當傳送端只有一個傳送資料序列時，將有限回授預編碼技術結MIMO-OFDM 系統，可以提高系統的分集效能以降低系統錯誤率，若傳送端有多個傳送資料序列時，將有限回授預編碼技術結合MIMO-OFDM統，則可以提高頻譜使用效率增加資料傳送速度。而要使用預編碼技術則在傳送端需要知道通道狀態資訊，由於我們的系統為MIMO-OFDM統，所以我們必須回傳每個子載波的通道資訊給傳送端使用，對於整個回
授系統來說是極大的負擔，為了降低系統回授的資訊量，我們利用在相鄰OFDM symbol 中相同的頻率的子載波的通道頻域響應的相關性結合改良的球型內插法，從兩種不同的角度切入，化簡回授資訊量。由系統模擬結果可知，本論文提出降低回授資訊量的方法在不犧牲太多的效能的前提下，比起傳統降低回授資訊量的方法可以有效的降低回授資訊量。

The limited feedback Precoding scheme combining with the MIMO-OFDM system is a simple technique to exploit spatial diversity and improve bit error probability for one data stream transmission, or increase spectral efficiency and rise transmission data rate for multiple data stream transmission. However it requires feedback channel state information (CSI) at the transmitter for all subcarriers. We
use a codebook to reduce the feedback requirements, but this way still costs too much data rate due to the CSI feedback. To solve this problem, we propose a new feedback CSI reduction method. we calculate the correlation of channel frequency responses in the adjacent OFDM symbol for the same subcarrier to find the precoding matrix. Besides, the sphere interpolation method is utilized for the precoding matrix at the transmitter. Through the proposed method, we can successfully reduce the CSI feedback information with remaining similar bit error rate performance to the existing method.

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