Mobile Radio Transmission System -7.VSELP and PSI-CELP
VSELP is a CELP voice coding process that is adopted for the full-rate system in North America and Japan. Because it uses a specially devised noise codebook, it offers such advantages as a small memory requirements, minimal impact of code errors, and limited need for calculation operations. On the other hand, one disadvantage is that quantized noise is relatively large.
PSI-CELP is also a CELP voice coding system adopted in the PDC half-rate system that uses the noise codebook to provide pitch synchronization. This process allows for the faithful reproduction of speech by extracting and repeating only the basic cycle portion from the head of the noise codebook. The system makes it possible to achieve equivalent quality at only half the bit rate of VSELP.
In order to reduce code-error distortion, moreover, PSI-CELP carries out error correction coding (bit-selection error protection) wherein the redundancy varies depending on error sensitivity.