As the target tracking and positioning technique develop, research on time delay estimation emerged. As one of the decisive factors, the accuracy of time delay estimation is important for underwater positioning system. According to different demands, there are several methods of time delay estimation, including correlation estimation method, parameter estimation method, high order statistics method, etc. And the correlation estimation method is widely used because of its simple algorithm. However, the time resolution of the correlation is inversely proportional to the signal bandwidth. Therefore, wideband transmitting signal is needed for the high accuracy of time delay estimation.

Underwater acoustic signal is propagated in multipath channels. And the received signal becomes a combination structure of many interface reflecting interferences besides the direct wave. Hence, the correlation peak of direct wave could be resolved difficultly. To obtain an accurate time delay estimation of direct wave, it is important to detect correct peak of direct wave in underwater positioning system.

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 research.

As the second correlation method improves the detectable signal-to-noise (SNR) ratio by suppressing the background noise to certain extent, it could accumulate the multipath reflections including the direct wave on the energy effectively. The superiority of the second cross-correlation method is that time delay could be estimated in a lower SNR ratio environment and in the complex multipath channels compared to the first cross-correlation method. At last, the field trial results show that the second correlation could suppress the multipath interference in underwater channel efficiently. Consequently, it is valuable that the second correlation is implemented efficiently and simply.

This research acknowledges the financial support of National Defense Pre-Research Project No.513220505.

The research entitled “Time Delay Estimation in Underwater Positioning for Pattern Time Delay Shift Coding” has been published in Image and Signal Processing (CISP), 2013 6th International Congress on (Volume:03, 16-18, Dec. 2013, pp. 1618-1622).

Corresponding author:

WU Yongqing
Laboratory of Image Sonar Technology, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China

Email: wyq@mail.ioa.ac.cn