Time-domain transmit beamforming for MIMO-OFDM systems

Transmit beamforming (BF) and receive combining are simple and popular methods for performance enhancement in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. In this paper, we propose a novel time-domain BF (TD-BF) scheme for MIMO-OFDM systems which uses cyclic BF filters (C-BFFs). Assuming perfect channel state information (CSI) at the transmitter, the C-BFFs are optimized for maximization of the average mutual information per sub-carrier. Using a global vector quantization approach the C-BFFs are quantized for practical finite-rate feedback channels. Simulation and numerical results for typical IEEE 802.11n channels confirm the excellent performance of the proposed scheme and show that TD-BF has a more favorable performance/feed back rate trade-off than previously proposed frequency-domain BF (FD-BF) schemes.