GSM to UMTS Transition

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Lucent Technologies - ProprietaryThis document contains proprietary information

of Lucent Technologies and is not to be disclosed or usedexcept in accordance with applicable agreements

Copyright 2000 Lucent TechnologiesUnpublished and Not for Publication

All Rights Reserved

GSM to UMTS

Transition

RF Engineering Guideline

EG: GSMUTR

401-380-373Issue 1.1July 2000


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Copyright 2000 by Lucent Technologies. All Rights Reserved.

This material is protected by the copyright laws of the United States and other countries. Itmay not be reproduced, distributed, or altered in any fashion by any entity (either internal orexternal to Lucent Technologies), except in accordance with applicable agreements, contracts,or licensing, without the express written consent of the Customer Training and InformationProducts organisation and the business management owner of the material.

For permission to reproduce or distribute, please contact:

The Manager, RF Systems & Capacity Engineering Group01793 883275 (domestic)(44) 1793 883275 (international)

Notice

Every effort was made to ensure that the information in this information product was completeand accurate at the time of printing. However, information is subject to change.


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Contents

Issue 1.1 - July 2000 Lucent Technologies Proprietary

See Notice on first page

iii

1. ABOUT THIS DOCUMENT 1

1.1. Purpose 1

1.2. Contents 2

1.3. Scope 3

1.4. Audience 3

2. INTRODUCTION TO THE UMTS AIR INTERFACE 5

2.1. Background 5

Frequency allocation 5

Standards 5

UMTS summary 7

2.2. Band plan 8

Satellite allocation 8

Terrestrial allocation 8

2.3. UTRAN air interface attributes 11

2.4. Channel mapping on the air interface 13

Access stratum 13

Logical channels 14

Transport channels 15

Physical channels 17


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2.5. Channel spreading, coding and modulation 23

Uplink 23

Downlink 27

Synchronisation codes 29

2.6. Physical channel frame structure 29

Uplink time slot fields 29

Downlink time slot fields 31

2.7. Speech coding 34

Transcoder Free Operation 35

GSM Full Rate codec 36

GSM Half Rate codec 36

GSM Enhanced Full Rate codec 36

Adaptive Multi-Rate codec types 37

2.8. Codec speech quality 44

Fixed rate codecs 44

Disadvantages 45

Adaptive Multi Rate codecs 46

3. MOBILE HANDOVER 49

3.1. Handover types 49

3.2. Cell sets 51

3.3. Preparation for UTRAN to UTRAN handover 52

3.4. Preparation for UTRAN to GSM handover 53

Silence Duration parameters 54

3.5. Handover execution 58

UTRAN soft handover 58

UTRAN to GSM handover 58

3.6. GSM to UTRAN handover 59


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4. SUBSCRIBER SERVICES 61

4.1. Coding and interleaving for subscriber services 62

4.2. Services multiplexing 62

4.3. Rate matching 63

Uplink 63

Downlink 63

4.4. Control channel coding and interleaving 64

Dedicated Control Channel 64

Downlink Common Control Channels 64

4.5. Channel mapping examples 64

8kbs-1

bearer - speech 64

144kbs-1

bearer - data 65

384kbs-1

bearer - data 65

480kbs-1

bearer - data 66

5. LUCENT EQUIPMENT 67

5.1. Node-B (BTS) 68

Distributed Milli-cell 69

Microcell (Ultra-small cell) 70

Milli-cell 70

BTS traffic capacity 75

BTS further reference 77

5.2. BTS Antennas 78

No existing network 78

Existing single band network 78

Existing dual band network 80

Dual band and tri band GSM/UTRAN diplexers 84

Broadband power divider 87

Broadband indoor antennas 87

Antenna feeder 88

Masthead amplif ier 89


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Repeater 90

Active/smart/adaptive antennas 91

General antenna comments 92

Further reference antennas and BTS accessories 92

5.3. Radio Network Controller 93

RNC characteristics 96

RNC further reference 99

5.4. Radio Resource Control software 99

Radio resource allocation 99

Radio Resource Allocation functions 104

Radio Access Bearer parameters 107

Physical channel related parameters 107

Reverse outer loop power control 110

Further reference power control system 111

Power control parameters 111

Radio Resource Control software further reference 112

5.5. Handover 112

Measurement reporting 113

Measurement messages 116

Measurement performance 117

Soft (and softer) handover algorithm 117

Hard handover algorithm 122

UTRAN GSM handover algorithm 122

UTRAN GSM GPRS handover algorithm 122

Handover control software further reference 122

5.6. Lucent equipment capacity 123

Hardware (Lucent Network Release 1.0) 123

Software (Lucent Release 0.1) 123

6. RF NETWORK COVERAGE AND CAPACITY DESIGN 125

6.1. Frequency planning 126

Frequency planning criteria 126

Example UTRAN band assignment United Kingdom 127


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vii

6.2. Code assignment parameters 129

Primary Synchronisation Channel Code 129

Secondary Synchronisation Channel Code 129

Scrambling code 130

Code assignment summary 130

6.3. Air interface link power budget 131

Background 131

Effect of coding scheme on link power budget 131

Link power budget elements 133

Example link power budgets 145

Margins for fading and building attenuation 148

6.4. Estimating coverage and traffic capacity 149

Fixed cell loading 150

Adaptive cell loading 152

Estimating base station numbers 153

Land-use classification 159

UMTS Dimensioning tool further reference 159

6.5. Airpro coverage and traffic distribution prediction software 160

Introduction 160

Principal features 161

Airpro default values 173

6.6. BTS and antenna settings optimisation software 174

Introduction 174

Applications 175

Cellular radio standards 175

Optimising strategy 175

RF model 176

Results 177

Comparison trials 177

6.7. Inter-system boundary 178

6.8. Further reference 178


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7. RF NETWORK PRACTICAL IMPLEMENTATION 179

7.1. Use of existing sites 179

7.2. EMC at existing GSM sites 180

Transmitter isolation 180

Receiver performance degradation 181

Inter-system isolation criteria 183

Estimating inter-system isolation 183

Antenna coupling 184

Separate UTRAN and GSM antenna systems 185

Single UTRAN and GSM antenna system 190

UTRAN BTS spurious emissions 191

Worked example of co-siting GSM and UTRAN 193

7.3. Use of repeaters 198

Introduction 198

Design 199

Uniform range extension 200

Cascaded range extension 200

Repeater gain and composite noise factor 200Donor cell shrinkage 201

Median repeater link budget calculation 202

Median repeater link budget adjustment 203

Repeater donor cell antennas 203

Summary 204

7.4. Use of microcells 205

Embedded and non-embedded microcells 206

Microcell problems 207

Co-channel macrocells and microcells 207

Macrocells and microcells on different channels 208

Dual layer UTRAN 208

7.5. Masthead amplifiers 209

Without masthead amplif ier 210

With masthead amplif ier 212

Summary 214


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7.6. Practical antenna considerations 214

Intermodulation products 214

Front-to-back ratio 215

Variable electrical down-tilt 215

7.7. Transmit diversity 217

UTRAN implementation 218

Effect of UTRAN implementation 219

7.8. Coverage areas for different services 219

7.9. Survey test equipment 220

7.10. Site selection and design optimisation 222

RF network engineering requirements 222

8. DEPLOYMENT WORKED EXAMPLE 225

8.1. Scenario 225

Coverage area 226

Existing base station sites 226

8.2. Background 229

8.3. Estimating coverage and capacity 230

Coverage model 230

Traffic model 232

System model 233

Analysis results 237

8.4. Coverage prediction with Airpro (CE 5) 241

Existing 900MHz coverage 241

Existing 1800MHz coverage 244

Predicted UTRAN coverage 247

Results 260

Conclusion 260

8.5. EMC when using a common antenna 261


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900MHz receiver - in-band power 261

1800MHz receiver - in-band power 262

UTRAN receiver - in-band power 262

GSM 900MHz receiver out-of-band power 263

GSM 1800MHz receiver out-of-band power 264

UTRAN receiver out-of-band power 265

Conclusion 266

APPENDIX A SILENCE DURATION PARAMETERS 267

ACRONYMS 269


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About this Document

1

Issue 1.1 - July 2000 Lucent Technologies ProprietarySee Notice on first page

1

1. About this Document

1.1. Purpose

This document describes the principal Radio Frequency (RF) engineering implications whencellular radio networks make the transition from the GSM air interface standard to the UniversalMobile Telecommunications System (UMTS) standard.

