Multiple Access Protocols For Mobile Communications: GPRS, UMTS and Beyond

MultipleAccessProtocolsForMobileCommunications TV pdf Multiple Access Protocols for Mobile Communications GPRS, UMTS and Beyond Alex Brand, Hamid Aghvami Copyright  2002 John Wiley & Sons Ltd ISBNs 0[.]

Copyright  2002 John Wiley & Sons Ltd ISBNs: 0-471-49877-7 (Hardback); 0-470-84622-4 (Electronic)

MULTIPLE ACCESS PROTOCOLS FOR

MOBILE COMMUNICATIONS

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A catalogue record for this book is available from the British Library

British Library Cataloguing in Publication Data

Brand, Alex

Multiple access protocols for mobile communications: GPRS, UMTS and beyond/

Alex Brand, Hamid Aghvami

Typeset in 10/12pt Times by Laserwords Private Limited, Madras, India.

Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire.

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1.1 An Introduction to Cellular Communication Systems 1

1.1.2 Propagation Phenomena in Cellular Communications 2 1.1.3 Basic Multiple Access Schemes 3 1.1.4 Cell Clusters, Reuse Factor and Reuse Efficiency 6 1.1.5 Types of Interference and Noise Affecting Communications 6

1.2 The Emergence of the Internet and its Impact on Cellular

1.3 The Importance of Multiple Access Protocols in Cellular

1.4 A PRMA-based Protocol for Hybrid CDMA/TDMA 12

1.4.1 Why Combine CDMA and PRMA? 12 1.4.2 Hybrid CDMA/TDMA Multiple Access Schemes 14 1.4.3 Literature on Multiple Access Protocols for Packet CDMA 15 1.4.4 Access Control in Combined CDMA/PRMA Protocols 15

2.1 Advantages and Limitations of the Cellular Concept 232.2 1G and 2G Cellular Communication Systems 25

2.2.1 Analogue First Generation Cellular Systems 25 2.2.2 Digital Second Generation Systems 25

2.3.2 Evolution of 2G Systems towards 3G 29 2.3.3 Worldwide 3G Standardisation Efforts 31 2.3.4 The Third Generation Partnership Project (3GPP) 32 2.3.5 The Universal Mobile Telecommunications System (UMTS) 33 2.3.6 The Spectrum Situation for UMTS 35 2.3.7 UTRA Modes vs UTRA Requirements 36

2.3.8 3GPP2 and cdma2000 38

2.4.1 Support of IP Multimedia Services through EGPRS and

2.4.2 Improvements to cdma2000 1×RTT, UTRA FDD and TDD 41

3.1 Multiple Access and the OSI Layers 493.2 Basic Multiple Access Schemes 533.3 Medium Access Control in 2G Cellular Systems 57

3.3.1 Why Medium Access Control is Required 57 3.3.2 Medium Access Control in GSM 58

3.4 MAC Strategies for 2.5G Systems and Beyond 59

3.4.1 On the Importance of Multiple Access Protocols 59 3.4.2 Medium Access Control in CDMA 60 3.4.3 Conflict-free or Contention-based Access? 62

3.5 Review of Contention-based Multiple Access Protocols 63

3.5.1 Random Access Protocols: ALOHA and S-ALOHA 64 3.5.2 Increasing the Throughput with Splitting or Collision

3.5.3 Resource Auction Multiple Access 69 3.5.4 Impact of Capture on Random Access Protocols 70 3.5.5 Random Access with CDMA 72 3.5.6 Protocols based on some Form of Channel Sensing 72 3.5.7 Channel Sensing with CDMA 74 3.5.8 A Case for Reservation ALOHA-based Protocols 75

3.6 Packet Reservation Multiple Access: An R-ALOHA Protocol

3.6.1 PRMA for Microcellular Communication Systems 76 3.6.2 Description of ‘Pure’ PRMA 77

3.6.4 Proposed Modifications and Extensions to PRMA 81 3.6.5 PRMA for Hybrid CDMA/TDMA 84

3.7 MAC Requirements vs R-ALOHA Design Options 86

3.7.1 3G Requirements Relevant for the MAC Layer 86 3.7.2 Quality of Service Requirements and the MAC Layer 89 3.7.3 A few R-ALOHA Design Options 92 3.7.4 Suitable R-ALOHA Design Choices 94

