Enhanced Csi Acquisition Scheme For Nr Tdd Systems With Partial Channel Reciprocity

In 5G new radio (NR), time division duplex (TDD) is more preferred to massive multiple input multiple output (mMIMO) systems. Perfect channel state information (CSI) per user in TDD systems can greatly extract the huge potential spatial multiplex gain of mMIMO. For reducing terminal's cost while keeping downlink performance, asymmetric antenna configuration are used in terminal side. It breaks the channel reciprocity and brings more challenges on CSI acquisition in TDD systems. In this paper, one enhanced CSI acquisition scheme is proposed. According to user side antenna configuration, whole channel can be partitioned into two sub-channel, the first one with full channel reciprocity, and the second one has no channel reciprocity. For sub-channel with ideal reciprocity, traditional approaches are used to help TRP getting this part CSI. For sub-channel with no reciprocity, user specific adaptive codebook is developed based on the first sub-channel information, and new codebook is used for this part sub-channel quantization and recovering at UE side and TRP side, respectively. Exploiting partial channel reciprocity and adoptive codebook technologies jointly, accurate CSI can be acquired at TRP. Numerical simulation results show that the new designed solution can achieve near upper bound performance in NR TDD mMIMO systems with low uplink overhead.