本論文中我們針對正交分頻多工系統，使用適應性波束形成演算法來對抗寬頻與窄頻之干擾。我們所提出的頻域適應性波束形成器，結合了適應性線性修正型常模混和式最小均方值 (LCMCM-HLMS) 演算法，可以有效地提升通訊系統之效能。經由模擬得知，在可加性高斯白色雜訊通道中，窄頻干擾的消除能力可藉由我們所提出之適應性頻域波束形成演算法有效提升；在多路徑反射的環境中，；在多路徑反射的環境中，通道所具有的相位失真會導致時序之延遲，我們所提出的適應性頻域波束形成器亦能有效避免相位失真導致之系統效能低落。
為了進一步確認適應性頻域波束形成器所帶來之優點，我們將專注於可加性高斯白色雜訊 (AWGN) 通道中窄頻干擾；以及瑞雷快速型衰落 (Rayleigh fast fading)通道中隨機相位失真所帶來的效應。而為克服頻域波束形成器中，並非所有子通道都會具有領航信號的問題，我們進一步結合適應性線性修正型常模混和式最小均方值演算法。經由盲性演算法我們不需要領航信號就可以來修正波束形成器之權重。
藉由電腦的模擬驗證了本論文所提出之方法確實可以在各種不同情況中達到良好的干擾消除效能。相對於傳統的時域上之波束形成器，在某些情況中會有較好之效能；然而，在某些情況中，時域上之波束形成器將會有極差之干擾消除能力。我們將藉由模擬結果證明以上結論。

In this thesis, we investigate the use of adaptive antenna algorithms for OFDM systems to suppress interference in various channel conditions including narrowband and wideband interference, flat and frequency selective fading. We propose a novel frequency-domain beamformer, based on the linearly constrained modified constant modulus hybrid LMS (LCMCM-HLMS) algorithm for OFDM systems to improve the performance of interference suppression in AWGN channel with narrowband interference, Rayleigh fast fading channel with phase distortion, and the multipath environment.
To verify the merits of the frequency-domain beamformer, the effect due to narrowband interference and random phase distortion are investigated. Moreover, to improve the performance of adaptive beamforming algorithm, the frequency-domain linearly constrained modified constant modulus hybrid LMS (LCMCM-HLMS) algorithm is proposed. Computer simulation results show that the proposed frequency-domain LCMCM-HLMS beamformer has good capability of interference supression in various environment, and can mitigate the phase distortion of channel. However, in the time-domain beamformer based on LMS [33], RLS ,LC-LMS and LC-FLS algorithm for OFDM systems, the performance may severely degraded under some situations. We will show that in terms of output SINR, beampatern, received signal constellation and mean square error (MSE), for narrowband interference suppression in AWGN channel, phase distortion in Rayleigh fast fading channel and the multipath environment.

Acknowledgement i
Abstract ii
Contents iii
List of Figures v
List of Tables viii
Chapter 1 Introduction 1
Chapter 2 OFDM System Based on Time-Domain Adaptive Beamformer 4
2.1 Introduction 4
2.2 Overview of OFDM Systems 4
2.2.1 Orthogonal Frequency Division Multiplexing (OFDM) 7
2.2.2 Generation of OFDM Symbols 11
2.3 Fundamentals of Adaptive Arrays and Beamforming 13
2.3.1 Uniform Linear Array 13
2.3.2 Beamforming 17
2.4 Adaptive Beamforming algorithms 21
2.4.1 Least Mean Squares (LMS) Algorithm 21
2.4.2 Recursive Least Squares (RLS) Algorithm 23
2.5 Time Domain Adaptive Beamformer for Ofdm Systems 25
2.5.1 Description of System Model 25
2.5.2 Adaptive Beamforming Algorithm for OFDM systems 30

Chapter 3 OFDM Sysems Based on Frequency Domain Adaptive Beamforming Algorithm 33
3.1 Introduction 33
3.2 Frequency-domain Beamformer for OFDM Systems 33
3.2.1 Description of System Model 38
3.2.2 The Linearly Constrained Hybrid LMS Algorithm 40
3.2.3 The Linearly Constrained Constant Modulus Hybrid LMS Algorithm 45
3.2.4 The Linearly Constrained Modified Constant Modulus Hybrid LMS Algorithm 48
3.3 Computer Simulation Result 53
3.3.1 AWGN Channel with Wideband Jammers 55
3.3.2 AWGN Channel with Narrowband Jammers 62
3.3.3 Rayleigh Fast Fading Channel (with Phase Distortion) 69
Chapter 4 Conclusions 74
References 76

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