10-2, 10-3, 10-4, 10-5 10-3, 10-4, 10-6 10-3, 10-4, 10-6

Transfer delay (ms) 100 – maximum value

500 – maximum value

Guaranteed bit rate (kbps) <2000 <2000

Traffic handling priority 1, 2, 3

Allocation/Retention Priority 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3

Table 7.2. Value Ranges for UMTS Bearer Service Attributes


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7.8.2 Radio Access Bearers (RAB)

RAB is described by:

• Information quality of service

Bit rate

Bit error ratio

Maximum transfer delay

Delay variation

• Traffic characteristics

Point-point, uni-directional or bi-directional (symmetric or asymmetric)

Point-to-multipoint, uni-directional (multicast and broadcast)

Chapter 8: Core Network

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8.1 Introduction

The UMTS core network will be based in the existing GSM core network, or GSM Network

Switching System (GSM NSS).

Keeping GSM as the core network for the provision of third-generation wireless services has

distinct commercial advantages: protecting the investment of existing GSM operators; helping

ensure the widest possible customer base from day one; and fostering supplier competition

through the continuous evolution of GSM systems.

A wide customer base from day one is achieved with the help of dual mode GSM/UMTS

mobile terminals, full roaming and hand-over from one system, and with mapping of services

between the two systems as far as possible. The use of dual mode mobiles in the early phases

of introduction of third-generation systems will ensure that UMTS subscribers will able to

enjoy roaming and interworking with the global GSM community.

The GSM standard offers a sound base for UMTS core networks, whether as evolved GSM

core networks or as newly-built pure UMTS networks (albeit with different topology and

physical implementation).

8.2 GPRS, an Important Stepping Stone Towards a UMTS Core Network

The real point of moving to third generation systems is to give users high speed access to

wireless multimedia services and other wireless data services. Bearing this in mind it is worth

noting that today’s wireless data market is still in its infancy: among wireless subscribers,

penetration of wireless datacom services is still less than three per cent, excluding Short

Message Service (SMS).


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The problem is that the current wireless networks are not best equipped to deal with these new

forms of data use, and do not meet the UMTS requirements. As circuit switched networks,

they are inefficient at handling small, frequent data calls and bursty IP traffic.

General Packet Radio Service (GPRS), the packet-based data bearer service for GSM, offers

current GSM operators an opportunity to kickstart the predicted mass market for wireless

data services. And important to note, it is relatively small step from building a core network

capable of delivering GPRS services to enhancing it to meet the requirements of UMTS.

In other words, implementing GPRS will provide a core network platform for current GSM

operators not only to expand the wireless data market in preparation for the introduction of

third-generation services, but also to build upon for IMT-2000.

GPRS will provide end-to-end packet switching capability from the mobile terminal upwards,

enhancing GSM data services significantly, especially for bursty Internet/intranet traffic. Call

set-up will be almost instantaneous and users will be charged on the basis of actual data

transmitted, rather than connection time. GPRS does not require any end-to-end connection

and only uses network resources and bandwidth when data is actually being transmitted. This

make extremely efficient use of available radio bandwidth to be shared between many users.

All the widely-used data communication protocols, including IP will be supported by GPRS,

so it will be possible to connect to any data source from anywhere in the world using a GPRS

mobile terminal. By providing seamless interconnection with existing data services, via for

example TCP/IP and X.25 interfaces, GPRS will support applications ranging from low-speed

short messages to high-speed corporate LAN communications.

The introduction of GPRS is one of the key staging posts in the evolution of GSM networks

to third-generation capabilities. GPRS can therefore help remove the network barriers to

large-scale take-up of wireless data services by allowing familiar, user-friendly interfaces like

the Internet to be used, permitting volume-based charging and providing high-speed user data

rates.

So what needs to happen in the core network to support the move to GPRS and, ultimately,

UMTS?


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8.3 Upgrading the GSM Core for GPRS

Compared with establishing a completely new communications system, building GSM-UMTS

infrastructure based on an existing GSM network will be a relatively fast exercise. An

intermediate move to a GSM-GPRS network will make the transition even easier.

While GPRS will require new functionality in the GSM network, with new types of

connections to external packet data networks, it will essentially be an extension of GSM.

Moving to a GSM-UMTS core network will likewise be an extension of this evolved network.