In particular it discusses the following areas:

Air interface

Handover

Subscriber services

Lucent equipment

RF network coverage and capacity

RF network practical implementation

Future developments

Owing to the wide range of environments in which UMTS systems will be deployed, and thediffering operational and commercial priorities of network operators, the choice ofimplementation technique will be territory and customer specific. As a result, this document canonly provide an outline guide to the main issues involved in the network design and deployment


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2 Lucent Technologies ProprietarySee Notice on first page


process. It is not a substitute for the detailed analysis and design that will be required on a siteby site basis.

1.2. Contents

Chapter 2 - Air Interface

This chapter provides a brief introduction to the main characteristics of the radio link, includingthe function of transport channels and their mapping to the physical channels transmitted overthe air.

It describes the concept of channel codes, which are used to implement Code Division MultipleAccess (CDMA) to the shared RF channel (frequency), and identifies the main codes applied tothe air interface. It also describes spreading factor (and associated de-spreading gain) andbearer data rate concepts.

As this document deals with the physical layer of the link, protocol aspects are not covered.

Chapter 3 - Handover

This chapter describes the main UMTS handover types, with particular emphasis on intersystem handover with a neighbouring or overlaid GSM network.

Chapter 4 - Subscriber Services

This chapter describes the basic subscriber services, from the viewpoint of their associatedbearer data rates and spreading factors.

Later chapters use these concepts when looking at the effect of the anticipated mix of services

on RF network capacity and design.

Chapter 5 - Lucent Equipment

This chapter describes the network elements that form the base station system. It describes themain attributes of Lucents equipment, and equipment capacity and interdependencies as theyrelate to RF network capacity and design.

Chapter 6 - RF Network Coverage and Capacity Design

This chapter describes the network design process from the RF perspective, including radio linkpower budget calculation, estimated coverage techniques, and traffic modelling. It alsodescribes Lucent software tools and techniques for network design.

Chapter 7 - RF Network Practical Implementation

This chapter discusses some of the practical issues involved in upgrading an existing networkfrom GSM to UMTS.


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Areas considered include inter system interference, equipment that can be shared betweensystems, and the extent to which a UMTS service can be provided from an existinginfrastructure of GSM base station sites.

Chapter 8 - Deployment Worked Example

This chapter describes a worked example of UMTS deployment. Where possible, the data usedis based on actual traffic projections and infrastructure configurations provided by existingnetwork operators.

Appendix A - Silence Duration Parameters

Appendix A reproduces an extract from ETSI UMTS xx.15 v1.0.0 1999-02 regarding theDefinition and Setting of Silence Duration Parameters.

1.3. Scope

This document covers the radio engineering implications of the transition from the use of theGSM air interface to that of UMTS, for the provision of cellular radio services. It is primarilyintended to cover circumstances where existing GSM network operators wish to upgrade theirnetwork, in whole or part, to provide a UMTS service.

In view of the range of this subject, many topics can only be covered in outline. However,sufficient information is included to identify the major issues involved and to identify areas forfurther planning and investigation.

This document describes the features and facilities available in Lucent Network Release 1.0software.

1.4. Audience

This document concentrates on the World Radio Conference (WRC) Region 1 (Europe, Middle-East and Africa) as this is where UMTS networks will be first established. However, many of thesubjects covered will be relevant to other WRC regions.

It is intended for use by the following groups:

Engineers undertaking first-time design of GSM to UMTS upgrades

Technicians who want an appreciation of UMTS design considerations

Sales or support staff

Managers or administrative staff who want a high-level understanding of UMTS designprocesses


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A working knowledge of the following topics will be useful:

GSM air interface (such as power budget and the basic structure of control and trafficchannels)

CDMA concepts


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Introduction to the UMTS AirInterface

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2. Introduction to the UMTS AirInterface

This chapter describes the main features of the UMTS radio link. It concentrates on the systemaspects that have most impact on the design and implementation of a customer network, ratherthan on the design of individual network elements.

2.1. Background

Frequency allocationThe World Radio Conference (WRC) has allocated a frequency band around 2GHz for use byPublic Land Mobile Networks (PLMNs) to support third generation public mobile phone anddata services. These are expected gradually to replace the existing second generationnetworks (largely based on GSM and IS95).

The International Telecommunications Union Radio (ITU-R) has overall responsibility fordefining the third generation system, known as the International Mobile Telecommunications2000 (IMT-2000).

The IMT-2000 system will be an integrated system that allows terminals to access both satelliteand terrestrial based stations. Bands 1885MHz to 2025MHz and 2110MHz to 2200MHz areallocated to the terrestrial component. Bands 1980MHz to 2021MHz and 2170MHz to 2200MHz

are allocated to the satellite component.

Standards

The ITU-R has produced high-level documents covering the performance, service type, andinter-working requirements for IMT-2000.


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Various international standards bodies such as the European Telecommunications StandardsInstitute (ETSI) are responsible for the detailed technical specifications of the equipmentrequired to provide an IMT-2000 compatible service. A number of different standards are likely

to emerge; but they are expected to have sufficient inter-working capability to allow anintegrated IMT-2000 service for subscribers.

IMT-2000 networks will support five interface standards:

IMT-DS Frequency Division Duplex (FDD) version of UMTS (discussed in thisdocument)

IMT-MC US CDMA 2000 standard

IMT-TC Time Division Duplex (TDD) version of UMTS

IMT-SC GSM EDGE (IS-136) standard

IMT-FT DECT standard

The four Technical Specification Groups (TSGs) of the ETSI-supported 3rd

GenerationPartnership Project (3GPP) have approved the detailed specification parts of their submissionto the ITU-R for the IMT-2000 radio interface standard. This is a terrestrial radio interfacespecification known as the Universal Terrestrial Radio Access Network (UTRAN). The UTRANis based on a Wide-band Code Division Multiple Access (WCDMA) air interface.

The ITU-R intend to approve the detailed specification of the IMT-2000 radio interface in May2000, based on submissions received f rom the international standards bodies.


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UMTS summary

A UMTS network can consist of one or more access networks, using different radio accesssystems, linked to the same core network. Together they form a single UMTS network. Theterm UMTS covers all the network elements in both the access network and the core network.

The UTRAN specified by ETSI is one such UMTS access network. It supports wide areaterrestrial mobile telecommunications services, using the Frequency Division Duplex (FDD)IMT-2000 bands. This document concentrates primarily on the ETSI FDD UTRAN.

The UTRAN comprises the network elements that correspond to the Base Station Subsystem(BSS) in a GSM network:

Base Transceiver Station (BTS)

Base Station Controller (BSC)

In the UTRAN, the equivalent of the GSM BTS is referred to as either the BTS or the Node B.The equivalent of the GSM BSC is referred to as the Radio Network Controller (RNC). TheUTRAN BTS and RNC together form the Radio Network System (RNS).

Owing to differences in the radio standards currently used, and consequently those used toprovide a IMT-2000 service, this document concentrates on WRC Region 1, where the UTRANRNS will be used as the UMTS access network.


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2.2. Band plan

The WRC of 1992 allocated 230MHz of the 2GHz spectrum to IMT-2000 services with theintention of providing a uniform band plan for all three WRC regions.

The allocated spectrum consists of two blocks:

140MHz for TDD and FDD uplinks from 1885 to 2025MHz

90MHz for FDD downlinks from 2110 to 2200MHz

Satellite allocation

Within each block, two 30MHz sub-blocks with a 190MHz duplex separation are allocated tosatellite operation:

1980MHz to 2010MHz for uplinks

2170MHz to 2200MHz for downlinks

Terrestrial allocation

FDD systems

1920 to 1980MHz Uplink Mobile Transmit (60MHz band, duplex separation 190MHz)

2110 to 2170MHz Downlink Base Transmit (60MHz band, duplex spacing 190MHz)

TDD systems

1885 to 1920MHz (35MHz band)

2010 to 2025MHz (15MHz band)


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The IMT-2000 band plan and that of the existing major PLMN systems is illustrated in thefollowing figure, according to their primary geographic area of use.

Figure 1 IMT-2000 band plan compared to existing PLMN systems

In many areas, part of the IMT-2000 band is already in use by other PLMN systems. The lowerTDD IMT-2000 band will have to coexist with the Digital European/Enhanced CordlessTelephone/Telecommunications (DECT) and Personal Handy-phone System (PHS) systems.

