在現有的無線通訊系統中，使用中繼站 (Relay) 以增加 傳輸的效能和訊號傳輸範圍已是未來的趨勢，在現有的中繼站傳輸策略中，較常見的有放大後傳輸 (Amplify-and-Forward,AF)，即在中繼站將接收訊號放大後傳輸，與解調後傳輸 (Decode-and-Forward,DF)，即在中繼站將接收訊號做解調之後再放大傳輸。但兩種策略有各自的優缺點，AF 對通道增益的影響較敏感，而 DF 需要在中繼站接收到可靠的訊號。本篇提出以最大概似比 (MaximumLikelihood,ML) 為偵測訊號的 MIMO 模型，在兩種傳輸策略中做決策，選擇要用何種方式傳輸，分析 BPSK、QPSK、16QAM 三種調變方式的錯誤率後，利用切爾諾夫邊界 (Chernoff bound) 取上界算出平均錯誤率 (Average Error Probability)，以簡易的判斷式做決策。一方面降低回傳通道資訊 (Channel State Information,CSI) 的即時性，一方面提出將既有傳輸方式最佳化的策略。 Using relays to improve the performance and extend cover- age area is the future trend in modern wireless transmission systems.Amplify-and-Forward (AF) and Decode-and-Forward (DF) are the most popular strategies discussed for relay transmission. AF and DF have their specific disadvantages, e.g. AF is sensitive to channel gains while DF requires reliable received signals. This thesis proposes to make decision between two transmission strategies for relay based on the ML-based MIMO transmission model. To find an intelligent strategy, we analyze three modulation types, including BPSK, QPSK and 16-QAM, and make decision rely on the average error probability obtained by the Chernoff bound. The proposed decision strategy does not need the Channel State Information(CSI) in time for reaching optimum performance.
