Packet Loss Concealment of Voice-over IP Packet using Redundant Parameter Transmission Under Severe Loss Conditions

This paper describes an outline of a project for developing a VoIP codec that can be used under a very severe communication environment where half of the packets drop. The codec is based on G.729 CS-ACELP, and a packet loss concealment (PLC) methods with redundant information will be used for enhancing speech quality. First, we assessed the importance of G.729 parameters, where we found that parameters related to the spectral shape and gain were relatively important. Then we evaluated speech quality when those important parameters were redundantly transmitted. Next, we developed two methods to reduce bitrate of the redundant parameters: one is to use the bit-flip function, and the other one is to use a discriminative model. From the experimental result, we found that both of the methods gave similar results, where quality improvement is almost in proportion to the redundant bitrate.