Cognitive Networks: Towards Self-Aware Networks

13.6. Multiple Description Codes

Multiple description coding (MDC) is a recent source coding approach that is gaining popularity as a viable coding mechanism for delivery of multimedia data over networks, especially because networks typically have multiple paths between the transmitter and the receiver. In such a scheme, several representations of the source, called descriptions, are generated such that the quality of the received signal is proportional to the number of descriptions received and not which descriptions were actually received ^[], ^[]. Such a coding scheme is well suited to packet networks and fading wireless channels. Unlike layered coding, however, the quality of the received video does not depend on which descriptions are actually received only on how many of them are received and hence we can consider MDC as a generalization of the layered coding.

MDC is a form of data partitioning, thus comparable to layered coding as it is used in MPEG-2 and MPEG-4. Yet, in contrast to MDC, layered coding mechanisms generate a base layer and n enhancement layers. The base layer is necessary for the media stream to be decoded, enhancement layers are applied to improve stream quality. However, the first enhancement layer depends on the base layer and each enhancement layer n + 1 depends on its subordinate layer n, thus can only be applied if n was already applied. Hence, media streams using the layered approach are interrupted whenever the base layer is missing and, as a consequence, ...