LMS adaptive beamforming based on pre-FFT combining for ultra high-data-rate OFDM system

In this paper, we propose four adaptive beamforming schemes for the ultra high-data-rate orthogonal frequency division multiplexing (OFDM) system which is capable of supporting beyond 100 Mbit/s data rate. These schemes are based on the least mean square (LMS) algorithm and pre-FFT combining. Their differences result from two factors: one is the pilot arrangement in each OFDM block and the other is either the frequency-domain or time-domain pilot vector used in the beamforming. These schemes are compared under the condition that the pilot-to-data ratio is the same. The performance investigation shows that the different schemes present different performance in the convergence behavior and estimation accuracy. Provided that enough time is allowed to guarantee the accomplishment of the antenna weight convergence, all proposed adaptive beamforming schemes can decrease the mean square error (MSE) to very low values. Therefore, their BER performance is very similar.