近年來，合作式通訊已受到許多關注。在合作式通訊上，它的多樣性能使多用戶環境中裝備一根天線的移動節點去分享它們的天線來構成一個虛擬的多天線的傳送器並達成空間上的多樣性。
在合作式通訊中，由於本身即為非同步系統，所以在傳輸時要達到同步是很困難的，而且隨著使用者數目的增加，要達到完美的通道估測也是一個龐大的工程，因此在過去的paper中都是假設通道是已知。基於上述的想法我們在此使用DSTNC-TDMA[1]的方法去克服不完美的同步以及複雜的通道估測。在TDMA系統下，每一個使用者在第二階段將自己與接收到其他使用者的訊號做線性組合再給予傳送。但在DSTNC-TDMA下，接收端會遇上解碼複雜度過高及通道變化速度增加造成的錯誤率上升的問題，因此我們探討如何利用差分解碼和訊號重置來解決。

In recent years, cooperative communications has received much attention. The diversity in the cooperative communications enables mobiles equipped with a single antenna to share their antennas in a multi-user environment, and with the virtual multiple-antenna, transmitter spatial diversity is provided.
In cooperative communications, simultaneous transmissions from two or more nodes are challenging due to its asynchronous nature. In addition, channel estimation is a costly task, especially when the number of cooperative users is large. Most of the papers assume the channel state information is known, which is not practical in reality. In this thesis, we study a differential space-time network coding (DSTNC) system with time division multiple access (TDMA) [1] to overcome the problems of imperfect synchronization and channel estimation. In this system, each user in the second phase of cooperative communication linearly combines his signal and the received signals from other users, and then the combined signal is transmitted to the destination. Take consideration the high-complexity maximum-likelihood (ML) decoding in receiver and the channel variation; we consider the scheme that uses direct differential decoding and symbol resetting.

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