Study On Digital Speech Coding And Its Application In Underwater Acoustic Communication

Digital speech technology has been widely used in many fields of communication in recent years, but it is just at beginning to use acoustical wave to implement underwater digital speech communication. It mainly results from the underwater acoustic channel which has the characteristics of large noise, narrow bandwidth, low carrier frequency, great propagation latency and multipath effect varying with time-space-frequency. With the development of national security and marine economy, the research on underwater digital voice communication is getting more and more important. In this thesis, digital speech coding technologies are studied with the purpose of implementing underwater digital speech communication.Since an underwater acoustic communication channel is bandwidth-limited, transmission of quantized speech samples at high bit rates is restricted, hence speech signal must be greatly compressed. In this research, the algorithms of speech coding at low bits rates are mainly studied. Code Excited Linear Prediction (CELP) coder exhibit the good performance of amplitude coder and parameter coder, which can provide high quality speech at very low bit rates. According to the FS-1016 standard of CELP which are the important and international algorithm, a new method of speech coding based on the fast search algorithm of adaptive code-book is proposed. The results show that the algorithm performs well against high BER and large noise, and it can satisfy the requirements of underwater digital voice communication well.Researchful results in the thesis are summarized as follows:1. Basing on the study of FS-1016 algorithm, a digital speech codec scheme in technic is presented and a simulation system is constructed for it. Simulation results illustrate that the codec scheme is feasible and the simulation system can provide high quality speech as well as represent the favorable performance.2. Capability of the codec scheme and the simulation system for resisting bit error rates (BER) are studied deeply. It shows that the simulation system based on the codec scheme represents favorable capability of resisting BER, and it can realize clear voice communication when the BER below 2.5%.3. A new method of speech coding based on the fast search algorithm of adaptive code-book is proposed for reducing the complexity of FS-1016 algorithm. The new...