Research On Several Key Techniques Of The Signal Processing For Long Baseline Location

Acoustic navigation and positioning technologies are the kernels in the field of tracking underwater targets, are the key components of the Ocean technology. Along with the government attaching great importance and investing huge finance to the exploitation of the Ocean and the construction of the coast defenses, acoustic positioning and navigation technology is facing a new challenge and a good opportunity for development.Several key technologies of the signal processing in the long baseline acoustic positioning system were researched, including the design of multi-channel adaptive Notch filter based on the combined application of notch channel and filtering channel, the time delay estimation technology based on the anti-multi-path strategy, the signal detection technology based on instantaneous parameter estimation, and so on.Single-channel adaptive Notch filter is an effective means to extract single-frequency signal, but its performance often decreases significantly when faced with various spectral components. The characters of parallel multi-channel and serial multi-channel adaptive Notch filters were analyzed. A new kind of multi-channel adaptive Notch filter structure was designed by combining the filtering channel and notch channel. This structure can not only extract a number of different single-frequency signals, but also can avoid the envelope fluctuation caused by sinusoidal interferences, thus enhancing the signal detection capability. Recently, this structure has been used in practice and performed very well.Time-delay estimation error is one of the most important factors in the coastdown of positioning precision. Because of the underwater acoustic multi-path channel, the signal received was distorted in amplitude, phase and frequency, which would reduce the time-delay estimation precision. Based on the positioning and navigation property of long baseline system, the effect of single sensor's time-delay estimation error on positioning precision was analyzed, the changing law of the phase difference between direct sound and surface reflected sound was demonstrated when the target lies in different location, the physical mechanism about interfacial reflection influence on positioning precision was researched, and a new signal processing measure was presented to overcome multi-path effect using the character of wrapped signals. The proposed anti-multi-path method can upgrade the offset interference signal detection ability and improve the time-delay estimation precision, so as to improve the capability and performance of underwater acoustic positioning systems.Parameter estimation theories have been applied on signal detection field successfully, which improved signal detection ability enormously. Variance-of-Instantaneous-Frequency Detector (VIFD) is a typical detector based on Instantaneous-Frequency estimation, which is robust and simple in operation. So far, VIFD has solved many technical problems, such as detecting multi-channel CW signal, restraining signal leakage among different channel and reverberation, etc. But VIFD is only suitable for the signal with constant carrier frequency. By means of promoting VIFD principle, two kinds of variance-instantaneous-parameter detector for HFM and LFM signal were proposed, which was called as Variance-of-Frequency-Modulation-Slope Detector (VFMSD) and Variance-of- Period-Slop Detector (VPSD). In addition, using the concept of minimum mean square error from parameter estimation theories, a new kind of detector in terms of other forms signal was put forward, called mean-square-error-of-Instantaneous-frequency Detector (MSEIFD), and an thought of combining the matched filter (MF) and the MSEIFD for detection was presented. The simulation result shows that the proposed detectors are effective.Acoustic transceiver is one of the key components of the SUNO system, which is a large measure and control equipment. According to the principle of SUNO system, a multi-function acoustic transceiver was designed and realized. The design thought of the software and hardware as well as the implementary scheme was introduced, and the capability of the system was verified by electricity simulator and trials in lake and sea. Meanwhile, positioning precision was analyzed by the means of fixed point Location in anechoic pool and trace calibration using High Precision Location System in Ocean. The result shows that SUNO system is robust and satisfying for use.