Reduced-Complexity synchronization technique for MIMO-OFDM WLAN systems

Abstract

In this paper, we study the application of a robust and Reduced-Complexity (RC) synchronization technique to the IEEE 802.11n Wireless Local Area Networks (WLAN). The studied technique exploits a preamble of two identical parts and splits the synchronization processing into two stages: a first auto-correlation based coarse stage and a second differential correlation based fine stage. The coarse synchronization aims to roughly localize the preamble position by auto-correlating the received signal using a correlation shift equal to the preamble sub-sequence length. The calculated metric exhibits a plateau that results in an uncertainty in the time detection accuracy. In the second stage and to mitigate the plateau effect, differential correlation is performed using a correlation shift different from the preamble sub-sequence length. The calculated metric provides high sharp peak that results in a very accurate detection. The fine stage is processed over a short interval centered on the coarse time estimate, which reduces the computational load of differential correlation operations. The repetitive structure of the preamble proposed in the IEEE 802.11n standard allows the application of the RC technique on it, using either the first legacy short preamble part or the second legacy long preamble part. Moreover, by choosing a correlation shift equal to the delay used to implement the Cyclic Delay Diversity (CDD) scheme, the RC technique allows to overcome the pseudo-path problem caused by the CDD. As a byproduct, the fractional part of the frequency offset is also estimated through the evaluation of the timing metric at the fine estimate. Simulation results show that, when applied to the IEEE 802.11n signal, the RC synchronization technique provides high detection accuracy that outperforms the considered benchmark.