Study On The Key Techniques For Digital Underwater Personal Communication

Speech technology has been widely used in wireless communication, cable communication, satellite communication and other fields, but the research in digital voice acoustic communication underwater has just started. With the wide ocean use and exploitation in each passing day, the use of acoustic digital communication technology has become increasingly necessary, which has tremendous significance for national defense development and ocean economy. Influenced by the multi-path spreading, frequency and space variability, the signal underwater is seriously distorted. In order to ensure the security, accuracy and high-speed information transmission under water, it is necessary to study the shallow channel properties,underwater modulation and demodulation techniques,and anti-multi-path and anti-fading techniques.A model structure of the personal voice underwater communication system is proposed in this paper. CELP code excited linear predictive coding, π / 4 - DQPSK and FH/MFSK modulation, convolution coding and decision feedbackequalization are used in this model. Meanwhile the performance of the key technique are analyzed by comparison and validated by simulation. The results show that the system can be used in underwater channel to transmit the voice and information with little distortion, which has strong practical value and development potential. The following are the main research procedures and results:1. The acoustic characteristics of the shallow water channel are studied, and a simulation model on the basis of Rayleigh fading is also constructed by simulating the shallow channel and analyzing data of the experiment in the lake, it can be concluded that this approach to model of the shallow water channel has project significance.2. A kind of underwater frequency-hopping communication system project is proposed, adaptive hopping frequence, variable filter Banks controlled by the frequency-hopping sequence as well as the spectrum estimation based on periodogram are proposed in this system project. The results show this system has good performance in robustness of the system and realize 10^-3 under low SNR=-10 and multi-path conditions.