CARRIER RECOVERY IN BURST-MODE 16-QAM A Thesis Submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Electrical Engineering University of Saskatchewan Saskatoon, Saskatchewan by Jingxin Chen June 2004 © Copyright Jingxin Chen, 2004. All rights reserved. PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, the author agrees that the Libraries of this University may make it freely available for inspection. The author further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor who supervised this thesis work or, in his absence, by the Head of the Department or the Dean of the College of Graduate Studies and Research at the University of Saskatchewan. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without the author’s written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Requests for permission to copy or to make other use of material in this thesis in whole or part should be addressed to: Head of the Department of Electrical Engineering University of Saskatchewan Saskatoon, Saskatchewan, Canada S7N 5A9 i ABSTRACT Wireless communication systems such as multipoint communication systems (MCS) are becoming attractive as cost-effective means for providing network access in sparsely populated, rugged, or developing areas of the world. Since the radio spectrum is limited, it is desirable to use spectrally efficient modulation methods such as quadrature amplitude modulation (QAM) for high data rate channels. Many MCS employ time division multiple access (TDMA) and/or time division duplexing (TDD) techniques, in which transmissions operate in bursts. In many cases, a preamble of known symbols is appended to the beginning of each burst for carrier and symbol timing recovery (symbol timing is assumed known in this thesis). Preamble symbols consume bandwidth and power and are not used to convey information. In order for burst-mode communications to provide efficient data throughput, the synchronization time must be short compared to the user data portion of the burst. Traditional methods of communication system synchronization such as phase- locked loops (PLLs) have demonstrated reduced performance when operated in burst- mode systems. In this thesis, a feedforward (FF) digital carrier recovery technique to achieve rapid carrier synchronization is proposed. The estimation algorithms for determining carrier offsets in carrier acquisition and tracking in a linear channel environment corrupted by additive white Gaussian noise (AWGN) are described. The estimation algorithms are derived based on the theory of maximum likelihood (ML) parameter estimation. The estimations include data-aided (DA) carrier frequency and phase estimations in acquisition and non-data-aided (NDA) carrier phase estimation in tracking. The DA carrier frequency and phase estimation algorithms are based on oversampling of a known preamble. The NDA carrier phase estimation makes use of symbol timing knowledge and estimates are extracted from the random data portion of the burst. The algorithms have been simulated and tested using Matlab® to verify their ii functionalities. The performance of these estimators is also evaluated in the burst- mode operations for 16-QAM and compared in the presence of non-ideal conditions (frequency offset, phase offset, and AWGN). The simulation results show that the carrier recovery techniques presented in this thesis proved to be applicable to the modulation schemes of 16-QAM. The simulations demonstrate that the techniques provide a fast carrier acquisition using a short preamble (about 111 symbols) and are suitable for burst-mode communication systems. iii ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my supervisor, Professor David M. Klymyshyn, for being the guiding force behind the research necessary for the completion of this thesis. Without his guidance, encouragement, support, ideas, and scientific enlightenment this work would not have been possible. I also extend my sincere gratitude to Professor Ha Nguyen who performed as my acting supervisor in the final stage of this work, when Professor Klymyshyn was away and worked on research in Germany. Professor Nguyen has been abundantly helpful and given me a lot of valuable advice on my final oral exam and thesis. My great appreciation also goes to the management and staff of TRLabs in Saskatoon for providing support and wonderful research environment. My thanks especially go to Jack Hanson, Dan Aspel, Trevor Hamm, and Garth Wells who always provided me technical help as I needed. Finally, I would like to thank my parents, Shang Xun Chen and Yi Wen Rong, my parents-in-law, my husband Peter, and my friends for all the encouragement and support they have provided me throughout my academic career. No words can express my gratitude to them. iv DEDICATION To my adorable daughter, Yuan Yuan v TABLE OF CONTENTS PERMISSION TO USE................................................................................................i ABSTRACT..................................................................................................................ii ACKNOWLEDGEMENTS........................................................................................iv DEDICATION..............................................................................................................v TABLE OF CONTENTS............................................................................................vi LIST OF FIGURES.....................................................................................................x LIST OF TABLES....................................................................................................xiii LIST OF ABBREVIATIONS..................................................................................xiv LIST OF SYMBOLS................................................................................................xvi 1 INTRODUCTION...................................................................................................1 1.1 Background.........................................................................................................1 1.2 Motivation...........................................................................................................3 1.3 Objectives............................................................................................................5 1.4 Literature Review................................................................................................6 1.5 Thesis Organization.............................................................................................8 2 MODULATION AND DEMODULATION FOR THE AWGN CHANNEL..10 2.1 Overview...........................................................................................................10 2.2 Digital Modulation............................................................................................11 2.2.1 QAM.......................................................................................................12 2.2.2 16-QAM..................................................................................................14 vi 2.3 Channel..............................................................................................................17 2.4 Coherent Demodulation....................................................................................19 2.5 Performance of the Optimum Detection...........................................................22 2.6 Filtering and Intersymbol Interference..............................................................24 2.7 Summary...........................................................................................................30 3 CARRIER RECOVERY SYSTEM DESIGN....................................................31 3.1 Carrier Recovery Description............................................................................31 3.1.1 Carrier Rcovery Parameters....................................................................32 3.1.2 Carrier Recovery Processes.....................................................................34 3.2 Design Considerations.......................................................................................36 3.2.1 Preamble Selection..................................................................................36 3.2.2 Synchronizer Structure Selection............................................................38 3.3 System Design...................................................................................................39 3.3.1 Carrier Acquisition Estimator.................................................................40 3.3.2 Carrier Tracker........................................................................................41 3.4 Summary...........................................................................................................43 4 CARRIER RECOVERY ALGORITHMS.........................................................45 4.1 The Received Signal Model..............................................................................45 4.2 ML Parameter Estimation.................................................................................47 4.2.1 MAP and ML..........................................................................................47 4.2.2 Likelihood Function................................................................................48 4.2.3 ML Condition..........................................................................................51 4.3 Carrier Acquisition............................................................................................52 vii 4.3.1 DA Frequency Offset Estimation............................................................52 4.3.2 DA Phase Offset Estimation...................................................................55 4.4 Carrier Tracking................................................................................................58 4.4.1 Overview.................................................................................................58 4.4.2 NDA Carrier Phase Estimation...............................................................59 4.4.3 Window Size Selection...........................................................................62 4.5 Summary...........................................................................................................63 5 SIMULATION RESULTS AND PERFORMANCE EVALUATION OF CARRIER RECOVERY SYSTEM..........................................................................65 5.1 Performance Measurement of Estimators.........................................................65 5.1.1 Estimation Error Measurement...............................................................66 5.1.2 BER Measurement..................................................................................66 5.1.3 BER Degradation due to Synchronization Errors...................................68 5.2 Simulation Issues...............................................................................................71 5.2.1 Baseband Simulation...............................................................................72 5.2.2 Simulation Setup.....................................................................................73 5.3 Performance Evaluation of Carrier Recovery System......................................79 5.3.1 DA Frequency Estimator........................................................................79 5.3.2 DA Phase Estimator................................................................................88 5.3.3 NDA Phase Tracker................................................................................91 5.4 Summary...........................................................................................................94 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS......................96 6.1 Summary...........................................................................................................96 viii 6.2 Conclusions.......................................................................................................98 6.3 Recommendations for Future Study..................................................................99 REFERENCES.........................................................................................................101 APPENDIX A MATLAB MODULES FOR SIMULATION BLOCKS.......104 ix