有限回授預編碼技術結合MIMO-OFDM系統，當傳送一個資料序列時，可以提高系統的分集效能以及降低系統錯誤率(BER)，若傳送多個資料序列時，系統則可以提高頻譜使用效率增加資料傳送速度。在MIMO-OFDM預編碼系統中，碼簿已廣泛的被使用作為有限回授的依據。當通道是具有相關性，我們提出了矩陣旋轉法來設計子載波的預編碼矩陣降低回授資訊量。這個方法計算一適當旋轉角度並將旋轉角度量化回授到傳送端，相較於改良球形內插法與縮減碼簿法，我們所提出的矩陣旋轉法有較低的位元錯誤率，且其通道容量也比較大。The limited feedback precoding scheme for MIMO-OFDM systems is a simple technique to exploit spatial diversity and has the advantage of improving bit error rate (BER). In addition, It also increases spectral efficiency and rises transmission throughput rate for multiple data stream transmission. To implement the precoding scheme, using codebook for the precoding matrix has been adopted in limited feedback MIMO-OFDM precoding systems. We propose a rotation matrix method to reduce feedback information for the precoding matrix in temporally correlated channels. The new method calculates an appropriate rotation angle between two successive precoding matrices at the receiver and only the information about the quantized rotation angle is returned to the transmitter. Compared with the widely used interpolation and codebook reduction methods, the proposed method can achieve a lower BER along with higher channel capacity.
