快速衰退通道下結合資訊傳遞演算法之時空碼多天線偵測

時空碼正交分頻多工 (Space Time Block Coded Orthogonal frequency Division Multiplexing STBC-OFDM) 系統被證實能夠獲得更多通到分級增益 (Diversity Gain) ，時空碼正交分頻多工系統通常假設在相對穩定通道環境下執行，但是當通道為快速衰退 (Fast Fading) 條件下，假設也同時無法成立，此時，不同天線之間的干擾 (Co-channel Interference CCI) 以及載子上訊號互相的影響 (Inter Carrier Interference ICI) 會造成效能嚴重的降低。因此學者們提出許多針對降低載子間互相影響的方法，然而，效能依然無法達到需求，近年來提出一種預先處理的方式使得載子自我消除彼此的影響 (ICI Self Cancellation) ，此種方式確實消除大部份干擾，可惜此種技術必付出須降低傳輸速率以及頻寬的代價。在此篇論文中，我們提出一套適用於時空碼正交分頻多工系統的資訊傳遞演算法 (Message Passing Algorithm MPA) ，透過修改與創新，此種方法可以交互消除不同天線與載子訊號之間的干擾以及影響。演算法中將通道模型視為因子圖 (Factor graph)，在少量內外部反覆運算下，透過資訊傳遞演算法將訊息收斂，而外部則透過鄰近載子干擾消除機制 (Neighboring ICI Cancellation) 在既有資訊下消除干擾，我們還提出交互式通道架構 (Interleaving Channel Structure) 使得天線之間的影響可以使得一些訊號被偵測前提早消除干擾，更重要的是，我們發展一控制機制 (SR-controller) 可以在反覆運算中略過沒有必要的運算，如此一來，我們的演算法可以在不浪費任何傳輸速率或頻寬下明顯提升效能，模擬結果證實演算法的低複雜度以及突出之效能。

關鍵字

時空碼；多天線收發；正交分頻多工；資訊傳遞演算法

並列摘要

It has been shown that space-time block coded orthogonal frequency-division multiplexing (STBC-OFDM) system is capable to achieve full diversity in MIMO detection. The STBC-OFDM system assumes a quasi-static block fading channel over the codeword. When the channel is fast fading, the assumption is no longer valid. The co-channel interference (CCI) and inter-carrier interference (ICI) in fast fading channel introduce severe performance degradation. Several ICI cancellation methods have been proposed. However, performances are still unsatisfactory even with considerable computation complexity. Recently, ICI selfcancellation methods are proposed. Although these methods can mitigate ICI efficiently, the techniques of ICI self-cancellation need to decrease the transmission rate or the bandwidth efficiency by 50 percents. In this work, we propose an interleaved message passing algorithm (MPA) with ICI cancellation for MIMO detection to achieve the CCI problem and reduce ICI jointly. The MIMO channel model is represented as a factor graph, and the co-channel MPA (CC-MPA) converges co-channel information with few inner iterations. An neighboring ICI cancellation (NIC) uses the prior information to reduce neighboring ICI effect with outer iteration. Interleaving channel structure can make CC-MPA obtain the received signal without ICI earlier. Moreover, we develope a SR-controller to skip unnecessary computations. The proposed scheme does not decrease any transmission rate or reduce the bandwidth efficiency. Significant BER improvement is achieved through few iterations. The simulation results show that the proposed scheme achieves near maximum likelihood sequence decoder error performance with low complexity for STBC-OFDM in fast fading channels.

並列關鍵字

space time block code ； MIMO ； OFDM ； message passing algorithm

參考文獻

[10] S. W. Kang, K. H. Kim, J. S. Song, and K. H. Chang, “Perfomance degradation of a

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快速衰退通道下結合資訊傳遞演算法之時空碼多天線偵測

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