Analysis of a frame synchronization method using periodic preamble for OFDM based WLANS

Frame and frequency synchronization schemes are critical in the design of OFDM receivers. In burst communications, such as HIPERLAN/2 and IEEE 802.11a WLANs, synchronization must be achieved at the beginning of the packet using only the given preamble. Thus, for such systems, it´s important to design accurate synchronization methods that converge quickly. The most common approach combines an autocorrelation based metric with a max (or min) search. However, such methods typically achieve only coarse synchronization and need to be made more accurate through combinations with other approaches (such as cross-correlation or maximum-likelihood). An autocorrelation based metric is also used, but instead the correct timing is estimated by looking for changes in the gradient of the metric. The proposed method achieves higher accuracy than autocorrelation based max/min searches and has lower latency than many other methods. We provide an approximate closed-form expression for the gradient change that is statistically accurate in both AWGN and frequency-selective channels and offer simulation results illustrating the performance of the proposed method in 802.11a networks.