PERFORMANCE ENHANCEMENTS IN A FREQUENCY HOPPINGGSM NETWORK

Performance Enhancements in aFrequency Hopping GSM Network

by

Thomas Toftegaard NielsenAalborg University, CPKERICSSON Telebit

and

Jeroen WigardAalborg University, CPKNOKIA Networks

KLUWER ACADEMIC PUBLISHERSNEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW

eBook ISBN: 0-306-47313-5Print ISBN: 0-792-37819-9

©2002 Kluwer Academic PublishersNew York, Boston, Dordrecht, London, Moscow

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Contents

PREFACE

ACKNOWLEDGEMENTS

1 INTRODUCTION

xi

xiii

1

1

3

5

778

10131516

1617

18

1.

2.

3.

Evolution of Digital Systems

Performance of a Mobile Network

The aim of the book

2 PERFORMANCE ENHANCING STRATEGIES AND EVALUATIONMETHODS

1. Radio Performance Enhancements1.11.21.31.41.5

Engineering of the Network InfrastructureRadio Interface Channel Allocation TechniquesTechniques to Limit the Influence of InterferenceData Services for GSMClosing Comments on Performance Enhancements

2. Computer Aided GSM network Design2.1 The Simulation Tool

3. Classic Traffic Theory

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vi Performance Enhancements in a Frequency Hopping GSM Network

4. Network Field Trials

3. A BRIEF INTRODUCTION TO THE GSM SYSTEM

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313334

353536

3737393943

434450

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9.

GSM System Structure

Multiple Access Scheme in GSM

Channel Types in GSM

Mapping Logical to Physical Channels

Modulation Scheme in GSM

Typical Cell Architecture

Measurement Reporting in GSM

Frequency Hopping in GSM

Discontinuous Transmission in gsm

10. The Dropped Call Algorithm

4. LINK MODELLING AND LINK PERFORMANCE

1. The GSM Link1.11.2

The Channel CodingInterleaving

2. The GSM Link Simulator2.12.2

Structure of the Link SimulatorOutput Parameters from the Link Simulator

3. Influence of Frequency Hopping on the Link Performance3.13.23.33.4

Aim of Frequency HoppingLink Simulation Reference ConditionsLink Simulation ResultsPerformance Comparison to Existing GSM Mobiles

4. Predicting the BER/FER with FH4.14.2

The FER/BER Prediction MethodAccuracy of the BER/FER Prediction Method

Preface vii

5. Summary and Conclusions 51

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67696971

75757580

84848586

888889929394

959697

5. COMPUTER AIDED NETWORK DESIGN

1.

2.

3.

4.

5.

6.

Introduction to Computer Aided Network Design

Network Modelling by CAPACITY2.1 The General Program Structure

Available Output Parameters

Dropped Call Algorithm comparison

Accuracy of simulation results

Default simulation Parameters

6. INFLUENCE OF FH ON A GSM SYSTEM

1. Capacity Limits of a FH GSM Network1.11.21.3

Defining CoverageDetermining the Hard BlockingDetermining the Soft Blocking

2. Network Simulation Results2.12.22.3

Introduction to the Network SimulationsThe CAPACITY Network Simulation ResultsAlternative Network Topologies

3. Interaction between Network Quality Parameters3.13.23.3

Simulations on Dropped Calls versus RXQUALLive Network Measurements on Dropped Calls versus RXQUALFER on the SACCH versus FER on the TCH

4. Using Frequency Hopping in Band Limited One Layer Networks4.14.24.34.44.5

The Basic ProblemThe MAIO-Management ConceptSoft Capacity versus MAIO-ManagementNetwork Simulation Results using CAPACITYConcluding Remarks on MAIO-Management

5. Exploiting Frequency Hopping in a LIVE Network5.15.2

IntroductionFrequency Hopping Trial Results

viii Performance Enhancements in a Frequency Hopping GSM Network

5.3 Summary on Live Frequency Hopping Trial 101

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110110113115121

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137137138146

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149149151155

155155160164166

168168172

6. Summary and Conclusions

7. POWER CONTROL AND DTX IN A FH GSM SYSTEM

1. An introduction to power control1.11.2

Previous Work Concerning Power ControlThe Potential Gain from Power Control

2. A Brief Introduction to Discontinuous Transmission

3. The GSM Power Control Algorithm3.13.23.33.43.5

IntroductionThe Simplified Power Control AlgorithmPerformance of the Simplified PC AlgorithmNetwork Simulations of the GSM PC AlgorithmTrial Results of Downlink Power Control and DTXin a FH Network

4. Discontinuous Transmission in GSM4.14.24.3

The Basic Functionality of DTX in GSMRXQUAL Estimation Accuracy with DTXThe Gain From DTX in a FH GSM Network

