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RADIO ACCESSNETWORKS FOR UMTSPRINCIPLES AND PRACTICE
Chris Johnson
Nokia Siemens Networks, UK
RADIO ACCESSNETWORKS FOR UMTS
RADIO ACCESSNETWORKS FOR UMTSPRINCIPLES AND PRACTICE
Chris Johnson
Nokia Siemens Networks, UK
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Library of Congress Cataloging-in-Publication Data
Johnson, Chris (Chris W.)Radio access networks for UMTS : principles and practice / Chris Johnson.
p. cm.Includes index.ISBN 978-0-470-72405-7 (cloth)
1. Mobile communication systems. I. Title.TK6570.M6J63 2008621.384–dc22 2007040535
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN 978-0-470-72405-7 (HB)
Typeset in 9/11pt Times by Thomson Digital, New Delhi.Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, England.This book is printed on acid-free paper responsibly manufactured from sustainable forestry in which at least twotrees are planted for each one used for paper production.
Contents
Preface ix
Acknowledgements xi
Abbreviations xiii
1 Introduction 1
1.1 Network Architecture 1
1.2 Radio Access Technology 4
1.3 Standardisation 10
2 Flow of Data 13
2.1 Radio Interface Protocol Stacks 13
2.1.1 Radio Interface Control Plane 14
2.1.2 Radio Interface User Plane 19
2.2 RRC Layer 27
2.2.1 RRC States 28
2.2.2 RRC Procedures 54
2.2.3 RRC Messages 56
2.2.4 UE RRC Timers, Counters and Constants 61
2.2.5 Other Functions 67
2.3 RLC Layer 74
2.3.1 Transparent Mode 75
2.3.2 Unacknowledged Mode 77
2.3.3 Acknowledged Mode 81
2.4 MAC Layer 101
2.4.1 Architecture of the MAC Layer 102
2.4.2 Format of MAC PDU 109
2.4.3 Other Functions 112
2.5 Frame Protocol Layer 112
2.5.1 Dedicated Channels - Data Frames 113
2.5.2 Dedicated Channels - Control Frames 118
2.5.3 Common Channels - Data Frames 121
2.5.4 Common Channels - Control Frames 126
2.6 Physical Layer 127
2.6.1 Physical Layer Processing 128
2.6.2 Spreading, Scrambling and Modulation 144
2.6.3 Other Functions 153
3 Channel Types 155
3.1 Logical Channels 155
3.2 Transport Channels 158
3.3 Physical Channels 166
3.3.1 Common Pilot Channel (CPICH) 168
3.3.2 Synchronisation Channel (SCH) 172
3.3.3 Primary Common Control Physical Channel (P-CCPCH) 174
3.3.4 Secondary Common Control Physical Channel (S-CCPCH) 176
3.3.5 Paging Indicator Channel (PICH) 182
3.3.6 MBMS Indicator Channel (MICH) 186
3.3.7 Acquisition Indicator Channel (AICH) 188
3.3.8 Physical Random Access Channel (PRACH) 191
3.3.9 Dedicated Physical Channel (DPCH) 204
3.3.10 Fractional Dedicated Physical Channel (F-DPCH) 228
4 Non-Access Stratum 231
4.1 Concepts 231
4.2 Mobility Management 233
4.3 Connection Management 239
4.4 PLMN Selection 244
5 Iub Transport Network 249
5.1 Protocol Stacks 249
5.1.1 Radio Network Control Plane 251
5.1.2 Transport Network Control Plane 253
5.1.3 Transport Network User Plane 257
5.2 Architecture 260
5.3 Overheads 264
5.4 Service Categories 268
6 HSDPA 273
6.1 Concept 273
6.2 HSDPA Bit Rates 278
6.3 PDCP Layer 283
6.4 RLC Layer 284
6.5 MAC-d Entity 287
6.6 Frame Protocol Layer 288
6.6.1 HS-DSCH Data Frame 289
6.6.2 HS-DSCH Control Frames 292
6.7 Iub Transport 294
6.7.1 ATM Transport Connections 294
6.7.2 Transport Overheads 296
6.8 MAC-hs Entity 300
6.8.1 Flow Control 301
6.8.2 Scheduler 304
6.8.3 Adaptive Modulation and Coding 307
6.8.4 Hybrid Automatic Repeat Request (HARQ) 313
6.8.5 Generation of MAC-hs PDU 320
vi Contents
6.9 Physical Channels 322
6.9.1 High Speed Shared Control Channel (HS-SCCH) 323
6.9.2 High Speed Physical Downlink Shared Channel (HS-PDSCH) 329
6.9.3 High Speed Dedicated Physical Control Channel (HS-DPCCH) 332
6.10 Mobility 337
7 HSUPA 343
7.1 Concept 343
7.2 HSUPA Bit Rates 349
7.3 PDCP Layer 355
7.4 RLC Layer 355
7.5 MAC-d Entity 357
7.6 MAC-es/e Entity (UE) 358
7.6.1 E-TFC Selection 359
7.6.2 Hybrid Automatic Repeat Request (HARQ) 368
7.6.3 Generation of MAC-es PDU 371
7.6.4 Generation of MAC-e PDU 372
7.7 Physical Channels 374
7.7.1 E-DCH Dedicated Physical Control Channel (E-DPCCH) 376
7.7.2 E-DCH Dedicated Physical Data Channel (E-DPDCH) 378
7.7.3 E-DCH Hybrid ARQ Indicator Channel (E-HICH) 387
7.7.4 E-DCH Relative Grant Channel (E-RGCH) 390
7.7.5 E-DCH Absolute Grant Channel (E-AGCH) 392
7.8 MAC-e Entity (Node B) 394
7.8.1 Packet Scheduler 395
7.8.2 De-multiplexing 399
7.9 Frame Protocol Layer 399
7.9.1 E-DCH Data Frame 400
7.9.2 Tunnel Congestion Indication Control Frame 401
7.10 MAC-es Entity (RNC) 402
7.11 Mobility 402
8 Signalling Procedures 405
8.1 RRC Connection Establishment 405
8.2 Speech Call Connection Establishment 429
8.2.1 Mobile Originated 430
8.2.2 Mobile Terminated 454
8.3 Video Call Connection Establishment 459