GPRS will be implemented simply by adding new packet data nodes and upgrading existing

nodes to provide a routing path for packet data between the wireless terminal and a gateway

node. The gateway node will provide interworking with external packet data networks for

access to the Internet, intranets and databases, for example.

8.3.1 New Nodes for Packet Data

Two new logical nodes will be introduced to handle GPRS applications in the GSM:

• Serving GPRS Support Node (SGSN)

• Gateway GPRS Support Node (GGSN)

The SGSN will provide packet routing, including mobility management, authentication and

ciphering to and from all GPRS subscribers located in the SGSN service area. A GPRS

subscriber may be served by any SGSN in the network, depending on location. The traffic is

routed from the SGSN to the Base Station Controller (BSC) and to the mobile terminal via the

Base Transceiver Station (BTS).

The GGSN will provide the gateway to external ISP networks, handling security and

accounting functions as web as dynamic allocation of IP addresses to serve mobile terminal.

From the external IP networks point of view, the GGSN is a host that owns all IP addresses of

all subscribers served by the GPRS network.

The nodes will be interconnected by an IP backbone network. The SGSN and GGSN

functions may be combined in the same physical node, or separated, even residing in different

mobile networks.


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A key requirement for these new nodes is that they are scalable, so that GSM operators can

start to offer high-speed packet data services using small nodes in selected areas cost-

effectively, and add extra capacity as it is needed. The SGSN and GGSN should also support

several radio networks (those with compliant open interfaces) at the same time.

8.3.2 Upgrades to Existing GSM Nodes

Few or no hardware upgrades will be needed in the existing GSM nodes, and the same

transmissions links will be used between BTSs and BSCs for both GSM and GPRS. A special

interface will be provided between the MSC/Visitor Location Register (VLR) and the SGSN

to co-ordinate signalling for mobile terminals that can handle both circuit-switched and

packet-switched data.

The HLR will contain GPRS subscription data and routing information, and will be accessible

from the SGSN. The HLR will also map each subscriber to one or more GGSNs. The BSC

will require new capabilities for controlling the packet channels: new hardware in the form of

a Packet Control Unit (PCU) and new software for GPRS mobility management and paging.

The BSC will also have a new traffic and signalling interface from the SGSN.

The BTS will have new protocols supporting packet data for the air interface, together with

new slot and channel resource allocation functions. The utilisation of radio channels will be

optimised through dynamic sharing between the two traffic types (circuit and packet switched

traffic), handled by the BSC.

8.4 Moving to UMTS in the GSM/GPRS Core

UMTS will have an evolved GSM core network, which will be backward compatible with the

GSM network in terms of network protocols and interfaces (MAP, ISUP, etc.). This core

network will support both GSM and UMTS, with hand-over and roaming between the two.

UMTS Terrestrial Radio Access Network (UTRAN) will be connected to the GSM-UMTS

core network using a new multi-vendor interface (the Iu).

The transport protocol within the new radio network and to the core network will be ATM.

There will be a clear separation between the services provided by the UTRAN and the actual

channels used to carry these services. All radio network functions (such as resource control)


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will be handled within the radio access network, and clearly separated from the service and

subscription functions in the core network.

The GSM-UMTS network will consist of three main parts:

• GSM-UMTS core network

• UMTS Radio Access Network (URAN)

• GSM Base Station Subsystem (BSS)

Like the GSM-GPRS core network, the GSM-UMTS core network will have two different

parts: a circuit switched part (MSC) and a packet-switched part (GSN). The core network

access point for GSM circuit switched connections is the GSM MSC, and for packet switched

connections is the SGSN. GSM-defined services (up to and including GSM Phase 2+) will be

supported in the dual “GSM” way. The GSM-UMTS core network will implement

supplementary services according to GSM principles (HLR-MSC/VLR).

Modifications to support UMTS will be requires in all core network nodes. MSC and SGSN

must be upgraded to handle the new signalling and traffic protocols towards UTRAN.

Furthermore, HLR and VLR must be modified to store UMTS service profiles and

subscription data. Last but not least, all nodes must be upgraded to handle the new range of

data rates and the concept of quality of service negotiation and re-negotiation.

Apart from the new range of higher data rate bearer services and more advanced QoS

procedures, the UMTS core network introduces a third major novelty – as compared to pre-

UMTS networks - in how services will be handled.