3.8 Summary and Scope of Further Investigations 96

4.1.2 GSM Phases and Releases 101

4.1.4 Approach to the Description of the GSM Air Interface 105

4.2.1 GSM Carriers, Frequency Bands, and Modulation 107 4.2.2 TDMA, the Basic Multiple Access Scheme — Frames,

4.2.3 Slow Frequency Hopping and Interleaving 111 4.2.4 Frame Structures: Hyperframe, Superframe and

4.2.5 Parameters describing the Physical Channel 115

4.3 Mapping of Logical Channels onto Physical Channels 115

4.3.2 Signalling and Control Channels 116 4.3.3 Mapping of TCH and SACCH onto the 26-Multiframe 120 4.3.4 Coding, Interleaving, and DTX for Voice on the TCH/F 120 4.3.5 Coding and Interleaving on the SACCH 124 4.3.6 The Broadcast Channel and the 51-Multiframe 124

4.4 The GSM RACH based on Slotted ALOHA 126

4.4.3 The Channel Request Message 127

4.4.5 Contention Resolution in GSM 131 4.4.6 RACH Efficiency and Load Considerations 132

4.6 Resource Utilisation and Frequency Reuse 140

4.6.1 When are Resources Used and for What? 140 4.6.2 How to Assess Resource Utilisation 143 4.6.3 Some Theoretical Considerations —

4.6.4 Resource Utilisation in Blocking-limited GSM 145 4.6.5 Resource Utilisation in Interference-limited GSM 152

4.8 GPRS Physical and Logical Channels 164

4.8.1 The GPRS Logical Channels 164 4.8.2 Mapping of Logical Channels onto Physical Channels 165 4.8.3 Radio Resource Operating Modes 168 4.8.4 The Half-Rate PDCH and Dual Transfer Mode 169

4.9.1 Services offered and Functions performed by the Physical

4.9.2 The Radio Block Structure 171 4.9.3 Channel Coding Schemes 171 4.9.4 Theoretical GPRS Data-Rates 172 4.9.5 ‘Real’ GPRS Data-rates and Link Adaptation 175 4.9.6 The Timing Advance Procedure 177

4.11 The GPRS Random Access Algorithm 197

4.11.1 Why a New Random Access Scheme for GPRS? 197 4.11.2 Stabilisation of the Random Access Algorithm 198 4.11.3 Prioritisation at the Random Access 206 4.11.4 The GPRS Random Access Algorithm 207

5 Models for the Physical Layer and for User Traffic Generation 221

5.1 How to Account for the Physical Layer? 221

5.1.1 What to Account For and How? 221 5.1.2 Using Approximations for Error Performance Assessment 222 5.1.3 Modelling the UTRA TD/CDMA Physical Layer 223 5.1.4 On Capture and Required Accuracy of Physical Layer

5.2 Accounting for MAI Generated by Random Codes 225

5.2.1 On Gaussian Approximations for Error Performance

5.2.2 The Standard Gaussian Approximation 227 5.2.3 Deriving Packet Success Probabilities 228 5.2.4 Importance of FEC Coding in CDMA 229

5.2.5 Accounting for Intercell Interference 231 5.2.6 Impact of Power Control Errors 236

5.3 Perfect-collision Code-time-slot Model for TD/CDMA 237

5.3.1 TD/CDMA as a Mode for the UMTS Terrestrial Radio

5.3.2 The TD/CDMA Physical Layer Design Parameters 238 5.3.3 In-Slot Protocols on TD/CDMA 240

5.4 Accounting for both Code-collisions and MAI 241

5.6.2 The UMTS Web Browsing Model 247

5.6.4 A Word on Traffic Asymmetry 252

5.7 Some Considerations on Video Traffic Models 2535.8 Summary and some Notes on Terminology 255

6.2.7 Resource Allocation Strategies for Different Services 263 6.2.8 Performance Measures for MD PRMA 263

6.3 MD PRMA with Time-Division Duplexing 264

6.3.1 Approaches to Time-Division Duplexing 264 6.3.2 TDD with Alternating Uplink and Downlink Slots 266 6.3.3 MD FRMA for TDD with a Single Switching-Point per

