UMTS Fundamentals

Proprietary and Confidential

1: UMTS Fundamentals

Version 2.0

West Region - UMTS RF Engineering

Proprietary and Confidential Slide 2

Module 1: UMTS Fundamentals • Module Overview

1.1 Introduction

1.2 CDMA Multiple Access Fundamentals

1.3 UMTS System

• Technology & Physical Interfaces

• WCDMA Air Interface

• UMTS Key Concepts

1.4 HSDPA

1.5 HSUPA

The overall aim of Module 1 is to give a broad grounding of UMTS concepts on

which to build on in the following modules


Introduction


Introduction • abc


Multiple Access Fundamentals


FDMA – Frequency Division Multiple Access

frequency

time

User 1

Frame Period (we may still need

frames/timeslots for signalling)

Channel

Bandwidth

User N


TDMA - Time Division Multiple Access

freq

ue

ncy

time

User 1 User 1

Timeslot Period Frame Period

Channel

Bandwidth


FDMA/TDMA

frequency

time

Channel

Bandwidth

Timeslot Period Frame Period

User 1 User 1


CDMA - Code Division Multiple Access

frequency

time

code

Frame Period (we may still need

frames/timeslots for signalling)


Code Division Multiple Access

Identica

l codes

Tx Bit Stream

P

f

Code Chip Stream

Spreading

P

f

Channel

Air Interface

Chip Stream

P

f

Code Chip Stream

Despreading

P

f

Rx Bit Stream

P

f



Rx Bit Stream

Air Interface

Chip Stream

Tx Bit Stream 1

-1

Code Chip Stream

X Spreading

Code Chip Stream

X Despreading



Air Interface

Chip Stream

Tx Bit Stream 1

-1

Code Chip Stream

X Spreading

X Despreading Code Chip Stream Y

Rx Bit Stream


WCDMA System Overview


WCDMA Network Topology

Iu-CS

Iub

PSTN

IP Domain

(Wap, Internet, Streaming)

GGSN 3G

SGSN

WCDMA Air Interface

Uu

Iu-PS

User Equipment (UE) & USIM

Node Bs RNC

2G Net

MSC (Voice & Video calls)


WCDMA Air Interface Concepts


Key WCDMA Concepts • Key WCDMA concepts to be covered

– AIR INTERFACE OVERVIEW

– POWER CONTROL

• Open

• Closed (Fast/Slow)

– HANDOVER

• Intra-Frequency (Soft/Softer)

• Inter-Frequency (Other WCDMA carrier)

• Inter-System (3G->2G)

– RADIO RESOURCE MANAGEMENT

• Admission Control

• Load Control

• Packet Scheduler

• Resource Management

• Mobility Management

• Power Control


WCDMA Air Interface Overview


WCDMA Air Interface

UMTS FDD UMTS TDD

Multiple Access

CDMA CDMA

Modulation QPSK/16QAM QPSK

Carrier Spacing 5MHz (200kHz raster)

5MHz (200kHz raster)

Frame Length 10ms/2ms 10ms

Slots per Frame

15 15

Multiple Rates Multi-code, Variable

Spreading Factor

Multi-code, multi-slot

Chip Rate 3.84Mcps 3.84Mcps

Max Data Rate 14.4Mbps 2Mbps

Synchronous No Yes

Handover Soft Hard


WCDMA Spreading Codes

SF 4

SF 8

SF 16

SF 2

• WCDMA used Orthogonal Variable Spreading Factor (OVSF) Codes to

spread user data in both the uplink and the downlink

• Spreading separates the different users in the code domain

• The maximum spreading factor used in UMTS is 512

• DL Speech uses SF=128

• DL 384k used SF=8


WCDMA Scrambling Codes (SC)

• After spreading the bit stream is scrambled

• In the uplink – one SC per UE

• In the downlink – (typically) one SC per sector

• Spreading separates the different base stations in the code domain

Spreading Code

Spreading

User Bit Stream

Scrambling

Scrambling Code

TX Bit Stream


WCDMA Code Summary Synchronisation Codes Channelisation Codes Scrambling Codes, UL Scrambling Codes, DL

