Multi-cell pseudo-random beamforming: Opportunistic feedback and beam selection

In this paper, we propose a novel pseudo-random beamforming (BF) technique in multi-cell downlink networks consisting of multiple base stations (BSs) and one BS coordinator. In the proposed technique, each BS first generates M BF matrices with a pseudo-random manner and each mobile station (MS) opportunistically feeds back the received signal-to-interference-and-noise (SINR) ratio for each random beam to its home-cell BS. Then, each BS selects MSs for each beam based on the feedback information, and it also feeds back the achievable sum-rate for M BF matrices to a BS coordinator via wired backhaul links. Finally, the BS coordinator determines the optimal BF matrix that maximizes the sum-rate over the network, and sends the index of the optimal BF matrix to BSs. Each BS sends data to MSs by using the optimal BF matrix among M BF matrices. Main results indicate that there exists a trade-off between the feedback overhead and the achievable sum-rate, but the sum-rate of the proposed technique with opportunistic feedback approaches to that with full feedback as the number of MSs in each cell increases.