Research Of Phase-Coherent Communications And Adaptive Equalization For UWA Channels

With the rapid development of ocean exploitation and the need of national defense, the research of underwater acoustic (UWA) communications, especially high-speed underwater communications, has drown much attention. The underwater acoustic channel is one of adverse wireless channel, characterized as a band-limited time-dispersive fading channel, and exhibits the characters of time-varying multipath propagation, frequency offsets and phase fluctuations。Phase coherent communications have higher bandwidth efficiency, but its applications for time-varying UWA need perfect synchronizations of frequency and time and compensations of intersymbol interference etc. with the developments of advanced equalization and carrier synchronization techniques, the applications of high-speed phase coherent UWA communications seem more feasible.This thesis focuses on the phase coherent UWA communication techniques. The developments of UWA communications are reviewed at first, the characteristics of the UWA channels were introduced. The thesis proposes the statistic model of time-varying UWA channel for the evaluation of the communication system and adaptive algorithms. The thesis investigates the performances of phase coherent receiver with adaptive decision-feedback equalizer (DFE) embedded phase-locked loop (PLL), and the performances of the receiver implemented with multipath combiner and DFE-PLL. The thesis proposes a novel receiver structure combined the Doppler compensation and DFE-PLL for the applications in UWA channel with Doppler frequency offsets. The key techniques of the receivers are investigated and the number simulations and analyses are given. At last, the lake trial data are used to evaluate the performance of the receiver.