6.4.1 The Concept of Channel Access Functions 267 6.4.2 Downlink Signalling with Load-based Access Control 269 6.4.3 Load-based Access Control in MD PRMA vs Channel Load

Sensing Protocol for Spread Slotted ALOHA 269

6.5 Backlog-based Access Control 270

6.5.1 Stabilisation of Slotted ALOHA with Ternary Feedback 270 6.5.2 Pseudo-Bayesian Broadcast for Slotted ALOHA 270 6.5.3 Bayesian Broadcast for Two-Carrier Slotted ALOHA 271

6.5.4 Bayesian Broadcast for MD PRMA with Orthogonal

6.5.5 Accounting for Acknowledgement Delays 273 6.5.6 Bayesian Broadcast for MD FRMA 274 6.5.7 Estimation of the Arrival Rate 274 6.5.8 Impact of MAI on Backlog Estimation 275

6.6 Combining Load- and Backlog-based Access Control 276

7.1 System Definition and Choice of Design Parameters 279

7.1.1 System Definition and Simulation Approach 279 7.1.2 Choice of Design Parameters 280

7.2 The Random Access Protocol as a Benchmark 281

7.2.1 Description of the Random Access Protocol 281 7.2.2 Analysis of the Random Access Protocol 282 7.2.3 Analysis vs Simulation Results 283 7.2.4 On Multiplexing Efficiency with RAP 284

7.3.1 The Minimum-Variance Benchmark 288 7.3.2 The ‘Circuit-Switching’ Benchmark 291 7.3.3 Access Control based on Known Backlog 291

7.4 Choosing Channel Access Functions 293

7.4.1 The Heuristic Approach 293 7.4.2 Semi-empirical Channel Access Functions 293

7.5 On the Benefit of Channel Access Control 298

7.5.1 Simulation Results vs Benchmarks 298 7.5.2 Benefits of Fast Voice Activity Detection 301 7.5.3 Interpretation of the Results and the

7.6 Impact of Power Control Errors and the Spreading Factor on

7.6.1 Impact of Power Control Errors on Access Control 303 7.6.2 A Theoretical Study on the Impact of Power Control Errors

7.6.3 ‘Power Grouping’: Another Way to Combat Power Control

8.1 System Definition and Simulation Approach 311

8.1.1 System Definition and Choice of Design Parameters 311 8.1.2 Simulation Approach, Traffic Parameters and Performance

8.2 Comparison of PRMA, MD PRMA and RCMA Performances 314

8.2.1 Simulation Results, No Interleaving 314 8.2.2 Performance Comparison and Impact of Interleaving 316

8.3 Detailed Assessment of MD PRMA and MD FRMA Performances 317

8.3.1 Impact of Acknowledgement Delays on MD PRMA

8.4 Combining Backlog-based and Load-based Access Control 323

8.4.1 Accounting for Multiple Access Interference 323 8.4.2 Performance of Combined Load- and Backlog-based Access

9.1 Prioritisation at the Random Access Stage 3299.2 Prioritised Bayesian Broadcast 331

9.2.1 Bayesian Scheme with Two Priority Classes and

Proportional Priority Distribution 331 9.2.2 Bayesian Scheme with Two Priority Classes and

Non-proportional Priority Distribution 332 9.2.3 Bayesian Scheme with Four Priority Classes and

Semi-proportional Priority Distribution 332 9.2.4 Bayesian Scheme with Four Priority Classes and

Non-proportional Priority Distribution 333 9.2.5 Priority-class-specific Backlog Estimation 334 9.2.6 Algorithms for Frame-based Protocols 335

