Standardization activity in ITU of extending 16-kbit/s LD-CELP for personal communication systems

This paper introduces the standardization activity in ITU-T (International Telecommunication Union, Telecommunication Standardization Sector) of extending 16-kbit/s LD-CELP (low-delay code-excited linear-predictive) speech coding for personal communication systems. ITU-T Recommendation G.728 (LD-CELP) provides toll quality at 16 kbit/s with very low algorithmic delay time (0.625 ms). However, its quality significantly falls under conditions when-the received codewords are lost for 10 to 100 ms that tend to occur in radio channels. The extension of LD-CELP consists of the decoder modification proposed by AT&T that conceals the erasure of channel frames. Subjective test results using Japanese speech shows fairly good quality with this concealment for frame-erasure conditions.