Study on feedback reduction techniques in MIMO-OFDM beamforming systems

In multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems, the recursive feedback encoding method is proposed to reduce the feedback overhead by using a small-size codebook. However, the recursive feedback encoding method will introduce error propagation in the case where the channel frequency response (CFR) has abrupt changes between adjacent subcarriers. In order to overcome this problem, we propose a periodic recursive feedback encoding method in this paper. Through using a full-size codebook periodically across subcarriers, the error propagation problem can be avoided. Additionally, we propose a modified clustering method to reduce the feedback load. In this method, the receiver informs the transmitter of new optimal precoding matrix only when the current optimal precoding matrix is different from the former, which makes the feedback more efficient. Simulation results demonstrate the effective of our proposed approaches.