9.3 System Definition and Simulation Approach 336

9.3.3 Traffic Scenarios Considered 338

9.4 Simulation Results for Mixed Voice and Web Traffic 339

9.4.1 Voice and a Single Class of Web Traffic 339 9.4.2 Voice and Two Classes of Web Traffic 340

9.5 Simulation Results for Mixed Voice and Email Traffic 341

9.5.1 Performance with Unlimited Allocation Cycle Length 341 9.5.2 Impact of Limiting Allocation Cycle Lengths 342

9.6 Simulation Results for Mixed Voice, Web and Email Traffic 344

9.6.1 Equal Share of Data Traffic per Priority Class 344 9.6.2 Unequal Share of Data Traffic per Priority class 344

10.1 UTRAN and Radio Interface Protocol Architecture 349

10.1.2 Radio Interface Protocol Architecture 350 10.1.3 3GPP Document Structure for UTRAN 352

10.2 UTRA FDD Channels and Procedures 358

10.2.1 Mapping between Logical Channels and Transport Channels 358 10.2.2 Physical Channels in UTRA FDD 358 10.2.3 Mapping of Transport Channels and Indicators to Physical

10.2.6 Slotted or Compressed Mode 365

10.3 Packet Access in UTRA FDD Release 99 365

10.3.1 RACH Procedure and Packet Data on the RACH 366 10.3.2 The Common Packet Channel 370 10.3.3 Packet Data on Dedicated Channels 374 10.3.4 Packet Data on the Downlink Shared Channel 377 10.3.5 Time-Division Multiplexing vs Code-Division Multiplexing 378

10.4.1 Mapping between Logical and Transport Channels 380 10.4.2 Frame Structure and Physical Channels in UTRA TDD 381 10.4.3 Random Access Matters in UTRA TDD 382 10.4.4 Packet Data on Dedicated Channels 384 10.4.5 Packet Data on Shared Channels 384

10.5.1 Adaptive Modulation and Coding, Hybrid ARQ 386

10.5.5 And What About Increased Data-rates on the Uplink? 389

11.1 Towards ‘All IP’: UMTS and GPRS/GERAN Release 5 39111.2 Challenges of Voice over IP over Radio 394

11.2.3 How to Reduce the Header Overhead 396

11.3 Real-time IP Bearers in GERAN 399

11.3.1 Adoption of UMTS Protocol Stacks for GERAN 399 11.3.2 Shared or Dedicated Channels? 399 11.3.3 Proposals for Shared Channels 401 11.3.4 Likely GERAN Solutions 402

11.4 Summarising Comments on Multiplexing Efficiency and Access

11.4.2 Hybrid CDMA/TDMA Interfaces 405

Hamid Ahgvami, the director of the Centre for Telecommunications Research at King’sCollege London, who supervised numerous research projects on third generation (3G)mobile communication systems at his centre, was intrigued by both code-division multipleaccess (CDMA) and packet reservation multiple access (PRMA) In the early 1990s, thesewere two prime multiple access candidates for 3G systems, the latter essentially enhancing

an air interface using time-division multiple access (TDMA) as a basic multiple accessscheme When Alex Brand arrived at King’s in 1994 as an exchange student to carry out

a project in conclusion of his studies at the Swiss Federal Institute of Technology (ETH)

in Zurich, his brief was simple: try to combine CDMA and PRMA

What started as a five-month research project resulted in several publications, a Ph.D.thesis, and quite a few follow-on publications by other researchers on the subject ofcombined CDMA/PRMA protocols, both at King’s and elsewhere In the following, we

refer to these protocols as so-called multidimensional PRMA (MD PRMA) protocols, an

umbrella term, which accommodates also ‘non-CDMA environments’ Nevertheless, weare mostly looking at ‘CDMA environments’

