應用凸型最佳化於多載波分碼多重接取系統偵測

MC-CDMA Detection with Convex Optimization

黃景煒(Jing-Wei Huang)

指導教授 ： 李彥文

國立暨南國際大學/科技學院/通訊工程研究所/碩士(2008年)

摘要

在多載波分碼多重接取(Multi-Carrier Code Division Multiple Access，MC-CDMA)系統中，其效能取決於偵測方法以及通道估測正確與否。在通道狀態資訊(Channel State Information，CSI)已知的情況下，對多使用者偵測器來說，最大概似(Maximum Likelihood，ML)偵測器是最佳偵測器。其缺點是當使用者數目增加時，複雜度將隨使用者數目呈指數增加。而有研究提出，從最大概似偵測器延伸而來的半正定放寬(Semidefinite Relaxation，SDR)偵測器，能有效降低系統複雜度並接近最佳偵測器效能。在本論文第一部分，我們將探討此類偵測器和傳統多使用者偵測器用於MC-CDMA系統之可行性與效能分析。而在通道狀態資訊未知的情況下，必須經由估測來獲得通道狀態時，必定會產生誤差值。在基於最大化訊號對干擾及雜訊比(Signal-to-Interference-plus-Noise Ratio，SINR)的前提下，常用之最小變異(Minimum Variance，MV)偵測器與對角載入最小變異(Diagonal Loading Minimum Variance，DLMV)偵測器都會造成效能大幅下降。因此在本論文第二部分，在不完美的通道狀態資訊下，透過使用二階錐形問題(Second-Order Cone Programming，SOCP)，我們提出兩種強健性偵測器，可以改善MC-CDMA偵測時的效能。利用估測的通道狀態值與誤差值資訊，我們證明了所提出的強健性偵測器效能會比傳統的最小變異與對角載入最小變異偵測器來的好。

關鍵字

多載波分碼多重接取 ； 半正定放寬 ； 二階錐形問題

並列摘要

For multi-carrier code division multiple access (MC-CDMA) systems, the performance is determined by the detection method and the accuracy of the channel estimate. With perfect channel state information (CSI) at the receiver, the maximum likelihood (ML) detector is known to be optimal for multiuser detection. However, its complexity is prohibitively high and increases exponentially with the number of users. In previous studies, it is shown that the semidefinite relaxation (SDR) detector derived from the ML detector can effectively reduce the system complexity and approach the optimal performance of the ML detector. In the first part of the thesis, we discuss the feasibility of applying this SDR detector to MC-CDMA systems. Its performance is compared with other well-known multiuser detectors under different scenarios, and the results show that the SDR detector can effectively reduce the complexity with negligible performance loss. On the other hand, since CSI is generally not known, some forms of channel estimation must be employed at the receiver. Channel estimation error is usually unavoidable. In this case, even with the minimum variance (MV) detector (which can maximize the signal-to-interference-plus-noise ratio (SINR)) or the diagonal loading minimum variance (DLMV) detector, the performance will degrade quite significantly. In the second part of the thesis, through the use of the second-order cone programming (SOCP), we formulate two robust detectors which can improve the performance of the MC-CDMA detection with imperfect CSI. By using the estimated CSI and error information, we show that the proposed SOCP robust detectors can outperform the conventional MV and DLMV detectors.

並列關鍵字

MC-CDMA ； SDR ； SOCP

參考文獻

[1] S. Hara and R. Prasad, “Overview of multicarrier CDMA,”IEEE Commun. Mag., pp.126–133, Dec. 1997.

[2] F. Riera-Palou, G. Femenias, and J. Ramis, “Performance Analysis of Multiuser Detectors for Uplink Quasi-synchronous MC-CDMA Systems,” Springer Wireless Personal Commun., vol.43, pp.1511–1521, Dec. 2007.

[3] J. G. Proakis, Digital Communications, Third ed. NewYork: McGraw-Hill, 1995.

[4] P. Patel and J. M. Holtzman, “Analysis of a simple successive interference cancellation scheme in a DS/CDMA system,” IEEE Journal on Selected Areas in Commun., vol. 12, no.5, pp. 796–807, 1994.

[5] P.W. Wolniansky, G.J. Foschini, G.D. Golden, and R.A. Valenzuela, “VBLAST: an architecture for realizing very high data rates over the rich-scattering wireless channel,” ISSSE’98, pp.295–300, Oct. 1998.