在本論文中，我們探討具有放大和前送中繼站的合作式通訊系統在快速雷利衰減通道下，使用差動二元相位鍵移調變之效能。當通道增益具有快速變化的特性時，使用差動調變可以使得通道估計的過程變得較為簡單，同時可以免除同調調變中導航信號所需消耗的功率及頻寬負擔。先前關於此主題的研究文獻，假設兩個相鄰符號週期的通道增益是相同的，且各通道間具有相同的都卜勒展延。於此論文中，我們將相鄰通道增益的時間選擇性及不同通道可能具有相異的都卜勒展延加入考慮。基於最大概似準則，我們針對具差動二元相位鍵移調變的合作式通訊系統推導出最佳多樣性組合權重。由於該最佳的組合權重值相依於中繼端到目的地端的通道增益，而使用差動二元相位鍵移調變的系統中確實得知通道狀態資訊是不實際的，因此我們提出了一種次佳多樣性的組合規則，它使用通道增益的二階統計量來取代瞬間通道增益。與並無考慮時間選擇性之多樣性組合規則在基於放大和前送中繼的合作式通訊系統於快速雷利衰減通道下之效能做一比較，電腦模擬的結果顯示出我們所提出的多樣性組合規則具有較優越的性能，尤其是當中繼節點和目的節點有不同的都卜勒展延時。 In this thesis, we consider the amplify and forward relaying cooperative communication system employing differential binary phase shift keying modulation in fast Rayleigh fading channels. When channel gains are fast varying, it is well known that differential modulation can ease the channel estimation process and reduce the power and bandwidth overhead occurred in coherent modulation schemes. Unlike the previous work on this topic which always assumed the channel gains are the same over two adjacent symbol periods, we model the channel time selectivity exactly in our formulation and derive the optimal diversity combining weights for the amplify and forward relaying system based on the maximum likelihood criterion. Since the optimum combining rule depends on the channel gains of the relay to destination links which are usually unavailable in the context of differential modulation, we propose a suboptimal diversity combining rule which replaces the instantaneous channel gains by their second order statistics. Compared with the performance of the diversity combining rule without taking the time selectivity into account, computer simulation results show that the proposed diversity combining rule has superior performance for the amplify and forward relaying system in fast Rayleigh fading channels, especially when the relay and destination nodes have different Doppler spreads.