The Ph.D thesis, while naturally focussing on specific research contributions related

to PRMA-based protocols, embedded these results in a quite thorough discussion ofmultiple access protocols for mobile cellular communications in general, which are themain topic of this book Accordingly, its starting point was the Ph.D thesis It was thensubstantially expanded to cover multiple access in GSM/GPRS and in UMTS, as well

as latest trends in the industry towards the merging of wireless communications and based data communications, including their impact on multiple access strategies for mobilecommunications Indeed, in tune with the increasing importance of IP technologies, themain focus of this book is on the support of packet-voice and packet-data traffic on the airinterface Topics of particular interest in this context include matters related to resourceutilisation and multiplexing efficiency and probabilistic access control used for accessarbitration at the medium access control (MAC) layer

IP-From an OSI layering perspective, the generic term ‘multiple access’ spans often bothlayer 1, the physical layer, and the lower sub-layer of layer 2, the MAC (sub-)layer We

associate ‘basic multiple access schemes’ with the physical layer, and ‘multiple access

protocols’ with the MAC (sub-)layer Unlike the few books dealing exclusively withmultiple access protocols, a key concern for the present book is the wider framework (ofmobile communications) in which they have to operate Apart from issues associated withthe physical layer and with layers above the MAC sub-layer, this includes also generaldesign principles and constraints of mobile communication systems, which have an impact

on these protocols

In its present shape, this book hopes to provide a good balance between specific researchresults, some disseminated already by the authors in scientific journals and conferenceproceedings, others published here for the first time, and useful considerations on mobilecommunications from 2G to evolved 3G systems The latter includes a discussion of theevolutionary path of the dominant 2G standard, GSM, first to a 2.5G system (mainlythrough the addition of GPRS), then to the first release of a ‘full’ 3G system in the shape

of UMTS, and finally to subsequent releases adopting more and more IP-based gies Possible 4G scenarios are also discussed This book is therefore a valuable source ofinformation for anybody interested in the latest trends in mobile communications, which

technolo-is accessible in Chapters 1 to 4, 10 and 11 without having to delve into lots of maths.Chapters 5 to 9 are more geared towards researchers and designers of multiple accessprotocols and other aspects of air interfaces for mobile communication systems Accord-ingly, some of these chapters feature a few mathematical formulas, mostly in the area ofprobability theory

Chapter 1 introduces first the main concepts related to mobile cellular communicationsystems It then discusses the importance of multiple access protocols and the impact

of the emergence of the Internet on cellular communications Finally, it summarises thespecific research contributions of the authors documented in detail in further chapters.They are mainly related to access control in the context of the multiple access protocolsinvestigated

Expanding on this introductory chapter, Chapter 2 provides more insight into currentand future cellular communication systems from 1G to 4G In particular, it discussesinitial requirements on which the design of 3G systems was based, how 2G systems can

be evolved to meet 3G requirements, and what drives the further evolution of 3G towards4G systems The latter includes a possible convergence between cellular communications,the Internet and the broadcast world The role which wireless local area networks (WLAN)are expected to play in such scenarios is also reviewed

In Chapter 3, MAC strategies for cellular communication systems, which help meetthe requirements for 3G and beyond, are examined in the context of the general problem

of multiple access in cellular communications A considerable effort is invested in posing PRMA-based strategies with possible alternatives, assessing the respective advan-tages and disadvantages qualitatively and/or quantitatively

juxta-Chapter 4 traces the evolution of the GSM air interface standards from the first systemrelease through to release 1999 of the standards, that is from a system designed primarilyfor voice to one which offers sophisticated support for packet data through an enhancedversion of GPRS The air interface spans roughly the first three OSI layers Naturally,our main interest lies at the MAC layer, but its description is embedded into an in-depthdiscussion of physical and logical channels defined for GSM In fact, for ‘plain GSM’, theMAC layer is a relatively minor matter anyway, of certain limited relevance for issuessuch as radio resource utilisation, another topic of interest on which we also presentsome research results From a MAC perspective, GPRS is much more interesting andthus featured more prominently than ‘plain GSM’ The GPRS MAC layer, in particularthe random access protocol, is explained in considerable detail The description of thelatter is complemented by research results we fed into the GPRS standardisation process.The release 1999 additions which are discussed include incremental redundancy and theso-called EDGE COMPACT mode

