OFDM Timing Synchronisation Under Multi-path Channels

Wireless OFDM signals typically have a cyclicprefixed guard interval. The FFT timing synchronisation at the receiver is traditionally based on the peak point of the correlation output between the guard interval and its corresponding duplicate at the OFDM symbol’s tail. This approach does not in general find the optimum timing position for the FFT when the channel contains more than one path. This is particularly true when the first arriving replica of the signal is not the strongest, potentially resulting in the timing position that is outside the acceptable range, causing ISI. In this paper, the OFDM FFT timing synchronisation problem under multi-path channel conditions are studied. Algorithms that produce improved FFT timing synchronisation are developed, which exploit either the channel information obtained, say, through scattered pilots or the characteristics exhibited by combining a modified correlation scheme with a special filtering process. Results from simulation study are presented which have shown a noticeable performance improvement.