Pre-UMTS systems have largely standardised the complete sets of teleservices, applications

and supplementary services which they provide. As a consequence, substantial re-engineering

is often required to enable new services to be provided and the market for services is largely

determined by operators to differentiate their services. UMTS shall therefore standardise

service capabilities and not the services themselves. Service capabilities consist of bearers

defined by QoS parameters and the mechanisms needed to realise services.

These mechanisms include the functionality provided by various network elements., the

communication between them and the storage of associated data. It is intended that these

standardised capabilities should provide a defined platform which will enable the support of

speech, video, multi-media, messaging data, other teleservices, user applications and


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supplementary services and enable the market for services to be determined by users and

home environments.

New services, beyond GSM Phase 2+, will thus no longer be standardised. Instead they will

be created using new the service capabilities (which are standardised) mentioned above.

These service capabilities may be seen as ‘building blocks’ that provide service mechanisms

in the UMTS network and UMTS mobile terminal that can be used for service creation. They

include for instance:

• Bearers defined by quality of service (QoS) parameters

• Intelligent network functionality

• Mobile Equipment Execution Environment (MEXE)

• WAP and Telephony value-added Services

• SIM Application Toolkit

• Location servers

• Open interfaces to mobile network functions

• Downloadable application software

So, in addition to new services provided by the GSM-UMTS network itself, many new

services and applications will be realised using a client/server approach, with servers residing

on service LANs outside the GSM-UMTS core network. For such services, the core network

will simply act as a transparent bearer. The core network will ultimately be used for the

transfer of data between the end-points, the client and the server.

8.4.1 Cell-Based Transport Network

To make the most of the new UTRAN capabilities, and to cater for the large increase in data

traffic volume, ATM (Asynchronous Transfer Mode) will be used as the transport protocol

within the UTRAN and towards the GSM-UMTS core network. The combination of ATM

and UTRAN capabilities and the increased volume of packet data traffic over the air interface

will mean a saving of at least 50% in transmission costs, compared with the equivalent current

solutions.


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ATM, with the newly-standardised AAL2 adaptation layer, provides an efficient transport

protocol, optimised for delay-sensitive speech services and packet-data services. Introducing

ATM as a transport protocol does not, however, imply a completely new transport

infrastructure: the ATM could well be run over existing STM lines.

8.5 UMTS Core Network Phase 1 (Release 99) Requirements

In the first phase of UMTS, the UMTS core network capabilities are a superset of the phase

2+ release 99 GSM core network capabilities. The additional requirements for the phase 1

UMTS core network are the following:

• The phase 1 UMTS core network shall support circuit switched data service capability of

at least 64 kbit/s per user. This shall not limit the user from choosing lower data rates.

• The phase 1 UMTS core network shall support packet switched data service capability of

at least 2 Mbit/s peak bit rate per user. This shall not limit the user from choosing lower

data rates.

• The phase 1 UMTS core network shall enable set-up, re-negotiation and clearing of

connections (i.e. CS calls or PS sessions) with a range of traffic and performance

characteristics. The re-negotiation of QoS attributes for a bearer service may be caused by

an application or the user via an application. It shall be possible to apply traffic policing

(e.g. connection admission control, flow control, usage parameter control…) on a

connection during its set-up and lifetime.

• The phase 1 UMTS core network shall support a range of traffic and performance

characteristics for connectionless (e.g. unicast, broadcast, and multicast) traffic.

• The range of traffic and performance characteristics that shall be supported by the phase 1

UMTS core network shall be at least those of GPRS phase 2+ release 99. This means that

the support of the full set of bearer services defined in the UMTS specifications is not

required for the phase 1 UMTS core network.

• Established bearers shall not prevent the set-up of a new bearer. These bearers can be of

any type (e.g. PS, CS). It is nevertheless expected that the terminal and network


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capabilities will put some limitations on the number of bearer services that can be handled

simultaneously. It shall be possible for each bearer to have independent traffic and

performance characteristics.

• In order to facilitate the development of new applications, it shall be possible to address

applications to/from a phase 1 UMTS mobile termination (e.g. the notion of Internet port).

• Operator specific services based shall be supported by the phase 1 UMTS core network.

This functionality could be provided through available toolkits (such as IN, MEXE, WAP

and SIM Toolkit).

• The phase 1 UMTS core network shall support interworking with PSTN, N-ISDN, GSM,

X.25 and IP networks with their respective numbering schemes.

• It shall be possible for the standardised classes of phase 1 UMTS mobile terminals

supporting the GSM BSS and UTRAN radio interfaces to roam in GSM networks and

receive GSM services.