8.3.1 Mobile Originated and Mobile Terminated 460
8.4 Short Message Service (SMS) 469
8.4.1 Mobile Originated 470
8.4.2 Mobile Terminated 474
8.5 PS Data Connection Establishment 477
8.5.1 Mobile Originated 478
8.6 Soft Handover 501
8.6.1 Inter-Node B 501
8.6.2 Intra-Node B 512
8.7 Inter-System Handover 514
8.7.1 Speech 515
Contents vii
9 Planning 533
9.1 Link Budgets 533
9.1.1 DPCH 535
9.1.2 HSDPA 545
9.1.3 HSUPA 547
9.2 Radio Network Planning 548
9.2.1 Path Loss based Approach 550
9.2.2 3G Simulation based Approach 553
9.3 Scrambling Code Planning 556
9.3.1 Downlink 557
9.3.2 Uplink 560
9.4 Neighbour Planning 561
9.4.1 Intra-Frequency 563
9.4.2 Inter-Frequency 564
9.4.3 Inter-System 566
9.4.4 Maximum Neighbour List Lengths 567
9.5 Antenna Subsystems 572
9.5.1 Antenna Characteristics 573
9.5.2 Dedicated Subsystems 576
9.5.3 Shared Subsystems 578
9.6 Co-siting 578
9.6.1 Spurious Emissions 581
9.6.2 Receiver Blocking 583
9.6.3 Intermodulation 585
9.6.4 Achieving Sufficient Isolation 586
9.7 Microcells 587
9.7.1 RF Carrier Allocation 588
9.7.2 Sectorisation 588
9.7.3 Minimum Coupling Loss 589
9.7.4 Propagation Modelling 590
9.7.5 Planning Assumptions 591
9.8 Indoor Solutions 592
9.8.1 RF Carrier Allocation 593
9.8.2 Sectorisation 593
9.8.3 Active and Passive Solutions 593
9.8.4 Minimum Coupling Loss 594
9.8.5 Leakage Requirements 595
9.8.6 Antenna Placement 596
References 597
Index 599
viii Contents
Preface
This book provides a comprehensive description of the Radio Access Networks for UMTS. It is
intended to address the requirements of both the beginner and the more experienced mobile
telecommunications engineer. An important characteristic is the inclusion of sections from example
log files. More than 180 examples have been included to support the majority of explanations and to
reinforce the reader’s understanding of the key principles. Another important characteristic is the
inclusion of summary bullet points at the start of each section. The reader can use these bullet points
either to gain a high-level understanding prior to reading the main content or for subsequent revision.
The main content is based upon the release 6 version of the 3GPP specifications. Changes since the
release 99 version are described while some of the new features appearing within the release 7 version
are introduced.
Starting from the high-level network architecture, the first sections describe the flow of data between
the network and end user. The functionality and purpose of each protocol stack layer is explained while
the corresponding structure and content of packets are studied. A section is dedicated to describing and
contrasting the sets of logical, transport and physical channels. The increasing importance of the
bandwidth offered by the transport network connecting the population of Node B to the RNC justifies
the inclusion of a dedicated section describing the Iub interface and the associated transport solutions.
Dedicated sections are also included for both HSDPA and HSUPA. The bit rates and functionality
associated with these technologies are described in detail. A relatively large section is used to describe
some of the most important signalling procedures. These include RRC connection establishment,
speech call connection establishment, video call connection establishment, PS data connection
establishment, SMS data transfer, soft handover and inter-system handover. The accompanying
description provides a step-by-step analysis of both the signalling flow and message content. Other
sections focus upon the more practical subjects of link budgets and radio network planning. Topics
include scrambling code planning, neighbour list planning, antenna subsystem design, co-siting,
microcells and indoor solutions.
The content of this book represents the understanding of the author. It does not necessarily represent
the view nor opinion of the author’s employer. Descriptions are intended to be generic and do not
represent the implementation of any individual vendor.
Acknowledgements
The author would like to acknowledge his employer, Nokia Siemens Networks UK Limited for
providing the many opportunities to gain valuable project experience. The author would also like to
thank his managers from within Nokia Siemens Networks UK Limited for supporting participation
within projects which have promoted continuous learning and development. These include Andy King,
Peter Love, Aleksi Toikkanen, Stuart Davis, Mike Lawrence and Chris Foster. The author would also
like to thank Florian Reymond for providing the opportunities to work on global projects within Nokia
Siemens Networks.
