Combination of adaptive beamforming and adaptive loading for OFDM packet transmission

We propose a combinational scheme of adaptive beamforming and adaptive loading for orthogonal frequency division multiplexing (OFDM). Two adaptive beamforming schemes based on least mean square (LMS) algorithm and pre-FFT combining are used to obtain the space diversity gain. Their difference, which lies in either the frequency-domain or time-domain pilot vector is used in the beamforming. In order to counter the severe frequency-selective fading which is inevitable in broadband wireless communications, we use the frequency-domain adaptive loading to load the bits and transmit power to the individual subcarriers. The performance investigations show that the combinational scheme based on the adaptive beamforming and adaptive loading is very effective in improving the performance of OFDM packet transmission.