ABSTRACT
This chapter discusses the technologies and issues involved in speech coding, with particular applications to digital cellular and Voice over IP (VoIP) for wireless access points. It explains the speech codecs used in digital cellular and wireless VoIP applications, and discusses the ITU-T standardized speech codecs because of the influence some of the ITU-T codec designs have had on the codecs in wireless systems and because some of these codecs appear in wireless applications. The chapter provides comparisons of the performance, complexity, and coding delay of the several most prominent standards, and examines key challenges for effective voice communications when the various codecs are employed in communications networks. It presents the requirements and current capabilities, some projected, of new speech coding standards under development at the time of this writing. The chapter outlines the basic issues in speech coding, followed by some details on the basic speech coding structures that are widely used.