The author would like to acknowledge colleagues from within Nokia Siemens Networks who have
supported and encouraged the development of material for this book. These include Poeti Boedhi-
hartono, Simon Browne, Gareth Davies, Martin Elsey, Benoist Guillard, Terence Hoh, Harri Holma,
Steve Hunt, Sean Irons, Phil Pickering, Kenni Rasmussen, Mike Roche, Lorena Serna Gonzalez, Ian
Sharp, Achim Wacker, Volker Wille and Nampol Wimolpitayarat. In addition, the author would like to
thank the managers and colleagues from outside Nokia Siemens Networks who have also supported the
development of this book. These include Mohamed AbdelAziz, Paul Clarkson, Tony Conlan, Patryk
Debicki, Nathan Dyson, Gianluca Formica, Dave Fraley, Ian Miller, Balan Muthiah, Pinaki
Roychowdhury, Adrian Sharples and Ling Soon Leh.
The author would also like to offer special thanks to his parents who provided a perfect working
environment during the weeks spent in Scotland. He would also like to thank them for their continuous
support and encouragement.
The author would like to thank the team at John Wiley & Sons Limited who have made this
publication possible. This team has included Mark Hammond, Sarah Hinton, Katharine Unwin and
Brett Wells.
Comments regarding the content of this book can be sent to [email protected]. These will be
considered when generating material for future editions.
Abbreviations
16QAM 16 Quadrature Amplitude Modulation
3GPP 3rd Generation Partnership Project
4PAM 4 Pulse Amplitude Modulation
64QAM 64 Quadrature Amplitude Modulation
AAL2 ATM Adaptation Layer 2
AAL5 ATM Adaptation Layer 2
ABR Available Bit Rate
AC Access Class
ACIR Adjacent Channel Interference Ratio
ACLR Adjacent Channel Leakage Ratio
ACS Adjacent Channel Selectivity
AI Access Indicator
AICH Access Indicator Channel
ALCAP Access Link Control Application Part
AM Acknowledged Mode
AMC Adaptive Modulation and Coding
AMR Adaptive Multi Rate
APN Access Point Name
ARFCN Absolute Radio Frequency Channel Number
AS Access Stratum
ASC Access Service Class
ASN Abstract Syntax Notation
ATM Asynchronous Transfer Mode
BCC Base station Colour Code
BCCH Broadcast Control Channel
BCD Binary Coded Decimal
BCH Broadcast Channel
BER Bit Error Rate
BFN Node B Frame Number
BLER Block Error Rate
BMC Broadcast/Multicast Control
BSIC Base Station Identity Code
CAC Connection Admission Control
CBC Cell Broadcast Centre
CBR Constant Bit Rate
CBS Cell Broadcast Services
CC Call Control
CCCH Common Control Channel
CCTrCh Coded Composite Transport Channels
CDMA Code Division Multiple Access
CDVT Cell Delay Variation Tolerance
CFN Connection Frame Number
CGI Cell Global Identity
CI Cell Identity
CID Channel Identifier
CIO Cell Individual Offset
CLP Cell Loss Priority
CLR Cell Loss Ratio
CM Compressed Mode
COI Code Offset Indicator
CPCH Common Packet Channel
CPCS Common Part Convergence Sublayer
CPI Common Part Indicator
CPICH Common Pilot Channel
CPS Common Part Sublayer
CQI Channel Quality Indicator
CRC Cyclic Redundancy Check
C-RNTI Cell Radio Network Temporary Identity
CS Circuit Switched
CTCH Common Traffic Channel
CTD Cell Transfer Delay
CTFC Calculated Transport Format Combination
DAS Distributed Antenna System
DCCH Dedicated Control Channel
DCH Dedicated Channel
DDI Data Description Indicator
DPCCH Dedicated Physical Control Channel
DPCH Dedicated Physical Channel
DPDCH Dedicated Physical Data Channel
DRT Delay Reference Time
DRX Discontinous Receive
DSAID Destination Signaling Association Identifier
DSCH Downlink Shared Channel
DTCH Dedicated Traffic Channel
DTX Discontinuous Transmit
E-AGCH E-DCH Absolute Grant Channel
Eb/No Energy per bit/Noise spectral density
ECF Establish Confirm
E-DCH Enhanced Dedicated Channel
E-DPCCH E-DCH Dedicated Physical Control Channel
E-DPDCH E-DCH Dedicated Physical Data Channel
EGPRS Enhanced General Packet Radio Service
E-HICH E-DCH Hybrid ARQ Indicator Channel
xiv Abbreviations
EIRP Effective Isotropic Radiated Power
E-RGCH E-DCH Relative Grant Channel
ERQ Establish Request
E-TFC E-DCH Transport Format Combination
E-TFCI E-DCH Transport Format Combination Indicator
FACH Forward Access Channel
FBI Feedback Information
FDD Frequency Division Duplex
F-DPCH Fractional Dedicated Physical Channel
FSN Frame Sequence Number
FTP File Transfer Protocol
GFR Guaranteed Frame Rate
GGSN Gateway GPRS Support Node
GMM GPRS Mobility Management
GMSK Gaussian Minimum Shift Keying
GPRS General Packet Radio Service
GRAKE Generalised RAKE
GSMS GPRS Short Message Service
GTP-U User plane GPRS Tunnelling Protocol
HARQ Hybrid Automatic Repeat Request
HCS Hierarchical Cell Structure
HEC Header Error Correction
HFN Hyper Frame Number
