Adaptive modulation for cognitive radios

TABLE OF CONTENTS

Page

ABSTRACT ……………………………………………………………………………..iii

ACKNOWLEDGEMENTS……..………………………………………………………..iv

LIST OF ILLUSTRATIONS………………………………………………………….…vii

SECTION

1. INTRODUCTION……………………………………………………….…….1

2. DEFINITION OF A COGNITIVE RADIO………………..…….……………4

3. OPERATION OF A COGNITIVE RADIO……………………….…………..6

3.1. STAGES OF OPERATION………………………….………………..6

3.2. THE COGNITION CYCLE………………………………….………..6

3.3. GAME THEORY AND COGNITIVE RADIO……….………………9

3.3.1. Game Theory…............................................................................9

3.3.2. Applying Game Theory to Cognitive Radios….…...……..…...10

4. PHYSICAL ARCHITECTURE OF A COGNITIVE RADIO………….…...12

5. SPECTRUM SENSING……………………….……………………………..15

5.1. SPECTRUM SENSING TECHNIQUES………………….…………15

5.1.1. The Matched Filter Method of Signal Detection…....................15

5.1.2. The Radiometric Method of Energy Detection……………......16

5.1.3. The Cyclo-Stationary Feature Detection Method……….….....17

5.2. SPECTRUM SENSING CHALLENGES…….…………………..........18

5.2.1. Interference Temperature Measurement……….…………...….18

5.2.2. Spectrum Sensing in Multi-user Networks…………….………19

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5.2.3. Detection Capability……………..…………………..…………19

5.2.4. The Hidden Terminal Problem………………………….……..20

5.3. SPECTRUM MOBILITY…………………………...………………..21

6. ADAPTIVE MODULATION……………………………...…………….…..23

6.1. DOPPLER EFFECT……………………………………...…………..23

6.2. MULTI-PATH PROPAGATION…………………………..………..25

6.2.1. Additive White Gaussian Noise (AWGN) Channel………...…26

6.2.2. Rayleigh Fading Channel………………………...…...................26

6.3. ADAPTIVE MODULATION TECHNIQUES…...……….……….27

6.4. ADAPTIVE MODULATION MODEL FOR COGNITIVE

RADIO……………………………………………..………….…...29

6.5. MATHEMATICAL MODEL FOR A FADING

CHANNEL…………………………………..………...……………31

6.6. BIT-ERROR RATE EXPRESSIONS….………………...…….........34

6.6.1. BER Expressions for AWGN Channel……………..…………34

6.6.2. BER Expressions for Rayleigh Fading Channel.....………...…36

7. SIMULATIONS AND RESULTS……………….…………………………37

7.1. BER PERFORMANCE CURVES FOR AWGN CHANNE..…..37

7.2. BER PERFORMANCE CURVES FOR RAYLEIGH FADING

CHANNEL……………………………………….……………...38

7.3. OPTIMAL MODULATION FORMATS IN ADAPTIVE

MODULATION…………………………………………….…...39

8. CONCLUSION……………………………………………………………...43

BIBLIOGRAPHY………………………………………………………………44

VITA……………………………………………………………………………46

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LIST OF ILLUSTRATIONS

Figure Page

3.1 The Cognition Cycle…………………..……………………………………..……..8

4.1 Physical Architecture of a Cognitive Radio…………….………………………..13

5.1 Implementation of an Energy Detector………...………………………………...16

5.2 Implementation of a Cyclo-Stationary Feature Detector….……………………..18

5.3 The Hidden Terminal problem…………………………………………………...20

6.1 Illustration of Doppler Effect…………………………………………………….24

6.2 Model of an Additive White Gaussian Noise (AWGN) channel………………...27

6.3 A typical Rayleigh fading envelope at a carrier frequency of 900 MHz

and receiver speed=100km/hr……………………………………………………28

6.4 Basic block diagram of an Adaptive Modulation based Cognitive Radio

system…………………………………………………….………………………30

7.1 BER performance of BPSK, QPSK, square 16-QAM, and square 64-QAM

in AWGN channel………………………………………………………………..37

7.2 BER performance of 4-AM, 8-AM, and 16-AM in AWGN channel…………..…38

7.3 BER performance of BPSK, 4-QAM, 16-QAM, and 64-QAM in

Rayleigh flat fading channel……………………………………………...………..39

7.4 Optimal modulation formats in adaptive modulation for BPSK, QPSK,

16-QAM, and 64-QAM in AWGN channel………………………...……………..40

7.5 Optimal modulation formats in adaptive modulation for 4-AM, 8-AM,

and 16-AM in AWGN channel……….…………………………..……………….42

7.6 Optimal modulation formats in adaptive modulation for BPSK, 4-QAM,

16-QAM, and 64-QAM in flat fading Rayleigh channel………………....….……42