Type

Gold Codes, Primary

Synchronization Codes (PSC)

and Secondary Synchronization

Codes (SSC)

Orthogonal Variable Spreading

Factor (OVSF) codes,

sometimes called Walsh codes

Complex-Valued Gold Code

Segments (long) or Complex-

Valued S(2) Codes (short)

Complex-Valued Gold Code

Segments

Length 256 chips 4-512 chips 38400 chips /256 chips 38400 chips

Duration 66.67 µs 1.04 µs - 133.34 µs 10 ms / 66.67 µs 10 ms

Number of

codes

1 primary code / 16 secondary

codes

= spreading factor, 4 ... 256 UL,

4 ... 512 DL16,777,216

512 primary / 15 secondary for

each primary code

Spreading No, does not change bandwidth Yes, increases bandwidth No, does not change bandwidth No, does not change bandwidth

UsageTo enable terminals to locate

and synchronise to the cells'

main control channels

UL: to separate physical data

and control data from same

terminal. DL: to separate

connection to different terminals

in a same cell

Separation of terminal Separation of sectors


WCDMA Logical Channels

• Control Channels

– BCCH Broadcast Control Channel

– PCCH Paging Control Channel

– CCCH Common Control Channel

– DCCH Dedicated Control Channel

• Traffic Channels

– DTCH Dedicated Traffic Channel

– CTCH Common Traffic Channel


WCDMA Transport Channels

• Common Channels

– BCH Broadcast Channel

– FACH Forward Access Channel

– PCH Paging Channel

– RACH Random Access Channel

– CPCH Common Packet Channel

• Dedicated Channels

– DCH Dedicated Channel

– DSCH Downlink Shared Channel


WCDMA Physical Channels

• Common Control Channels

– P-CCPCH Primary Common Control Physical Channels (DL)

– S-CCPCH Secondary Common Control Physical Channels (DL)

– P-SCH Primary Synchronisation Channel (DL)

– S-SCH Secondary Synchronisation Channel (DL)

– CPICH Common Pilot Channel (DL)

– AICH Acquisition Indicator Channel (DL)

– PICH Paging Indicator Channel (DL)

– PDSCH Physical Downlink Shared Channel (DL)

– PRACH Physical Random Access Channel (UL)

– PCPCH Physical Common Packet Channel (UL)

– AP-AICH Access Preamble Acquisition Indicator Channel (DL)

• Dedicated Channels

– DPDCH Dedicated Physical Data Channel (DL & UL)

– DPCCH Dedicated Physical Control Channel (DL & UL)


WCDMA Transport -> Physical Channel Mapping

BCH PCH CPCH RACH FACH DSCH DCH

DPDCH

DPCCH

PDSCH

S-CCPCH

P-CCPCH

PCPCH

PRACH

S-SCH

CPICH

AICH

PICH

AP-AICH

CD/CA-ICH

P-SCH

Physical Channels

Transport Channels Spreading/Modulation


WCDMA Air Interface Key Concepts


Scrambling Codes & CPICH

• The Common Pilot Indication Channel (CPICH) is broadcast from every cell

• It carries no information and can be thought of as a “beacon” constantly

transmitting the Scrambling Code of the cell

• It is this “beacon” that is used by the phone for its cell measurements for

network acquisition and handover purposes (Ec, Ec/Io).

CPICH


3G Coverage Measurements

• The majority of 3G coverage measurements are based upon measurements

of the CPICH

• Golden Rule: If the UE can’t see the CPICH the UE can’t see the cell.

