Multi-Antenna Downlink Spatial Division Multiplexing with Opportunistic Feedback

In this paper, a new opportunistic feedback and user selection protocol is proposed for the multiple antenna downlink. The proposed scheme uses the structure of zero-forcing dirty paper coding (DPC) at the transmitter and selects users using a contention-based feedback channel. The user selection procedure is divided into stages and within each stage, a user is selected for one spatial channel (defined by the zero-forcing dirty paper coding strategy). The user feedback is controlled by a feedback probability and a feedback threshold. This method of feedback significantly reduces the resources used for feedback compared to dedicating feedback resources for each user. We optimize an approximation to the sum rate expression with respect to these parameters and illustrate the sum rate performance by simulations. The simulation shows that we can achieve good sum rate performance despite the reduction in feedback resources.