PERFORMANCE EVALUATION OF CHIRP SPREAD SPECTRUM SYSTEM AND LAND MOBILE SATELLITE SYSTEM BY COMPUTER SIMULATION bv Junghwan Kim _ l Dissertation submitted to the Faculty of the Virginia Polytechnlc Institute and State University in partial fullillment of the requirements for the degree of Doctor of Philosophy in ° Electrical Engineering APPROVED: Timothy Prstt, Chairman - Richard O. Claus ‘ July, 1988 Blacksburg, Virginia PERFORMANCE EVALUATION OF CHIRP SPREAD SPECTRUM SYSTEM AND V LAND MOBILE SATELLITE SYSTEM BY COMPUTER SIMULATION bv Junghwan Kim Timothy Pratt, Chairman Electrical Engineering (ABSTRACT) 1— F The work presented in this dissertation examines the performance of two satellite radio j communication systems by computer simulation. Two simulations were separately performed for a spread spectrum chirp system as an analog communications system, and for the Land Mobile Satellite System (LMSS) channel as a digital communications system. For the simulation of analog communications, a spread spectrum system using chirp techniques called ’Coded Multiple Chirp Spread Spectrum’ was proposed as a simple, cost-effective alternative for conventional spread spectrum systems. Its application as a spread spectrum overlay service on analog FM-TV was examined through the mutual interference analysis and spectral analysis using soltware programming. For the simulation of digital communications, various digital modulation schemes as well as channel encoding, block interleaving/deinterleaving, and dltferential encoding techniques were used for a thorough performance evaluation of a Land Mobile Satellite System under fading conditions. For this purpose, an LMSS fading channel simulator capable of simulatlng diverse fading characteristics for a satellite channel was designed and tested to yield various performance measures such as symbol error rate and average bit error rate. Acknowledgements I am sincerely grateful to Dr. Timothy Pratt, my advisor, for his constant encouragement, invaluable and timely advice, and guidance right through the course of the work reported here. I thank Dr. Charles W. Bostian, for his guidance and countless support through the second part of this work. I also thank Dr. Tri T. Ha, my former advisor, for his support through the first part of this work. Also I wish to acknowledge with sincere appreciation the financial support of NASA Lewis Research Center and NASA Jet Propulsion Laboratory from 1986 to 1988. Acknowledgements Ill Table of Contents I. Introduction 1 II.Spread Spectrum Chirp System 11 2.1. Revlew of Chirp Spread Spectrum Systems 11 2.2. Coded Multlple Chirp Spread Spectrum System 18 2.2.1. Basic System Concept 18 ' 2.2.2. Performance Analysis 22 » System Parameters and Waveform Definitions 22 Cross-correlation of Up Chirp and Down Chirp 23 Cross-correlatlon between Code(Word) Sequence 27 Chip Error Probability(Dechirper BER) gg Performance of Digital Code Correlator 33 Table ol Contents iv Chirp Spread Spectrum Multiple Access 34 2.3. Summary 38 lll. Spread Spectrum Chirp Overlay Service 39 3.1. Overlay Servlce—An Overview 39 3.2. Interference Analysis I ( General Approach ) 41 3.2.1. Demodulation of FM-TV signal and Chirp 41 3.2.2. Chirp Interference to Analog FM-TV Signal 42 3.2.3. Simulation of FM-Discriminator Output 52 59 3.2.4. Analog FM-TV Signal Interference on Chirp Demodulation 3.3. Interference Analysls Il ( Modeling and Simulation ) 64 — 3.3.1. Analog FM-TV Signal Modeling l Without Preemphasis 65 3.3.2. Simulation of Wideband FM-TV Signal and Chirp I-No Preemphasis 67 77 3.3.3. Analog FM-TV Signal Modeling ll -· With Preemphasis Preemphasis Characteristic 77 Modeling of FM-TV Video Signal 83 — 3.3.4. Wideband FM-TV Signal Simulation ll With Preemphasis 88 3.3.5. Overlay System Link Analysis 91 FM-TV Overlay Link Analysis 94 Chirp Overlay Link Analysis 96 99 3.4. Performance Analysis of Overlay Service I-Without Preemphasis 3.4.1. Signal Power Calculation 100 3.4.2. Interference Power Calculation 103 Chirp Interference to FM-TV 103 Table of Contents v FM~TV lnterference to Chlrp 104 Performance Analysis of Overlay Service ll With Preemphasls 112 3.5. ·- 3.5.1. Signal Power 112 3.5.2. lnterference of Chlrp to FM-TV 115 3.5.3. lnterference of FM-TV to Chirp 115 3.6. Summary 121 IV. Review of Digital Modulation in LMSS Channels 122 4.1. Introduction 122 4.2. Land Moblle Satelllte System under Fadlng 124 4.3. Dlgltal Modulatlons ln LMSS 132 4.3.1. General Requirements for Digital Modulatlons 132 4.3.2. General Investigation of Some Candidate Modulatlons 133 4.3.3. Coherent Modulatlons : QPSK and MSK 138 4.3.4 .Principle of Differential Encoding and Decoding 148 4.3.5. Noncoherent Modulatlons : DGMSK and TCM·8 DPSK 151 