Downlink Multiple Antenna Transmitter Optimization on Spatially and Temporally Correlated Channels with Delayed Channel State Information

In this paper we present multiple antenna transmitter optimization schemes that are based on linear transformations and transmit power optimization, while keeping the average transmit power conserved. We consider the downlink of a wireless system with multiple transmit antennas at the base station and a number of mobile terminals (i.e., users) each with a single receive antenna. We consider the maximum achievable sum data rates in the case of (1) zero-forcing spatial pre-filter and (2) modified zero-forcing spatial pre-filter. Using a multiple input single output (MISO) channel model with temporal and spatial correlations, we study the effect of delayed channel state information (CSI) on these schemes. It is seen that as the CSI delay increases, spatially uncorrelated channels perform worse than spatially correlated channels, which is in contrast to the case of zero delay CSI.