Two⁃Codebook⁃Based Cooperative Precoding for TDD⁃CoMP in 5G Ultra⁃Dense Networks

[Abstract] In ultra⁃dense networks (UDN), the local precoding scheme for time⁃division duplex coordinated multiple point transmission (TDD⁃CoMP) can have a good performance with no feedback by using reciprocity between uplink and downlink. However, if channel is time⁃varying, the channel difference would cause codeword mismatch between transmitter and receiver, which leads to performance degradation. In this paper, a linear interpolation method is proposed for TDD⁃CoMP system to estimate the uplink channel at the receiver, which would reduce the channel difference caused by time delay and decrease the probability of codeword mismatch between both sides. Moreover, to mitigate severe inter⁃cell interference and increase the coverage and throughput of cell⁃edge users in UDN, a two⁃codebook scheme is used to strengthen cooperation between base stations (BSs), which can outperform the global precoding scheme with less overhead. Simulations show that the proposed scheme can significantly improve the link performance compared to the global precoding scheme.

[Keywords] ultra⁃dense networks; coordinated multiple point transmission; time⁃division duplex; two codebooks; cooperative precoding