(Qualcomm Code Excited Linear Prediction), also known as Qualcomm PureVoice
, is a speech codec
developed in 1994 to increase the speech quality of the IS-96A
codec used earlier in CDMA
networks. It was replaced later with EVRC
since it provides better speech quality with fewer bits. There are two versions available: QCELP8
and they use 8 and 13 Kbit/s respectively.
Adopted in CDMA system is a QCELP vocoder
with variable rates, which is actually a device converting a sound signal into the signal which can be transmitted in a circuit. The method adopted generally in a wire communication system is to first sample (8,000 sample values generated per second) a voice signal with an 8kHz signal and then implement 8-bit quantization
coding for each sample value. Therefore, each voice channel in a wired system has the rate of 64K. However, because the air resource in a wireless system is very precious, a more effective coding mode is needed to use a rate as low as possible in the case where voice quality is guaranteed. A QCELP vocoder with variable rates is such a device. The main principles of it are to extract some voice feature parameters when a person speaks and transmit these feature parameters to the peer party. Then, the peer party will recover the voice with these parameters based on the promise between the two parties. Thus, a far lower rate is needed.
Let's give an example. The information of a triangle can be transmitted from one place to another in two... Read More