HLBS Highest Priority Logical Channel Buffer Status
HLID Highest Priority Logical Channel Identity
HLR Home Location Register
HLS Higher Layer Scheduling
HPLMN Home Public Land Mobile Network
H-RNTI HS-DSCH Radio Network Temporary Identity
HSCSD High Speed Circuit Switched Data
HSDPA High Speed Downlink Packet Access
HS-DPCCH High Speed Dedicated Physical Control Channel
HS-DSCH High Speed Downlink Shared Channel
HS-PDSCH High Speed Downlink Shared Channel
HS-SCCH High Speed Shared Control Channel
HSUPA High Speed Uplink Packet Access
ICP IMA Control Protocol
IE Information Element
IETF Internet Engineering Task Force
IMA Inverse Multiplexing for ATM
IMEI International Mobile Equipment Identity
IMSI International Mobile Subscriber Identity
IPDL Idle Period Downlink
IPv4 Internet Protocol version 4
IPv6 Internet Protocol version 6
ITP Initial Transmit Power
Abbreviations xv
ITU International Telecommunications Union
LAC Location Area Code
LAI Location Area Identity
LLC Logical Link Control
LSN Last Sequence Number
MAC Medium Access Control
MAP Mobile Application Part
MBMS Multimedia Broadcast Multicast Services
MBS Maximum Burst Size
MCC Mobile Country Code
MCCH MBMS Control Channel
MCL Minimum Coupling Loss
MCR Minimum Cell Rate
MDC Macro Diversity Combination
MDCR Minimum Desired Cell Rate
MFS Maximum Frame Size
MHA Mast Head Amplifier
MIB Master Information Block
MICH MBMS Indicator Channel
MIMO Multiple Input Multiple Output
MLP MAC Logical channel Priority
MM Mobility Management
MNC Mobile Network Code
MSCH MBMS Scheduling Channel
MSS Maximum Segment Size
MTCH MBMS Traffic Channel
MTU Maximum Transmission Unit
MUD Multi User Detection
NAS Non-access Stratum
NBAP Node B Application Part
NCC Network Colour Code
NI Notification Indicator
NMO Network Mode of Operation
NNI Network to Network Interface
NRT Non Real Time
NSAP Network Service Access Point
NSAPI Network layer Service Access Point Identifier
OSAID Originating Signalling Association Identifier
OTDOA Observed Time Difference of Arrival
PAP Password Authentication Protocol
PCA Power Control Algorithm
PCCH Paging Control Channel
P-CCPCH Primary Common Control Physical Channel
PCH Paging Channel
PCR Peak Cell Rate
xvi Abbreviations
PDCP Packet Data Convergence Protocol
PDH Plesiochronous Digital Hierarchy
PDU Packet Data Unit
PER Packed Encoding Rules
PI Paging Indication
PICH Paging Indication Channel
PLMN Public Land Mobile Network
PRACH Physical Random Access Channel
PS Packet Switched
P-SCH Primary Synchronisation Channel
PSTN Public Switched Telephone Network
P-TMSI Packet Temporary Mobile Subscriber Identity
PWE3 Psuedo Wire Emulation Edge to Edge
QoS Quality of Service
QPSK Quadrature Phase Shift Keying
RAB Radio Access Bearer
RAC Routing Area Code
RACH Random Access Channel
RAI Routing Area Identity
RAN Radio Access Network
RANAP Radio Access Network Application Part
RAT Radio Access Technology
RB Radio Bearer
RDI Restricted Digital Information
RFN RNC Frame Number
RIP Radio Interface Protocol
RL Radio Link
RLC Radio Link Control
RM Rate Matching
RNC Radio Network Controller
RNS Radio Network Sub-system
ROHC Robust Header Compression
RPP Recovery Period Power control
RRC Radio Resource Control
RRM Radio Resource Management
RSCP Received Signal Code Power
RSN Re-transmission Sequence Number
RSSI Received Signal Strength Indicator
RT Real Time
RV Redundancy Version
SA Service Area
SAC Service Area Code
SAI Service Area Identity
SAR Segmentation and Reassembly
SAW Stop and Wait
S-CCPCH Secondary Common Control Channel
SCH Synchronisation Channel
Abbreviations xvii
SCR Sustainable Cell Rate
SDH Synchronous Digital Hierarchy
SDU Service Data Unit
SEAL Simple and Efficient ATM Adaptation Layer
SF Spreading Factor
SFN System Frame Number
SGSN Serving GPRS Support Node
SI Scheduling Information
SIB System Information Block
SID Size Index Identifier
SIR Signal to Interference Ratio
SM Session Management
SM-AL Short Message Application Layer
SM-RL Short Message Relay Layer
SMS Short Message Service
SM-TL Short Message Transfer Layer
SONET Synchronous Optical Networking
SRB Signalling Radio Bearer
SRNS Serving Radio Network Sub-system
S-RNTI SRNC Radio Network Temporary Identity
SS Supplementary Services
SSADT Service Specific Assured Data Transfer
SSCF Service Specific Coordination Function
S-SCH Secondary Synchronisation Channel
SSCOP Service Specific Connection Orientated Protocol
SSCS Service Specific Convergence Sublayer
SSDT Site Selection Diversity Transmit
SSSAR Service Specific Segmentation and Reassembly
SSTED Service Specific Transmission Error Detection
STTD Space Time Transmit Diversity
SUFI Super Field
TB Transport Block
TBS Transport Block Set
