Approaching downlink capacity of multiplexing relay channels with imperfect channel information

This paper studies the multi-antenna relay downlink channel with quantized channel information feedback from both two-hop links. By characterizing the system capacity loss due to channel quantization, we propose a strategy of controlling feedback sizes to help the system approach the channel capacity with respect to full channel information case within an arbitrary predetermined capacity loss. It reveals that the feedback load B1 from the relay station (RS) to the base station (BS) needs to scale in proportion to both the transmit power at the BS and RS while the feedback size B2 from each user to the RS only needs to scale linearly with the transmit power at the RS. Simulation results illustrate the effectiveness of the proposed design strategy.