Robust Multimode Selection in the Downlink Multiuser MIMO Channels with Delayed CSIT

TDD multiuser downlink MIMO channels with delayed channel state information at the transmitter (CSIT) are considered. Block diagonalization is applied at the base station (BS). In order to cope with the inter-user interference caused by the delayed CSIT, we develop a novel capacity estimation method at first and then propose robust delayed CSIT aware multimode selection schemes based on the estimation. The robust schemes can choose the mode with appropriate number of data streams and corresponding user and receive antenna set to compromise the multiuser spatial multiplexing gain and the rate loss caused by the inter-user interference. The proposed schemes are applicable to the heterogeneous case in which the moving speed of each user is different. Through simulation, the proposed schemes outperform the previous naive schemes and are promising in the practical system.