18.6.1 Introduction

During the early to mid 1960s the coding of various signals, including television, had been studied with a view to their transmission via digital telecommunications transmission networks. The stimulus for these networks derived from the coming together of semiconductor technology and pulse code modulation (PCM). Now, the convergence of technologies capable of processing images is such that computing, telecommunications and broadcasting are merging into an integrated whole. In the future, this distinction will disappear, not only for the image producers but also for the viewers.

The digitisation of broadcasters' signals had a major advantage for contribution and distribution applications in that, once in the digital format, there would be no significant difference between them and, say, multiplexed telephony signals and so these early ideas were a step on the way to the integrated services digital network (ISDN). They would mean the removal of separate link systems and procedures for television and telephony with an attendant reduction in cost and network flexibility34.

The remainder of this Chapter concentrates on the various aspects of digital video compression and its applications to satellite-delivered services. Both professional and domestic services are considered but the DTH/DBS application is given some prominence because of its greater public interest and because it represents the most significant technical and commercial challenges. The aspects considered below include: source coding, channel coding, error control, modulation and link performance, multiplexing and satellite-access methods. Finally, there is a summary of implementational aspects to give a practical conclusion.