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標題: 直接序列展頻分碼多工多使用者通訊系統中之適應性濾波器在恢復時間延遲之應用
Adaptive Receiver with Timing Recovery for multiuser DS-CDMA Communication Systems
作者: 林必峰
Lin, Pi-Feng
關鍵字: Adaptive Filter;分碼多工;DS/CDMA;ISI;MAI;LMS;MMSE;Single-user receiver;最小均方;單一使用者接收器;極小均方誤差
出版社: 電機工程學系
在多重使用者直序展頻分碼多工(Direct-sequence Code division multiple access)通訊系統伴隨多重路徑衰減通道的環境中,我們必須克服符間干擾(ISI)、多重存取干擾(MAI)等雜訊干擾,另外,經過多重路徑通道傳送,接收訊號與傳送訊號間的延遲位移也是影響整各系統架構效能的一各重要議題。
本文使用適應性陣列接收機架構均使用最小均方 (Least mean square)的演算法,以調整更新展頻係數,我們稱此架構為Wiener解碼濾波器。此濾波器可以解決上一段所提出的種種第三代通訊上的問題,因為適應性波束合成器的權重和展頻碼是每訊符間更新一次,所以計算的複雜度非常低。
在本文中,我們的重點就是使傳送與接收端訊號的同步化,也就是解決彼此之間訊號的延遲位移,使系統效能更加完善。而我們提出的架構和必須追蹤訊號(code tracking)的架構做比較,顯然我們的架構在整體複雜度上較低,也更容易被運用開發在硬體的實現,而且在效能錯誤率上也是令人滿意的。我們所提出的架構表現的模擬範例會被提出來。這些架構的最佳化分析也會被提出來。

In direct-sequence code division multiple access (DS/CDMA) multiuser communication systems with multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) must be considered. The multipath channel characterizes the propagation effects including the timing offset and delays, etc. The proposed scheme employs an adaptive filter whose taps are adapted using a block least-mean square error algorithm (LMS) and solves the above-mentioned problems. The spread- spectrum (SS) communication requires that the transmitter and receiver spreading waveforms be synchronized. In conventional receivers, the code tracking algorithms are used to make code synchronized. The proposed receiver can solve the timing offset problems without using code tracking loop. Simulations confirm the good performance, including BER and theoretical analysis of minimum mean-square error (MMSE), of the proposed receivers.
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