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Áp dụng DSP lập trình trong truyền thông di động P9

Speech coding is at the heart of digital wireless telephony. It consists of reducing the number of bits needed to represent the speech signal while maintaining acceptable quality. Digital cellular telephony began in the late 1980s at a time when speech coding had matured enough to make it possible. Speech coding has made digital telephony an attractive proposition by compressing the speech signal, thus allowing a capacity increase over analog systems. Speech coding standards are necessary to allow equipment from different manufacturers to successfully interoperate, thereby providing a unified set of wireless services to as many customers as possible. . | The Application of Programmable DSPs in Mobile Communications Edited by Alan Gatherer and Edgar Auslander Copyright 2002 John Wiley Sons Ltd ISBNs 0-471-48643-4 Hardback 0-470-84590-2 Electronic 9 Speech Coding Standards in Mobile Communications Erdal Paksoy Vishu Viswanathan Alan McCree 9.1 Introduction Speech coding is at the heart of digital wireless telephony. It consists of reducing the number of bits needed to represent the speech signal while maintaining acceptable quality. Digital cellular telephony began in the late 1980s at a time when speech coding had matured enough to make it possible. Speech coding has made digital telephony an attractive proposition by compressing the speech signal thus allowing a capacity increase over analog systems. Speech coding standards are necessary to allow equipment from different manufacturers to successfully interoperate thereby providing a unified set of wireless services to as many customers as possible. Standards bodies specify all aspects of the entire communication system including the air interface modulation techniques communication protocols multiple access technologies signaling and speech coding and associated channel error control mechanisms. Despite the objective of achieving widespread interoperability political and economic realities as well as technological factors have led to the formation of several regional standards bodies around the globe. As a result we have witnessed the proliferation of numerous incompatible standards sometimes even in the same geographic area. There have been many changes since the emergence of digital telephony. Advances in speech coding have resulted in considerable improvements in the voice quality experienced by the end-user. Adaptive multirate AMR systems have made it possible to achieve optimal operating points for speech coders in varying channel conditions and to dynamically trade off capacity versus quality. The advent of low bit-rate wideband telephony is set to offer a .