Beamforming design for a cooperative relay system with limited feedback

In this paper, we focus on a half-duplex downlink cellular system with relay cooperation. We consider the beam-forming design problem with a limited amount of feedback for channel state information (CSI), which is only available at the receiver side. Based on this structure, we calculate the sum-rate lower bound when zero forcing (ZF) or eigen-beamforming is implemented at the macro base station and relay station. With the lower bound, we optimize the numbers of feedback bits for quantizing the desired and interfering channels and propose an adaptive beamforming strategy with limited feedback which selects a suitable beamforming scheme from ZF or eigen-beamforming based on the received interference and noise power level of the users. Simulation result shows that the bit partitioning algorithm outperforms the equal bit distribution scheme especially when the signal to noise ratio (SNR) is large. In addition, our proposed adaptive beamforming strategy outperforms existing schemes in different interference scenarios.