Statistical pre-filtering for OFDM systems with multiple transmit antennas

The incorporation of orthogonal frequency division multiplexing (OFDM) with space-time/frequency coding is a robust and effective method to achieve transmit diversity gain and also suppress both multipath fading and inter-symbol interference for broadband wireless transmissions. This paper is concerned with downlink performance improvement using multiple transmit antennas for OFDM systems with large delay spread. We propose a delay spread reduction method using space frequency block coding and statistical pre-filtering, which combines signal pre-alignment and multiple transmit beamformers, designed with the statistical knowledge of downlink channel state information. The proposed method transforms a large delay spread channel into multiple channels with small delay spread, thus not only shortening the required cyclic prefix length, but also maintaining path diversity by the use of space-frequency coding. By computer simulations we evaluated the effectiveness of the proposed method.