Fine-search synchronisation for a switching satellite

An analysis is presented which examines the problem of synchronisation of ground stations to the synchronisation window of a switching satellite. The physical model considered includes the effects of uplink space delay and attenuation, uplink noise, motion of the satellite, downlink space delay and attenuation and downlink noise. Assuming the use of either p.s.k. or f.s.k. synchronisation bursts and a coherent receiver in the ground station, it is shown that the timing error between the synchronisation burst and the synchronisation window can be represented by an error-detection characteristic. This characteristic provides an error voltage which can be used by the ground station to adjust the frequency of a voltage-controlled oscillator (v.c.o.) and thus reduce the timing error. The analysis shows that repeated transmission of synchronisation bursts and adjustments of the v.c.o. leads, in a convergent series of steps, to reduced timing errors. The final timing error thus depends only on uplink and downlink signal/noise ratios and satellite motion.