MIMO-OFDM系統之偵測與解碼-設計與實現

Abstract

傳統上，在MIMO-OFDM系統中V-BLAST及Viterbi解碼器是分開考量的。由於V-BLAST演算法會在Viterbi解碼之前做符元(symbol)決策(decision)，因此高錯誤率便往往導致嚴重錯誤延展(error propagation)問題。在本論文中，我們發展出一個結合傳送器之位元資料流先前排序(stream pre-ordering)、接收器之V-BLAST處理及Viterbi解碼器的系統來將錯誤率最小化。在本方法中，首先接收器會將能使V-BLAST有最大效能(在每個子載波上)的解碼順序回傳給傳送器。傳送器便根據這個順序將位元資料流做先前排序。接收訊號之後，接收器便將接收訊號做反排序的動作再經過V-BLAST處理及Viterbi解碼。模擬結果也証實了此演算法的確能達到較佳的效能。在IEEE 802.11n WLAN系統下，我們也使用了FPGA設計流程實現了MMSE估測器、軟性反對映(soft-bit demapper)及Viterbi解碼器。

Conventionally, the V-BLAST and Viterbi decoding algorithms are considered separately in MIMO-OFDM systems. Since the V-BLAST algorithm makes its own symbol decisions before Viterbi decoding, the performance of the overall system is not satisfactory. If the V-BLAST algorithm can use the decisions from the Viterbi decoder, the performance can be enhanced. In this thesis, we propose a scheme to realize this idea. The distinct feature of the proposed scheme is a pre-ordering technique allowing an optimal combination of V-BLAST processing and Viterbi decoding. Simulations conform that the proposed algorithm significantly outperforms the conventional approach. Using an FPGA design flow, we also implement an IEEE 802.11n back-end receiver including an MMSE estimator, a soft-bit demapper, and a Viterbi decoder.