Digital television on ATM networks: optimum chain for coding and transmission

This paper presents a global optimization of the transmission chain for video on asynchronous transfer mode (ATM) channels. This optimum control includes compression, transmission, and decoding. First, the gain in statistical multiplexing is put forward to demonstrate that transmitting at variable rates on asynchronous multiplexing links is more efficient than exploiting the constant rate on synchronous links. The joint optimization relies on both the entropy rate and the end-to-end image quality. This requires the characterization of the video sources as entropy generators, and the development of the entropy rate-distortion functions in the coder and the transmission channel. Quantizers and variable-length entropy coders in coding, traffic, and queues in transmission multiplexing each lead to performance functions expressing quality in terms of entropy rate. The objective measures of quality are, respectively, the PSNR in terms of the output data rate and the cell loss in terms of the network loads. The main advantage of transmitting on variable bit-rate channels is to permit the generation of image sequences at constant subjective quality on the coding side, and the saving of transmission bandwidth through a gain in statistical multiplexing on the network side. Mirrored control actions are described for coding and multiplexing; they lead to a unique global optimum of the transmission chain. Since the decoders are generally slaved to the coding and transmission performances, they are restricted to perform independent optimum signal reconstruction.