Progressive channel state information for advanced multi-user MIMO in next generation cellular systems

We propose an enhanced precision channel state acquisition scheme for downlink Multi-User MIMO (MU-MIMO) transmission with a large number of transmit antennas at the base station. The proposed scheme is an attempt to harvest the Channel State Information (CSI) at the transmitter by incrementally improving the precision of the channel knowledge. We show how, in an LTE-Advanced system, CSI harvesting mechanism followed by the conventional Zero-Forcing Beam-Forming (ZFBF) results in improved MU-MIMO performance, relative to the current method for acquiring CSI at the transmitter. The proposed progressive CSI harvesting scheme is also shown to yield significant saving in terms of feedback overhead. The implications of the larger MIMO systems and higher MU-MIMO ranks, and sensitivity to higher mobility are also discussed.