5. Conclusion on Power Control and DTX in a FH GSM network

8. HANDOVER ALGORITHMS IN A GSM SYSTEM

1. Introduction1.11.21.3

Handover BasicsLiterature StudyChapter Outline

2. The Simulation Model2.12.22.32.4

Modelling and Implementation in CAPACITYSimulation ResultsLive Network MeasurementsFrequency Hopping in Relation to Handovers

3. Theoretical Handover Modelling3.13.2

Simple theoretical analysis of handover probabilityBirth Dead Model

Preface ix

3.33.4

Multiple cells scenarioMobility Dependency

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179179184189197

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4. Handover Improvements4.14.24.34.4

Channel Reservation for Handover TrafficChannel Reservation Combined with QueuingTraffic Reason HandoverDynamic HO Margin

5. Summary on handover algorithms in a gsm network

9. COMBINING REUSE PARTITIONING AND FREQUENCY HOPPINGIN A GSM NETWORK

1. Introduction to Frequency Reuse Partitioning1.11.21.31.4

Reuse Partitioning in a Cellular Communication System like GSMPrevious Frequency Reuse Partitioning StudiesIdealised Frequency Reuse Partitioning ConsiderationsPractical Considerations Concerning Reuse Partitioning

2. The Intelligent Underlay-Overlay Algorithm2.12.22.32.4

Estimating C/I in GSMPractical Frequency Planning Difficulties of IUOEstimating the Hard Blocking Limit of an IUO CellRemarks on the IUO Algorithm

3. The Capacity Enhancement Proposal

4. Preliminary Simulation Studies of IUO with Frequency Hopping4.14.2

Problems Discovered with the Original IUO Algorithm and FHImprovements to Enhance the IUO Algorithm

5. The Improved IUO Algorithm5.15.2

Improved Handover Characteristics with IUOHard Blocking Traffic Model of the Improved IUO

6. Implementation of IUO in CAPACITY6.16.2

The IUO Input Parameter ListImplementation of the Handover Algorithm

7. Outline for CAPACITY Simulations Concerning IUO7.17.2

IUO Parameter SettingsNetwork Parameter Settings

x Performance Enhancements in a Frequency Hopping GSM Network

8. CAPACITY Simulation Results 246247254

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8.18.2

Simulations of the Functionality of IUO and FHCAPACITY Simulations of IUO and Baseband FH

9. Live Network Trials Related to the combination of IUO and FH

10. Concluding Comments on the Combination of IUO and FH for GSM10.110.2

Analytical Calculations and Network SimulationsIdeas for Future Improvements of IFH

10. FREQUENCY PLANNING OF FREQUENCY HOPPING NETWORKS

1. Introduction1.11.21.3

The Frequency Planning ProblemExisting TechniquesChapter Outline

2. The Frequency Allocation Principle2.12.22.32.4

Propagation Prediction InputFrequency Planning in FH NetworksBroadcast Channels versus Traffic ChannelsThe Frequency Planning Method

3. Performance of the FH Planning Tool3.13.23.3

Performance of the Search AlgorithmEvaluation Method for a Frequency Plan with Frequency HoppingResults from Live Network

4. Other Parameters to be planned4.14.2

Frequency Hopping ParametersTraining Sequences

5. Conclusions and Improvements5.15.2

SummaryFuture Improvements

REFERENCES

INDEX

Preface

Mobile communications has during the last couple of years undergone anexplosive progress in terms of number of subscribers as well in the effort put intorelated research. The subscriber increase has lead to requirements concerning betternetwork quality and higher network capacity in order for the operators to be able tohandle the requests. During the last 5 years a substantial amount of resources hastherefore been put into enhancement to existing mobile radio systems like GSM.

This book provides a detailed description on how to enhance the BSS part of aGSM network using frequency hopping. The intention is to present a newlydeveloped method for modelling a frequency hopping GSM network as well as toshow the performance gains of different capacity enhancements. Everything is donewithin the scope of enhancing the performance of a frequency hopping GSMnetwork.

One of the main issues in this book is to describe a new way of designing radiosystem performance enhancement features by using detailed computer networkmodelling. It has been done by combining link level and system level simulations tobe able to achieve a high resolution in time. The link simulator developed andexploited provides a link performance model of the slow associated control channel(SACCH) as well as the full rate traffic channel (TCH/FS) in GSM. The networksimulator, able to model the BSS part of the GSM network, is described and usedextensively. Effects like cell structure, handover and power control algorithms,discontinuous transmission, traffic distribution, radio propagation and other networkfunctionality’s are modelled. In the book a model of the gain from frequencyhopping is described and used for link as well as for system level calculations.Correspondingly the book treats the issue of measuring network quality in afrequency hopping network using simulations as well as real data. Alternative waysof exploiting frequency hopping using MAIO-management are also proposed.