• Standardised protocols shall be defined for the operation, administration and maintenance

of the UMTS phase 1 core network in co-operation with relevant groups within ETSI.

Chapter 9: Handover (Downlink Case Example)

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In this chapter a complete case of handover is presented. A GSM macro cell and six UMTS

macro cells compose the scenario. The four RNCs and the BSC are connected through the

common Core Network.

9.1 Position 1

The UE receives information from the Node B that controls the cell with Scrambling Code 1,

SC1. All the information of the first Node B is received from the Radio Network Controller 1,

RNC1.

9.2 Position 2

The UE enters in a new cell using the same frequency. This cell has a different Scrambling

Code (SC2) and is controlled by a new Node B that depends on the same RNC1.

The RNC1 is transmitting to two different Node Bs. This operation is known like combining

and splitting and is performed by the RNC Signal Processing.

In this short period a soft handover, SOHO, is performed. The handover decisions are taken

in the RAB Management of the RNC1.

9.3 Position 3

The UE is completely inside the cell number two (SC2) and is receiving from the second

Node B.

9.4 Position 4

The UE is crossing the cell border to enter in the cell number three (SC3) that is controlled by

the same Node B. Now the combining operation is realised by Node B with the RNC

supervision. In this case a softer handover is performed. This is the simplest case that can be

found.


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9.5 Position 5

The UE is completely inside the cell number three (SC3) and is receiving from the second

Node B.

9.6 Position 6

The UE is crossing the cell border to enter in the cell number four (SC4) that is controlled by

the third Node B. This Node B is controlled by a second RNC, RNC2. In this case an Iur

interface is present between the two RNCs. The RNC1, that controls the Serving Radio

Network Subsystem, SRNS, is called Serving RNC and the RNC2, that controls the Drift

Radio Network Subsystem, DRNS, is called Drift RNC.

The combining and splitting operations are performed by the Serving RNC, RNC1, where the

handover decision are taken. Even SRNS relocation is realised. In this case a soft handover is

performed. The SOHO condition has the drawback that is necessary to transmit more power.

9.7 Position 7

The UE is completely inside the cell number four (SC4) and is receiving from the third Node

B.

9.8 Position 8

The UE is crossing the cell border to enter in the GSM cell controlled by the BTS. All the

information regarding the UE in position 7 is transmitted to the BSC through the Core

Network. In this case only a hard handover (UMTS-GSM) can be performed.

9.9 Position 9

The UE is crossing the cell border to enter in a UMTS cell controlled by RNC3. The

downlink is realised to frequency f1. Even in this case only a hard handover (GSM-UMTS)

can be performed. All the information regarding the UE in position 8 is transmitted to the

RNC3 through the Core Network.


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9.10 Position 10

The UE is crossing the cell border to enter in a new cell controlled by RNC4. The downlink is

realised to frequency f2. In this case only a hard handover can be performed because of the

different frequencies within the two cells. Even in this case to transmit all the information

regarding the UE in position 9 to the RNC4 the Core Network is used.

For the Uplink case the analogue considerations can be done

Chapter 10: Cell Planing

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10.1 Introduction to Cell Planning

Network planning covers two major areas: radio network planning and network dimensioning.

Radio network planning includes the calculation of the link budget, capacities, and thus the

required number of cell sites. Furthermore, radio network planning includes detailed coverage

and parameter planning for individual sites.

Planning an immature network with a limited number of subscribers is not the real problem.

The difficulty is to plan a network that allows future growth and expansion. Wise re-use of

site location in the future network structure will save money for the operator.

In this chapter we will look at different cell types, the different steps in cell planning, the

differences compared to GSM cell planning as well as some of the advantages of co-siting

with GSM.

10.2 Different Cell Types

A cellular network is created by means of placing equipment in strategic places to guarantee a

certain perceived Quality of Service. Idealistic then would be to place a base station in every

street corner, this though is not cost efficient. Which dell type to use, must be weighed against

cost and expected penetration (see Figure 10.1).

