Multi-user Mimo Downlink Precoding for Time-variant Correlated Channels

Multi-user multiple-input multiple-output (MU-MIMO) systems provide a significantly increased capacity and spectral efficiency by exploiting the benefits of space division multiple access (SDMA). The channel state information (CSI) at the base station (BS) is used to precode the transmit signals and to simplify the processing at the users’ terminals. If perfect CSI is available at the transmitter, the multi-user interference (MUI) can be effectively eliminated at the BS. If the channel varies too fast to obtain short-term CSI, long-term CSI can be used alternatively to improve the system performance. In this paper we propose a new approach to multi-user precoding based on long-term CSI, which can be applied to previously defined precoding techniques originally requiring perfect CSI at the BS. It is shown that a significant performance improvement is achieved by the new approach as compared to a state of the art approach [1] to multi-user precodingwith long-term CSI, especially for the case when a user has a line of sight (LOS) channel.