Encoding sequence design for a reduced complexity time synchronization approach for OFDM systems

We here deal with a recently proposed data-aided reduced-complexity approach for OFDM time synchronization. In the considered approach, an encoding sequence generated from the preamble is differentially correlated with the received signal to estimate the frame start. In this paper, we study the off-line design of the encoding sequence. We present two efficient algorithms for deriving QPSK encoding sequence that allows replacing the differential correlation process, characterized by its high complexity, by a simple sign change. The resulting quantified encoding sequence performs well in both AWGN and multipath channels, compared to the optimal, previously used, encoding sequence. Furthermore, the complexity involved for the metric calculation, using the herein proposed encoding sequence, is reduced considerably by applying the sign change operations. The simulation results show that the use of sub-optimal sequence gives near best detection performances which are provided by the optimal sequence with lower complexity.