“…It is worth noting that beamforming design or AP clustering in most of these references, e.g., [3], [5], [6], [9], [16], [17], optimistically assumes the availability of perfect CSI, which leads to system performance degradation in practice. To this end, it is highly desired to take the CSI estimation errors into account, and there have been some studies on robust beamforming design, especially for multicellular networks, e.g., in [18], [19], [20].…”