Multiple antenna transmission with channel state information: a low-rate feedback approach

This paper presents a novel multiple antenna transmission scheme that depends on channel state information. The proposed approach uses low-rate feedback to adaptively estimate the downlink fading channel at the base-station. The optimal transmission scheme given channel state information can in turn be determined from these channel estimates. It is shown that the channel estimation requires selective feedback of the adaptive filter prediction errors, that can be computed at the mobile by receiving a beamformed pilot signal. To this end, a randomized channel inversion pilot beamforming scheme is developed that makes possible this feedback of prediction errors possible. Further, this method is shown to be relatively insensitive to feedback quantization effects for a given average feedback rate. Simulation results indicate that the feedback scheme provides significant closed-loop beamforming gains with low bit rate feedback even for large number of transmit antennas.