Figure 10.1. The Choice of Cell Types Affecting Several Posts on The Scale

Important when designing a network is to find a balance regarding which combination of the

types of cells to use. The most common ones today are macro, micro and pico cells, but

Coverage

Capacity

Penetration

Cost

Spectrum

Quality

Coverage

Capacity

Penetration

Cost

Spectrum

Quality


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sometimes also mini cells are mentioned. As co-siting is one key design objective for UMTS

networks, it is very likely that UMTS will have the same type of cells as today’s second

generation systems. However, it should be noted that high bit rates have lower coverage than

low bit rates. Thus, if the UMTS network is designed to handle high bit rates, i.e. 384 kbps

and above, the majority of the cells will be micro and pico cells.

Macro cells, have a typical coverage range from 1 to 35 km (several vendors offers special

high coverage solutions that will extend the coverage beyond 35 km). Normally the site

location is on a hilltop or a rooftop, guarantying good coverage. The main rays are propagated

over the rooftops.

Micro cells have a typical coverage range from o.1 to 1 km, where the major part of the radio

waves is propagated along the streets. The base station antenna placement is below the

rooftops of the surrounding buildings. A micro cell can maintain indoor coverage in the lower

levels of a building.

Pico cells supplies coverage in indoor environment (or possibly outdoors in environments

physically distinctly limited – a backyard e.g.). The base station is transmitting at low output

power and the antennas could be mounted on walls or in the ceiling. Pico cells are used when

the capacity needed is extremely high in certain hot spots.

Mini cells are between macro and micro cells, as the antenna is typically placed at the same

level as the rooftops.

HCS (Hierarchical Cell Structures) is an example of how different cell types can be deployed

in the same area. Traditionally, the different cell types, i.e. macro and micro cells use different

frequency bands. HCS offers a high capacity solution, as the micro band is capable of handle

a high load. HCS also allows for the possibility to conduct load sharing between the different

cell layers. In order to limit the amount of handovers in the system, one may also consider the

user’s velocity when deciding which cell layer to use.

In the theoretical part of cell planing, base station coverage areas or cells are shown as

hexagons. This is so because the system is designed to let the mobile always operate on the

nearest or best base station. Thus, boundaries between the base station cells will theoretically

form straight lines, perpendicular to the connection lines between the sites, and these will

form a hexagonal cellular pattern (see ).


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Figure 10.2. Cell Coverage Shown as a Hexagon

The use of different types of cells on the same area introduces the concept of a hierarchical

structure, leading to increasingly complex handover relations and planning.

10.3 Steps in the Cell Planning Process

Cell planning means building a network able to provide service to the customers wherever

they are. This work can be simplified and structured in certain steps (see Figure 10.3). Some

of these steps are performed frequently whilst other are more rare. Normally the output from

one box is the input of another. A cell planner most likely is dealing with the content of

several of these boxes at the same time.

The following describes the content of the boxes and what each step may involve. This

process is by no means complete or unbeatable, each operator has its own flowchart of

processes.

Figure 10.3. Different Steps in The Cell Planning Process

This process should not be considered just as it is depicted, in a single flow of events. For

instance, the radio planning and surveying actions are interlinked in an ongoing iterative

process that should ultimately lead to the individual site design.

System Requirements

Define Radio Planning

Initial Cell Plan

Surveys Individual Site Design

ImplementationLaunch of Service

On-going Testing

System Growth

System Requirements

Define Radio Planning

Initial Cell Plan

Surveys Individual Site Design

ImplementationLaunch of Service

On-going Testing

System Growth


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10.3.1 System Requirements:

• Licence (available bandwidth may also set coverage requirements).

• Coverage for different customers in different environments.

• Traffic behaviour of customers in different regions (uplink and downlink may differ).

• Quality of Service (dropping and delay) and GoS (blocking).

• Phase of build out (expansion and future investments?).

10.3.2 Define Radio Planning Guidelines:

• Coverage and interference: which prediction model to use, fading margins for indoor,

outdoor and in-car.

• Traffic planning: choice of models and processes.

• Testing and optimisation strategy.

10.3.3 Initial Cell Plan:

• Idealised overview of site locations (consider GSM initially also WCDMA for expansion).

• Predicted composite coverage and interference map.

• Cell configuration, parameter setting, channel loading plan (if co-siting, consider existing

site).

10.3.4 Surveys:

• Radio environment survey: Investigate path loss, interference and time dispersion.

Investigate other system’s antenna and interfering transmitters.

• Sit Survey: Pinpoint exact location with GPS. The ideal planned locations have to be

searched for any suitable building, tower or vacant lot that could be leased for a

reasonable cost. Check space for antenna mounting, isolation, diversity, roof clearance

(first Fresnel zone empty).

