A Dynamic FEC for Improved Robustness of CELP-Based Codec

The strong interframe dependency present in Code Excited Linear Prediction (CELP) codecs renders the decoder very vulnerable when the Adaptive Codebook (ACB) is desynchronized. Hence, errors affect not only the concealed frame but also all the subsequent frames. In this paper, we have developed a Forward Error Correction (FEC)-based technique which relies on energy constraint to determine frame onset which will be considered for sending the FEC information. The extra information contains an optimized FEC pulse excitation which models the contribution of the ACB to offer a resynchronization procedure at the decoder. In fact, under the energy constraint the number of Fixed Codebook (FCB) pulses can be reduced in order to be exploited by the FEC intervention. In return, the error propagation is considerably prevented with no overload of added-pulses. Furthermore, the proposed method greatly improves the CELP-based codec robustness to packet losses with no increase in coder storage capacity.