Research On Application Of Vector Sensor For Underwater Acoustic Communication

Underwater acoustic (UWA) communication which is not only used in military, but also used in commercial and civilian areas is an important field in underwater acoustic research. Underwater acoustic channel is the most complicated wireless communication channel in which the system bandwidth is limited and exist time-varying multipath propagation and high level sea environment noise, therefore high-speed and robust UWA communication is a global difficult problem.Compared to acoustic pressure sensor, acoustic vector sensor is combined by traditional omni-directional pressure hydrophone and natural dipole independent of frequency, which can simultaneously and independently measure pressure and particle velocity of acoustic field of the point. Therefore, acoustic vector sensor is widely used for signal detecting and target ranging. Here acoustic vector sensor is attempted to use in high-speed UWA communication improving the quality of communication system, which is the research object of the thesis.In the isotropic noise field,4.8dB of directivity gain could be obtained using weighted processing combined with both of pressure and particle velocity. The directivity gain was of 6dB using the optimal weighting processing with four components vector sensor. Adaptive interference cancellation, time reversal equalization and diversity combining were applied in OFDM UWA communication system to reduce the BER.By using the spatial directivity of acoustic vector sensor, it can not only improve the SNR of received noise, but also suppress multi-access interference and could be used in multi-user communication. On condition that the directions of the sources are known, three sources'signals, at the furthest, could be separated from each other by using two-dimension vector sensor, multi-access technology could be actualized without additional channel occupancy, a certain SNR gain could be obtained on the separated signals. As compared with other multi-access technologies, the one based on single acoustic vector sensor could be realized much more easily. It is also mentioned in the thesis that the amount of users the system supported will be doubled by fully use of frequency and spatial information which was actualized by combining OFDMA with multi-access technology based on acoustic vector sensor.According to acoustic covering and focusing technology, different sources could be distinguished by the channel difference between sources and receive array, and the multi-access technology could be actualized by covering interference source signal and focusing target source signal. After using acoustic covering and focusing process in multi-user OFDM communication system, multi-access interference could be effectively suppressed without additional channel occupancy, meanwhile, through the focusing processing, the source signal is enhanced and the effect of multi-path is significantly reduced. The principle of acoustic covering is expounded and different sensor (acoustic pressure array, single acoustic vector sensor and acoustic vector array) are compared for multi-access. The results show that the performance of vector array using acoustic shielding and focusing technology is better than that of the pressure sensor array which has the same element number. Single acoustic vector sensor has the worst performance, and it could not distinguish different users in'the same direction by acoustic covering and focusing process. However, for its easier realization, it has a good application prospect in underwater acoustic network node.