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xii Performance Enhancements in a Frequency Hopping GSM Network

The second major issue of the book, concrete capacity and qualityenhancements, are documented throughout several of the chapters. Investigations ofthe how to improve the capacity along with the implications when combiningdownlink power control and discontinuous transmission in a frequency hoppingGSM network are described. Also, a handover algorithm for GSM is studied for thefrequency hopping GSM environment. Several handover enhancements are proposedand investigated. A detailed study, using a handover algorithm that enables reusepartitioning, of how to increase the cell capacity is also treated. This principle isbased on a combination of the IUO reuse partitioning algorithm and frequencyhopping. Various models are developed to investigate the absolute capacitypotential. Several enhancements are furthermore proposed, increasing the cellcapacity even further. The last performance enhancing subject treated takes a morepractical view. It concerns frequency planning in a frequency hopping GSMnetwork. Initially a newly developed method of how to do frequency planning offrequency hopping networks is described. This method includes the gain fromfrequency hopping directly in the allocation process. Concerning the same issue animproved method for graphical visualisation of a frequency plan for frequencyhopping networks has been developed and is also described.

In general Chapter 1 through 6 provides an overview of the overall subject andthe methods used to treat frequency hopping in GSM. In Chapter 7 the issue ofdownlink power control and DTX is treated in combination with frequency hopping.Chapter 8 deals with various existing and newly proposed handover algorithms. InChapter 9 the network capacity is enhanced by combining reuse partitioning andfrequency hopping. The book concludes treating the issue of frequency planning offrequency hopping GSM networks.

The book is written in such a way that it should be possible to read each of thedesign chapters (4 through 10) individually if only a certain subject is of interest. Ingeneral throughout the book many references have been used. Frequently more thanone reference is used at a time. The idea of this is to provide the reader with easyaccess to related literature. In that way the book can be used as a work of reference.The literature list is included in the end of the book.

The book is intended for everyone interested in mobile radio communicationsystems. In general a high level of practical relevance relates to all the subjectstreated, making the book especially relevant for network infrastructuremanufacturers and network operators.

Acknowledgements

The material in this book originates from the research conducted as part of thetwo Ph.D. theses we have finalized in the spring of 1999, at Aalborg University,Center for PersonKommunikation (CPK), Denmark

We would like to thank our supervisors Bach Andersen and Preben E.Mogensen for assigning us to this very interesting project and providing us withrelationships to the industry, which has been of great help during the project. Severaldifferent participants have been involved in the project, where all have been more orless directly involved in the conducted research and the chosen subjects. The DanishGSM-900/1800 network operator SONOFON has sponsored Thomas ToftegaardNielsen, while the Finish telecommunications vendor NOKIA Telecommunicationshas sponsored Jeroen Wigard.

Initially two completely separate Ph.D. projects were initiated with the sameobjective, namely capacity enhancements of the radio resources in a GSM system.However, quickly it became obvious that if possible, there would be a uniquepossibility of research teamwork between the research institution Center forPersonKommunikation (CPK) at Aalborg University, SONOFON and NOKIA, ifthe research was carried out jointly. Besides exploiting the experience from bothSONOFON and NOKIA the possibility of developing complex network features inclose co-operation with CPK, having NOKIA implementing the specific feature intheir system and finally enable real live tests in the SONOFON network has beensignificant for the work carried out. Furthermore, from SONOFON, the manypractical everyday comments have initiated very up-to-date and relevant research.The interaction of all involved parties reflecting this close co-operation is shown inFigure 1.

We would like to acknowledge SONOFON as well as NOKIA for their financialsupport, which has made the research possible. We are also grateful for the many

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xiv PerformanceEnhancements in a Frequency Hopping GSM Network

discussions and proposals of new ideas, which have influenced quite a lot on thethemes treated.

During the entire process we have had terrific colleagues with whom we havebeen able to discuss relevant as well as irrelevant research issues. The pleasantworking environment at the cellular system group (CSG) at CPK and the capacityplanning group at SONOFON has been greatly appreciated. In particular it should besaid that a great part of the work has been done in co-operation with CSG at CPK, towhich we are both formally employed. The development of the software toolCAPACITY, presenting a new way of modelling a mobile communications network,has been done in a close co-operation with Per Henrik Michaelsen for which wethank him.

Finally we acknowledge with gratitude the support of our girlfriends, Berit andAnita, who have provided constant encouragement during the writing of this book.They have both been impressively patient with our sometimes absent state of mindand extreme working schedule.

We hope this book will help explain the functionality of frequency hopping inGSM as well as the potential advantages and problems associated with frequencyhopping. Correspondingly we would greatly appreciate if the proposed performanceimprovements will inspire further studies to enhance GSM in the future to come.

Jeroen WigardThomas Toftegaard Nielsen

January 2000