• Initial 3G network optimisation will be performed purely from CPICH

measurements

• Three key related measurements for 3G optimisation are

• Ec - The Received Signal Level of a particular CPICH (dBm)

• Io - The Total Received Power (dBm)

• Ec/Io - The CPICH Quality (The ratio of the above two values)


Total Received Power Io

• In a WCDMA network the User Equipment (UE) may receive signals from

many cells whether in handover or not

• Io* = The sum total of all of these signals + any background noise (dBm)

*Note: Sometimes Io is referred to as No, RSSI or ISSI

Io


Received Power of a CPICH (RSCP)

• Using the properties of SCs the UE is able to extract the respective CPICH

levels from the sites received

• RSCP* = The Received Power of a Particular CPICH (dBm)

*Note: Sometimes RSCP is referred to as Ec

Ec1 Ec2


The CPICH Quality (Ec/Io)

• From the previous two measures we can calculate a signal quality for each

CPICH (SC) received

• Ec/Io = RSCP - Io (dB)

*Note: Sometimes Ec/Io is referred to as Ec/No

RSCP1 RSCP2


Example

• From the above three measurements we can calculate for each pilot the

RSCP level for that particular pilot

RSCP1 = -80 - 5 = -85dBm

RSCP2 = -80 - 10 = -90dBm

Ec/Io1= -5dB Ec/Io2 = -10dB

Io=-80dBm


Ec, Io and Ec/Io Measurement • All commercial scanners and test UEs are capable of making Ec, Io and Ec/Io

measurements

• It is these measurements that are used for coverage analysis and basic

optimisation


Power Control


Power Control • The near far problem

– In any CDMA network, the power of the BTS and UE must be tightly controlled

to avoid interference to other BTSs/UEs


Power Control • Types of Power Control

– Open Loop Power Control – Used to set the initial transmit power of the BTS/UE

– Closed Loop Power Control – Used to control power of uplink/downlink DCHs

• Inner Loop (Or Fast Power Control) used to control TX Power (UL/DL)

• Outer Loop (Or Slow Power Control) used to control SIR Targets (UL/DL)


Open Loop Power Control • Open Loop Power Control (UPLINK)


– UPLINK: Uses a measure of DL path loss to provide estimate uplink path loss

– UPLINK: CPICH measurement by the UE along with the reported BTS Noise

Floor are used to determine the initial TX power of the UE

Preamble_Initial_power = CPICH_Tx_power – CPICH_RSCP + UL_interference + UL_required_CI

CPICH_Tx_power

UL_Interference

UL_required_CI

CPICH_RSCP


Open Loop Power Control • Open Loop Power Control (DOWNLINK)


– DOWNLINK: Uses a measure of DL path loss to set initial DL TX power

PPDPCH_Initial = Eb/No - PG + CPICH_Tx_Power – CPICH_Ec/Io

CPICH_Tx_power

CPICH_Ec/Io

Eb/No

PG


Closed Loop Power Control • Closed Loop Power Control

– Enables the BTS/UE to rapidly adjust their DCH TX powers to track the

changing channel conditions (path loss & interference) in order to maintain the

required SIR at the receiving UE/BTS

– Uses feedback (power control commands) in the opposite link to adjust Tx

power accordingly


Closed Loop Power Control • Closed Loop Power Control

– Closed Loop Power Control – Used to control power of uplink/downlink DCHs

– Two components to Closed Loop Power control in WCDMA

• Inner Loop (Or Fast Power Control) used to control TX Power (UL/DL)

• Outer Loop (Or Slow Power Control) used to control SIR Targets (UL/DL)

Iu-CS

Iub

Iu-PS User Equipment (UE)

& USIM Node Bs RNC

Uu

Inner Loop PC

Outer Loop PC


Closed Loop Power Control • Closed Loop: Inner Loop Power Control

– Transmit Power Control (TPC) commands (up/down) issued to UE (Uplink) and

BTS (Downlink) to maintain Target SIR every time slot (1500 Hz)

– Power control step size typically 1dB (Algorithm 1)

