Achievability of the channel reciprocity and its benefit in TDD system

For the shared frequency band between uplink and downlink, the channel reciprocity has been regarded as the most important advantage of a TDD system, in which the eNB can obtain the downlink channel state information (CSI) based on the uplink channel estimation, and thus perform advanced multi-antenna technologies to enhance the downlink transmission in TD-LTE/TD-LTE-Advanced systems. In this paper, the achievability of the TDD channel reciprocity from the product implementation point of view is analyzed and some measurement results of the hardware response difference before and after the antenna calibration have been shown to verify the achievability. Based on the channel reciprocity of TDD system, the performance of Single-User and Multiple-User Beamforming (SU/MU-BF) and Coordinated Multipoint Transmission (CoMP) have been enhanced significantly.