Synchronization technique for MIMO-OFDM WLAN systems with space time diversity

In this paper, we propose the use of differential space-time block coding to improve the synchronization for Wireless Local Area Networks (WLAN) without any channel estimation requirement. We study the application of an efficient synchronization technique recently proposed for 2×1 MISO-OFDM systems in the IEEE 802.11n WLAN for 2×1 and 2×2 MIMO configurations. The proposed technique exploits a preamble of two identical parts and splits the synchronization processing into two stages: an auto-correlation based coarse stage and a cross-correlation based fine stage. The coarse synchronization aims to detect a repetitive pattern within the received signal in order to roughly localize the preamble start. Then, to benefit from the spatial diversity, differential decoding must be achieved before carrying the fine synchronization. The cross-correlation based fine metric is calculated over a short interval centered on the coarse time estimate, which provides accurate preamble start estimation with relatively reduced computational load. As a byproduct, the fractional part of the frequency offset is also estimated through the evaluation of the timing metric at the estimated preamble start. Simulation results show that, when applied to the IEEE 802.11n signal, the proposed synchronization scheme provides better detection performance compared to the considered benchmark.