– Below 30km/h 1.5KHz and 1dB is fast enough to track changes

– Above 30km/h other schemes such as (Algorithm 2) maybe more suitable

User Equipment (UE) & USIM

Node Bs

Uu

Inner Loop PC

Required SIRDL Required SIRUL


Closed Loop Power Control • Closed Loop: Outer Loop Power Control

– RNC compares uplink BLER with BLER target and sets SIRUL accordingly

– UE compares downlink BLER with BLER target and set SIRDL accordingly

– Frequency 10 to 100 Hz

– Step size 0.1 to 1dB

Iub

User Equipment (UE) & USIM Node Bs RNC

Uu

Outer Loop PC


WCDMA Handovers


Handovers in WCDMA • Soft Handover

– Intra-system Handover

• Hard Handover

– Inter-frequency Handover

– Inter-system Handover


Handovers in WCDMA - Softer HO

• Softer handover occurs between sectors of the same site


• Soft handover occurs between sectors of the different sites

• For both softer and soft handover UE Ec/Io measurements are used to

determine whether a cell should be added or removed from the active set

Handovers in WCDMA - Soft HO


Soft Handover • Mechanics of Soft Handover

– In WCDMA to avoid interference the UE must be connected to its best serving

cell at all times

– Another mechanism to minimize interference is Soft Hanover – the “Make

Before Break” handover

– In order to ensure this when in-call the UE constantly monitors the CPICH signal

quality (Ec/Io) of its serving cell and its serving cell’s declared neighbors


Soft Handover • Neighbor List

– In WCDMA like GSM each cell has to declare at list of valid neighbors

• Intra-system neighbors (32 Max)

• Inter-frequency neighbors (32 Max)

• Inter-system neighbors (32 Max)


Soft Handover • The Active Set

– The Active Set is defined as the list of cells the UE is connected to during

dedicated mode

– Active set size = 1: UE Not in Soft Handover

– Active set size > 1: UE in Soft Handover

– Typically Active set size limited to 3


Soft Handover • Updating the Active Set

– Addition Window

– Drop Window

– Replacement Window

Io

RSCP1

RSCP3

RSCP4

-60dBm

-65dBm

RSCP2 -70dBm

-77dBm

-83dBm



– Addition Window

– Drop Window


Io

RSCP1

RSCP3

RSCP4

-60dBm

-65dBm

RSCP2 -70dBm

-77dBm

-83dBm


Soft Handover

Ec/Io1

Ec/Io2

Addition Window

Drop Window

Tadd Tdrop


Soft Handover

Ec/Io1

Ec/Io3

Addition Window

Drop Window

Tadd Tadd Treplace

Ec/Io2

Ec/Io4



– Addition Window

– Drop Window


Io

RSCP1

RSCP3

RSCP4

-60dBm

-65dBm

RSCP2 -70dBm

-77dBm

-83dBm


Handovers - Inter frequency HO

• Inter frequency handover occurs between two WCDMA carriers

• Used once operator deploys its second carrier, for microcell layer or capacity

purposes


Handovers - Inter system HO

• Inter system handover occurs between 3G and other systems (2G, TDD,

WiMAX)

• As with all handovers, accurate adjacencies will be required

3G 2G


Inter System Handover -3G/2G

• Inter System HO occurs at the boundary of 3G coverage

– 3G Network Edge

– In building?

– Area of poor 3G coverage

3G 2G


Inter System Handover -3G/2G

• Currently most vendors only support Intersystem HO for Voice and PS Data

services

• 3G->2G Voice HO is a real Hard Handover (seamless from user point of view)

• 3G->2G PS Data HO is effectively a reselection (disruption in data

communications for a number of seconds)

3G 2G


Inter System Handover -3G/2G Voice

• Typical Dual Mode 3G/2G UEs utilize a single TRX

• During a voice call on WCDMA TRX utilise 100%

• However during 3G/2G HO UE needs to detect 2G neighbours

• Therefore some time sharing of TRX (RX actually) is required to detect

potential 2G Handover candidates

• This time sharing mode is know as “Compressed Mode”