To investigate the performance of multiple access protocols, it is necessary to modelsomehow the physical layer, on the services of which the MAC layer depends In addition,one has to be aware of what services higher layers expect from the MAC layer For ourresearch on PRMA-based protocols, as far as higher layers are concerned, the main focus

is on the traffic generated, which will be handed down to the MAC layer and which it has

to transfer making best possible use of the available physical link Appropriate models forphysical layer performance assessment and traffic generation are discussed in Chapter 5.Chapter 6 will define MD PRMA in detail, and introduce the two fundamental approa-ches considered to probabilistic access control at the MAC, namely load-based andbacklog-based access control As mentioned previously, access control is one of theresearch topics to which we devote particular attention

In Chapter 7, results of investigations on the benefit of load-based access control in MDPRMA are reported To this end, for voice-only traffic, the performance of MD PRMA

in the presence of intracell and intercell interference is compared with that of a randomaccess protocol and with various benchmarks The impact of power control errors is alsodiscussed

In Chapter 8, backlog-based access control for MD PRMA is treated in detail and

an assessment of its advantages compared to fixed permission probabilities is provided.This includes a comparison of the multiplexing efficiencies achieved in TDMA-only,hybrid CDMA/TDMA, and CDMA-only environments The impact of acknowledgementdelays and a protocol mode for time-division duplex are discussed The combination ofbacklog-based and load-based access control is studied Again, only packet-voice traffic

is considered

Chapter 9 provides a discussion of approaches to prioritisation at the random access

It then presents simulation results for the chosen prioritised pseudo-Bayesian algorithm,tested in a mixed traffic environment consisting of voice, Web browsing, and email traffic

In Chapter 10, after having introduced basic concepts of the UMTS air interface and theradio access network architecture, UTRA FDD channels and procedures are reviewed Themain effort is invested in exploring how packet-data traffic can be supported on UTRAFDD according to release 1999 of the standards Packet access in UTRA TDD is alsoreviewed Further, we discuss to what extent some of the research results on access controldocumented in the previous chapters can be applied to UTRA FDD and UTRA TDD.Finally, the nature of possible enhancements beyond release 1999 providing high-speedpacket access is explained

Chapter 11 concludes the main body of this book It introduces architectural ments to the UMTS packet-switched core network for the support of real-time IP-basedtraffic, the new IP multimedia subsystem, and enhancements to the GPRS/EDGE radioaccess network which allow the latter to be connected to the UMTS core network Theseendeavours can be viewed as an important step towards ‘all-IP’ Challenges relating tothe support of real-time IP services over cellular air interfaces are discussed and possiblesolutions are outlined on how to overcome problems such as the spectral inefficiencyassociated with standard voice over IP over radio Enhancements to the GPRS/EDGEair interface, enabling it to support real-time packet-data services, are reviewed The lastsection provides summarising comments on multiplexing efficiency and access control,two key topics dealt with extensively throughout this book

enhance-Each chapter is preceded by a short outline of the topics to be treated Chapters aredivided into a number of sections (e.g Section 4.2), which may in turn be split into

several subsections (such as Subsection 4.2.3) With two exceptions, chapters close with

a summary and some intermediate conclusions Readers may find the list of abbreviationsuseful, and also another list containing the symbols used throughout this book They can

be found after the acknowledgements following this preface Care was taken to choose thesymbols in a manner so that ambiguities are avoided At times, this required the choice ofsymbols other than those used in previous publications, possibly untypical ones, such as Xfor the spreading factor instead of the widely used N , because N is also commonly used

to denote the number of time slots per TDMA frame As far as acronyms are concerned,

we made an effort to write them out in full whenever they occurred first in each chapter,but exceptions include regularly recurring acronyms and cases where they are used inpassing first, and explicitly introduced soon after Finally, following a list of references,

an appendix provides some useful information on GSM and UMTS standard documents