快速衰減OFDM系統下採用複數球狀解碼之
群組式載波間干擾消除器

由快速衰減通道產生的載波間干擾(ICI)會破壞正交分頻多工(OFDM)訊號的正交性並造成接收器效能嚴重下降。本論文中，我們提出二階段的干擾消除器，結合群組式的強制歸零等化器(Group-based Zero-Forcing, G-ZF)跟複數球狀解碼(complex sphere decoding, CSD)，來處理正交分頻多工嚴重的載波間干擾。這個演算法主要利用載波間干擾矩陣稀疏的特性，也就是說令我們感興趣的主對角線子載波的通道能量主要會漏進到鄰近的子載波中。首先我們用群組式的強制歸零等化器來取代直接的強制歸零等化器來找初始的估計值，這樣做我們可以避免做過於龐大的反矩陣。第二，在消去群組中的載波間干擾項後，複數球狀解碼用來做更進一步準確的資料估測。複數球狀解碼是由最大似然準則跟QR分解推導而來。由複雜度的分析看出複數球狀解碼演算法比實數球狀演算法(real-valued SD)可以減少一半的乘法運算。最後，電腦模擬結果顯示我們提出的二階段的消除器比直接強制歸零等化器跟直接複數球狀解碼有更優越的效能。

關鍵字

載波間干擾；球狀解碼；正交分頻多工；快速衰減

並列摘要

The intercarrier interference (ICI) resulted from fast fading channel destroys the orthogonality of the orthogonal frequency-division multiplexing (OFDM) signal and deteriorates receiver performance. In this paper, we propose two-stage interference canceller, which combines zero-forcing (ZF) equalizer with complex sphere decoder in a group-based version, to tackle the severe ICI on the OFDM. The algorithm is developed in accordance with the sparsity of ICI matrix, in which the channel power of subcarrier of interest primarily leaks to its neighboring subcarriers. First, we use the group-based ZF equalizer in place of direct ZF to obtain initial estimates. In so doing, prohibitive complexity of large matrix inversion can be avoided. Second, after removing the out-of-group ICI components, the complex sphere decoder (CSD) is presented further improving the accuracy of data estimates. The CSD algorithm is based on maximum-likelihood criterion and QR decomposition. Complexity analysis shows that CSD algorithm can saves a half of multipliers which is required in the real-valued SD. Finally, simulation results demonstrate the proposed two-stage canceller has superior performance than those of direct ZF and of direct CS

並列關鍵字

intercarrier interference ； fast fading ； orthogonal-frequency-division multiplexing (OFDM) ； sphere decoding algorithm

參考文獻

[2] W. G. Jeon, K. H. Chang and Y. S. Cho, “An equalization technique for orthogonal frequency-division multiplexing systems in time-variant multipath channels,” IEEE trans. Commun., vol. 47, pp. 27-32, Jan. 1999.

[3] E. Agrell, T. Eriksson, A. Vardy and K. Zeger, “Closest point search in lattices,” IEEE Trans. Information Theory, vol. 48, pp. 2201-2214, Aug. 2002.

[6] Y. J. Kou, W.-S. Lu and A. Antoniou, ” Application of sphere decoding in intercarrier-interference reduction for OFDM systems” IEEE Pacific Rim Conference, pp.360-363, Aug. 2005.

[7] H. C. Wu, X. Huang and D. Xu, "Novel semi-blind ICI equalization algorithm for wireless OFDM systems," IEEE Transactions on Broadcasting, , pp. 211-218, June 2006.

[8] Y. Zhao and S. G. Haggman, "Intercarrier interferenceself-cancellation scheme for OFDM mobile communication systems," IEEE Transactions on Communications, vol.49, no.7, pp.1185-1191, Jul 2001.

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快速衰減OFDM系統下採用複數球狀解碼之群組式載波間干擾消除器

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