Blind and semiblind spatio-temporal diversity for OFDM systems

Adaptive antenna arrays can be used to improve the performance of Orthogonal Frequency Division Multiplexing systems. They are usually applied in the frequency domain, after the FFT demodulation. In this paper, the selected algorithms are applied in time domain. A blind method is firstly proposed for the maximization of the temporal Signal to Noise plus Interference Ratio (SNIR) in frequency selective channels exploiting the temporal redundancy introduced by the cyclic prefix (CP). This algorithm may cope well with non-stationary interference that appears during the burst transmission. This blind technique is extended so as to take advantage of the preamble that precedes the useful data in the HIPERLAN/2 (HL/2) specification. Simulations show that this latter semiblind approach improves the overall performance of the system with respect to the traditional Sample Matrix Inversion (SMI) algorithm even in interference stationary scenarios. Additionally, a moving pilot structure is proposed to perform more accurate channel estimation, which further improves the performance of the semiblind technique.