Studies On Data Transmission Techniques In Shallow Water Acoustic Channels

Shallow water area is a very important strategic area for both military and nonmilitary purposes. People have applied the techniques of underwater acoustic communication to a variety of purposes in their use and exploration of the seas. In recent years, studies on data transmission in shallow water acoustic channels have attracted people's wide interests and got a rapid development. It provides important techniques to solve the problems of the reliability of information exchange in the seas.On the basis of general analysis of the features of shallow water acoustic channels, the key techniques and the difficult points in underwater acoustic (UWA) communications, this dissertation proposes a simple but effective model for multi-path interference, which is then used to simulate the communication system for underwater acoustics. Associated with the experimental results of the field test, we present a data transmission technique using frequency-hopping communication in underwater acoustic channels.The main research contents in this dissertation are as follow:1. Discusses the unfavorable effects of the shallow water acoustic channels on data transmission, and objectively introduces recent certain advanced in UWA communication.2. Studies on the simulation of communication system for underwater acoustics. A UWA channel model has been developed based on the sound ray. Special emphasis has been given to the effects of the bottoms, the surfaces of the shallow sea, and the absorption of the signal caused by the shallow water. The dissertation introduces the impulse response of the shallow acoustic channel, utilizes windowing techniques to determine the effect of the signal-to corruptive multi-path signal ratio (SMR) on UWA communication in the observation window.3. Experimental studies on the statistical characteristics of the sound transmission in the shallow water in Xiamen Harbor. The dissertation gives the PDFs (probability density functions) of amplitude and time correlativity coefficient function of the direct-path signal and multi-pathinterference, measures the frequency spectra distribution of the noise in Xiamen Harbor. With these test results, we obtain correlate parameter for UWA communication system.4. Introduces the diversity methods and frequency hopping (FH) communication techniques to reduce the signal fading and eliminate inter-symbol interference (ISI) of multi-path interference. The dissertation analyses the principle of data transmission with FH communication to anti-multi-path in shallow water acoustic channels, and designs a method to implement data transmission in UWA.5. Synchronization is one of the key techniques of FH communication. A method of displacement waiting auto-synchronization with match filters is put forward to realize the synchronization of FH communication in UWA. We deduce from theory that this method can reduce the time of acquisition, then the dissertation designs and implements a method of synchronization with correlated detection for UWA FH communication.6. Based on basic research and experiments, a data transmission system in shallow water acoustic channels is designed and the field test is performed in Xiamen Harbor. Experimental results shows: a data rates of 600bits/s with the bit error rates on the order of 10"4 was demonstrated at distance 6000m in the shallow water channel of Xiamen harbor.The innovation of this dissertation is that:1. Both the channel model simulation and experimental study on the statistics characteristics of data transmission in shallow water channels are been obtained in this dissertation.2. The dissertation put forwards a method of displacement waiting auto-synchronization with match filters for UWA communication.3. The dissertation designs and implements the system of data transmission with FH communication in underwater seas, which is performed in field test in Xiamen Harbor.