TCP Transmission Control Protocol
TCTF Target Channel Type Field
TDD Time Division Duplex
TDMA Time Division Multiple Access
TEBS Total E-DCH Buffer Status
TF Transport Format
TFC Transport Format Combination
TFCI Transport Format Combination Indicator
TFCS Transport Format Combination Set
TFI Transport Format Indicator
TFO Tandem Free Operation
TFS Transport Format Set
TGD Transmission Gap Distance
TGL Transmission Gap Length
TGPL Transmission Gap Pattern Length
TGPRC Transmission Gap Pattern Repetition Count
xviii Abbreviations
TGPS Transmission Gap Pattern Sequence
TGPSI Transmission Gap Pattern Sequence Identifier
TGSN Transmission Gap Starting Slot Number
THP Traffic Handling Priority
TM Transparent Mode
TMSI Temporary Mobile Subscriber Identity
toAWE Time of Arrival Window End point
toAWS Time of Arrival Window Start point
TPC Transmit Power Control
TPDU Transfer Protocol Data Unit
TR Technical Report
TrFO Transcoder Free Operation
TS Technical Specification
TSN Transmission Sequence Number
TSTD Time Switched Transmit Diversity
TTI Transmission Time Interval
TTL Time To Live
UARFCN UTRA Absolute Radio Frequency Channel Number
UBR Unspecified Bit Rate
UDI Unrestricted Digital Information
UE User Equipment
UEA UMTS Encryption Algorithm
UIA UMTS Integrity protection Algorithm
UM Unacknowledged Mode
UMTS Universal Mobile Telecommunications System
UNI User to Network Interface
UPH UE Power Headroom
URA UTRAN Registration Area
U-RNTI UTRAN Radio Network Temporary Identity
USIM Universal Subscriber Identity Module
UTRAN UMTS Terrestrial Radio Access Network
UUI User to User Indication
VBR Variable Bit Rate
VCC Virtual Channel Connection
VPC Virtual Path Connection
VCI Virtual Channel Identifier
VoIP Voice over IP
VPI Virtual Path Identifier
VPLMN Visited Public Land Mobile Network
WCDMA Wideband Code Division Multiple Access
Abbreviations xix
1
Introduction
1.1 Network Architecture
� The RAN includes RNC, Node B and UE. RNC are connected to Node B using the Iub interface.
Neighbouring RNC are connected using the Iur interface. UE are connected to Node B using the
Uu interface. The RAN is connected to the CN using the Iu interface.
� Each Node B has a controlling RNC and each UE connection has a serving RNC. The serving
RNC provides the Iu connection to the CN. Drift RNC can be used by UE connections in addition
to the serving RNC.
The network architecture defines the network elements and the way in which those network elements
are interconnected. Figure 1.1 illustrates a section of the network architecture for UMTS. This book
focuses upon the Radio Access Network (RAN) rather than the core network. The RAN represents the
section of the network which is closest to the end-user and which includes the air-interface.
The RAN includes the Radio Network Controller (RNC), the Node B and the User Equipment (UE).
The MSC and SGSN are part of the core network. An example UMTS network could include thirty
RNC, ten thousand Node B and five million UE. The UE communicate with the Node B using the air-
interface which is known as the Uu interface. The Node B communicates with the RNC using a
transmission link known as the Iub interface. The RNC communicates with the core network using a
transmission link known as the Iu interface. There is an Iu interface for the Circuit Switched (CS) core
network and an Iu interface for the Packet Switched (PS) core network. The capacity of the Iu interface
is significantly greater than the capacity of the Iub interface because the Iu has to be capable of
supporting a large quantity of Node B whereas the Iub supports only a single Node B. Neighbouring
RNC can be connected using the Iur interface. The Iur interface is particularly important for UE which
are moving from the coverage area of one RNC to the coverage area of another RNC.
Each Node B has a controlling RNC and each UE connection has a serving RNC. The controlling
RNC for a Node B is the RNC which terminates the Iub interface. The serving RNC for a UE
connection is the RNC which provides the Iu interface to the core network. Figure 1.2 illustrates an
example for a packet switched connection and four Node B.
RNC 1 is the controlling RNC for Node B 1 and 2 whereas RNC 2 is the controlling RNC for Node
B 3 and 4. The controlling RNC is responsible for managing its Node B. RNC 1 is the serving RNC for
the packet switched connection because it provides the connection to the PS core network. The serving
Radio Access Networks for UMTS Chris Johnson
# 2008 John Wiley & Sons, Ltd
RNC is responsible for managing its UE connections. As this example illustrates, an RNC can be
categorised as both controlling and serving.
