分散式空時碼為一種合作通訊技術，它藉由多個具備一根天線的中繼點相互合作形成虛擬的陣列天線，以獲取空間多樣性，並獲得更好的系統效能。其中，分散式相差空時調變藉由相差編碼，可以使接收端不需要知道通道係數。
在本論文中，我們研究使用高速率相差空時網路編碼的多訊號源合作通訊，它可以避免不完美同步與複雜的通道估測問題；我們也研究使用高速率分散式相差空時調變的多訊號源合作通訊，並比較它與相差空時網路編碼的錯誤效能。由模擬結果顯示，在不考慮同步問題下，分散式相差空時調變架構皆比使用網路編碼有較好的錯誤效能。另外，我們也將上述非同調架構與同調架構相比，發現分散式非同調架構效能差約3db，而網路編碼非同調架構效能差異較大。

Distributed space-time coding, one kind of cooperative communications, uses multiple relays with single antenna to form virtual antenna arrays. By doing so, it acquires spatial diversity and thus improves the system performance. Among them, distributed differential space-time modulation utilizes differential encoding such that the receiver does not need channel coefficients.
In this thesis, we study high-rate differential space-time network coding for multi-source cooperative communication which overcomes the problems of imperfect synchronization and complicated channel estimation. We also study high-rate distributed differential space-time modulation for multi-source cooperative communications, and compare its error performance with differential space-time network coding. According to the simulation results, distributed differential space-time modulation scheme has better error performance than network coding, irrespective of synchronization issue.
Besides, we also compared the non-coherent and coherent scheme, found that distributed space-time coding is about 3db better than non-coherent scheme. The other hand, the performance gap between the space-time network coding and non-coherent scheme is wide.

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