Problems in combining source and channel coding

Some problems in combining source and channel coding are discussed. By the example of DPCM coded video signals the effects of channel errors were analyzed to see how these effects could be minimized. An adaption strategy for source- and channel codecs is proposed based on the fact that channel decoders are particulary suited to correct small numbers of errors occurring with high probability so that greater numbers of errors occurring less frequently are left to the source decoder for reconstruction. For protection of the compressed signals a low cost tri-state channel code is proposed and its performance is outlined. Finally, the problem of optimizing a transmission system as a whole is shown to be a variational problem relating the cost of the system to the signal quality (distortion) produced at the receiver. Its solution leads to a cost-distortion function which may include all relevant parameters of the transmission system's components.