In the case of UE mobility, an RNC can also be categorised as a drift RNC. If a UE starts its
connection within the coverage area of RNC 1 then that RNC becomes the serving RNC and will
provide the connection to the core network. If the UE subsequently moves into the coverage area of the
second RNC then the UE can be simultaneously connected to Node B controlled by both RNC 1 and
RNC 2. This represents a special case of soft handover, i.e. inter-RNC soft handover. This scenario is
illustrated in Figure 1.3. In general, soft handover allows UE to simultaneously connect to multiple
Node B. This is in contrast to hard handover in which case the connection to the first Node B is broken
before the connection to the second Node B is established. Soft handover helps to provide seamless
mobility to active connections as UE move throughout the network and also helps to improve the RF
conditions at cell edge where signal strengths are generally low and cell dominance is poor. In the case
of inter-RNC soft handover, the UE is simultaneously connected to multiple RNC. The example
illustrated in Figure 1.3 is based upon two RNC but it is possible for UE to be connected to more than
two RNC if the RNC coverage boundaries are designed to allow it. In this example, RNC 1 is the
serving RNC because it provides the Iu connection to the core network. RNC 2 is a drift RNC because
it is participating in the connection, but it is not providing the connection to the core network. A single
connection can have only one serving RNC, but can have more than one drift RNC.
Communication between the UE and the serving RNC makes use of the Iur interface when a drift
RNC is involved. The Iur interface is an optional transmission link and is not always present. For
Figure 1.1 UMTS network architecture
2 Radio Access Networks for UMTS
example, if a network is based upon RNC from two different network vendors then it is possible
that those RNC are not completely compatible and the Iur interface is not deployed. If the Iur interface
is not present then inter-RNC soft handover is not possible because there is no way to transfer
information from the drift RNC to the serving RNC. In this case, the UE has to complete a hard
handover when moving into the coverage area of the second RNC. The inter-RNC hard handover
procedure allows the second RNC to become the serving RNC while the first RNC no longer
participates in the connection.
Assuming that the Iur interface is present and that a UE continues to move into the coverage area of
the drift RNC then it becomes inefficient to leave the original RNC as the serving RNC. There will be a
time when the UE is not connected to any Node B which are controlled by the serving RNC and all
information is transferred across the Iur interface. In this scenario it makes sense to change the drift
RNC into the serving RNC and to remove the original RNC from the connection. This procedure of
changing a drift RNC into the serving RNC is known as serving RNC relocation, or Serving Radio
Network Subsystem (SRNS) relocation. A Radio Network Subsystem (RNS) is defined as an RNC and
the collection of Node B connected to that RNC.
The radio network plan defines the location and configuration of the Node B. The density of Node B
should be sufficiently great to achieve the target RF coverage performance. If the density of Node B is
not sufficiently great then there may be locations where the UE does not have sufficient transmit power
to be received by a Node B, i.e. coverage is uplink limited. Alternatively, there may be locations where
a Node B does not have sufficient transmit power to be received by a UE, i.e. coverage is downlink
limited. The connection from the UE to the Node B is known as the uplink or reverse link whereas the
connection from the Node B to the UE is known as the downlink or forward link.
Figure 1.2 Categorising controlling and serving RNC
Introduction 3
1.2 Radio Access Technology
� The air-interface is based upon full duplex FDD with a nominal channel bandwidth of 5 MHz.
Channel separations can be <5 MHz because the occupied bandwidth is <5 MHz.
� Operators are typically assigned between 2 and 4 UMTS channels.
� A frequency reuse of 1 is applied allowing both soft and hard handovers.
� Multiple access is based upon Wideband CDMA with a chip rate of 3.84 Mcps.
� The release 7 version of the 3GPP specifications defines 9 operating bands.
� The most common Node B configuration for initial network deployment is three sectors with
1 RF carrier, i.e. a 1þ1þ1 Node B configuration.
� HSDPA and HSUPA offer significantly increased throughput performance.
The UMTS air-interface makes use of separate RF carriers for the uplink and downlink. This
approach is known as Frequency Division Duplexing (FDD) and is in contrast to technologies which
use the same RF carrier for both the uplink and downlink. Using the same RF carrier for both the uplink
and downlink requires time sharing, i.e. the RF carrier is assigned to the uplink for a period of time and
then the RF carrier is assigned to the downlink for a period of time. This approach is known as Time
Division Duplexing (TDD). A set of operating bands have been standardised for use by the UMTS air-
interface. These operating bands are presented in Table 1.1.
Figure 1.3 Categorising serving and drift RNC
4 Radio Access Networks for UMTS
The availability of each operating band depends upon existing spectrum allocations and the strategy
of the national regulator. The majority of countries deploying UMTS make use of operating band I as
the core set of frequencies. The remaining operating bands can either be used as extension bands or can
be used by countries where operating band I is not available. For example, operating band II is used in
North America because operating band I is not available. Operating band II cannot be used as an
extension for operating band I because the two sets of frequencies overlap with one another. Operating
band VIII is commonly viewed as an extension band which benefits from improved coverage
performance as a result of using lower frequencies. Operating band VIII is the same as the extended
GSM 900 band and so its use for UMTS may require re-farming of any existing GSM 900 allocations.
