Joint Exploitation of Residual Source Information and MAC Layer CRC Redundancy for Robust Video Decoding

This paper presents a MAP estimation method allowing the robust decoding of compressed video streams by exploiting the bitstream structure (Le., information about the source, related to variable-length codes and source characteristics) together with the knowledge of the MAC layer CRC (here considered as additional redundancy on the MAC packet). This method is implemented via a sequential decoding algorithm in which the branch selection metric in the decoding trellis incorporates a CRC-dependent factor, and the paths which are not compatible with the source constraints are pruned. A first implementation of the proposed algorithm performs exact computations of the metrics, and is thus computationally expensive. Therefore, we also introduce a suboptimal (with tunable complexity) version of the proposed metric computation. This technique is then applied to the robust decoding of sequences encoded using the H.264/AVC standard based on CAVLC and transmitted using a WiFi-like packet structure. Significant link budget improvement results are demonstrated for BPSK modulated signals sent over AWGN channels, even in the presence of channel coding.