tion of fully defined and measurable QoS is essential to business success. Downloaded from Digital Engineering Library @ McGraw-Hil (www.digitalengineeringlibrary.com) Copyright© 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Quality of Service (QoS) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright© 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Source: CDMA CAPACITY AND QUALITY OPTIMIZATION Chapter Speech Coding The digitization of voice is a two-step process. In the first step, a microphone converts sound waves into electrical waves following the same pattern. This is an analog signal, a signal where the electrical pattern is analogous to the original pattern. Prior to digi- tal technology, in telephone communications the analog signal was transmitted and then retranslated back into sound at the far end. Vinyl phonograph records created an analog pattern of bumps in the vinyl that reproduced sound waves. Magnetic audiotape recorders created an analog pattern of magnetized iron on the tape that could generate an electrical signal that reproduced the audio tone. If we take the electrical wave pattern and translate it into a digital signal, this is en- coding, which is the second step of creating a digital signal. Digital telephony, includ- ing digital cellular telephony, creates a digital signal for transmission. Digital encoding also can be used for storage. Audio compact disks (CDs) use digital coding. Whether the system is used for transmission, for storage, or for both, the sound going in is the au- dio input, and the sound coming out is the audio output. Turning an audio or video signal into a code is performed by a device called a coder, and the reverse process is performed by a decoder. The output of a decoder is an ana- log audio signal that can be sent to an amplifier or speaker. Typically, a single physical devi