Coded channels. Digital television by satellite

摘要

Digital compression techniques will allow satellite TV broadcasting to continue to compete effectively with broadband cable. Instead of transmitting a continuously varying analogue electrical voltage to represent the picture, digital television converts each of the pixels that makes up a TV picture into a coded message. Provided that a receiver can decode the digital message, it can build up a completely new picture, dot by dot, on the screen, with perfect results. As digital compression of television signals becomes the norm, and broadcasters try to squeeze ten or more, services down the same bandwidth that used to carry just one analogue picture, lessons will be learned-about what is acceptable on different types of picture material. Variable rates of compression could perhaps be applied to different scenes in real time, and the channel bandwidth provided for each programme being transmitted over a satellite transponder could be varied dynamically according to the data rate that each scene requires. The author discusses these various aspects of data compression and channel coding.