Investigate physical necessities such as space for equipment, power and PCM links.


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10.3.5 Individual Site Design and Parameter Setting:

• Radio engineers need to select best site location from the options available from the site

acquisitors.

• Dimensioning of node B, transport network and RNC.

• Antenna type and gain, direction and tilt and ERP need to be decided.

• “Final” parameter setting (power planning, HO margin, neighbour list (GSM), scrambling

code, functionality).

10.3.6 Implementation:

• Install: node B, power, termination equipment for PCM link, air-conditioning equipment,

earth bar, lightning equipment and antennas. Adjust output power, set parameters.

• Commissioning tests of node B. Drive testing to detect blank spots and interference and to

confirm correct call set-up, handover, location updating and to detect missing neighbour

relationships.

10.3.7 Launch of Commercial Service:

When the network is operational a commercial launch can be made.

10.3.8 On-going Testing, Analyses and Optimisation:

• System diagnostics: collect statistics in OMC, MSC or RNC to analyse traffic behaviour,

traffic distribution, Grade of Service, call success rate, handover failures, dropped calls,

radio channels quality, access links statistics, and to study trends.

• Drive testing to localise weak signal strength, interference, time dispersion or other radio

problems. Also to investigate problems reported by customers and to validate changes

undertaken.

• Analysis of the results above, and

• Optimisation of parameters, timers, physical implementation of antenna directions or tilts

or any other measures to counteract detected problems.


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10.3.9 System Growth

• More traffic, due to more users or new services.

• Expansion of existing sites.

• New sites added.

10.4 Differences With 2G TDMA Systems - Deployments

10.4.1 Exploiting Existing Networks

• Re-use of site locations and equipment (site Co-sting).

• Information about traffic and propagation conditions.

• Handover to GSM (for coverage or load sharing purpose).

10.4.2 Multi Service

• Load from several different types of services..

• Different services have different coverage.

• Delay requirements.

10.4.3 New Air Interface

• Trade-off between coverage and capacity.

• Power planning instead of frequency planning.

10.5 Calculation of Coverage and Capacity

In WCDMA power is the common shared resource. Thus, in order to achieve high spectrum

efficiency WCDMA supports a fast quality based power control. The combination of these

two features together with the fact that WCDMA use a frequency re-use of one results in that

WCDMA offers a trade-off between coverage and capacity.


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This means that at low load, i.e. low interference, the users can be further away from the base

station, and still supported, compared to when there is a high load, i.e. high interference in the

system.

10.5.1 Needed Input Parameters

The needed input parameters are:

• Coverage requirements (indoor, probability, bit rate at cell border).

• Supported services.

• GoS.

• Available spectrum, i.e. number of carriers.

• Area to cover and which type of area it is (urban, suburban,...).

• Users within the area.

• Traffic that each user generates (uplink and downlink separately).

Based on that information, the amount of traffic per carrier in a given area can be calculated.

Further, the C/I for the different services can be calculated by taking the Eb/No values from

the WCDMA RTT. The C/I = Eb/No – 10log(chip rate/bit rate)

10.5.2 Uplink Design

The first step in the uplink design is to make an initial assumption about the uplink load. The

initial assumed load usually corresponds to a low load. By using the load assumption in

combination with the coverage requirement, a link budget can be calculated. From the link

budget, the cell range can be calculated and thus also the cell area. Knowing the area, the

traffic within that area can be calculated. By using the GoS input requirement, we can

calculate how much interference we should design for.

In the next step, the assumed load is compared to the calculated design load. If the assumed

load is greater than the calculated load, the process is completed and we have found a design

that handles the traffic in the system. Otherwise, one should check if the assumed load equals

or exceeds the maximum load in the system. If it does, then the system is capacity limited and

the number of sites needed can be found from dividing the total traffic with the traffic that one


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site can handle. If the system is not capacity limited, one assumes a new load and repeats the

process.

10.5.3 Downlink Design

From the uplink, one gets the cell range and the cell area. Having the cell area, traffic within

that area is calculated. By using the GoS for the different supported services, the needed

resources are calculated. Then by using the downlink plot, it can be seen whether the design

supports the downlink load or not. If the downlink load is supported, the design process is

completed. Otherwise, the cell range and the cell area must be reduced until the downlink

load is handled.

