將多輸入多輸出方法與正交分頻多工技術結合，以提升系統在應付多路徑與行通通道的效能，已經廣泛地被使用在無線通訊系統上。例如，在有限導引訊號的無線網路應用裡，為了應付時變通道所造成之通道效應，考慮通道追蹤已成為重要之研究課題。本篇論文在兩根傳送天線及兩根接收天線的時空碼多輸入多輸出正交分頻多工系統下，研究使用常數模演算法與決策迴授方法作自動切換的通道追蹤演算法，並應用在考慮相鄰兩符元間通道變化的子載波干擾消除法中。從模擬結果中顯示，在時空碼多輸入多輸出系統下所提出的常數模演算法與決策迴授法自動切換方式可得到較僅使用決策迴授法或常數模演算法更佳的性能。 The combination of multiple input and multiple output (MIMO) technology and orthogonal frequency division multiplexing (OFDM) to combat multipath and mobile channels is widely used in wireless communications. For example, in wireless network applications with limited number of pilots, channel tracking is an important scheme to deal with time-varying channels. Here, the Alamouti space-time block code is applied to a two-by-two MIMO OFDM system in which we explore a new channel tracking algorithm that can alternatively operate between the constant modulus algorithm (CMA) and the decision feedback algorithm based on the proposed mechanism. The proposed algorithm is also further verified in an intercarrier interference cancellation algorithm that can solve the time-varying channel with changed status even between two consecutive OFDM symbols. Simulation results show that the proposed algorithm can achieve better performance than the method employing only the CMA method or the decision feedback method.
