Precision Underwater Positioning System

Acoustic positioning system has wide application in the Ocean Scientific field. However, most existing systems have disadvantages of bulkiness, perplexing operation, limited position range or low precision, resulting in their incompetence of many application requirements. With the development of Acoustics and Signal Processing theory, it is possible for us to develop more advanced positioning systems.This article first reviews the principle and structure of three traditional kinds of acoustic position system, and analyses their performance individually. Some typical products are showed to illuminate the performence and the application. Combined with the need of submarine exploration, it designed the portable long base line position system for slow velocity vessel to position and to identify the transponds underwater. By broadcasting periodly, the transponders in the scope will answer the spread spectrum modulation data packets after it recognizes the correct information. Through the multi-point measurement of travel time, the transceiver uses the curve intersection method to positon the targets. In order to improve the accuracy of long base line position system and to overcome the impact of multipath and Doppler frequency shift, the data packets begin with the Linear Frequency Modulation (LFM) signal packet which is used to synchronize the receiver to the start of the data and to get the travel time. Then a packet of the GOLD coding signal follows the LFM packet so that the address data can be recognized without codes interrupted. From this way, it resolves the key technology solutions on the detection of the low SNR signals and Multi-targets.The research of this article mainly focuses on the technicals of the design of low power consumption acoustic transponder, and the realization of the platform of long base line transceiver. Basing on the downlink modulation, it explains the key technologies in hardware and software design of the transponder to reduce the power consumption. The design of the transceiver is the most important part of this article. According to the function, the transceiver is disassembled into four parts: Digtal Signal Processing board, Transmit board, Receive board and Power Supply board. Combination of the spread spectrum modulation, the key algorithm of software design is described in details. Finally, using the experiment in the pool, it shows that the design basically meets the demands of system.