DECT

DECT is widely used in the EU, Africa, Asia, and Caribbean to provide cordless telephony,wireless Private Branch Exchanges (PBX), and Wireless Local Loop (WLL) services. DECTuses dynamic channel allocation, and except where used for WLL applications, is usuallydeployed on a self-provision basis. This means there is limited scope for frequency co-ordination with a wide area IMT-2000 network. The output power of most DECT systems islimited to 250mW peak, 10mW average. For indoor systems, interference to outdoor IMT-2000systems is further reduced by building attenuation.


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PHS

PHS was designed in Japan. In recent years subscriber numbers have declined sharply, andseveral networks have closed. PHS can be considered as functionally similar to DECT. It israrely used outside SE Asia, Australia and New Zealand, owing to problems arising from itspartial use of DECT frequencies. Similar problems to those found with DECT are likely to beexperienced when coexistence with TDD IMT-2000 is attempted.

PCS

The Personal Communication System (PCS) 1900 is currently being deployed as a secondgeneration cellular system in the Americas. Some areas are adopting a CDMA air interfacebased on the IS95 standard (J-STD-008), and others the GSM air interface. Whichever airinterface is used, there is a significant overlap with the IMT-2000 TDD and FDD uplink band.

In view of this, the American Federal Communications Commission (FCC) has allocated a

different band for third generation cellular systems. The FCC has adopted licensing and servicerules governing operation for 30MHz of the 700MHz spectrum auctioned in the spring of 2000.

It has established two license bands, one of 20MHz (two paired 10MHz bands) and one of10MHz (two paired 5MHz bands) that can be used for advanced wireless services, includingthird generation broadband wireless access. Spectrum is made up in part from 746-764MHzand 776-794MHz (TV channels 60-62 and 64-66).

The FCC will auction the licenses in six Economic Area Groupings across America and willallow interested parties to bid for both license bands in one area. The remaining 6MHz will beused as guard band comprising 4MHz (two paired 2MHz bands) and 2MHz (two paired 1MHzbands). FCC plans to invite comments on technical and operational issues regarding thesefrequencies.

In many parts of America, third generation cellular services may not be able to use thesefrequencies until 2007 owing to the use of television channels 60 to 69.

GS M 1800 /DCS 1800

There is no direct overlap between the GSM 1800 (also known as DCS 1800) downlink band,and the IMT-2000 TDD and FDD uplink bands. However, in view of the possibility of co-sitingbase station equipment, and sharing antenna systems, particular care is required to ensureadequate isolation in order to avoid interference. This topic is covered in Chapter 7 RF NetworkPractical Implementation.


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2.3. UTRAN air interface attributes

This document concentrates on the ETSI UTRAN system. There are two versions of UTRAN,one that uses TDD mode and one that uses FDD mode. This document deals mainly with theterrestrial FDD version of UTRAN. This is the standard that forms the basis for the wide areadeployment of 3

rdgeneration PLMNs.


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The principal air interface attributes of the FDD and the TDD UTRANs are:

Feature Terrestrial FDD UTRAN TDD UTRAN

Uplink frequency /MHz 1920-1980 1885-1920 & 2010-2025

Downlink frequency /MHz 2110-2170 1885-1920 & 2010-2025

Channel bandwidth /MHz 5 5

Carrier raster /MHz 0.2 0.2

Duplex separation /MHz 130 (min) but variable N/A

Frequency stability /ppm 0.05 base, 0.1 mobile 0.05 base, 0.1 mobile

Chip rate /Mcs-1

3.84 3.84

Spreading factor 4 to 256 1 to 16

BSS separation codes Gold code 10ms, 38400chips, length 2

41-1

Scrambling code of length16 chips

Modulation QPSK QPSK

Modulation filter Root raised cosine roll-offfactor 0.22

Root raised cosine roll-offfactor 0.22

Power control Fast closed loop & slowquality loop

Open loop & slow closedloop

Power control steps /dB 0.25 to 1.5 0.25 to 1.5

Minimum output power /dBm -50 -50

Power control dynamic range /dB 80 uplink, 30 downlink 80 uplink, 30 downlink

Power control sample rate /kHz 1.6

Channel coding & interleaving forservices tolerating BER > 10

-6

Convolutional,rate 1/2 or 1/3

Convolutional,rate 1/2 or 1/3

Channel coding & interleaving forservices requiring BER < 10

-6

Turbo coding Turbo coding

Modulation symbol rate /M symbol s-1

0.016 to 1.024 0.256 to 4.096

Radio super-frame length /ms 720 240

Radio frame length /ms 10 10

Radio slot per frame 15 of 666.7us2,560 chips

15 of 666.7us2,560 chips

Channel allocation Network controlled Dynamic


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Feature Terrestrial FDD UTRAN TDD UTRAN

Handover control Mobile assistedmeasurement of signallevel & timing.

GSM measurementssupported.

Probing for ODMA

Base output power class 1 macro, 2 micro, 3 pico

Mobile output power/dBm [class number]

+21 [4]+33 [1], +27 [2], +24 [3],

+10 [5], 0 [6]

+21 [4]+33 [1], +27 [2], +24 [3], +10

[5], 0 [6]

Table 1 Air interface attributes

2.4. Channel mapping on the air interface

This section summarises the mapping of logical channels and transport channels to thephysical channels transmitted over the air interface.

Access stratum

The access stratum on the air interface is divided into three layers:

Layer 1

Layer 2

Layer 3

Layer 1

Layer 1 is the physical layer. Signalling and traffic data is borne on the air interface by physicalchannels. The physical channels are defined by code set and frequency in FDD mode and bycode, timeslot, and frequency in TDD mode.

Layer 2

Layer 2 is divided into two sub-layers:

Medium Access Control (MAC) layer (lower layer).

The MAC layer is responsible for the random access procedures, physical link control, errorprotection, ciphering, multiplexing, and channel mapping to the physical layer (Layer 1)

Radio Link Control (RLC) layer (upper layer).


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The RLC layer is responsible for logical link control, and acknowledgement/unacknowledgement of data transfer

Layer 3

Layer 3 is the Radio Resource Control (RRC) layer. The RRC layer is responsible forcoordination and control of bearers, monitoring processes, power control, measurementreporting, paging, and broadcast control functions.

In order to define a process for each different type of information, sets of logical channels aremapped onto transport channels, and ultimately physical channels are defined.

Logical channels are defined between the RLC and the MAC. Transport channels are definedbetween the MAC and the physical layer (Layer 1).

Logical channels

The following logical channels are used to transfer signalling information:

Broadcast Control Channel (BCCH) -downlink

The BCCH is a downlink broadcast channel which carries system information. There aretwo types: BCCH-Constant (BCCH-C) and BCCH-Variable (BCCH-V), the data on whichmay be constantly updated.

Paging Control Channel (PCCH) - downlink

The PCCH is a downlink channel which carries paging messages. It is used when thenetwork does not know the location cell of the mobile or the mobile is in sleep mode.

Common Control Channel (CCCH)

The CCCH is a bi-directional channel which carries data when the mobile has no RRCconnection to the network.

Dedicated Control Channel (DCCH)

The DCCH is a bi-directional channel which carries point-to-point dedicated control databetween the network and a mobile. It is used when a dedicated connection has beenestablished through RRC connection set up procedures.

ODMA Common Control Channel (OCCCH)

The OCCCH is a bi-directional channel which carries control data directly between mobiles.

It is used when the mobile has no RRC connection with the network.

ODMA Dedicated Control Channel (ODCCH)


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The ODCCH is a bi-directional point-to-point channel which carries dedicated control datadirectly between mobiles. It is used when a dedicated connection has been establishedthrough the RRC connection set-up procedures.

Shared Channel Control Channels (SHCCH) TDD mode only

The SHCCH is used in TDD mode only. It is a bi-directional channel which carries controldata for the uplink and downlink shared channels.

Synchronisation Control Channel (SCCH) TDD mode only

The SCCH is used in TDD mode only. It is a downlink channel which carries the locationand structure of the BCCH.

The following logical channels are used to transfer user data:

Dedicated Traffic Channel (DTCH)

The DTCH is a bi-directional dedicated point-to-point channel which carries user databetween the network and the mobile.

ODMA Dedicated Traffic Channel (ODTCH)

The ODTCH is a dedicated point-to-point channel which carries user data directly betweenmobiles, used as a relay link.

Common Traffic Channel (CTCH)

The CTCH is a uni-directional point-to-multipoint channel which carries user data for aspecified group of mobiles.

