Impact of Channel Asymmetry on Base Station Cooperative Transmission with Limited Feedback

To exploit the full benefit of base station (BS) cooperative transmission, also known as coordinated multi-point (CoMP) transmission, large amount of feedback is required to gather the channel information. In this paper, we analyze the impact of channel asymmetry, which is inherent in CoMP systems, on downlink coherent BS cooperative transmission using zero-forcing beamforming with limited feedback. Per-cell quantization of multicell channels is considered, which quantizes the local channel and cross channels separately and is more feasible in practice. We analyze the per-user rate of limited feedback multi-user CoMP systems, and provide approximate expressions for both the inter-cell and intra-cell residual multi-user interference introduced by the quantization errors. When the desired user is at the cell center, the former is weak, but the latter is strong and depends not only on the signal to noise ratio but also on the location of its co-scheduled users. Simulation results validate our theoretical analysis.