Sum rate analysis of coordinated beamforming in multi-cell downlink with imperfect CSI

In this paper, we analyze the ergodic sum rate in a multiuser multi-cell downlink. Coordinated beamforming is employed to mitigate the interference, including intra-cell and inter-cell interference. However, due to the limited capacity of the backhaul link, only partial channel state information (CSI) is obtained at the base stations (BSs), resulting in residual interference even with coordinated beamforming. By quantifying the impact of imperfect CSI, we derive closed-form ergodic sum rate results for a multiuser multi-cell downlink in terms of i. CSI accuracy, ii. transmit signal-to-noise ratio (SNR) and iii. channel condition. Furthermore, through asymptotic analysis of the performance loss induced by imperfect CSI, we obtain some clear insights on the performance. Finally, our theoretical claims are validated through extensive simulations.