Frame Synchronization Algorithm for Sub-Band FSK Signal in Underwater Acoustic Communications

This paper presented an efficient transceiver structure using sub-band processing for underwater communication in terms of performance improvement. In aspect of performance improvement, the performance of underwater communication mainly depends on multi-path propagation characteristics, Doppler-spread, and frame synchronization. Accordingly, in order to overcome these effects, non-coherent energy detector and turbo equalization method are employed in receiver side. Frame synchronization which indicate start of frame is also very important part of affecting on performance. Finding the correct frame is directly related to performance, and even if only one sample is missed, it lead to performance degradation. Therefore, this paper proposed two types of frame synchronization algorithm. First type is to find start of frame by correlation between received and transmitted preamble data which are known to transmitter and receiver side. Second type is to find which peak point has the lowest error rates among adjacent several peak points. After first peak is being detected, preamble error rates are calculated. If preamble error rates is over 10%, we tried next peak point as an optimal start point of frame. Through the lake experiment, as result of applying optimal frame synchronization method to receiver structure, errors were corrected in most frames.