在同步式上傳的分碼多工調變存取系統裡, 多重存取干擾是一個重要課
題。在本篇論文, 我們使用陣列天線在接收端, 探討遞迴式特徵序列最佳化演
算法。在多使用者的狀態和採用最小均方誤差法則時, 通常採用分群機制, 可
以使計算複雜度降低。群組內的使用者採用特徵序列最佳化演算法得以加快
其最佳化速度。但由於跨群組間使用者的互相干擾, 卻也因分群的原因而提
高, 使得其位元錯誤率較未分群前來得高。基於此一原因, 本論文將探討如何
降低跨群組間使用者的干擾, 來提升分群後最佳特徵序列多使用者偵測器效
能, 以達到分群機制在特徵序列最佳化的可行性。
由於一般作特徵序列最佳化時,通常採用多使用者偵測技術的最小均方差
偵測器, 因而計算複雜度甚高。為了能使複雜度降低, 我們提出分群的機制,
使得每一群因為人數減少而降低複雜度。但這麼作, 將增加群和群之間的干
擾,而降低系統的效能。所以我們在每一群使用和其他群組互相正交的片碼波
形(chip waveform)。如此,每一群裡面的序列因為經過更新,所以每一群裡的使
用者相關性降到最低。而且跨群組之間又有正交的片碼波形作區隔, 因此整個
系統在解調後, 除了計算複雜度降低外, 系統的效能也隨著每一群內與跨群組
間的干擾降低而提升。
另外,我們提出動態式天線分配法則,作為使用者分群的方式,解出各群組
訊號的另一種作法。如此一來, 除了各群組訊號可用極低的運算量取得外, 對
於使用者分怖過於密集, 我們可分配較多的接收天線於該群, 進而取得更佳的
解析機制, 使系統效能得以提升。

Multiple Access Interference (MAI) is one of the major impairments in the
reverse link of Code Division Multiple Access (CDMA) systems. An effective
scheme to overcome this setback is the minimum mean squared error multiuser
detection (MMSE MUD),whose performance can be further enhanced with the
optimization of the signature sequences. However, the computational complexity
of the above scheme, in particular with antenna arrays at the receiver, calls for enormous amount of computations. To alleviate the computational load, in this thesis we consider a groupwise iterative signature sequence optimization algorithm in conjunction with the MMSE MUD. Based on the proposed scheme, all users are divided into appropriate groups based on the spatial location of users with signature sequence being optimized within each group, so the computational complexity can be reduced. Furthermore, to mitigate the interferences among groups, we also consider to assign orthogonal chip waveforms for different group. As such the correlation can be reduced for users in different groups. Also, a dynamic antenna assignment method is addressed, which assigns more antennas to the groups that have more users. Conducted simulations show that the new schemes can provide satisfactory performance with reduced complexity in various scenarios.

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