Research On Digital Underwater Acoustic Voice Communications Systems

Digital speech technology has been widely used in many fields of communications in recent years, but it is just at beginning to use acoustical wave to implement underwater digital speech communications, which mainly results from the bandwidth-limited underwater acoustic communications channel and its high temporal and spatial variability. With the development of modem military and the improvement of utilizing and developing the resource of the sea, the research on underwater digital voice communications is getting more and more important. This thesis makes a research on the design and implementation of an underwater digital voice communications system, which can realize the high speed transmission of digital voice streams in real time and implement voice communications with a good quality.Since an underwater acoustic communication channel is bandwidth-limited, transmission of quantized speech samples at high bit rates is restricted, hence speech signals must be compressed. In this study, the G.723.1 algorithm which is a voice compression standard adopted by the International Telecommunications Union(ITU) is chosen to encode the voice signals. After channel coding, a QPSK modulation is adopted to transmit the useful signal. For the receiver, a scheme where synchronization and equalization are jointly optimized is used to reduce intersymbol interference caused by channel multipath propagation.This thesis mainly deals with the hardware design of whole system, on the basis of summarization of underwater voice communication systems, this thesis analyzes some key technology used in underwater digital voice communications, demonstrates the feasibility of the whole system, and then provides a scheme to realize the whole system. After that, this paper provides a block diagram of the prototype system, analyzes every sub-system and its internal structures and then defines the DSP as the key processors in the whole system, gives a comprehensive, detailed presentation about the hardware design. Finally, the software design isdiscussed in detail, after analyzing the problems found during the debug work, the correspondent solution is also brought forward.