On the Performance of MIMO-OFDM Beamforming Systems with Feedback Delay

Transmit beamforming and receive combining in multiple input and multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems are an efficient way to combat fading in frequency-selective channel. In the absence of channel state information (CSI) at the transmitter, the receiver computes the optimal beamforming vectors for all subcarriers according to the known CSI and sends their information back to the transmitter through a feedback channel. However, in practical situation, the transmitter may acquire outdated information about the beamforming vectors when there is a delay in the feedback channel. In this contribution, we use the predicted channel to calculate the optimal beamforming vector at the receiver and send it in advance. In this way, the impact of feedback delay to the system can be cancelled out. Simulation results show that the proposed scheme with the feedback delay performs a little degradation than with the perfect feedback