Terminal timing synchronisation in DVB‐RCS systems using on‐board NCR generation

In DVB‐RCS systems, Return Channel Satellite Terminals (RCST) receive a stream of Network Clock Reference (NCR) packets from a central Hub station to regenerate their internal clocks and aid network synchronisation. Where the NCR is generated at a ground Hub station the delays between Hub and satellite (and the reverse path) must be measured; an allowance for the measurement error is made in the guard time. The bandwidth efficiency gains of locating the NCR clock on‐board the satellite are evaluated: for high transmission rates the gain may be worthwhile whereas for lower rates a negligible benefit exists. In some applications, on‐board processing may be used to switch packets on the forward link (for routing to different beams). With an on‐ground NCR source, the satellite switching most likely results in NCR delay variance (jumps) beyond acceptable limits for correct RCST frequency regeneration. An on‐board NCR clock aids a system architecture that encompasses forward link switching and can be justified in these circumstances.