Speech-and Network-Adaptive Layered G. 729 Coder for Loss Concealments of Real-Time Voice Over IP

In this paper, we propose a layered CELP speech coding (LC) scheme that adapts dynamically to the characteristics of the speech encoded and the network loss conditions in real time transmissions of voice over IP. Based on the ITU G.729 CS-ACELP codec operating at 8 Kbps, we design a variable bit-rate codec that is robust to losses and delays in IP networks. To cope with bursty losses while maintaining an acceptable end-to-end delay, our scheme employs LC with redundant piggybacking of perceptually important parameters in the base layer, with a degree of redundancy adjusted according to feedbacks from receivers. Under various delay constraints, we study trade-offs between the additional bit rate required for redundant piggybacking and the protection of perceptually important parameters. Experimental results show that our scheme works well and has quality comparable to full replication