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Travel time processing for LBL positioning system

Long Baseline (LBL) positioning is an important and high-precision method for underwater vehicle navigation. It has the highest accuracy among all the acoustic positioning methods. LBL positioning system use one-way-travel-time measured between target and beacons, which is the raw data of measured values. But there are some problems in travel-time measurements: firstly, due to other signal interferences or multi-paths, there is a large scale error in travel-time estimation; secondly, because of moving targets and the distance difference between target and beacons, the target receives ranging signals at different times and in different positions. In order to improve positioning accuracy, the following time measurement processing method is proposed in this paper. Aiming at the large scale error, we propose a target motion model, which combines the cycle of a long baseline positioning system, with target speed and travel-time measurement. This method can eliminate travel-time measurement with large scale error. To solve the problem of the target receiving ranging signal at different times and in different positions, we propose the ellipsoid trilateration method, which uses the cycle of the long baseline positioning system, turnaround time of beacon and the round-way-travel-time. This method can calculate the travel time between target and beacons when the target sends signals. The results of the simulation show that we can work out the position information when the target is sending signals by using the travel-time value after travel-time processing. The resultant positioning error is at the centimeter level. The method of travel-time processing is applied to deep-sea data from the 6000 m Autonomous Underwater Vehicle (AUV) in the South China Sea. The 6000 m AUV is developed by Shenyang Institute of Automation and uses the LBL positioning system produced by IXSEA company. The effectiveness and robustness of the algorithm is verified.