Transport channels

The information is transferred from the MAC layer and mapped onto physical channels via aset of transport channels.

There are two types of transport channel:

Common transport channels

Dedicated transport channels

Common transport channels

Broadcast Channel (BCH) downlink

The BCH is transmitted from the base station to all mobiles in the cell coverage area andbroadcasts system configuration information.


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Paging Channel (PCH) downlink

The PCH is also broadcast from the base station to all mobiles in the cell coverage area. Itpages mobiles when they are in idle mode and only their Location Area, not their specificcell, is known.

Forward Access Channel (FACH) downlink

The FACH is transmitted from the base station to mobiles and carries relatively smallamounts of control data and very short packets of user data, without the use of powercontrol.

Random Access Channel (RACH) uplink

The RACH is a contention-based uplink channel used for initial access, non-real timededicated control or very short packets of traffic data.

ONMA Random Access Channel (ORACH)

The ORACH performs a similar function to the RACH when a relay link is used.

Common Packet Channel (CPCH) FDD mode only

The CPCH is a contention-based channel carrying bursty traffic data in shared mode usingfast power control.

Downlink Shared Channel (DSCH)

The DSCH is a downlink channel shared between several mobiles for carrying control ortraffic data.

DSCH Control Channel

The DSCH Control Channel is a downlink channel used in conjunction with the DSCH forsignalling of DSCH resource allocation.

Broadcast Channel (BCH)

The BCH is a downlink broadcast channel carrying system information for the whole cell.

Synchronisation Channel (SCH) TDD mode only

The SCH is a downlink TDD mode channel carrying synchronisation data for the whole cell.Note: This SCH has no connection with the physical channel SCH used in FDD mode.

Uplink Shared Channel (USCH) TDD mode only

The USCH is an uplink TDD mode channel shared by several mobiles for carrying controlor traffic data.


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Dedicated transport channels

Dedicated Channel (DCH) duplex channel pair

For the duration of a call, one DCH is transmitted from the mobile to the base station andone DCH is transmitted from the base station to the mobile. They form a duplex circuit thatcan be used to carry a number of different types of user data (or logical channels).

Fast Uplink Signalling Channel (FAUSCH)

The FAUSCH is an uplink channel used to allocate dedicated channels in conjunction withthe FACH.

ODMA Dedicated Channel (ODCH)

The ODCH is dedicated to one mobile when used for relay links.

With the exception of the FAUSCH, each transport channel has an associated transport format.This is defined by a combination of encoding, interleaving, bit rate, and mapping onto physicalchannels. Some transport channels may use variable formats.

Physical channels

The transport channels are mapped to the physical channels transmitted over the air interface.This mapping process is flexible and for some logical channels there are several optionsdepending on their function and the type of information being transferred.

Different transport and physical channels are used in the uplink and downlink directions.Depending on the type and data rate of the transport channel, coding and multiplexing/demultiplexing may be applied prior to the data being carried by the physical channel.

The channels carrying broadcast information are directly mapped. That is, BCCH to BCH andPCCH to PCH.

Mapping for the other control and traffic channels is more flexible. For example, the downlinkDCCH can be mapped onto either the FACH or the DSCH depending on the informationrequirements. In the uplink, the DCCH may take information from the CPCH, FAUSCH, RACH,USCH or DCH. The logical channel DTCH has access to a similar range of transport channels.The CCCH can only use the RACH and FACH for bi-directional communication.

Downlink mapping of transport to physical channels

Three common control channels are used in the downlink: BCH, PCH and FACH. Each have aspecific coding process and are mapped onto a physical channel that is specific to common

control.

For DCH coding, multiplexing and mapping to physical channels is similar to that for the uplink.


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Uplink mapping of transport to physical channels

Two common control channnels are used in the uplink: RACH and FAUSCH. Each one hasspecific coding mechanisms and is mapped onto a physical channel.

The DCH channels (DCCH and DTCH) are coded and multiplexed to form a Coded CompositeTransport Channel (CCTrCH). Depending on its data rate the CCTrCH is then mapped onto onephysical channel or demultiplexed onto several physical channels. The physical channel usedfor the CCTrCH carries data from the DCH transport channel only. The DCH data is notmultiplexed with data from other transport channels.

Transmit Power Control (TPC) bits and Transport Format Combination Indicator (TFCI) bits areadded to the DCH (as Layer 1 information) before it is transmitted over the physical channel.

Figure 3 Mapping of uplink transport and physical channels

Physical channel types

The physical channels are defined by their basic resource characteristics, in terms of code andfrequency plans, modulation and transmission. A number of different physical channel typesare used in both the uplink and downlink.

Downlink physical channels

Downlink physical channels are grouped into four types:

Synchronisation Channel (SCH)

The SCH transmits the synchronisation codes used by the mobile to synchronise to a basestation. It comprises a primary and a secondary channel, which are transmittedsimultaneously.

OVSF Code 1

OVSF Code 2

OVSF Code 3

OVSF Code n

DPCH

DPCH

DPCH

DCH

DCH

DCH

RACH

(comprising DCCH and DTCH)

Base Station

Code

Divide -If CCTrCH exceedscapacity of onePhysical Channel

Code& Mux.

Code

Transmit Power Control (TPC)Transmit Format Combination Indicators(TFCI)added prior to transmission for BTS power control

PRACH


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Common Pilot Channel (CPICH)

The CPICH provides the phase reference for the downlink common channels, and isimplemented as either a Primary or Secondary Pilot Channel.

Common Control Physical Channel (CCPCH)

The CCPCH is the bearer for the Broadcast Channel (BCH), the Paging Channel (PCH), orthe Forward Associated Control Channel (FACCH). If the CCPCH carries the BCH it is thePrimary CCPCH, if it carries either the PCH or FACCH it is the Secondary CCPCH.

Dedicated Physical Channel (DPCH)

The DPCH carries the downlink Dedicated Channel (DCH) transport channel together withLayer 1 data comprising the Channel Associated Pilot, Transmit Power Control (TPC) bits,and Transmit Format Combination Indicator (TFCI) bits. The DPCH can be considered to

be formed from the Dedicated Physical Data Channel (DPDCH) carrying the DedicatedChannel (DCH) and the Dedicated Physical Control Channel (DPCCH) carrying the Layer 1data, time multiplexed together to form the DPCH

The downlink physical channel arrangement is shown in the following diagram:


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21

Figure 4 Downlink physical channels

Base Station

Dedicated PhysicalChannel (DPCH)

DTCHDCCH

(Dedicated Physical Control Channel (DPCCH))

(Channel Associated Pilot, TPC, TFCI)

(DCH Transport Channel)

(Dedicated Physical Data Channel (DPDCH))

Common ControlPhysical Channel(CCPCH)

Primary CCPCH

(Paging (PCH) and Forward Access (FACH) channels)

(BCH at 32 kb/s)

Secondary CCPCH

SynchronisationChannel (SCH) (Layer 1 Data - chip rate, framing, group of Golay codes)

(Sync. code, short Golay code, already chipped. BTS specific)

Primary SCH

Secondary SCH

Common PilotChannel (CPICH)

Primary CPICH

Secondary CPICH


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Uplink physical channels

The uplink physical channels are:

Physical Random Access Channel (PRACH)

The PRACH carries the Random Access Channel (RACH) and the FAUSCH.

Dedicated Physical Channel (DPCH)

The DPCH carries the uplink Dedicated Channel (DCH) transport channel, together withLayer 1 data comprising the Channel Associated Pilot, Transmit Power Control (TPC) bits,Transmit Format Combination Indicator (TFCI), and Feedback Information (FBI) bits.

The DPCH can be considered to be formed from the Dedicated Physical Data Channel(DPDCH) carrying the Dedicated Channel (DCH) and the Dedicated Physical Control

Channel (DPCCH) carrying the Layer 1 data. These are fed separately to the I & Q ports ofthe mobiles QPSK modulator to form the DPCH.

The uplink physical channel arrangement is shown in the following diagram:

Figure 5 Uplink physical channels

Base Station

Physical Random Access Channel (PRACH)

Random AccessChannel (RACH)

Dedicated PhysicalChannel (DPCH)

DTCHDCCH

(Dedicated Physical Control Channel (DPCCH))

(Channel Associated Pilot, TPC, TFCI)

(DCH Transport Channel)

(Dedicated Physical Data Channel (DPDCH))


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23

2.5. Channel spreading, coding and modulation

This section describes channel spreading, coding and modulation concepts in the uplink anddownlink.

