Design and experiment of frequency offset estimation and compensation in high-speed underwater acoustic communication

In underwater acoustic (UWA) communication, Doppler effect is particularly severe due to the slow velocity of sound and the complex variant UWA channel environment. Carrier frequency offset (CFO) can result in extension and compression of the received signal in time domain and has a direct effect on the performance of decoding. In this paper, we propose a new scheme of CFO estimation and compensation for a high speed UWA communication system. There are three steps including coarse CFO estimation, fine CFO estimation and linear interpolation, which are taken to estimate and compensate the CFO. The scheme can eliminate the phenomenon of ambiguous phase and tolerate quick random variation of the CFO in UWA channel. A UWA communication experiment was carried out in December 2012 in the Indian Ocean, off Rottnest Island, Western Australia. With the proposed algorithm in this paper, the UWA system can achieve an average of 1.95% uncoded BER with QPSK modulation at the 1km range and 5.57% with BPSK at the 10km range.