Each operating band is divided into 5 MHz channels. Operating bands I and II have 12 uplink
channels and 12 downlink channels. Operating band I has a frequency difference of 190 MHz between
the uplink and downlink channels whereas operating band II has a frequency difference of 80 MHz.
The difference between the uplink and downlink frequencies is known as the duplex spacing. Large
duplex spacings cause more significant differences between the uplink and downlink path loss. The
uplink is assigned the lower set of frequencies because the path loss is lower and link budgets are
traditionally uplink limited. Small duplex spacings make it more difficult to implement transmit and
receive filtering within the UE. Transmit and receive filtering is less of an issue within the Node B
because larger and more expensive filters can be used. The uplink and downlink channels belonging to
operating band I are illustrated in Figure 1.4.
National regulators award the 5 MHz channels to operators. Those operators then become
responsible for deploying and operating UMTS networks. It is common to award between two and
four channels to each operator. For example, a country which has four operators could have three
channels assigned to each operator. It is possible that not all twelve channels are available and only a
subset of the channels are allocated. Once an operator has been assigned a subset of the 5 MHz
channels then the operator has some flexibility in terms of configuring the precise centre frequencies of
its RF carriers. A UMTS RF carrier occupies less than 5 MHz and so the frequency separation between
adjacent RF carriers can also be less than 5 MHz. An example deployment strategy is illustrated in
Figure 1.4. In this example, three 5 MHz UMTS channels have been awarded to operator 2 while the
adjacent channels have been awarded to operators 1 and 3. Adjacent channel interference mechanisms,
e.g. non-ideal transmit filtering and non-ideal receive filtering are less significant when RF carriers are
co-sited, or at least coordinated. Operator 2 is likely to co-site adjacent RF carriers which are assigned
to the macrocell network (multiple RF carriers assigned to the same Node B) and is likely to coordinate
adjacent RF carriers which are assigned to the microcell layer or to any indoor solutions. The Node B
belonging to operators 1 and 3 may be neither co-sited nor coordinated with the Node B belonging to
operator 2. Operator 2 can help to reduce the potential for any adjacent channel interference by
reducing the frequency separation between its own RF carriers. This allows an increased frequency
Table 1.1 UMTS operating bands for the FDD air-interface
Operating Uplink Downlink Duplex spacing Equivalent
Band (MHz) (MHz) (MHz) 2G band
I 1920–1980 2110–2170 190
II 1850–1910 1930–1990 80 PCS 1900
III 1710–1785 1805–1880 95 DCS 1800
IV 1710–1755 2110–2155 400
V 824–849 869–894 45 GSM 850
VI 830–840 875–885 45
VII 2500–2570 2620–2690 120
VIII 880–915 925–960 45 E-GSM
IX 1749.9–1784.9 1844.9–1879.9 95
Introduction 5
separation from the adjacent operators. The RF carriers within operating band I have been standardised
using a 200 kHz channel raster. This means that the centre frequency of each RF carrier can be adjusted
with a resolution of 200 kHz.
The Node B configuration defines characteristics such as the number of sectors and the number of
RF carriers. The most common configuration for initial network deployment is three sectors with one
RF carrier. This is known as a 1þ1þ1 Node B configuration. It requires at least three antennas to be
connected to the Node B cabinet, i.e. at least one antenna serving each sector. If uplink receive diversity
or downlink transmit diversity is used then either six single element antennas or three dual element
antennas are required. If six single element antennas are used then there should be spatial isolation
between the two antennas belonging to each sector. This tends to be less practical than using three dual
element antennas. It is common to use cross polar antennas which accommodate two antenna elements
within each antenna housing. In this case, isolation is achieved in the polarisation domain rather than
the spatial domain. Figure 1.5 illustrates an example 1þ1þ1 Node B configuration using cross polar
antennas.
When diversity is used then a separate RF feeder is required for each diversity branch. A 1þ1þ1
Node B with uplink receive diversity requires six RF feeders to connect the antennas to the Node B
cabinet. Likewise, if Mast Head Amplifiers (MHA) are used then six of them would be required. The
1þ1þ1 Node B configuration has three logical cells, i.e. a logical cell is associated with each sector of
the Node B. When the capacity of a single RF carrier becomes exhausted then it is common to upgrade
to a second RF carrier. The Node B configuration is then known as a 2þ2þ2. This configuration has
three sectors, but now has two RF carriers and six logical cells. Alternatively, a six sector single RF
carrier configuration could be deployed which would be known as a 1þ1þ1þ1þ1þ1. This config-
uration also has six logical cells but has six sectors and 1 RF carrier.
When a UMTS operator deploys a single RF carrier then that carrier must be shared between all
users of the network and the frequency re-use is 1, i.e. all cells make use of the same RF carrier. GSM
networks make use of frequency re-use patterns to assign different RF carriers to neighbouring cells.
