超寬頻（UWB）無線通訊技術的特點為具有極寬的頻帶以及極低的傳輸功率，故可用來提升傳輸速率並且降低和其他無線通訊系統的干擾，而直序展頻分碼多工（DS-CDMA）技術則可以提供這個高傳輸速率的需求，除了以脈衝（pulse）形式傳輸資料以外，DS-CDMA UWB系統的基本概念與傳統的DS-CDMA是相似的，而DS-CDMA技術的一個主要問題在於系統的容量（capacity）受限於多用戶存取干擾（MAI）的多寡，這個情形同樣也出現在DS-CDMA UWB系統之中，因此我們必須使用多用戶偵測技術來解決這個問題。
和其他無線通訊系統不同的是，UWB系統所面臨的通道是一個短距離的室內環境同時具有嚴重的多重路徑干擾。在本論文中，我們將介紹幾種傳統的多用戶偵測技術，例如平行干擾消除（PIC）、部份平行干擾消除（PPIC）、以及簡化的部份平行干擾消除（SPPIC），然後針對UWB系統的通道模型修改這些多用戶偵測技術。
為了進一步改善PPIC的效能，我們將討論一些調整PPIC權值（partial weight）的方法，其中一種較普遍的方法為適應性多級平行干擾消除（adaptive multistage PIC）。但是對於像DS-CDMA UWB這樣高速傳輸的系統來說，過高的資料傳輸速率使得這種方法難以實現。為了解決這個問題，我們提出了一種新的適應性部份平行干擾消除技術，稱之為位元層級適應性加權部份平行干擾消除（bit-level adaptive weighted PPIC），目的在於將原本操作在片碼速率（chip-rate）的運算速度降低到位元速率（bit-rate）。
最後，我們將以電腦軟體模擬比較本論文提出的演算法以及幾種傳統多用戶偵測技術的不同。由模擬的結果我們可以看出，我們所提出的演算法確實可以用較少的運算複雜度來提升DS-CDMA UWB系統的效能。

i
The significant features of ultra-wideband (UWB) technology are broader spectrum
and lower power transmission, which can be applied to improve data rate and reduces
interference in wireless communications. In order to meet the demand for high data
rates, the direct-sequence code-division multiple access (DS-CDMA) technology is
applied to UWB systems. The basic operations of a DS-CDMA UWB system are
similar to the conventional DS-CDMA system except that the pulses are transmitted
rather than carriers. One major problem associated with DS-CDMA is that its capacity
is seriously limited by multiple access interference (MAI), and this is the same issue
for DS-CDMA UWB systems. To overcome this problem, we have to employ some
multiuser detection techniques to deal with the MAI problems for DS-CDMA UWB
systems.
Unlike other wireless communication systems, a UWB system faces a short
range indoor environment and serious multipath channels. In this thesis, we first
introduce several conventional multiuser detection techniques, such as parallel
interference cancellation (PIC), partial parallel interference cancellation (PPIC), and
simplified partial parallel interference cancellation (SPPIC). Then we modify the
conventional multiuser detection techniques by re-defining the channel model for
UWB systems.
To further improve the performance of PPIC, some approaches that adjust the
partial weights of PPIC are discussed. One common approach of weight selection is
adaptive multistage PIC, but this approach has to be operating at the chip rate and is
difficult to implement for an ultra-high rate situation such as DS-CDMA UWB
systems. To solve this problem, we propose a new adaptive weighted PPIC by
simplifying the adaptive frequency from the chip rate to the bit rate, called bit-level
adaptive weighted PPIC. Similar to the original multiuser detection technique, we
derive this new adaptive weighted PPIC for UWB channels.
Finally, we show some computer simulation results of proposed algorithm and
different multiuser detection techniques. The results indicate that this proposed
algorithm can actually improve the system performance of DS-CDMA UWB with
lower computational complexity.

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