Uplink

Spreading Dedicated Physical Data and Control Channels

Dual-channel Binary Phase Shift Keying (BPSK) modulation is used to spread the DedicatedPhysical Data Channels (DPDCH) and Dedicated Physical Control Channels (DPCCH). Theuplink DPDCH and DPCCH are mapped to the I & Q branches of the modulator respectively.

The I & Q branches are spread to the chip rate with two Orthogonal Variable Spreading Factor(OVSF) codes and then scrambled using a mobile specific scrambling code cscramb.

This process is illustrated in the following diagram:

Figure 6 Uplink spreading and modulation

When more than one code is used for transmission, additional uplink DPDCHs may betransmitted on either the I or Q branches. For each branch, each additional DPDCH is assigned

its own channel code. Uplink DPDCH channels on different branches may share a commonchannel code.

Spreading & Modulation for Uplink DPDCH/DPCCH

++

DPDCH

DPCCH

OrthogonalVariableSpreadingFactor (OVSF)Codes

OVSFCodes

Cscramb

c os ( t )

si n ( t )

Realp(t)

p(t)

Imag

I

Q

I+jQ


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Spreading Physical Random Access Channels

The message component of the Physical Random Access Channel (PRACH) is spread andmodulated in a similar manner to that used for the uplink dedicated physical channels. Theuplink DPDCH is replaced with the data part and the DPCCH is replaced with the control part.The scrambling code used for the message component is chosen based on the base station-specific preamble code in use.

Channel codes

Orthogonal Variable Spreading Factor (OVSF) codes are used as channel codes, which ensurethat a number of mobiles can share the same RF channel (frequency) without causingunacceptable interference. These codes allow Code Division Multiple Access (CDMA) to theshared RF channel (frequency).

The OVSF codes are illustrated in the following code tree:

Figure 7 OVSF code tree for channel codes

The code tree defines the code length used to provide the specified spreading factor. Thehigher user data rate services use shorter codes and hence lower spreading factors (andassociated de-spreading gain).

A given mobile cannot use all channel codes simultaneously. A channel code can only be used

by a mobile if no other code on the path from the specific code to the root of the code tree, or inthe sub-tree below the specific code, is used by that mobile. Thus the number of availablechannel codes is not fixed, but depends on the data rate and associated spreading factor ofeach physical channel used.


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25

For each call, the mobile is allocated at least one uplink channel code, for an uplink DPCCH.Usually, at least one further uplink channel code is allocated for an uplink DPDCH. Additionaluplink channel codes may be allocated if the mobile needs more DPDCHs. All channel codes

used for the DPDCH must be orthogonal to the channel code used for the DPCCH.

As each mobile using the same RF channel uses a unique uplink scrambling code, no co-ordination of the allocation of uplink channel codes to mobiles is needed. They are allocated ina predefined order that exploits the design of the scrambling codes used by the mobiletransmitter.

The mobile and the network may negotiate the number and length (spreading factor) of thechannel codes needed for the call, and the network allocates the necessary codes.

Scrambling codes

To allow identification during inter-cell handover, each mobile is assigned a unique code whichis not repeated at other cells.

The uplink uses either short or long scrambling codes, depending on the capabilities of thebase station receiver. In both cases complex scrambling is used, in which each code allocationconsists of a pair of I & Q codes.

Short scrambling codes are used in cells that use a sophisticated receiver with a multiple userdetector and interference canceller.

With short codes, the cross correlation between different physical channels and users does notvary with time as it does with long codes. Consequently the cross correlation matrices used inthe advanced receiver have to be updated less frequently, reducing the complexity of thereceiver design. The base station informs the mobile of its code allocation using the AccessGrant message (although it is possible to change the code allocation during a call).

Owing to their better interference averaging properties, long codes are used if the base stationdoes not support multiple user detection.

Each long code maps to an indicated short code, and the Access Grant message informs themobile whether it is to use the indicated short code or the corresponding long code.

Random access codes

The base station broadcasts a cell specific spreading code for the preamble part of the RandomAccess Message. Additional codes may be broadcast if the traffic loading is high. Thesepreamble spreading codes must be co-ordinated between cells to avoid interference. A real-valued 256 chip orthogonal Gold code is used, and all 256 codes may be used by the system.

A preamble signature code is used that carries one of 16 different orthogonal complexsignatures of length 16 based on a set of orthogonal Gold codes of length 16. The base stationbroadcasts the signatures that may be used in a cell.


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The preamble signature specifies one of the 16 nodes in the code tree that correspond tochannel codes of length 16. The sub-tree below the specified node is used to spread themessage part of the Random Access Message.

In addition to spreading, the message part is also scrambled with a 10ms complex code. Thiscode is cell specific, and is associated with the spreading code used for the preamble part.Although the scrambling code is the same for each access slot, the scrambling codes do notcollide in different access slots, as the slots are time shifted by 1.25ms.

Modulation

Quadrature Phase Shift Keying (QPSK) is used with a chip rate of 3.84M chips/s.

To reduce the linearity requirements on the power amplifier and hence improve its efficiency,the scrambling codes are designed so that N-1 out of N consecutive chips produce +/- 90

0

rotations of the I&Q multiplexed data and control channels. The remaining 1 out of N chipsproduces 0,+/- 90

0, or 180

0rotation.

In addition to scrambling codes design, compatible uplink channel codes must be chosen. Thislimits the phase transitions of the baseband signal, prior to input to a pulse-shaping filter whichensures the resulting modulated signal is constrained within the RF spectrum channel mask(that is, adjacent channel interference is limited).


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27

Downlink

Spreading Dedicated Physical Channel and CommonControl Physical Channel

QPSK data modulation is used to spread Dedicated Physical Channels (DPCH) and CommonControl Physical Channels (CCPCH) in the downlink. Pairs of baseband data bits are taken inserial form and applied in parallel to the I & Q branches of the spreading and modulation chain.The I & Q branches are then spread to the chip rate with the same channel code cch (that is,real spreading) and then scrambled using the same cell specific scrambling code cscramb.

This is illustrated in the following diagram:

Figure 8 Downlink spreading and modulation

Each physical channel uses a different channel code, but the same scrambling code.

In addition to the DPCH and CCPCH the Synchronisation Channel (SCH) is also multiplexedonto the downlink transmission.

The SCH is transmitted intermittently, one code word per slot, and multiplexed onto thedownlink after the DPCH and CCPCH have been scrambled. The SCH is therefore notorthogonal to the other downlink channels.

This is illustrated in the following diagram:

Spreading & Modulation for Downlink DPCH & CCPCHs

++

DedicatedPhysicalChannel

(DPCH)andCommon

ControlPhysical

Channel(CCPCH)

OrthogonalVariableSpreadingFactor (OVSF)Code (c )

ch

OVSFCode(c )

ch

Cscramb

c os ( t )

si n ( t )

Realp(t)

p(t)Imag

I

Q

I+jQSerialto ParallelConversion


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Slot Format Channel Bit

Rate /kbs

-1

Channel

Symbol Rate/k symbols s-1

Spreading

Factor

Bits per

Frame

Bits per Slot Ndata Number

of Data Bits

0 15 15 256 150 10 10

1 30 30 128 300 20 20

2 60 60 64 600 40 40

3 120 120 32 1200 80 80

4 240 240 16 2400 160 160

5 480 480 8 4800 320 320

6 960 960 4 9600 640 640

Table 2 Formats for DPDCH data fields in uplink radio time slot

When the time slot carries the DPCCH, it has four data fields per time slot

Pilot (Npilot )

Transport Format Combination Indication (TFCI) (NTFCI )

Feedback Information (FBI) (NFBI)

Transmit Power Control (TPC) (NTPC)

The bit assignment according to slot format is shown below:

SlotFormat

ChannelBit Rate

/kbs-1

ChannelSymbolRate /ksymbol

s s-1

SpreadingFactor

Bits perFrame

Bits perSlot

NpilotNumberof Pilot

DataBits

NTPCNumberof TPCDataBits

NTFCINumberof TFCI

DataBits

NFBINumberof FBIDataBits

0 15 15 256 150 10 6 2 2 0

1 15 15 256 150 10 8 2 0 0

2 15 15 256 150 10 5 2 2 1

3 15 15 256 150 10 7 2 0 1

4 15 15 256 150 10 6 2 0 2

5 15 15 256 150 10 5 1 2 2

Table 3 Formats for DPCCH data fields in uplink radio time slot


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Transport Format Combination Indication (TFCI) (NTFCI )

DPCCH

Data Field 1 (Ndata1)

DPDCH

Transmit Power Control (NTPC )

DPCCH

Data Field 2 (Ndata2)

DPDCH

Pilot (Npilot )

DPCCH


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2.7. Speech coding

Prior to transmission over a digital radio system, the analogue audio signal must be digitised.This function can be performed by a coder/decoder (codec). There are two types of codec:

Waveform codecs

Voice codecs (also known as vocoders)

Waveform codecs replicate the analogue waveform as faithfully as possible. Voice codecsextract the essential intelligibility information from speech, and reproduce it in acomprehensible manner, without regard to the accuracy with which the original analogue signalis reproduced.

