Field trial of mixed analogue and digital TV carriers in one transponder and analysis of mutual effects

Abstract

Techniques of TV digital coding and transmission via communication satellites is being developed rapidly. The traditional analogue technique will be replaced by the digital modulation in the next few years. During this transition period, there will be a lot of situations where analogue and digital carriers share the same transponder. In this experiment, an INTELSAT 45Mbit/s IDR circuit combined with a 45Mbit/s video codec was established and transmission characteristics including video and audio quality were measured. It was confirmed that a contribution quality digital TV signal can be transmitted up to three channels over the single 45Mbit/s digital carrier. Mutual effects between an analogue and a digital TV carriers transmitted in a same transponder were investigated. In the case where a digital and an analogue carriers share a same transponder with the same e.i.r.p., the C/N of analogue carrier turns out to be 1 dB lower than the value for the case of two analogue carriers in one transponder. In order to preserve the analogue carrier C/N, the digital carrier input backoff should be set more than 2dB lower than that of the analogue carrier. The degradation is caused by the AM-PM and the AM-AM conversion of the satellite transponder operating at small input and output backof f s .