Higher Throughput and Less Feedback: Multi-Antenna Broadcast Channels with Partial Users and Limited Bits Feedback

Multi-antenna downlink system with much more users than transmit antennas is considered. With both quantized channel direction and unquantized channel magnitude fed back from all users, this system becomes interference limited with large number of users due to the quantized error of channel direction. We provide a novel method that only partial users feed back the channel information, which can reduce the quantized error of channel direction without increasing the feedback bits of each user. This scheme achieves a higher throughput than that of the system with quantized channel direction and unquantized channel magnitude from all users. Meanwhile, feedback overhead is decreased significantly because of only partial user feedback. Moreover, instead of becoming interference limited, the proposed scheme of partial user feedback maintains the same multiuser diversity as that of the system with perfect CSIT, even with a large number of users.