Optimized unequal error protection for voice over IP

In voice over IP, typical forward error correction (FEC) schemes to combat packet loss allocate an equal amount of error-control resources to each voice packet, regardless of the perceptual importance of a packet. Recognizing the unequal perceptual importance of voice packets, we propose signal-adaptive unequal error protection methods in which certain packets are allocated more error-control resources than others. In particular, the amount of error protection provided to a packet is determined through an analysis by the expected decoder synthesis paradigm ensconced within a rate-distortion Lagrangian optimization framework. Therefore, the sender evaluates various protection policies by anticipating the behavior of the decoder's packet loss concealment (PLC) algorithm for various loss event probabilities. In this manner, perceptually critical voice packets that cannot be easily replaced by a PLC are provided with greater error protection. For a given average bit-rate, a simple unequal error protection scheme provides a 0.2 to 0.3 advantage in PESQ-MOS (perceptual evaluation of speech quality mean opinion score) over the conventional equal error control schemes.

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