4.4. Efficient Channel Encoding in LMSS Channels 162 166 4.5 Summary l Table of Contents vi V. LMSS Channel Simulator Modeling 168 5.1. Modellng Overview 168 5.2. System Level Modeling 176 5.2.1. Coherent Systems: QPSK and MSK 179 5.2.2. Noncoherent Systems: TCM 8-DPSK and DGMSK 183 5.3. Components Level Modeling 195 5.3.1. Random Symbol Generation 196 5.3.2. Coherent QPSK/MSK Modulators and Demodulators 198 l 5.3.3. Transmit(Tx) and Receive(Rx) Filtering 201 5.3.4. Satellite Transponder Nonlinearity 206 5.3.5. Trellls Encoding and Decoding 211 5.3.6. Differential Encoding and Decoding 224 5.3.7. TCM·8 DPSK/DGMSK Modulators and Demodulaotrs 229 5.3.8. Block lnterleaverlDeinterleaver 237 5.3.9. Method of Fadlng Effects lnsertion 239 5.3.10.Performance Evaluator 240 5.4. Summary 243 VI. Performance Analysis of LMSS Channel under Fadin%45 6.1. Slmulatlon Overview 245 6.2. Performance ol Coherent QPSK and MSK 247 6.2.1. Modem Back to Back Test 248 Table of Contents vii 251‘ 6.2.2. Fading Channel Test 6.3. Performance of Noncoherent TCM-8 PSK and GMSK 272 6.3.1. Intermediate Simulation Result 273 6.3.2. Modem Back to Back Test 279 6.4. Summary 288 VII. Concluding Remarks 289 7.1. Chlrp Spectrum System and Overlay Service 289 7.2. Land Mobile Satellite System under Fading 291 IIX. References 296 ” Vita . 303 u Table of Content: vi 'I 'I List of Illustrations Fig. 1 Within chirp modulations 14 Flg. 2a Multiple chirp modulations 15 Fig. 2b Typical waveforms of multiple chirp modulations 16 5 Fig. 3a Coded multiple chirp spread spectrum system 19 Fig. 3b Typical waveforms of coded multiple chirp S.S. system (proposed) 20 Flg. 4 Autocorrelation (matched case) and crosscorrelation (mismatched . 26 case) Flg. 5a Chip error probability of dechirper 31 32 Fig. 5b BER Comparison of noncoherent FSK and chirp for different BT product U Fig. 6 Word miss probability vs. dechirper BER 35 ‘ 36 Fig. 7 Word false alarm probability vs miss probability Flg. 8 Time waveform of FM-discriminator output error voltage for 43 unmodulated TV carrier plus chirp interference Fig. 9 Time waveform of FM-discriminator output error voltage for FM-TV 44 carrier plus chirp interference ( m(t)= 0.5V dc ) Fig. 10 Simulated 9 step staircase function (time plot) 54 Fig. 11 Received and lowpass filtered simulated 9 step stalrcase function 55 Flg. 12 Error output voltage of FM~discriminator alter bandpass filtering 56 Fig. 13 Spectrum of error output after bandpass liltering (3-4 MHz) 57 Flg. 14 Spectrum of 9 step staircase function 58 Fig. 15 Typical compression filter output for chirp signal input 62 Liu ai Illustration: ix Fig. 16 Compression filter output for FM-TV signal with amplitude = 0.1V 63 Flg. 17 Time plot of simulated 200 step staircase function model for video 66 signal Flg. 18 Time plot of simulated 256 step random amplitude model for video 70 signal Fig. 19 Transmitted FM-TV signal time plot (random) 71 Fig. 20 Frequency spectrum of Fig. 19 (random) 72 Fig. 21 Transmitted FM-TV signal time plot (linear) 73 Flg. 22 Frequency spectrum of Fig. 21 (linear) 74 Flg. 23 Transmitted chirp signal time plot 75 Fig. 24 Frequency spectrum of Fig. 23 76 - Fig. 25 Typical NTSC modem structure with preemphasis/deemphasis 79 Flg. 26 TV preemphasis characteristics (525, 625, 819 and 405 lines) 80 81 Flg. 27 NTSC 525 line - CCIR REC.405 preemphasis characteristics Fig. 28 Simulated preemphasis filter for NTSC 525 line TV system 82 Fig. 29 TV message m(t) before preemphasis (time plot); random 84 amplitude Flg. 30 TV message m(t) after preemphasis (time plot); random amplitude 85 Flg. 31 TV message m(t) before preemphasis (time plot); linear staircase 86 function Fig. 32 TV message m(t) after preemphasis (time plot); linear staircase 87 function Fig. 33 Transmitted FM-TV spectrum (m(t) = random, preemphasis 89 version) Flg. 34 Transmitted FM-TV spectrum (m(t) = linear, preemphasis version) 90 Fig. 35 Spread spectrum chirp overlay scheme on FM-TV in C-band 93 Fig. 36 36dB attenuated chirp signal spectrum 102 Fig. 37 Overlapped spectrum of FM-TV (staircase m(t)) and 36 dB 107 attenuated chirp Flg. 38 Overlapped spectrum of FM-TV (random amplitude m(t)) and 36 dB 108 attenuated chirp Fig. 39 C/I ratio vs lF offset frequency (random amplitude message and 109 linear staircase) Flg. 40 Overlapped spectrum of FM-TV (preemphasis) and 36dB attenuated 113 chirp (random) Flg. 41 Overlapped spectrum of FM-TV (preemphasis and 36dB attenuated 114 chirp (linear staircase) · Llst of Illustratlons X Fig. 42 C/I ratio vs IF offset frequency (preemphasis case) 116 Flg. 43 C/I ratio vs IF offset frequency (preemphasis case and no 117 preemphasis case) Flg. 44 Offset (IF) frequency vs chip error rate for some compresslon gain 118 Fig.