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.