For example, a frequency re-use of 12 means that the radio network is planned in clusters of 12 cells
and each cell within a cluster can use 1/12th of the available RF carriers. This type of approach helps to
reduce co-channel interference, but leads to a requirement for hard handovers and a relatively large
Figure 1.4 UMTS FDD operating band I
6 Radio Access Networks for UMTS
number of RF carriers. GSM channels have a bandwidth of 200 kHz and so it is possible to place
25 GSM channels within the bandwidth of a single UMTS channel. The use of a wide bandwidth and a
frequency re-use of 1 for UMTS provides benefits in terms of receiver sensitivity and spectrum
efficiency. The air-interface of a single UMTS cell can support approximately 50 speech users when
assuming the maximum Adaptive Multi-Rate (AMR) bit rate of 12.2 kbps. A single GSM RF carrier
can support a maximum of 8 speech users when assuming Full Rate (FR) connections. This means that
5 MHz of GSM spectrum can support a maximum of 200 speech users (ignoring the impact of the
broadcast channel which in practise would reduce the maximum number of GSM speech users).
Assuming a frequency reuse of 10 reduces this figure to 20 speech users per 5 MHz in contrast to the 50
speech users supported by UMTS. The spectrum efficiency of GSM can approach that of UMTS when
using small frequency re-use patterns which require more careful planning to avoid co-channel
interference. Frequency hopping can also be used to improve the performance and spectrum efficiency
of GSM. The number of speech users supported by both UMTS and GSM can be increased by
decreasing the bit rates assigned to each connection. The UMTS AMR codec supports bit rates ranging
from 4.75 to 12.2 kbps. The GSM Half Rate (HR) feature may be used to reduce the GSM speech
bit rate.
GSM RF carriers are shared between multiple connections using Time Division Multiple Access
(TDMA). A GSM radio frame is divided into eight time slots and these time slots can be assigned to
different connections. An RF carrier belonging to a cell is never simultaneously assigned to more than
one connection. A GSM speech connection is assigned different time slots within the radio frame for
the uplink and downlink, i.e. the GSM MS does not have to simultaneously transmit and receive. This
approach is known as half-duplex and tends to make the MS design easier and less expensive. GSM
Figure 1.5 Example 1þ1þ1 Node B configuration
Introduction 7
base stations have to simultaneously transmit and receive because they serve multiple connections and
the uplink time slot of one connection can coincide with the downlink time slot of another connection.
This is known as full-duplex operation.
UMTS RF carriers are shared between multiple connections using Code Division Multiple Access
(CDMA). CDMA allows multiple connections to simultaneously use the same RF carrier. Instead of
being assigned time slots, connections are assigned codes. These codes are used to mask the transmitted
signal and allow the receiver to distinguish between signals belonging to different connections. The RNC
assigns codes to both the uplink and downlink during the establishment of a connection. The version of
CDMA used for UMTS is known as Wideband CDMA (WCDMA) because the bandwidth is relatively
large compared with earlier CDMA systems. WCDMA connections are able to use all time slots in both
the uplink and downlink directions. This means that WCDMA is full-duplex rather than half-duplex
because UE must be capable of simultaneously transmitting and receiving.
The WCDMA air-interface makes use of two types of code in both the uplink and downlink.
Channelisation codes are used to increase the bandwidth of the connection subsequent to physical layer
processing at the transmitter. These codes are sometimes referred to as spreading codes. For example, a
connection could have a bit rate of 240 kbps after physical layer processing. Each individual bit would
then be multiplied by a 64 chip channelisation code. This would increase the bit rate of 240 kbps by a
factor of 64 to a chip rate of 3.84Mcps. The chip rate of 3.84Mbps is standardised for WCDMA and all
connections have the same chip rate after spreading. If the bit rate after layer 1 processing had been
480 kbps then each individual bit would have been multiplied by a 32 chip channelisation code. This
would have increased the bit rate of 480 kbps by a factor of 32 to a chip rate of 3.84Mcps. The chip rate
of 3.84Mcps defines the approximate bandwidth of the WCDMA signal in the frequency domain, i.e. the
approximate bandwidth after baseband filtering is 3.84MHz. Once the transmitted signal has been spread
by a channelisation code then it is multiplied by a scrambling code. Scrambling codes have a chip rate of
3.84Mcps and do not change the chip rate of the already spread signal. In the downlink direction,
channelisation codes are used to distinguish between different connections and scrambling codes are used
to distinguish between different cells, i.e. each connection within a cell is assigned a different
channelisation code and each cell within the same geographic area is assigned a different scrambling
code. In the uplink direction, channelisation codes are used to distinguish between the different physical
channels transmitted by a single UE and scrambling codes are used to distinguish between different UE.
Table 1.2 summarises some of the most important characteristics of the GSM and UMTS air-
interfaces.
Table 1.2 Comparison of GSM and UMTS air-interfaces
GSM WCDMA
Duplexing FDD FDD
Multiple access TDMA CDMA
MS transmit and receive Half-duplex Full-duplex
Handover Hard Hard and soft
Frequency re-use 4–18 1
Channel bandwidth 200 kHz 5 MHz
RF carrier bandwidth 200 kHz 3.84 MHz
Typical maximum bit rates GSM 9.6 kbps DPCH 403.2 kbps
HSCSD 43.2 kbps HSDPA 7.2Mbps
GPRS 62.4 kbps HSUPA 1.44Mbps
EGPRS 179.2 kbps
Power control rate 2 Hz or lower 1500 Hz
Typical maximum uplink transmit power 33 dBm 24 dBm
Typical minimum uplink transmit power 5 dBm �50 dBm
8 Radio Access Networks for UMTS