直序展頻分碼多工超寛頻(DS-CDMA UWB)通訊系統是IEEE 802.15.3a標準的解決方案之一。它具備有許多優點，如低成本、低功率頻譜密度和對抗大量且密集的多路徑干擾的能力等。然而，在高資料傳輸速率且多重存取的室內環境中，多路徑干擾和多重存取干擾(MAI)是DS-CDMA UWB通訊系統的兩個主要問題。為了解決多路徑干擾的問題，我們可以利用UWB使用脈衝(pulse)傳送所擁有的高通道解析度特性，使用基本的犁耙式(RAKE)接收機來有效地減輕這個問題的影響。另一方面，對抗多重存取通訊系統中會降低系統性能的MAI，使用多用戶偵測技術是常見的解決方案。為適合系統的高資料傳輸速率，在多用戶偵測技術中，從接收訊號中消除部分重建MAI的部分平行干擾消除(PPIC)技術，可以有效的降低系統處理延遲和提供簡單的接收機架構。
在本篇論文中，我們研究在高資料傳輸速率DS-CDMA UWB系統且採用對數常態(lognormal)分佈的多路徑衰減超寬頻通道模型中，不同的犁耙式接收機結合PPIC偵測器的性能表現。在使用100 Mbps的資料傳輸速率且通過多路徑通道的環境下，藉由電腦模擬來比較最大比結合(MRC)和最小均方差結合(MMSEC)這兩種犁耙式接收機的性能並結合PPIC偵測器來探討在UWB系統下使用多用戶偵測技術的必要性。為了實現容易，我們使用正規化最小均方(NLMS)適應性演算法來達到最小均方差(MMSE)解。並藉由使用NLMS演算法所獲得的犁耙式接收機的MMSEC權重(weights)，來估測在PPIC偵測器中重建MAI時所需的通道衰減增益。模擬結果顯示MRC犁耙式接收機結合PPIC偵測器和MMSEC犁耙式接收機結合PPIC偵測器比MRC犁耙式接收機和MMSEC犁耙式接收機有較好的性能。結果亦顯示在高訊雜比(SNR)時，MMSEC犁耙式接收機結合PPIC偵測器且僅用估測出的通道衰減增益比MRC犁耙式接收機結合PPIC偵測器且使用精確的通道資訊有較好的性能。

The direct-sequence code-division multiple access ultra-wideband (DS-CDMA UWB) communication system is one of the solutions for the IEEE 802.15.3a standard. This system has some advantages, including low cost, low power spectral density, good resistance to the dense multipath environment, etc. However, multipath interference and multiple access interference (MAI) are two major problems of the DS-CDMA UWB system at high data rate multiple access indoor environments. In the first place, due to the fine channel resolution by using the pulse transmission, the RAKE receiver is an effective and primitive structure to mitigate this problem. On the other hand, multiuser detection is a general solution to resist MAI which degrades the system performance in the multiple access communication system. To improve the system performance, the partial parallel interference cancellation (PPIC) structure canceling the partial reconstructed MAI from the received signal has a small processing latency and simple structure in multiuser detection techniques.
In this thesis, we investigate performance of the PPIC receiver with various RAKE combining schemes for high data rate DS-CDMA UWB systems over a realistic UWB multipath channel model with lognormal distributed multipath fading gain. Under a data rate condition of 100 Mbps, some performance comparisons between two RAKE receiver combining schemes, maximal ratio combining (MRC) and minimum mean-squared error combining (MMSEC), with the PPIC detector over the multipath channel are illustrated by computer simulations. For ease of implementation, we use an adaptive structure with the normalized least mean-squared (NLMS) algorithm to approach the MMSE solution. Using the NLMS algorithm, the channel fading gains which are required for MAI reconstruction in the PPIC detector can be estimated by the obtained MMSEC weights in the RAKE receiver. Simulation results show that the MRC RAKE receiver with PPIC and the MMSEC RAKE receiver with PPIC have better performance than the MRC RAKE receiver without PPIC and the MMSEC RAKE receiver without PPIC. As the results also indicate that, in high signal-to-noise ratio (SNR), the MMSEC RAKE receiver with PPIC and estimated channel fading gains has better performance than the MRC RAKE receiver with PPIC and accurate channel information.

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