Speech Coding at Low Bit Rate and its Application in Mobile Radio

Abstract

Recently, low bit rate speech coding is necessary in many applications. The class of speech coding that can produce a low bit rate with a good quality is known as hybrid coding or Analysis-by-Synthesis (AbS) predictive coding. This new class of speech coding can produce high-quality speech in the bit rate range from 4.8 to 16 kb/s. However, at bit rates below 9.6 kb/s, the encoding algorithms become computationally demanding due to the vector quantization of the excitation frames. Digital mobile radio telephony is one of the most important applications of this class of speech coding, where it is very important to improve the coder robustness to guarantee high quality speech reception over the hostile mobile radio channel. The work in thesis has concentrated on firstly, reducing the bit rate below 9.6 kb/s with maintaining good speech quality and low complexity, Secondly, a comparison studies between different types of AbS linear predictive techniques, and Finally, show the robustness of the AbS linear predictive coders below 9.6 kb/s over mobile radio channel.