Where bandwidth efficiency is not essential, such as in the landline telephone network,waveform codecs are used (for example, ITU-T G.711 1972). Where bandwidth efficiency is

essential, such as in mobile radio systems, voice codecs are normally used.

As accuracy of the original analogue signal reproduction is not a measure of vocoderperformance, their performance is based on subjective tests of perceived voice quality. Onecommonly used measure is the Mean Opinion Score (MOS). This is based on a jury markingthe intelligibility and speaker recognition of pre-defined phrases spoken through the vocodersystem.

The MOS value of 4.3 for the land-line standard ITU-T G.711 for Pulse Code Modulation (PCM)64 bit is normally used as a base reference level.

In the case of residential subscribers and small businesses requiring only a few lines, G.711circuits are not terminated at the customer premises, but are presented by an analogue localloop.

The quality degradation introduced by the local loop varies greatly, depending on its length andtransmission means. For example, several miles of analogue catenary with loading coils(typically used in rural locations) can introduce significant degradation. It has been reported thata typical G.711 circuit presented by analogue local loop has a MOS of 4.0.

A wide variety of vocoder techniques are used depending on the application involved; butgenerally the faster the resultant data stream, the better the voice quality and resulting MOSvalue. When comparing MOS values, the comparison must be made when the vocoders areoperating at the same Bit Error Rate (BER).


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35

Currently the GSM and UMTS standards define six codecs supported by the UTRAN airinterface:

GSM Full Rate

GSM Half Rate

GSM Enhanced Full Rate

GSM Adaptive Multi-Rate

- Full Rate

- Half Rate

UMTS Adaptive Multi-Rate

The definition of the common codec list in 3GPP for GSM and UMTS follows the specificationsgiven in ITU Q.765.5.

Transcoder Free Operation

The UMTS Technical Specifications outline the 3GPP internal codec list for both GSM andUMTS codecs to be used by the Bearer Independent Call Control protocol to set up or modify acall in Transcoder Free Operation (TrFO).

TrFO allows the transport of speech signals in the coded domain from one mobile to anotherthrough the radio access network and core network, and possibly through an additional transitnetwork. This enables high speech quality, low transmission costs and high flexibility.

Codec type selection and resource allocation is negotiated out-of-band before and after callsetup.

Possible Codec (re-)configuration, Rate Control and Discontinuous Transmission (DTX)signaling may be performed after call setup by additional in-band signaling, or by a combinationof in-band and out-of-band signaling.

Up to release 99, GSM does not support TrFO and specifies Tandem Free Operation (TFO)instead. TFO offers similar advantages to TrFO but is based on pure in-band signaling after callsetup. The UMTS Technical Specifications allow interaction between TrFO and TFO. They alsoprovide a GSM evolutionary path toward TFO.


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GSM Full Rate codec

The Regular Pulse Excited Long Term Prediction (RPE-LTP) vocoder was selected for GSM in1989. This generates an output bit rate of 13kb/s, and has a maximum MOS of 3.7. This datarate is termed the Full Rate for a GSM system.

The RPE-LTP vocoder is formed from the following sections: LTP filter, Linear PredictionCoder (LPC), and de-emphasis filter. (The RPE-LTP is also known as the RPE-LPC.)

DTX can be independently enabled in the uplink and/or downlink, as defined by the network ona cell basis. It cannot be negotiated at call setup or during the call. The DTX scheme uses oneSilence Information Descriptor (SID) frame to mark the end of a speech burst and to startcomfort noise generation. Identical SID frames for comfort noise updates are sent in speechpauses about every 480 ms, aligned with the cells TDMA frame structure.

TFO allows the reception of GSM-FR DTX information for the downlink direction in all cases.

GSM Half Rate codec

The GSM Half Rate codec type supports one fixed Codec Mode with 5.6kbs-1

. DTX may beused as in GSM Full Rate.

Owing to poor speech quality, this codec is not widely used in GSM networks.

GS M Enhanced Full Rate codec

The GSM Enhanced Full Rate codec type supports one fixed Codec Mode with 12.2kbs-1

.

Again, DTX may be enabled in the uplink and/or the downlink independently, as defined by thenetwork on a cell basis and cannot be negotiated at call setup or during the call.

The DTX scheme uses one SID frame to mark the end of a speech burst and to start comfortnoise generation. It is important to note that the parameters for the start of comfort noisegeneration are calculated at the transmitter side from the previous eight speech frames. A DTXhangover period therefore needs to be applied at the transmitter side before sending the firstSID frame.

SID frames with incremental information for comfort noise updates are sent in speech pausesapproximately every 480 ms, aligned with the TDMA frame structure of the cell. The definedTFO allows reception of GSM EFR DTX information for the downlink direction in all cases.


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37

Adaptive Multi-Rate codec types

Adaptive Multi Rate (AMR) is a new mobile technology that introduces a speech and channelcodec able to support both GSM full rate (22.8kbs-1 gross bit rate) and half rate (11.4kbs-1 grossbit rate) channel modes. For each channel mode a number of different Codec Mode bit ratescan be employed.

The Lucent GSM AMR feature is realised using a speech codec located in the SpeechTranscoding Frame (STF-2000) and the mobile, and a channel codec located in the BTS-2000and the mobile.

AMR differs from existing GSM speech codecs, in that it can adapt its data rate (speechcoding) and error protection level (channel coding) in accordance with the prevailing radiochannel conditions. By selecting the most appropriate channel mode (AMR Half Rate or AMRFull Rate) and the Codec Mode (combination of speech and channel bit rates), AMR is able tooffer a balance between speech quality and network capacity.

The sampling rate is 8 000 samples/s leading to a bit rate for the encoded bit stream of 4.75,5.15, 5.90, 6.70, 7.40, 7.95, 10.2 or 12.2kbs

-1.

The coding scheme for the multi-rate coding modes is the Algebraic Code Excited LinearPrediction Coder (ACELP). The multi-rate ACELP coder is referred to as MR-ACELP.

The AMR Codec algorithm is applied in GSM and UMTS in three different codec types:

Full Rate AMR

Half Rate AMR

UMTS AMR


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The AMR operating modes are shown below.

Channel type Source coding bit rate

TCH/FS/AMR

(TCH/AFS)

12.2 kbit/s

10.2 kbit/s (GSM EFR)

7.95 kbit/s

7.40 kbit/s (IS136 EFR)

6.70 kbit/s

5.90 kbit/s

5.15 kbit/s

4.75 kbit/s

TCH/HS/AMR

(TCH/AHS)

7.95 kbit/s

7.40 kbit/s (IS136 EFR)

6.70 kbit/s

5.90 kbit/s

5.15 kbit/s

4.75 kbit/s

Table 7 AMR Codec Modes

At call set-up the network selects a suitable Codec Mode set (containing a maximum of 4Codec Mode bit rates) appropriate for the call. The uplink and downlink must use the sameCodec Mode set. However, during the call the respective links may use different Codec Modebit rates from within the chosen Codec Mode set.

During a call, Codec Mode adaptation is controlled by the BTS. Quality measurements madeby the BTS (uplink) and MS (downlink) are compared against pre-defined threshold/hysteresisvalues from which the BTS is able to decide whether a Codec Mode change is required. TheBTS informs the MS and TRAU of any Codec Mode changes using in-band signalling. In theoryCodec Mode adaptation can take place every speech frame. However, due to propagationdelays and necessary filtering in the codec adaptation functions, a lower rate is recommended.


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AMR benefits

AMR provides improved speech quality in both FR and HR modes. Recent characterisationtests on the AMR codec conducted by ETSI have shown AMR Full Rate (AFS) to be superior toGSM EFR, particularly under bad interference conditions. AMR Half Rate (AHS) was equivalentor better than GSM FR under good radio channel conditions down to 16dB CIR.

