Improved Packet Loss Concealment for Pcm Voip

Voice-over-IP (VoIP), the transmission of packetized voice over IP networks, is gaining much attention as a possible alternative to conventional public switched telephone networks (PSTN). However, impairments present on IP networks, namely jitter, delay and channel errors can lead to the loss of packets at the receiving end. This packet loss degrades the speech quality. Model-based speech coders, such as the International Telecommunication Union (ITU-T) G.729A and G.723.1 standards, have been extensively used for speech coding over IP networks because of their low bit rates requirements (5.3 to 6.4 kbit/s for G.723.1 and 8 kbit/s for G.729A). Also, they have an inherent ability to recover from erasure: using their model-based structure they include a built-in packet loss concealment scheme which makes their quality drop slowly with increasing amount of packet loss. However, their model requires a few frames to adapt to the transition from a concealed state to a correct state. Thus, model-based speech coders actually tend to corrupt a few good packets before recovery, as a result of a phenomenon known as “State Error”[1].