Enhanced CSI feedback and update for downlink CoMP Joint Transmission

Joint Transmission (JT), through which inter-cell interference could be utilized to enhance the desired signal, is regarded as a promising coordinated multi-point (CoMP) transmission scheme to improve the cell-edge user performance. To achieve coherent CoMP IT, besides per-point channel state information (CSI), additional channel information is necessary such as the inter-point phase, aggregated channel quality indicator (CQI), and aggregated precoding matrix indicator (PMI). Due to the feedback overhead, not all of these types of information can be obtained. In this paper, under the assumption that the inter-point phase information is allowed for additional feedback, we propose a new inter-point phase selection method and a new CQI update method that jointly consider the JT combining gains and CQI update accuracy. Based on the system level simulation evaluation, the proposed methods achieve better cell-edge user throughput than JT scheme with conventional CSI feedback and CQI update.