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

摘要

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 in- ternal clocks and aid network synchronisation. Where the NCR is generated at a ground Hub station the delays be- tween Hub and satellite (and the reverse path) must be mea- sured, 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 re- sults in NCR delay variance (jumps) beyond acceptable lim- its for correct RCST frequency regeneration. An on--board NCR clock aids a system architecture that encompasses for- ward link switching and can be justified in these circum- stances.