Joint time-frequency beamforming for MIMO-OFDM systems

Orthogonal frequency division multiplexing (OFDM) with multiple transmit and multiple receive antennas (MIMO) is one of the most promising technology in broadband wireless communications due to its capability in combating the multi-path fading channels. Frequency domain beamforming is a popular technology that can be used in MIMO-OFDM systems to achieve good performance. However, it induces considerable complexity due to the huge number of FFT (Fast Fourier Transform) blocks required. In contrast, time domain beamforming can be used to significantly reduce the complexity but with a significant performance loss especially when the number of distinct paths in the channel is large. In this paper, we propose a new beamforming technology for MIMO-OFDM systems, where the principle of time domain beamforming and the principle of frequency domain beamforming are simultaneously employed. Using the proposed scheme, we will show that complexity and performance can be effectively traded off. Furthermore, we propose an iterative algorithm to calculate both the frequency domain weighting coefficients and the time domain weighting coefficients. Simulation results show that good performance can be achieved with the iterative weighting coefficients calculation algorithm. © 2005 IEEE