Improved Local Precoder Design for JT-CoMP with Periodical Backhaul CSI Exchange

Joint transmission (JT) in coordinated multipoint (CoMP) systems can be used to significantly improve the data rate of the cell-edge users (UEs) via cooperation of base stations (BSs). In a frequency division duplex system, the UEs need to feedback the channel state information (CSI) to its strongest BS. In a distributed JT-CoMP setup, the exchanging of CSI can occur periodically over the backhaul. Any feedback of CSI would need to trigger immediate exchange of CSI among the BSs to preserve the gains of JT-CoMP. We propose to utilize the newly available local CSI to locally improve the precoding performance. This is performed in-between the triggered periodic CSI exchange between BSs. We characterize the performance between exchanging and not exchanging the CSI for local precoder design (LPD) in terms of the average sum rate with UE mobility and different feedback intervals. We solve the decentralized LPD for weighted sum rate maximization with partial new CSI, and show that significant part of the JT-CoMP gains can still be preserved.