• During compressed mode the UE the instantaneous transmit power is

increased in the compressed frame in order to keep the quality (BER, FER,

etc.) unaffected by the reduced processing gain

3G 2G


Inter System Handover -3G/2G Voice

• During compressed mode UE attempts to detect 2G candidate cells (ARFCN)

and reports detected neighbours to RNC

• RNC may requests further verification (BSIC)

• Finally RNC will instruct UE to handover to the chosen 2G cell and the call

continues on GSM

3G 2G


Inter System Handover -3G/2G PS Data

• As with voice, during PS 3G/2G HO the UE needs to detect the 2G neighbors

• Again compressed mode is used to detect 2G candidate cells (ARFCN) and

report detected neighbours to RNC

• RNC may requests further verification (BSIC)

• Finally RNC will instruct UE to reselect to the chosen 2G cell and initiate PS

Data transfer on GSM (GPRS)

3G 2G


Radio Resource Management


Radio Resource Management • Overview of Radio Resource Management (RRM)

– Aim of RRM is to efficiently manage the Radio Resources of the WCDMA air

interface

– Different vendors have implemented different RRM strategies and algorithms

– Generally RRM functions can be group as follows


• Load Control



• Power Control

• Mobility Control

Cell Based

Connection Based


Radio Resource Management • Admission Control

– Responsible for determining if the system (Air Interface, Code Tree, Channel

Elements, Iub, RNC, Iu etc), can accept the call

• Air Interface (Uplink Load, Downlink Load/Tx Power) ?

• Code Tree – Fragmentation ?

• Processing Capacity ?

• Iub Capacity ?

• RNC Capacity ?

– May give priority to different types of calls

• Typically voice/video take precedent

– Considers reports from Load Control Entity to assist decisions


Radio Resource Management • Load Control

– Responsible for ensuring cell does not go into overload condition

– Constantly monitoring Uplink Rx power and Downlink Tx power

– Preventative action taken to avoid overload condition

– Load reports sent to Admission Control and Packet Scheduler


Radio Resource Management • Packet Schedule

– Responsible for maximizing throughput of cell/users

– Considers reports from Load Control Entity to assist decisions

– Should allocate the best bearer for the job

• HSDPA / 384k / 128k / 64k / 32k / FACH etc.

Time

Load

Load Target

CS Load

Free Capacity for

PS or HSDPA


Radio Resource Management • Resource Manager

– Responsible for ensuring efficient use of cells processing capacity

• Code use

• Channel element use

SF 4

SF 8

SF 16

384 user #1 128 user #1

384 user #2


Radio Resource Management • Power Control

– As shown earlier power control is used to maintain the quality of the radio link

– Minimizing the uplink and downlink transmission power maximizes system

capacity

Iu-CS

Iub

Iu-PS User Equipment (UE)

& USIM Node Bs RNC

Uu

Inner Loop PC

Outer Loop PC


Radio Resource Management • Mobility Manager

– Responsible for maintaining radio links with UE during mobility

• Intra-system handover

• Inter-system handover

• Link Adaptation

3G 2G 3G 3G


Key WCDMA Concepts Summary • Key WCDMA concepts to be covered

– AIR INTERFACE OVERVIEW

– POWER CONTROL

• Open

• Closed (Fast/Slow)

– HANDOVER

• Intra-Frequency (Soft/Softer)

• Inter-Frequency (Other WCDMA carrier)

• Inter-System (3G->2G)

– RADIO RESOURCE MANAGEMENT


• Load Control



• Mobility Management

• Power Control


Module 1. UMTS Fundamentals Summary


Module 1: UMTS Fundamentals • Module Summary

1.1 Background & Evolution to 3G and beyond

1.2 CDMA Multiple Access Fundamentals

1.3 UMTS System

• Technology & Physical Interfaces

• WCDMA Air Interface

• UMTS Key Concepts

1.4 WCDMA Link Budgets

1.5 West Region Planning Process Overview

The overall aim of Module 1 is to give a broad grounding of UMTS concepts on

which to build on in the following modules

UMTS Fundamentals

Documents

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