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室内无线局域网定位研究多普勒频移对OFDMA性能的影响

作　者: 约翰
导　师: 刘威
学　校: 华中科技大学
专　业: 信息与通信工程
关键词: Mobile WiMax OFDMA Doppler Shift pilot signals Frequency Bank Signal (FBS)
分类号: TN929.531
类　型: 硕士论文
年　份: 2009年
下　载: 17次
引　用: 0次
阅　读: 论文下载

内容摘要

Wireless communication fast development and accessibility to an increasing number of users in the recent years have placed much demand on broadband wireless access (BWA) technology that has attracted much attention. As a BWA solution, Worldwide Interoperability for Microwave Access (WIMAX) is accepted by carriers of worldwide for broadband wireless service. It can be classified as fixed WIMAX (IEEE 802.16d version) using OFDM transmitting technique and mobile WIMAX (IEEE 802.16e version) using OFDMA transmitting technique. One of the main benefits of those transmitting techniques in wireless communication is that the receiver does not need to constantly adapt an equalizer as a single carrier system would. They also show much favorable properties such as high spectral efficiency, robustness to channel fading, immunity to impulse interference, capability of handling very strong echoes (multipath fading). But one of their main drawbacks is the sensitivity to frequency errors caused by the frequency differences between the local oscillators in the transmitter and the receiver.In mobile radio environment these frequency errors are due to the relative movement between transmitter and receiver. It is known as the Doppler frequency shifts phenomenon which causes a broadening of the signal spectrum.The main purpose of this thesis is to study the effect of Doppler Shift on OFDMA modulation technique conducting to orthogonality destruction which in its turn leads to ICI. The method of Frequency Bank Signal (FBS) based on Walsh functions is described in order to combat high Doppler Shift impairment suffered by mobile wireless communication system like Mobile WiMax. FBS is a hybrid of CDMA and OFDMA but without pilots signals (used for estimation) whose effect becomes negative in signal reception in a high Doppler shift environment.Simulations are conducted by using MATLAB codes to evaluate the different performances of BER between OFDMA with and without pilots in Rayleigh environment. The comparison study shows that OFDMA without pilots in presence of Doppler Shift gives better performance of BER compared to OFDMA with pilots in presence of high Doppler Shift.

全文目录

ABSTRACT  4-6
ACKNOWLEDGEMENTS  6-10
CHAPTER I INTRODUCTION  10-18
  1-1-Overview of Mobile wireless communications  10-15
    1-1-1 History and evolution  10-13
    1-1-2 Mobile WiMax  13-15
  1-2 Motivation  15-16
  1-3 Objectives  16-17
  1-4 Thesis structure  17-18
CHAPTER 2 ORTHOGONAL FREQUENCY MULTIPLE ACCESS  18-31
  2.1 OFDMA basics  18-20
  2.2 OFDMA transmission technology  20-27
    2.2.1 Introduction  20-21
    2.2.2 Evolution of OFDMA  21-23
    2.2.3 OFDMA technique  23-27
  2.4 OFDMA applications  27
  2.5 Advantages and Drawbacks  27-29
    2.5.1 OFDMA Advantages  27-29
    2.5.2 OFDMA Drawbacks  29
  2.6 Summary  29-31
3 DOPPLER SHIFT IN MOBILE WIRELESS COMMUNICATION  31-39
  3-1 Introduction  31
  3-2 Physical and Mathematical meaning  31-33
  3-3 Effect of Doppler Spread  33-34
  3-4 Doppler shift influence on OFDMA signal  34-36
    3-4-1 Frequency offset  35-36
    3-4-2 Time offset  36
  3-5- Frequency and time offset compensations in OFDMA  36-38
  3.6 Summary  38-39
CHAPTER 4 FREQUENCY BANK SIGNAL METHOD  39-57
  4-1 Introduction  39-40
  4-2 OFDMA model  40-42
  4-3 Frequency Bank Signal method principals  42-47
    4.3.1 Walsh functions  43-45
    4-3-2 Mathematical description  45-47
  4-4 Method description  47-55
    4-4-1 Phase inversion at the receiver  48-50
    4-4-2 Phase compensation  50-51
    4-4-3 Phase shift influence  51-52
    4-4-4 Restrictions and mathematical proofs  52-55
  4-5- Summaries  55-57
CHAPTER5: SIMULATIONS  57-62
  5-1-OFDMA with pilots and OFDMA without pilots  57-60
  5-2-Simulationsanalysis  60-62
CHAPTER6: CONCLUSION AND FUTURE WORKS  62-64
  6-1- Research summary  62-63
  6-2- Future works  63-64
REFERENCES  64-67
LIST OF FIGURES  67-68
TABLES LIST  68-69
LIST OF ABBREVIATIONS  69-72
LIST OF SYMBOLS  72-75
APPENDIX  75-79

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