在本篇論文我們探討的是一個合作式的分碼多工(code division multiple access, CDMA)網路，使用者採取合作的方式去傳遞彼此的訊號至目的端，由於非同步的傳輸會提升系統的複雜度，故假設訊號傳輸為同步(synchronous)接收。由於分碼多工系統設計的考量，用來傳送各個使用者訊號的展頻碼(spreading code)之間並非完美正交，因此中繼端和目的端在偵測時往往會有多重擷取的干擾(multiple-access interference, MAI)，進而造成解調錯誤率上升，這裡為了消除多重擷取的干擾，在上傳鍊路中，常見的方法是採用多個使用者解相關偵測(decorrelating multi-user detection, Decorrelating MUD)[16,17]，但是多個使用者解相關偵測會造成雜訊能量放大。故本篇論文使用中繼端協助消除相關性的應用於多使用者的偵測器(relay-assisted decorrelating multiuser detector, RAD-MUD) [1]，藉由中繼端和目的端各解一半的相關性，以消除多重擷取的干擾，並且不造成傳送功率擴張及雜訊能量放大，所以錯誤率也大幅被降低了，而且中繼端會根據通道資訊(channel state information, CSI)掌握多寡，採用不同的合作式傳輸策略，如波束賦形的傳送(transmit beamforming)和選擇性的中繼(selective relaying);且目的端使用最小期望均方差偵測器(minimum mean-square error detector, MMSE detector)[18]，在傳統文獻中的通道環境，是假設中繼端和目的端回傳給訊號源的通道資訊是完美無誤，但是通道估測也可能發生失真，為了預防這種情況發生，所以本篇論文的目標在於以系統通道估測結果失真為前提，利用通道係數的估測值，根據最佳化的理論為中繼端設計出穩健的(robust)預編碼器(precoder)以及解碼器(detector)[26]，使系統能夠在有通道估測失真的情況下依然有著極佳的傳輸效益，並從模擬結果可以看出有通道誤差統計特性的穩健系統，比起缺乏通道估測誤差統計特性的系統有著較低的錯誤率，並且能夠挽回較多的傳輸增益。

In this paper, we explore a cooperative code-division-multiple-access(CDMA) network. Users cooperate by forwarding each other’s messages toward the destination. For simplicity, we assume that signal reception at the destination is well-synchronized. Due to practical design issues of CDMA systems, spreading waveforms allocated to users are not perfectly orthogonal in general. This results in multiple-access interference(MAI) at relays and destination. In CDMA uplink networks one common approach is to adopt decorrelating multi-user detection, but it will lead to noise amplification[16,17]. Therefore, we employ relay-assisted decorrelating multiuser detector(RAD-MUD) to mitigate MAI[1] by performing half of decorrelation at the relay and destination respectively. Based on the availability of CSI at relays, we can further adopt cooperative strategies to improve performance, e.g., transmit beamforming and selective relaying. The destination side will use minimum mean-square error(MMSE) detector to demodulate source symbols. In the existing literatures, channel state information(CSI) is assumed to be perfectly known at relay and destination. Actually, CSI is obtained from channel estimation, which usually contains estimation errors. In order to alleviate effects of channel estimation, one goal of this thesis is to design a robust system. Using estimated CSI and statistical property channel estimation errors, we design robust precoder and detector for the relay and destination. It shows that, even with distortion on channel estimations, the system still achieve excellent transmission efficiency. From the simulation results, it shows that the robust design is better than the system without consider channel estimation errors. Finally, we can see that the stable robust design can effectively mitigate effects of imperfect CSI.

摘要...... .........................................................................................................................i
abstract.......................................................................................................................... ii
目錄.............................................................................................................................. iii
圖索引.......................................................................................................................... .v
第一章 簡介.............................................. ...............................................................01
第二章 相關背景....................... ..............................................................................05
2-1 CDMA及多使用者偵測…...... ………………………………………..………05
2-2合作式系統簡介................... …………………………………………..………08
2-3不完美通道資訊及其統計特性………………………………………..………11
第三章 系統模型......................................................................................................13
3-1第一階段的傳輸................... …………………………………………..………13
3-2第二階段的傳輸........................ .........................................................................16
3-3中繼端協助消除相關性的應用於多使用者的偵測器.................….. .….……17
3-3-1解碼後傳送...................................................................................................... 19
3-3-2放大後傳送................................... ........... ...................................................... 20
第四章 在完美通道資訊下的最小均方差偵測器和預編碼器設計…….….……22
4-1中繼端多使用者的最小均方差偵測器............................................................. 22
4-2目的端多使用者的最小均方差偵測器............................................................. 24
4-2-1解碼後傳送...................................................................................................... 24
4-2-2放大後傳送................................... ........... ...................................................... 26
4-3合作式的傳輸策略.......................... .......... ................................................... ....27
4-3-1解碼後傳送........................................................ ............................................. 28
4-3-1-1傳輸的波束賦形.......................................................................................... 28
4-3-1-1選擇的中繼.................................................................................................. 30
4-3-2放大後傳送...................................................... ............................................... 30
4-3-2-1傳輸的波束賦形.......................................................................................... 30
4-3-2-2選擇的中繼.................................................................................................. 32
第五章 在不完美通道資訊下的最小均方差偵測器和預編碼器設計…….….…34
5-1中繼端多使用者的最小均方差偵測器............................................................. 34
5-2目的端多使用者的最小均方差偵測器............................................................. 36
5-2-1解碼後傳送...................................................................................................... 36
5-2-2放大後傳送................................... ........... ...................................................... 38
5-3合作式的傳輸策略.......................... .......... ................................................... ....40
5-3-1解碼後傳送........................................................ ............................................. 41
5-3-1-1傳輸的波束賦形.......................................................................................... 41
5-3-1-1選擇的中繼.................................................................................................. 42
5-3-1放大後傳送...................................................... ............................................... 43
5-3-2-1傳輸的波束賦形.......................................................................................... 43
5-3-2-2選擇的中繼.................................................................................................. 45
第六章 模擬結果和比較…………..…....................................................................47
第七章 結論………..……...........….........................................................................55
第八章 未來的展望…………..……..……………………………….…..……….. 56
附錄一………………………………………………………………….…..……….. 57
附錄二………………………………………………………………….…..……….. 59
附錄三………………………………………………………………….…..……….. 61
附錄四………………………………………………………………….…..……….. 64
參考文獻..................................................................................................................... 67

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