適應性最小均方誤差干擾抑制之功率控制

Abstract

直接序列分碼多重接取(direct-sequence code division multiple access)傳輸技術已被廣泛地討論並用於實際的無線行動通訊系統，本論文主旨在探討多用戶的情況下，以最小均方誤差(MMSE)濾波器抑制干擾，並結合功率控制，以最小的總發射功率達到用戶的目標訊號對干擾雜訊比(SIR)，且討論四種適應性演算法的效能，以及結合功率控制的特性。在衰落通道下，快速的時間變化使得傳統遞迴最少平方(RLS)演算法難以收斂，以差異編碼及改變誤差函數的差異最少平方(DLS)演算法能克服快速時間變化的問題。而適應性功率控制結合最小均方誤差抑制干擾濾波器在衰落通道下必須估計訊號對干擾雜訊比及通道參數，我們提出了以差異最少平方(DLS)演算法為基礎的通道估計法，這一個方法不須額外的計算，只須將濾波器輸出做時間平均。以估計的通道參數做為估計訊號對干擾雜訊比的資訊，並以電腦模擬在平坦衰落下，結合適應性差異最少平方干擾抑制法則的適應性功率控制。

The direct-sequence code division multiple access (DS/CDMA) transmission technique has been widely investigated and used in practical wireless communication system. In this thesis, MMSE interference suppression combined with adaptive power control is investigated. This method achieves the users’ target SIR with the minimum total transmitted power. Four adaptive MMSE interference suppression algorithms are discussed, so are their adaptive power control methods. In Rayleigh fading channel, conventional recursive least square (RLS) algorithm cannot converge easily under fast time variation. The differential least square (DLS) algorithm that adopts differential encoding and another error function can overcome the problem. The SIR of interference suppression filter output and channel parameter must be estimated in adaptive power control combined with DLS algorithm. We propose a channel estimation method based on DLS algorithm that doesn’t need extra computations and just takes time average over the interference suppression filter output. The SIR of filter output will be acquired through the method of channel estimation. We have used the computer to simulate adaptive power control combined with DLS interference suppression in flat Rayleigh fading channel.