Exploiting the cyclic prefix for beamforming in OFDM receivers

Blind and semiblind antenna array algorithms are proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems in the time domain. A blind technique is proposed for the maximization of the temporal Signal to Noise plus Interference Ratio (SNIR) in frequency-selective channels exploiting the Cyclic Prefix (CP). In OFDM systems, this maximization does not imply the minimization of the Bit Error Rate (BER). Thus, a semiblind method that takes advantage of both known training data and the CP is obtained, which provides the best results in terms of link quality. Simulations are conducted for Hiperlan/2 (HL/2) parameters, and a slight modification of its fixed pilot position is proposed, so as to improve the BER performance of the algorithms and to obtain estimates of the channel for the blind method.