Time delay estimation in underwater positioning for pattern time delay shift coding

Based on the pattern time delay shift coding regime, a structure of positive and negative frequency modulation calling pulses of underwater ultra-short base line acoustic positioning system is given, and the second correlation method of time delay estimation is proposed in this paper. As the second correlation method improves the detectable signal-to-noise ratio of calling end to certain extent, it could accumulate the multipath reflections in the underwater channel on the energy including the direct wave effectively in the complex environment, so as to finish the peak detection accurately and to improve the accuracy of time delay estimation. At last, the sea trial results show that the second correlation method could suppress the multipath interference from interface reflections under different signal-to-noise (SNR) ratio efficiently.