DSTM(differential space-time modulation)是一種用於多天線的非同調通道編碼，它使用正方形矩陣去編碼資料位元，再以矩陣乘法完成差分編碼，使得差分編碼後的矩陣為正方形，因此每個區塊所需的時間長度必須與傳送天線相同。近期，一種稱作非正方形DSTM (nonsquare differential space-time coding)的新作法被提出，與傳統的正方形DSTM相比，它在每個傳輸區塊(block)使用的時間長度更少。NDSTC使用額外的處理程序，它是正方形到非正方形的映射，因此生成的矩陣是非正方形，也意味著更少的時間長度。
在NDSTC中，原來的資料矩陣是針對原始的正方形矩陣所設計，並不是針對非正方形矩陣，然而，這樣的映射會破壞原本正方形矩陣的特性，例如時間長度減少的關係導致多樣性(diversity)以及編碼增益(coding gain)的減少。在本篇論文中，我們提出了一個新的不使用投射的NDSTC方案，在這個新的方案中，差分編碼直接應用在非正方形的傳輸碼字上，我們考慮兩種接收器。第一種是遞迴決策回饋差分檢測(recursive decision feedback differential detection)，而這種接收器是適合在變化緩慢的通道，另一種是能夠比DSTM有更少的同調時間(coherence time)的接收器。最後我們從模擬結果中證實此方案有更好的錯誤率。

DSTM is a noncoherent channel coding for multiple antenna system, DSTM utilizes square matrices to encode data bits and then uses matrix multiplication to perform differential encoding. The resulting matrix after differential encoding is square, so the number of time slots for each transmission block is the same as the number of transmit antennas, NDSTC uses additional process which is square-to-nonsquare projection, so the resulting matrix is nonsquare which means less time slots.
In NDSTC, the data matrix is designed for the original square DSTM, not for the nonsquare transmission matrix. However, the projection in NDSTC destroies the properties of square DSTM. For example, the diversity and coding gains achieved by square DSTM are decreased due to reduced time units for transmission.In this thesis, we propose a new NDSTC scheme that does not use the square-to-nonsquare projection. In the proposed scheme, differential encoding is directly applied to the nonsqaure transmitted codewords. Two types of receivers are considered. One is the recursive decision feedback differential detection which is suitable for slowly-varying channels, and the other is the receiver requiring less coherence time than DSTM. Finally, we confirm from the simulation results that this scheme has a better error rate.

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