10.5.4 Co-Siting With GSM Case

When the aim is to co-site with GSM, the process is slightly different as the site locations

already are known. By knowing the cell range, one can make an uplink link budget in order to

find out now large interference margins can be tolerated. By comparing the load that a 5 MHz

carrier can handle and compare it with the uplink traffic demand within the cell area, the

needed number of frequencies can be estimated.

In the downlink, the supported load per carrier can be found from the downlink plot once the

cell range is given, i.e. the cell range used in the existing GSM network. The needed amount

of carriers can then be calculated, just as in the uplink, by dividing the traffic demand within

the cell area with the traffic that one carrier can handle.

Chapter 11: WORLD-WIDE CONSENSUS ON ADDITIONAL SPECTRUM FOR 3RD GENERATION

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IMT-2000 IS ANOTHER GIANT LEAP FORWARD FOR EVERYONE’S MOBILE

FUTURE

June 1st 2000: The promise of tomorrow’s global information society has taken a major step

forward with the successful identification of additional radio spectrum to support the rapid

rollout of "third generation" (3G) UMTS/IMT-2000 mobile communications services for all

the world’s regions.

The historic announcement - finally approved at the WRC 2000 plenary - was made at the

conclusion of the month-long WRC-2000 (World Radiocommunication Conference) meeting

in Istanbul after four weeks of intense work by spectrum administrators representing every

government. Representatives of the UMTS Forum’s Spectrum Aspects Group (SAG)

provided support and expert inputs to the Conference, following four years involvement in

this uniquely important and complex project.

The Inter-governmental Conference reached a global consensus to identify additional bands

for the terrestrial component of UMTS/IMT-2000. Crucially, as well as providing additional

capacity to support the future mass market for mobile multimedia services - calculated by the

UMTS Forum to approach 2 billion users within the next decade - this result also paves the

way for the introduction of 3G services even in regions where the core spectrum has not

hitherto been available for IMT-2000.

This means that mobile users will be able to access their personal information services using

affordable handheld terminals wherever they travel. The additional terrestrial bands agreed by

WRC2000 for IMT-2000 cover three alternative areas of spectrum to complement the IMT-

2000 core bands (1885 - 2025 and 2110 - 2200 MHz) identified by a previous Conference in

1992.

The new bands are:


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• 806-960 MHz

• 1,710-1,885 MHz

• 2,500-2,690 MHz

All of these three bands meet the UMTS Forum’s call for 160 MHz of global additional

spectrum that is required to support the forecast growth of traffic and services that will

outstrip the capacity of the present IMT-2000 core band in many markets before the end of

this decade. This 160 MHz of additional spectrum in every ITU Region was calculated on the

basis of traffic forecasts and the existing available mobile bands for 2nd and 3rd generation

services.

This groundbreaking news comes at a time when the UMTS licensing process is rapidly

progressing in many countries throughout Asia and Europe in order to commence commercial

services by 2001/2002. More than 100 licenses are to be awarded to operators of high-

capacity UMTS mobile multimedia services within the next 12-18 months.

Each government will make their own decision on the choice and timescale for making these

additional bands available for IMT-2000 use. Factors influencing the availability of these

additional frequencies include the local market demand for 3rd generation services and

economic factors such as the stage of development of present 2nd generation networks. Some

existing operators may also wish to consider migrating their networks to IMT-2000 in order to

offer the benefits of lower costs and high-speed packet data services up to 2Mbit/s and

beyond.

The decision on extension band spectrum follows an earlier milestone of equal importance

reached last month when the ITU Radiocommunication Assembly unanimously approved the

formal adoption of the first release of IMT-2000 radio interface specifications.

UMTS Forum Chairman Dr Bernd Eylert said today of the decision:

"The UMTS Forum wishes to congratulate the ITU and to thank all its members for this

successful result. It’s an incredible milestone in the development of tomorrow’s mobile

networks, and a fantastic result for the entire global mobile industry which is represented by

the membership of the UMTS Forum - the world’s largest pan-industry group dedicated to 3G

mobile matters."


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Dr Eylert continued: "This decision is particularly welcome as it provides a solid basis for the

regional introduction of 3G services, even in territories that were effectively blocked from the

benefits of 3G in the past because of limited spectrum. The stage is now set for UMTS/IMT-

2000 to deliver on its exciting promise of immense socio-economic benefits for all the

world’s mobile users. The UMTS Forum will continue its work in this very important field to

assist the regions in their IMT-2000/UMTS deployments."

Altran - Umts Overview Book

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