Source-based error mitigation for speech transmissions over erasure channels

In this paper we present a new mitigation technique for lost speech frames transmitted over loss-prone packet networks. It is based on an MMSE estimation from the last received frame, which provides replacements not only for the LPC coefficients (envelope) but also for the residual signal (excitation). Although the method is codec-independent, it requires a VQ-quantization of the LPC coefficients and the residual. Thus, in this paper we also propose a novel VQ quantization scheme for the residual signal based on the minimization of the squared synthesis error. The performance of our proposal is evaluated over the iLBC codec in terms of speech quality using PESQ and MUSHRA tests. This new mitigation technique achieves a noticeable improvement over the legacy codec under adverse channel conditions with no increase of bitrate and without any delay in the decoding process.