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A Comparison Between Synchronous CDMA and Orthogonal Frequency Division Multiplexing (OFDM) for Fixed Broadband Wireless Access

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A Comparison Between Synchronous CDMA and Orthogonal Frequency Division Multiplexing (OFDM) for Fixed Broadband Wireless Access A Comparison Between Synchronous CDMA and Orthogonal Frequency Division Multiplexing (OFDM) for Fixed Broadband Wireless Access Shital Ratilal Chheda Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering Charles W. Bostian, Chair Ira Jacobs Dennis G. Sweeney April 15, 2002 Blacksburg, Virginia Keywords: CDMA, OFDM, synchronous, broadband, wireless, 3G, Non-Line-of- Sight (NLOS), orthogonal, VOFDM, SCDMA Copyright 2002, Shital Ratilal Chheda A Comparison Between Synchronous CDMA and Orthogonal Frequency Division Multiplexing (OFDM) for Fixed Broadband Wireless Access Shital Ratilal Chheda (ABSTRACT) The growth of broadband Internet access has paved the way for the development of many new technologies. As the cost of implementing broadband access soars, the best alternative will be to use fixed wireless for these services. This thesis addresses the possibility of 3rd Generation (3G) mobile cellular wireless systems as the basis for fixed broadband wireless service. Two of the 3G technologies aimed at providing fixed broadband wireless access are Time Division Synchronous Code Division Multiple Access (TD-SCDMA) and Orthogonal Frequency Division Multiplexing (OFDM). This thesis aims to provide a preliminary study on using TD-SCDMA and OFDM for broadband wireless systems. Currently, there is not enough theory and information to establish the feasibility of using either of these technologies for broadband wireless access. First, the basic features and background on synchronous CDMA and OFDM are presented for the reader to better understand these technologies. Then, an example TD-SCDMA system is described, and some analytical and experimental results are presented. Finally, TD-SCDMA’s technologies, along with this system’s attributes, are compared analytically to that of Vector OFDM (VOFDM). ii Acknowledgements First of all, I would like to thank my advisor, Dr. Charles Bostian, for all his support during the course of my research and thesis. His dedication to the improvement of the wireless communications program at Virginia Tech was instrumental in my continued education. The Center for Wireless Telecommunications (CWT) provided me with the resources and support necessary to pursue my research and complete my thesis properly. The time spent and advice lent by Dr. Ira Jacobs and Dr. Dennis Sweeney reviewing this thesis, helping with my research, and participating as part of my thesis committee is very much appreciated. I would also like to thank Tim Gallagher for his continued help and advice with my research. Also, the administrative support from the other faculty and staff of CWT is appreciated. I would also like to thank my sponsor, the Center for Innovate Technology (CIT) and especially Jean Woods for spearheading and funding this project. I would also like to thank Navini Networks and especially Phillip Levy and Walter Marusak for allowing me to use their system and field trial data for my thesis. Without their Ripwave system details and experiment results, this thesis would have not been possible. Finally, I would like to thank nTelos and especially Steve Garber and Noel Munson for their support of this research and thesis. It has been my pleasure to work with the Graduate Research Assistants in the CWT graduate labs. Their technical advice and constant source of entertainment made coming to work a pleasure on even the busiest of days. I wish them all the best in their future endeavors. iii Finally, I would like to thank my family. My parents Ratilal and Rekha Chheda and my sister Jeenal supported my decision to return to Virginia Tech for my Masters degree. Without their continued support and encouragement I would not have had the resolve to complete this degree. iv Contents 1 INTRODUCTION............................................................................................... 1 1.1 NEED FOR WIRELESS BROADBAND .................................................................................. 1 1.2 MARKET SITUATION......................................................................................................... 2 1.3 KEY FEATURE OF BROADBAND WIRELESS ....................................................................... 3 1.4 CHALLENGES OF FIXED BROADBAND WIRELESS.............................................................. 5 1.4.1 Attenuation .............................................................................................................. 5 1.4.2 Multipath ................................................................................................................. 6 1.4.3 Delay Spread........................................................................................................... 7 1.4.4 K-Factor (Ricean factor)......................................................................................... 8 1.4.5 Spectral Efficiency................................................................................................... 8 1.4.6 Line of Sight Issues.................................................................................................. 9 1.5 MULTIPLE ACCESS TECHNIQUES.................................................................................... 10 1.5.1 Frequency Division Multiple Access..................................................................... 10 1.5.2 Time Division Multiple Access.............................................................................. 11 1.5.3 Code Division Multiple Access ............................................................................. 11 1.6 EMERGENCE OF 3G ........................................................................................................ 13 1.7 THIRD GENERATION (3G) SYSTEMS PROPOSALS........................................................... 14 1.8 CONTRIBUTIONS AND SCOPE .......................................................................................... 15 v 2 SYNCHRONOUS CDMA ................................................................................ 16 2.1 TD-SCDMA BASIC PRINCIPLES .................................................................................... 16 2.2 RF CHANNEL PARAMETERS ........................................................................................... 22 2.3 FRAME AND MULTIPLEXING STRUCTURE ....................................................................... 23 2.3.1 Frame Structure .................................................................................................... 24 2.3.2 Burst Structure ...................................................................................................... 27 2.4 MODULATION................................................................................................................. 28 2.5 CODING .......................................................................................................................... 29 2.6 SYNCHRONIZATION ........................................................................................................ 31 2.6.1 Uplink Synchronization Establishment ................................................................. 31 2.6.2 Uplink Synchronization Maintenance ................................................................... 40 2.7 SMART ANTENNAS ......................................................................................................... 34 2.7.1 Smart Antenna Basics............................................................................................ 34 2.7.2 Joint Detection ...................................................................................................... 35 2.8 SUMMARY ...................................................................................................................... 36 3 NAVINI RIPWAVE.......................................................................................... 37 3.1 SYSTEM SPECIFICATIONS ............................................................................................... 37 3.1.1 Forward Link.........................................................................................................38 3.1.2 Reverse Link .......................................................................................................... 38 3.1.3 Bandwidth Allocation............................................................................................39 3.1.4 Modulation ............................................................................................................ 40 3.1.5 Frequency Selection .............................................................................................. 40 3.2 BASE STATION ............................................................................................................... 41 3.2.1 Base Transceiver Station....................................................................................... 41 3.2.2 Radio Frequency Subsystem.................................................................................. 42 3.2.3 Base Station Data Sheet ........................................................................................ 43 3.3 CUSTOMER PREMISE EQUIPMENT................................................................................... 44 3.4 FIELD TRIALS ................................................................................................................. 45 vi 3.4.1 Downlink Beamforming........................................................................................
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