Dynamically Adding Redundancy For Improved Error Concealment In Packet Voice Coding
Levent Tosun, P. Kabal · eScholarship@McGill (McGill) · 2004
Data is sent in packets of bits over the Internet. However, packets may not arrive in order or in time for playout. Packet loss is a frequently encountered problem in Voice-over-IP (VoIP) applications. Modern speech coders use past information to decode current packets in order to reach very low bit-rates. Therefore, when a packet is lost, the effect of this packet loss propagates over several subsequent packets. In this thesis, a new redundancy-based packet-loss-concealment scheme is presented. Many redundancy-based packet-loss-concealment schemes send a fixed amount of extra information about the current packet as part of the subsequent packet, but not every packet is equally important for packet loss concealment. We have developed an algorithm to determine the importance of packets and we propose that extra information should only be sent for the important packets. This provides a lower average bit-rate compared to sending the same amount of extra information for each and every packet. We use a linear prediction (LP) based speech coder (ITU-T G.723.1) as a test platform and we propose that only the excitation parameters should be sent as extra information since LP parameters of a frame can be estimated using the LP parameters of the previous frame. Furthermore, we propose that excitation parameters of an important frame that are sent as redundant information should be used in the reconstruction of the lost waveform---as a consequence, the states of the subsequent frame will also be updated.