A combined time-frequency domain beamforming method for OFDM systems

To suppress co-channel interferences in OFDM systems two main schemes namely, the pre-FFT and the post-FFT schemes have been proposed. While pre-FFT is a time-domain beamforming method, post-FFT uses beamforming in frequency domain to suppress directional interferences. It is generally believed that the post-FFT scheme is superior in performance than the pre-FFT method. In this study we first compare these two schemes in pilot-assisted OFDM systems under different channel and system conditions. It is shown that each of these methods shows better performance in a different condition. To take advantage of the strategy of each method, a combined time-frequency method is proposed which produces better results than each of the individual methods while its computational complexity is not much increased compared to the post-FFT scheme. The simple structure of the combined method makes it a suitable choice for interference suppression in the receiver of OFDM systems in practice.