多天線正交分頻多工系統在通道的偵測上比單天線的系統要來得複雜，這是由於利用多根天線傳送資料時，接收端收到的訊號為所有傳送天線送出去訊號之累加，因此，知道收到的訊號也是無法輕易估測出通道響應，倘若接收訊號還遭遇到多路徑延遲所帶來的符號間干擾以及載波間干擾的話，一般的通道估測演算法就更難利用受到干擾的訊號估測出準確的通道響應。在此篇論文中，我們將使用期望值最大化演算法的疊代計算能力，把多重的訊號各自分開後再來估測通道，並且再將演算法加以修改，使其得以處理遭受到符號間以及載波間干擾的訊號，進而估測出準確的通道響應以提升整體系統效能。

Channel estimation for MIMO OFDM systems will be more complicated than that for SISO OFDM systems. The reason is that the received signal at the received end is the sum of all transmitted signals from all transmitted antennas. Thus, it is not easy to estimate channel response by received signals. Furthermore, if the signals transmitted in the presence of ISI and ICI channel, channel estimation will be more complicated. Therefore, ISI and ICI will seriously affect the system performance. In this thesis, we consider the ISI and ICI cancellation in our MIMO-OFDM system and proposed a channel estimation scheme that can estimate correct channel response by training symbol, even if it’s influenced by ISI and ICI.

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