Pilot-aided OFDM/SDMA channel estimation with unknown timing offset

The paper presents a novel approach to estimating the multi-path channel of orthogonal frequency-division multiplexing (OFDM)/spatial-diversity multiple-access (SDMA) systems. Having OFDM/SDMA symbols transmitted not aligned with base station (BS) timing, demodulated signals may severely suffer from an inter-OFDM-symbol interference (ISI), namely the misalignment interference. Consequently, the interference degrades the channel estimation extensively. By appropriately designing pilots, the misalignment effects on the channel estimation can fully be cancelled and, the channel is optimally estimated in the minimum mean square error (MMSE) sense by a new estimation scheme. Owing to the interference cancellation, the new scheme is more robust against timing offsets (TO) and gives a better performance in estimating the SDMA channel than the existing approaches.