在這篇論文, 我們考慮一個分碼多工存取(code division multiple access) 的合作式上傳鍊路(uplink) , 使用者合作地傳遞彼此的訊號到目的端, 來源點藉由分碼多工存取共享中繼點提供的資源, 一般而言, 由於分碼多工存取系統設計的考量, 每個來源點的展頻碼 (spreading waveform) 之間多為非正交的, 因此在中繼點和目的端的接收訊號會受到多重接取干擾(multiple access interference) , 多重接取的干擾會使得訊號解碼的錯誤率增加, 而減少此合作式網路的多樣性; 為了消除多重接取干擾, 傳統上在上傳鍊路較常使用的是多使用者解相關偵測(decorrelating multiuser detection) , 在下傳鍊 (downlink)常使用的是迫零預編碼器(zero-forcing precoder) , 但是多使用者解相關偵測會有雜訊放大的影響, 而破零預編碼器則是有傳送功率擴張的缺點。因此在這篇論文使用了有中繼點幫助解相關的多使用者偵測器(relay-assisted decorrelating multiuser detector)[1]來減少多重接取干擾, 在此方法中, 中繼點進行了一半的解相關, 在目的端實現了另一半的解相關, 如此一來, 不僅減少了多重接取干擾的影響, 還不會造成傳送功率的擴張和雜訊的放大。但是在文獻[1]中, 作者假設所有來源點到中繼點之間的傳輸是同步的, 這個假設是很不切實際的, 因為很難去控制所有來源點到中繼點的傳輸為同步, 每個來源點和中繼點之間的傳遞延遲都不相同, 所以在本篇論文我們延續[1]的研究工作並放寬來源點到中繼點之間傳輸是同步的。此外, 有中繼點幫助解相關的多使用者偵測器可結合合作式傳輸的方法來進一步降低錯誤率, 論文中我們採用傳輸波束成形(transmit beamforming) 及選擇性的中繼(selective relaying) 。最後, 從模擬結果中可看到有中繼點幫助解相關的多使用者偵測相較其他多使用者偵測的方法可以達到最低的錯誤率。

In this thesis, we consider the uplink of a cooperative code division multiple access (CDMA) network, where users cooperate by relaying each other’s messages to the
base station. The sources adopt CDMA to share the informations offered by relays. In general, spreading waveforms of sources are not orthogonal to each others due to pratical design issues of CDMA network. Therefore, the source signals will suffer from multiple access interference (MAI) at the relays and destination. The MAI results in the increase of bit error rate increased, and diminishes the cooperative network diveristy gains. In order to mitigate MAI, the decorrelating multiuser detection and
zero-forcing precoder have been commonly adopted. But, the decorrelating multiuser detection causes noise enhancement, while the zero-forcing precoder causes power expansion. In this thesis, we adopt relay-assisted decorrelating multiuser detector (RAD-MUD) to mitigate MAI as proposed in [1].In this scheme, the relays perform
half of decorrelating operation and the destination performs the other half. In this way, neither noise enhancement nor power expansion will occur. However, in the reference [1], the authers assume the transmission is synchronous between sources and relays. The assumption is unrealistic, because it is difficult to achieve synchronization between all sources and relays due to various propagation delays. In this thesis, we extend the research in [1] and relax restriction of synchronization between all sources and relays. Besides, we also adopt cooperative strategies such as transmit beamforming or selective relaying to enhance system performance. Compared with other’s multiuser detection schemes, we show that the proposed schemes can effectively reduce the bit error rate.

1 介紹. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 相關背景. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 系統模型. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1 第一階段的傳輸. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
3.2 第二階段的傳輸. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4 訊號解調及多使用者偵測. . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1 有中繼點幫助解相關的多使用者偵測(RAD-MUD) . . . . . 23
4.2 在中繼點的最小均方差估測. . . . . . . . . . . . . . . . . . . . . . . . 26
4.3 在目的端使用多使用者最小均方差偵測. . . . . . . . . . . . . . 30
4.3.1 解碼後前送. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.3.2 放大後前送. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5 合作式傳輸的方法. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.1 解碼後前送. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
5.1.1 傳輸的波束賦形. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.1.1.1 中繼點和目的端間的通道的波束成形. . . . . . . . . .. . . 37
5.1.1.2 來源點中繼點和目的端間的通道的波束成形. . . . . . . 37
5.1.2 選擇性的中繼. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
5.1.2.1 起點值選擇的方法. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.1.2.2 最佳選擇的方法. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.2 放大後前送. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
5.2.1 傳輸的波束成形. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.2.2 選擇性的中繼. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6 模擬結果. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 43
7 結論. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .53

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