A fundamental issue in real-time interactive voice transmissions over unreliable IP networks is the loss or late arrival of packets for playback. Such losses cannot be recovered by retransmissions due to tight time constraints in interactive applications. This problem is especially serious in transmitting low bit-rate coded speech when pervasive dependencies are introduced in a bit stream, leading to the loss of subsequent dependent frames when a single packet is lost or arrives late. In this paper, we propose a novel LSP-based multiple-description coding method that adapts its number of descriptions to network loss conditions in order to conceal packet losses in transmitting low-bit-rate coded speech over lossy packet networks. Based on high correlations observed in linear predictor parameters, in the form of Line Spectral Pairs (LSPs), of adjacent frames, we generate multiple descriptions in a sender by interleaving LSPs, and reconstruct lost LSPs in a receiver by linear interpolations. Without increasing the transmission bandwidth, our scheme represents a trade-off between the quality of received packets and the ability to reconstruct lost packets. Our experimental results on FS CELP show good performance.
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