Research Of Key Technologies In Phase Coherent Underwater High Speed Communication

Underwater acoustic communication technology is the key for solving the transmission and processing of underwater information, and it's widely used in the fields of AUV, underwater communication network, telemetry, and target detection. Spread spectrum and MFSK modulation is primary modulation modes in beginning of underwater communication. They suit underwater communication of middle-long distance with transmission rate of several bps and several hundred bps. Because of limited frequency band of channel, spread spectrum and MFSK modulations can not resolve that high speed transmission is in contradiction with limited frequency band. So, MPSK become research hot point of high speed underwater communication, because MPSK has higher frequency validity since 1990's.According to characters of underwater channel and the development of communication technology, the key technologies of phase coherent underwater high speed communication are researched in this paper. These technologies are used to overcome characters of underwater channel, including stochastic time fading, serious multipath interference, limited frequency band. Every technology need to be meticulously researched in underwater high speed communication system, in order to maximum the product of transmission distance and information transmission rate on condition that error code rate is satisfactory.The main content and contributions in this paper are as follows:Firstly, key technologies of phase coherent underwater high speed communication are discussed in this paper. The key technologies include channel code, adaptive equalizing, diversity technology, compensation algorithm of Doppler. Theory and emulation results in different hydrologic condition of thesetechnologies are provided.Secondly, this paper proposed a method of waveform design that can restrain multipath interference. This method is implemented by folding signal at second zero point, keeping invariant information rate. Emulate experiments and lake experiment obtained lower error code rate than traditional waveform design method using this waveform structure with MPSK. The results of experiment show that the method of waveform design can improve performance of underwater communication system.Thirdly, Based on space diversity technology, this paper proposed a receive algorithm, that is angle diversity combined with spatio-temporal decision feedback equalizer. This paper also introduced implement method of the algorithm. Experiment results of space diversity and angle diversity are compared, and lower error code rate is obtained by using angle diversity algorithm.Fourthly, Based on emulation and implement of these technologies, a QPSK underwater high speed communication system is implemented. We completed three times lake experiments using this system, which validated the feasibility and validity of these algorithms. In the end, experiment results were analysed.