A Codebook Based Precoding Scheme for 3GPP TDD Systems

In time-division duplex (TDD) system, precoding matrix for downlink transmission can be obtained from estimation of uplink pilots by using reciprocity. However, if the channel is time-varying, the channel difference would cause codeword mismatch between transmitter and receiver, which leads to performance degradation. In this paper, a codebook based precoding scheme is proposed for TDD systems to decrease the probability of codeword mismatch between both sides. Moreover, a linear interpolation method is used to estimate the uplink channel at the receiver, which would reduce the channel difference caused by time delay. Simulations show that the proposed scheme could significantly improve the link performance compared to the existing methods.