AMR parameters

The AMR has additional parameters, which are optional at the originating side but mandatoryfor the terminating side:

Active Codec Set (ACS). Eight bits

- In FR AMR and HR AMR up to four modes may be selected by setting thecorresponding bits to 1

- In HR AMR only four out of the lower six modes can be selected

- In UMTS AMR all eight modes may be selected

- If the ACS is not specified at the originating side, all modes are supported there.The terminating side may then select freely

- If ACS is not provided, SCS and MACS (see below) also cannot be provided

Supported Codec Set (SCS). Eight bits

- In FR AMR and UMTS AMR up to eight modes may be selected by setting thecorresponding bits to 1

- In HR AMR only the lower six modes may be selected

- If the SCS is not specified at the originating side, all modes are supported there.The terminating side may then select freely

- If SCS is not provided, MACS (see below) also cannot be provided

Maximal number of Codec Modes (MACS). Three bits

- In FR AMR and HR AMR, one to four Codec Modes are allowed within the ACS

- In UMTS AMR, one to eight Codec Modes are allowed within the ACS

- If MACS is not specified at the originating side, then the maximum number ofmodes is supported there. The terminating side may then select freely

Initial Codec Mode. Three bits.

- One of the Codec Modes within the ACS is indicated as the starting mode

- If the ICM is not specified at the originating side, the terminating side may selectfreely


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41

- The Length Indicator field (LI) is set to 3, 4, 5 or 6 at the originating side, dependingon how many parameters are specified. The terminating side returns the selectedcodec with a full set of parameters. Hence LI is always set to 6 by the terminating

side. If any node in the path from the originating side to the terminating side doesnot support the parameter set offered by the originating side, it may restrict it. Ifnecessary the missing, optional parameter octets are inserted then

GSM AMR codec types

The GSM AMR codec types comprise eight Full Rate and six Half Rate different Codec Modes(for example, 12.2 4.75 kbs

-1).

The active Codec Mode is selected from the Active Codec Set (ACS) by the network (CodecMode Command) with assistance by the mobile station (Codec Mode Request). This CodecMode Adaptation, also termed Rate Control, can be performed every 40 ms by going oneCodec Mode up or down within the ACS. The Codec Modes in uplink and downlink at one radioleg may be different. In Tandem Free Operation both radio legs (A and B) are considered bythe Distributed Rate Control algorithm for the optimal selection of the active Codec Mode ineach direction (uplink A and then downlink B, and uplink B and then downlink A respectively).The worst of both radio legs determines the highest allowed Codec Mode, respectively themaximum allowed rate. Besides this Maximum Rate Control the active Codec Mode maysometimes be frozen to a fixed mode by either of the two radio legs to allow a smoothhandover procedure (Exact Rate Control).

All rate control commands are transmitted in-band: on the radio interface, the BTS-TRAUinterface and the TRAU-TRAU interface.

The Active Codec Set is configured at call setup or reconfigured during the call. It consists offrom one to four Codec Modes (MACS) at a given time, selected from the Supported CodecSet. The maximum number of MACS and the Supported Codec Set may be constrained by thenetwork to consider resources and radio conditions.

The same Active Codec Sets are available in both the uplink and downlink. Different sets maybe selected in the uplink and downlink.

At start up of Tandem Free Operation, both Active Codec Sets are taken into account todetermine the common Active Codec Set. In a later phase the Supported Codec Sets andMACSs of both radio legs may be taken into account to find the optimum Common ActiveCodec Set. All configuration data and update protocols are transmitted in-band.

DTX scheme

The DTX scheme of the AMR Codec Type marks the end of a speech burst with a specificSID_FIRST frame. SID_FIRST does not contain comfort noise parameters. It starts the comfortnoise generation with parameters calculated at receiver side from the most recently receivedseven speech frames. Therefore, a DTX hangover period needs to be applied at transmitterside before sending the SID_FIRST.


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45

Advantages

Enhanced full rate vocoders provide subscribers with improved perceived speech quality,close to that of a land-line link.

Enhanced full rate can increase the perceived speech quality MOS from 3.7 to 4.0,(compared to 4.3 for land-line)

Half rate vocoders provide increased network capacity (for example, an increase of up to40%, when 60% of mobiles are capable of half rate operation)

New base stations are not required

Additional back-haul link capacity is not required

Disadvantages

Subscribers may not consider half rate speech quality as acceptable, particularly in mobileto mobile calls

Additional network capacity provided by the use of Half-Rate Codecs depends on theproportion of subscribers with half rate mobiles

Enhanced full rate improved speech quality is only available to subscribers with new,enhanced full rate mobiles

Enhanced full rate and half rate speech coding will be superseded by Adaptive Multi Ratespeech coding from 2001 (this will require new mobiles and network infrastructureupgrades)


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51

3.2. Cell sets

The mobile maintains three cell sets:

Active Set

This lists all UTRAN cells that are currently assigning a downlink Dedicated PhysicalChannel (DPCH) to the mobile. It includes any cell with which the mobile is in soft or softerhandover.

Handover Monitoring Set

This lists all the cells (UTRAN and GSM) that the mobile has been tasked to monitor. Thelist corresponds to the BCCH Allocation (BA) list sent on the Slow Associated ControlChannel (SACCH) in the GSM network.

A separate set can be defined to monitor for cell selection, corresponding to the BCCHAllocation (BA) list sent on the Broadcast Control channel (BCCH) in the GSM network.

Handover Target Set

This lists the cells received by the mobile at a level sufficient for the associated DPCHs tobe decoded, butwhich are not currently in the Active Set. These cells may be on differentfrequencies from the current serving cell, and part of a UTRAN or GSM network.


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Silence D uration parameters

The absolute length of the Silence Duration (SD) depends on the time taken for the mobile toswitch from the UMTS frequency to a GSM frequency, decode and measure the GSM channeldata, and switch back to the UTRAN frequency.

Note: Appendix A contains Silence Duration parameter definitions reproduced from the ETSIUTRAN Handover standard.

GSM cell timing unknown

If there is no knowledge of the relative timing of the UTRAN and GSM cells, Silence DurationPatterns are used to search and decode the GSM Synchronisation Channel (SCH). Theprocess is repeated whenever the mobile receives a new SCH.

Depending on the mobiles capabilities, the SCH search may be either sequential (track first

GSM Frequency Correction Channel before decoding SCH), or parallel (parallel tracking ofFCH and SCH). The parallel option decodes the SCH faster and thus needs fewer SD patterns.

For example, a parallel search with 2 SD patterns every 0.48s alternately using T pattern1 (thedelay between successive SD patterns) of 226.92ms (47 * 4.615ms) and Tpattern2 263.08ms (57* 4.615ms) is as efficient as a sequential search with 4 SD patterns per 0.48s with Tpattern120ms.

The number of successive patterns used to scan a specific GSM frequency (Npattern) before it isassumed to be unsuccessful, can vary the probability of detection against the number of slottedframes (that is, the impact on UTRAN link). The default settings for N pattern is 11 for serialsearches and 6 for parallel searches, to ensure successful detection under worst case GSM celltiming conditions.

If the SDs are allocated by the UTRAN on a periodic basis, the mobile triggers the searchprocedure within the available SDs. So no specific signalling is needed between the mobile andthe UTRAN.

Alternatively, the mobile may initiate a search by sending a Request New Cell Search messageto the UTRAN, within which it indicates its serial/parallel search capability. The UTRANcalculates a suitable SD pattern and advises the mobile using the normal SD indicators. Thenetwork operator can delay implementation of this SD pattern according to the timing priorityassigned for New BSIC (Base Station Identity Code) identification. When the mobile completesits search, it signals to the UTRAN the timing of the associated SCH (or SCH Not Found).

Examples of Silence Duration and associated SD patterns are given in Appendix A.


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57

Monitoring and reporting GSM neighbour cells

A dual-standard mobile which is monitoring GSM neighbour cells, performs the measurementsspecified in the GSM recommendations:

Monitors up to 32 GSM carriers

Synchronises with up to 6 GSM carriers

Sends measurement reports back to the network on the 6 strongest GSM cells for whichthe BSIC is correctly decoded, (assuming the GSM Multi-band Reporting parameter is setfor Normal Reporting)

Performs the measurements down to the reference sensitivity and reference interferencelevels specified in GSM Recommendation 05.05

Demodulates the GSM SCH on the BCCH carrier of each neighbour cell and decodes theBSIC as often as possible, and as a minimum once every 10s

The UTRAN to GSM handover may be invoked in either of the following circumstances.

