MC-CDMA多用戶偵測之效能提升

在這篇論文中，我們首先提出適用於多載波分碼多工（multi-carrier code division multiple access, MC-CDMA）系統中多用戶偵測（multiuser detection, MUD）之相對門檻削樹（relative threshold tree pruning, RTTP）演算法. 相對門檻削樹較傳統的M-演算法（M-algorithm）俱淘選力和效率，並能在高訊雜比下達到較低的錯誤率。針對二維矩形傳輸符號，我們提出用戶分離（user partitioning, UP）來和好的用戶排序（user order sorting, UOS）結合以產生沒有用戶分離時無法達到的細緻的用戶順序。這當中，我們提出的DLUPS和DLUP-RMOPS適用於下傳通道及實數展頻碼，而UP-RMOPS則適用於所有的環境，其中RMOPS是一個前人提出的優良的用戶排序演算法，它也可以是任何其他有效的用戶排序。此外，在下傳系統中當各用戶都使用一維傳輸符號時，我們提出了一個簡單的下傳相位旋轉（downlink phase rotation, DLPHR），可以把任何實數展頻碼轉換成複數展頻碼以大幅降低多用戶干擾（multiple access interference, MAI）。下傳相位旋轉可視為一種在同樣有限的資源下增加傳輸維度的方法。當正交分頻多工（orthogonal frequency division multiplexing, OFDM）系統因為載波頻率誤差而存在載波相互干擾（inter-carrier interference, ICI）時，所有我們提出的演算法都依然適用。模擬結果顯示這些演算法能獲致較低的錯誤率，也因此降低了多用戶偵測的複雜度。

關鍵字

削樹；用戶分離；多用戶偵測

並列摘要

In this thesis, we rst proposed the relative threshold tree pruning (RTTP) al- gorithm suitable for pre-whitening tree pruning (PWTP) multiuser detection (MUD) for multi-carrier code-division multiple access (MC-CDMA). RTTP is more e cient and selective than the conventional M-algorithm and achieves relatively lower error rate at high signal-to-noise ratio (SNR). For rectangular 2-D symbols, user partitioning (UP) is proposed and, when combined with good user order sorting (UOS) produces a softer UOS not obtainable with- out UP. The proposed DLUPS and DLUP-RMOPS are applicable with the downlink channel and real-valued spreading code, while the proposed UP- RMOPS is suitable in the general cases; ROMPS is a previously proposed UOS that can be replaced by any other good UOS. A simple downlink phase rotation (DLPHR) is proposed to convert any real-valued spreading code into complex-valued and to signi cantly reduce multiple access interference (MAI) when 1-D symbols are used with downlink channel. DLPHR can be viewed as an increase of transmit diversity with the same limited resource. All proposed algorithms apply in the presence of carrier frequency o set which causes inter-carrier interference (ICI) of orthogonal frequency division multiplexing (OFDM). Simulation results show that the proposed algorithms indeed achieve lower error rate and thus enable low complexity MUD ap- proaching optimal performance.

並列關鍵字

tree pruning ； multiuser detection ； user partitioning ； MC-CDMA

參考文獻

[1] Shinsuke Hara and Ramjee Prasad, "Overview of Multicarrier CDMA",

IEEE Communication Magzine, pp. 126-133, Dec. 1997.

[2] Sergio Verdu, Multiuser Detection, Cambridge University Press, 1998.

[5] Yi-Lin Li, "Tree-Pruning and Sorting Algorithms and Signal Dimension-

ality Issues for Multi-User Detection in DS-CDMA and MC-CDMA",

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MC-CDMA多用戶偵測之效能提升

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