WIENER SOLUTION FOR OFDM PRE AND POST-FFT BEAMFORMING

Orthogonal Frequency Division Multiplexing (OFDM) is one of the most promising techniques for high-speed trans-mission over severe multipath fading channel. However, once delays of secondary multipath rays are greater than the guard interval duration, intersymbol interference causes a severe degradation in the transmission performance. To solve this problem, a multiple antenna array can be used at the receiver, not only for spectral efficiency or gain enhance-ment, but also for interference suppression. In this paper we analyze the asymptotical behavior of two beamforming algorithms, a low complexity pre-FFT method and a more efficient post-FFT system. The optimum weight set for beam-formers is derived on the basis of the minimum mean square error (MMSE) criterion and the Wiener solution is studied under different working conditions. 1