新式多輸入多輸出信號偵測用複數球面解碼器之設計與實作

下世代無線區域網路將提供越來越多樣化的服務，包括線上收看各種視訊影片、高畫質電視(High Definition TV, HDTV)、網路互動式遊戲等，因此對於傳輸速度還有品質的要求越來越高，再加上頻寬使用的限制，讓我們不得不尋找更有效使用有限頻寬提高傳輸速度以及品質的方法。繼正交分頻多工(OFDM)被廣泛使用在各通訊系統，並且成為各種規格採用的核心技術後，多輸入多輸出也因為可以有效提高頻帶使用效能漸漸成為一個被大量採用的技術。為了進一步提高多輸入多輸出技術的優點，我們需要增加傳輸與接收天線數目，但也隨之而來多輸入多輸出信號解碼的困難。球面演算法(Sphere Algorithm)原為解決柵欄最短向量(shortest vector in lattice)而被提出，後來被採用於通訊系統中處理多輸入多輸出信號最大相似等化(Maximum Likelihood Equalization)的問題，在可接受的複雜度下可以達到最大相似的錯誤率表現。本論文研讀了球面解碼器的相關文獻，並且實現了一新式複數球面解碼器，採用深度優先(depth first)的最近點優先(closest point first)搜尋順序，直接操作於複數信號系統，並且提出表列舉(List Enumeration)演算法解決複數球面解碼器最近點優先搜尋的列舉困難，包括統一表(Unified List)與個別表(Individual List)兩種方式實現，進一步提出兩種可以配合使用的演算法降低計算量，控制返回階層(Backward-Layer Controlled)演算法與降低維度(Diminished Dimensionality)演算法。最後以平行正反向搜尋(Parallel Forward/Backward Search)還有單計算單元(Single Calculation Unit)硬體架構實作此演算法，提供傳輸率(throughput)與硬體面積和功率的交換(tradeoff)，而且本論文的硬體架構可以支援許多天線組合還有不同星座圖的系統。軟體模擬結果還有硬體實作數據都顯現本論文提出之演算法與硬體架構優於目前文獻中提出的方法。

關鍵字

多輸入多輸出；球面解碼；表列舉；最大相似；返回階層控制

並列摘要

More and more services are provided in the next generation wireless communicaiton systems, including on-line videos, high definition TV (HDTV), interactive games and so on. The demand for throughput and QoS is getting higher. However, the bandwidth is limited. OFDM is widely adopted in many communication systems and has become a main modulation technique of many standards. MIMO will be the next widely accepted technique because of its provision for diversity and/or spectrum efficiency. To apply the MIMO techniques, the number of transmitting and receiving antennas needs be more than one. Among spatial multiplexing MIMO detection, sphere decoding algorithm is the first that was proposed to do maximum-likelihood equalization’detection with acceptable complexity. In the thesis, sphere decoder related literatures are surveyed and a new complex-plane sphere decoder is designed and implemented. Depth-first search with closest point first order is introduced directly on complex-valued signals. List-Enumeration algorithm is proposed to overcome the problem of enumeration in complex-plane sphere decoder. The list can be implemented by either an unified list and several individual lists. In addition, backward-Layer controlled algorithm and diminished dimensionality algorithm are proposed to further reduce the hardware complexity. Two architectures, parallel forward/backward search and single calculation unit, are proposed to implement the new algorithm. The tradeoffs of these two versions are between area, power, and throughput. The hardware can support different constellations and numbers of antennas. Simulation and implementation results indicate the proposed algorithm and architecture outperform other solutions and form a solid foundation for future wireless communication systems that adopt MIMO processing.

並列關鍵字

MIMO ； sphere decoding ； list enumeration ； maximum likelihood ； backward-layer controlled

參考文獻

[5] L. C. Wang and W. C. Liu, “Performance of Pulse Position Modulated Signals over the Ultra-Wideband Channel with Multiple Transmit and Receive Antennas,” in Proc. IEEE VTC 2004 , vol. 2, Sep. 2004. pp. 26-29

[6] J. P. Lien, “Design of a MIMO OFDM Baseband Transceiver for Cognitive Radio System,” MS Thesis, NTU, 2005.

[8] G. J. Foschini and M. J. Gans, ”On the limits of Wireless Communication in a Fading Environment When Using Multiple Antennas,” in Proc. Wireless Pers. Commun, pp.315-335, Mar. 1998.

[9] A. Paulraj, R. Nabar and D. Core, Introduction to Space-Time Wireless Communications. Cambridge University Press, 2003.

[10] B. Vucetic and J. Yuan, Space–Time Coding. New York: Wiley, 2003.

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新式多輸入多輸出信號偵測用複數球面解碼器之設計與實作

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