Handover owing to lack of UTRAN coverage

If the mobile can make systematic GSM neighbour cell measurements, it does so whenserved by a UTRAN cell on the edge of the UTRAN coverage area. If the mobile cannotmake systematic GSM neighbour cell measurements, the UTRAN decides whether toactivate this as a background task, based on the uplink and downlink received signal level.

Handover owing to bearer services

If a Dedicated Channel is allocated during call set-up, implementation of slotted mode onthe downlink is necessary to allow the mobile to make GSM cell measurements. If aDedicated Channel is not allocated during call set-up, no measurements are needed.

The handover procedure will stop in the following circumstances:

The mobile is instructed to execute a handover to GSM

The UTRAN includes a new cell in the Active Set (that is, start soft hand-off)

Execution of an inter frequency handover within the UTRAN


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3.5. Handover execution

This section describes the execution of intra-UTRAN soft handover and UTRAN-GSMhandover.

UTRAN soft handover

The bearer service used by the mobile is known to the serving cell(s) of the Active Set. When anew cell is added to the Active Set the UTRAN passes the following data to the new cell:

Maximum data rate and other service parameters associated with the duplex connection(for example, coding schemes, number of parallel code channels)

Mobile ID and uplink scrambling code

Timing information for the new cell, with respect to the time synchronisation of the mobilewith the current serving cell(s), as measured by the mobile at its current location. The newcell uses this to calculate the timing of its common channel (for example, BCH)transmission

The mobile is given the following information via its current serving cell(s):

The frame that the new cell uses to start transmission to the mobile, (assuming the ActiveSet update is accepted)

The channel code(s) used for the transmission by different cells need not be the same, andeach cell uses a different scrambling code

UTRAN to GSM handover

Handover owing to lack of UTRAN coverage

When the mobile executes the handover from the UTRAN to the GSM network it stopscommunication with the UTRAN and establishes its signalling link on the target GSM cell(as defined in GSM Recommendations 05.08 and 04.08). If the handover is not successfulthe mobile may attempt to resume communication with its previous UTRAN serving cell(s).

Handover owing to bearer services

If the call set-up involves Dedicated Channel allocation, after receiving the handoverexecution message from the UTRAN to the GSM network, the mobile stops communicationwith the UTRAN and establishes its signalling link on the target GSM cell (as defined inGSM Recommendations 05.08 and 04.08). If the handover is not successful the mobile

may attempt to resume communication with its previous UTRAN serving cell(s).

- If the call set-up does not involve Dedicated Channel allocation, the mobile isassigned a GSM channel and stops communicating with the UTRAN servingcell(s). As it has not yet synchronised to the GSM cell, the mobile then listens tothe GSM target cell BCH frequency to establish its time slot and frame


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Subscriber Services

4


61

4. Subscriber S ervices

UMTS supports numerous subscriber services. This chapter outlines a few of the most commonservices, and identifies a number of features which may impact network RF engineering from acoverage and capacity viewpoint.

Prior to transmission of user data services, the following channel coding and servicemultiplexing functions are performed:

Channel coding and interleaving for subscriber services

Service multiplexing

Rate matching

Channel coding and interleaving for control channels


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4.4. Control channel coding and interleaving

Dedicated Control Channel

The Dedicated Control Channel (DCCH) uses the same convolutional coding scheme as thetraffic channels. Intra-frame block interleaving is performed after channel coding. The DCCH ismapped to the Dedicated Physical Data Channel (DPDCH) in the same way as the DedicatedTraffic Channels.

Downlink Common Control Channels

The Downlink Common Control Channels (BCH, FACH and PCH) also use the sameconvolutional coding scheme as the traffic channels. Intra-frame block interleaving isperformed after channel coding, prior to mapping onto the primary and secondary CommonControl Physical Channels (CCPCH).

On the secondary CCPCH, the FACH and PCH are time division multiplexed on a frame-by-frame basis within the super-frame structure. The frame set used by the FACH and PCH isbroadcast to mobiles on the BCH.

4.5. Channel mapping examples

8kbs-1 bearer - speech

An 8-bit Cyclic Redundancy Check (CRC) and 8 tail bits are added to each 8kbs-1

speech frameprior to channel coding and mapping onto a DPDCH. Unequal repetition is used to match the28.88kbs

-1data rate after channel coding to the closest DPDCH rate of 32kbs

-1.

The mapping process is:

1. Data (80 bits) + CRC (8 bits) + Tail (8 bits) = 96 bits

2. Data of 96 bits (convolutional code rate 1/3 K=9) gives (96 * 3) = 288 bits

3. 288 bits (unequal repetition 9>10) gives (288 * 10/9) = 320 bits

4. 320 bits mapped onto the closest DPDCH rate of 32kbs-1


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144kbs-1 bearer - data

Each 144kbs

-1

data frame is Reed-Solomon coded, has tail bits added, and is convolutionallyframe coded. Code puncturing is used to match the 542.4kbs-1 data rate after channel coding tothe closest DPDCH rate of 512kbs

-1DPDCH.


1. Data (1440 bits) (Reed-Solomon code rate 180/225) gives 1800 bits

2. Data of 1800 bits + tail (8 bits) gives 1808 bits

3. 1808 bits (convolutional code rate 1/3, K=9) gives (1808 * 3) = 5424 bits

4. Data of 5424 bits (code punctured 339>320) gives (5424 * 320/339) = 5120 bits

5. 5120 bits mapped onto the closest DPDCH rate of 512kbs

-1


Each 384kbs-1

data frame is Reed-Solomon coded and convolutionally frame coded. Unequalrepetition is used to map the resulting 964.8kbs

-1data stream onto a 1024kbs

-1DPDCH.


1. Data (3840 bits) (Reed-Solomon code rate 192/240) gives 4800 bits

2. Data of 4800 bits + 3 tails (3*8 bits) gives 4824 bits

3. 4824 bits (convolutional code rate 1/2, K=9) gives (4824 * 2) = 9648 bits

4. Data of 9648 bits (unequal repetition 603>640) gives (9648 * 640/603) = 10240 bits



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Each of the sixteen parallel blocks (each block is 300 bits) have a 12-bit sequence number andCRC added, prior to convolutional coding and mapping onto a 1024kbs-1 DPDCH. Ratematching is not necessary.


1. Data (300 bits) +SN & CRC (12 bits) + tail (8 bits) gives 16 blocks per frame

2. Data of 16 blocks of 320 bits each (convolutional code rate 1/2, K=9) gives (16*2*320) =10240 bits



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Microcell (Ultra-small cell)

The Microcell (or Ultra-small cell) BTS is a single sector single carrier system, AC powered,and suitable for wall or pole outdoor mounting. If additional carriers are required, up to threeMicrocells may be linked together. The Microcell uses different circuit cards to the other BTSunits and can only output 5W per carrier.

Macrocell

The Macrocell BTS is a three sector system, transmitting three carriers with transmit diversity,fitted with any combination of baseband units (32 or 64 voice channels). It uses the sameindoor cabinet as the Milli-cell, but has more powerful power amplifiers and a second basebandcard frame.

The Macrocell BTS is not available in Lucent Network Release 1.0.

Milli-cell

The Milli-cell BTS is a three sector system, with one or two 20W carriers and transmit diversity,housed in either an outdoor or indoor cabinet. It supports either a masthead low noise amplifier(MHA) or the standard rack mounted receiver multi-coupler amplifier.


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Lucent circuit pack names in bold

N+1

Misc. Station

Interfaces

BTS-CNT

Radio Unit

BRU

BaseBandProcessor

BBU

BTS/RNCInterfaces

TX Amp

MCLA

Duplexer, LNAs

Clock Unit

CD U

(EXT-INF)EXTINF

LNA controller

BT S

CCNT

SCNT

NI U

MaintenanceTools

MT

Figure 15b Milli-cell BTS internal architecture

The Milli-cell rack incorporates a number of features to optimise reliability:

Hot-standby redundancy

- Precision oscillator card

- Clock distribution card

Warm-standby redundancy

- Controller cards

Load sharing redundancy

- Multiple back-haul interfaces (for example, 2Mbs-1

E1)

- Baseband processing cards

- Power supply units

- Transmitter power amplif ier (if the transmitter diversity option is used)

Documents

GSM to UMTS Transition