Time-domain transmit beamforming for MIMO-OFDM systems with finite rate feedback

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 single-data stream, 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 two different criteria, namely, maximum average mutual information (AMI) per sub-carrier and minimum average uncoded bit error rate (BER). If the C-BFF length L_g is equal to the number of sub-carriers N_c,closed-form solutions to both optimization problems exist. For the practically relevant case L_g < N_c we present numerical methods for calculation of the optimum C-BFFs for both criteria. Using a global vector quantization (GVQ) approach the C-BFFs are quantized for practical finite-rate feedback channels. Simulation results for typical IEEE 802.11 n channels confirm the excellent performance of the proposed scheme and show that TD-BF has a more favorable performance/feedback rate trade-off than previously proposed frequency-domain BF (FD-BF) schemes.