14.Voice CODEC

The voice CODEC used for the digital cellular system is VSELP for full-rate and PSI-CELP for half-rate transmissions. In comparison to analog systems, while the voice quality of the digital system is somewhat inferior to that of analog systems under ideal conditions with little noise, digital systems maintain an adequate quality up to the range where the average bit-error rate is about 1%. Moreover, shifting to half-rate still yields a quality almost equivalent to or better than that of full-rate even though the bit rate has been cut in half. The development of high-efficiency voice CODEC was essential in order to realize such high-quality voice transmission.

The CODEC combines an analog to digital (A/D) signal converter with a digital to analog (D/A) signal converter. Progress in hardware technologies such as the high-speed, low-power consumption digital signal processor (DSP) has substantially contributed to improving CODEC conversion efficiency.

Voice Transmission Quality

Created 1999/03