Evolution of digital HDTV transmission systems for outside broadcasting

The frequent occurrence of HD-MAC and digital HDTV live demonstrations, on the occasion of special events such as Olympic Games, has increased the demand for point-to-point outside broadcasting transmissions by satellite. Digital HDTV systems by satellite have proved their flexibility and high quality, allowing any part of Europe to be connected with transportable up-link stations, without the need of terrestrial links and without introducing the signal impairments typical of analogue systems. The RACE FLASH TV project, under the coordination of Eutelsat, is developing an innovative HDTV system for outside broadcasting, based on the principle of flexible bit-rate transmission. The basic operational bit-rate under normal propagation conditions is 70 Mbit/s, but three reduced bit-rate steps are available down to 35 Mbit/s, to cope with heavy rain fades or interferences. The rate switching is achieved automatically under the HDTV encoder control, without anomalous burst error generation and synchronisation losses. A fixed transmission symbol rate, compatible with the 36 MHz transponders of the communication satellites, is used for the various bit-rate steps