多輸入多輸出廣播通道下回饋策略之影響

Abstract

在下傳通道時，使用多根傳輸天線，能夠提升系統的傳輸速率(多工增益)，然而不太實際的是，傳送端必須知道正確無誤的通道資訊。我們假設系統的每一個接收端能夠獲得正確無誤的通道資訊，而傳送端只藉由接收端的回饋獲得部分通道資訊。我們提出兩種回饋的演算法，能夠在有限制的回饋之下有效率的去追蹤通道資訊，一種是利用碼書去追蹤通道資訊，另一種是用可變動步幅大小的符號演算法來追蹤。在多輸入多輸出廣播通道下，我們考慮迫零方法的通道逆處理系統速率。在相同的回饋速率之下，我們提出的兩種追蹤演算法利用通道在時間上的相關性是較為優秀的。特別是較為快速與穩定的可變動步幅大小符號演算法。模擬結果會與其他演算法做比較。

Multiple transmit antennas in a downlink channel can provide the sum rate advantage (multiplexing gain). The perfect channel information is often required at the transmitter, however it is impractical. We consider a system in which each receiver knows the perfect channel information and transmitter only has a partial channel information conveyed by the receivers. Two feedback algorithms are proposed to track the channel information efficiently under limited feedback. The one is tracking channel by codebook and the other is tracking channel by sign algorithm with variable step sizes. The sum-rate of zero-forcing channel inversion on a MIMO broadcast channels is considered. Under the same feedback rate, the two proposed tracking algorithm exploiting the channel correlation in time are superior. Especially, the feedback by sign algorithm with variable step size is faster and more stable. The simulation results are compared with other algorithms.