A new method of frame synchronization and frequency offset estimation in OFDM system

Abstract

In an orthogonal frequency-division multiplexing system, symbol synchronization and frequency offset estimation are very crucial for maintaining the orthogonality of the sub-carriers. Among the several recently proposed methods for frame/symbol synchronization, the technique suggested in T. M. Schmidl et. al. (1997) is robust to channel phase and frequency offset. The timing metric proposed in T. M. Schmidl et. al. (1997) reaches a plateau which, in the presence of noise and frequency-selective channel, can give rise to some ambiguity in the start of the frame. In this paper, for the same preamble as in T. M. Schmidl et. al. (1997), we propose a new timing metric, and considering an ideal scenario we show that it yields a sharp peak at the correct symbol boundary. We then analyze the metric and evaluate its mean at the symbol boundary and in its neighborhood for the case of AWGN and frequency-selective channels. The mean values predicted by the analysis are close to those obtained from simulations. Since the derivation of variance expression is tedious, we used simulations to evaluate this at the corresponding time instants. From the results of mean and standard deviation, it is clear that the proposed metric yields sharp peak at the symbol boundary.