ABSTRACT
The goal of speech coding, or speech compression, is to represent speech in digital form with as few bits as
possible while maintaining the intelligibility and quality required for the particular application. Interest in
speech coding is motivated by the desire or requirement to conserve bit rate or bandwidth. There is always a
tradeoff between lowering the bit rate while maintaining quality and intelligibility; however, depending on the
application, many other constraints also must be considered, such as complexity, delay, and performance with
bit errors or packet losses [1]. Two networks that have been developed primarily with voice communications
in mind are the public switched telephone network (PSTN) and digital cellular networks. Additionally, with
the pervasiveness of the Internet, voice over Internet protocol (VoIP) is growing rapidly and is expected to
continue to do so over the near future. A new and powerful development for data communications is the
emergence of wireless local area networks (WLANs) in the embodiment of the 802.11a, b, g standards,
collectively referred to as Wi-Fi. Because of the proliferation and expected expansion of Wi-Fi networks,
considerable attention is now being turned to voice over Wi-Fi, with some companies already offering
proprietary networks, handsets, and solutions. Each of these networks has its own set of requirements, and
these are discussed in the section ‘‘Networks for Voice Communications.’’
