Steganographic Pulse-Based Recovery for Robust ACELP Transmission over Erasure Channels

This paper presents an ACELP-based speech transmission scheme that is robust to frame erasures. The scheme is based on the steganographic transmission of media-specific FEC codes. These FEC codes are intended to prevent the adaptive codebook desynchronization frequently found in the decoder after a frame erasure. They are based on a multipulse representation of the previous frame excitation. By means of steganographic methods, the FEC codes are embedded into the codec bitstream, thus causing no bit rate increase. In particular, an ACELP-specfic steganography approach exploits the inefficiencies in the ACELP codebook search and imposes certain algebraic restrictions which allow the hiding of data in the ACELP codewords. Effectively, side information can be transmitted without compromising the codec speech quality. The performance of our proposal is evaluated with the well-known AMR ACELP codec, both in terms of speech quality and intelligibility. To this end, objective measures, i.e. PESQ and STOI, are applied. The proposed coding scheme achieves a noticeable improvement over the legacy codec under adverse channel conditions without consuming any additional bit rate.