Limited Channel Feedback for Coordinated Beamforming under SINR Requirements

We consider bit allocation for channel state information (CSI) feedback in coordinated beamforming (CB) systems. The optimization problem under consideration is to minimize the total transmission power subject to the target signal to interference and noise ratio (SINR) constraints. We obtain a suboptimal solution to the problem that provides closed-form expressions for the total feedback rate and the feedback rates of each user and its channels. The advantage of the proposed scheme over the methods with equally distributed feedback rates among the users and/or channels is demonstrated by computer simulation: the CB system employing the proposed scheme causes less outage with less transmission power.