具中繼通道與混合自動重傳機制及可適性編碼調變機制之無線通訊系統吞吐量最大化之設計

Abstract

近年來中繼通道被廣泛的應用在目前較新的無線通訊系統上。在具有中繼通道的無線通訊系統中，如何有效地應用鏈路調適(link adaptation)成為相當熱門的研究主題。在傳統的無線通訊系統中，最有名的鏈路調適機制是可適性編碼調變機制(adaptive modulation and coding)。在實際的系統設計上，可適性編碼調變機制通常使用固定的閾值(thresholds)來選擇不同的調變與編碼機制(modulation and coding schemes)，但是使用固定的閾值來選擇不同的調變與編碼機制往往因為通道品質隨著時間改變而挑選到不恰當的調變與編碼進而使得傳輸效能大幅降低。儘管我們可以利用混和式自動重傳機制(hybrid automatic repeat request)來減輕此影響並增進傳輸效能，但是引進自動重傳機制的同時也帶來重傳延遲的問題。在具有中繼通道的無線通訊系統中，除了原本的來源節點與目的地節點的鏈路之外(S-D)同時也會有來源節點與中繼節點的鏈路(S-R)以及中繼節點與目的地節點的鏈路(R-D)；因此我們必須同時考慮這三條鏈路的通道狀況使得整體系統的效能達到最佳化而非僅考慮來源節點與目的地節點的通道狀況。我們提出一個有效並且容易實行的演算法，使得在同時考慮可適性編碼調變機制與混和式自動重傳機制之下能夠讓具有中繼通道的無線通訊系統吞吐量達到最大化。為了得到更實際的結果，我們在WCDMA 系統以及4G LTE-Advance 系統環境下測試我們的設計。

In recent years, relay topics are widely considered in wireless communication standards. In the relay issues, the link adaptation in relay channel is a hot study topic. In traditional wireless communication systems, the most famous link adaptation method is the mechanisms of adaptive modulation and coding (AMC). In practical system design, the AMC mechanism is usually implemented with fixed switching thresholds for the modulation and coding schemes (MCS), and suffers performance degradation. Although the hybrid automatic repeat request (HARQ) is designed to offer robust transmissions and hence alleviates the performance degradation due to the use of unfavorable MCS, it also introduces the problem of retransmission latency. However, when the system operates in relay channel, in additional to the direct source destination (S-D) link, there are also source-relay (S-R) and relay-destination (R-D) links needed to be considered to optimize the whole system performance. To improve the performance of the AMC systems in relay channel, a novel algorithm considering both AMC and HARQ characteristics will be developed in this study to maximize the system throughput.