Algorithm to Improve Synchronization of USBL Underwater Multipath and Doppler Environments

USBL estimates signal source positions using the difference between the delay times of received signals at multiple sensors and those delay times are estimated by cross correlation. Therefore, it is important to accurately estimate the delay times. However, because multipaths and Doppler shift degrade the performance of cross-correlation, a method of mitigating and compensating them is required. Therefore, this paper proposes an algorithm to improve the synchronization performance of USBL in an underwater environment where multipath and Doppler shift exist. First, the Doppler shift is compensated after applying fast Fourier transform to the product of a transmitted signal and a received signal. Second, the impact of the multipath is mitigated by estimating the delay time of the first path using constant false alarm rate detector. Computer based simulation demonstrates that the proposed method outperformed the existing techniques in terms of synchronization accuracy by about 100 times.