Meinberg GPS LANTIME - Handbuch (Seite 11)

Booting the GPS receiver
If both the antenna and the power supply have been connected the system is ready to
operate. About 10 seconds after power-up the receiver’s oscillator has warmed up and
operates with the required accuracy. If the receiver finds valid almanac and ephemeris
data in its battery buffered memory and the receiver’s position has not changed
significantly since its last operation the receiver can find out which satellites are in view
now. Only a single satellite needs to be received to synchronize and generate output
pulses, so synchronization can be achieved maximally one minute after power-up.
If the receiver position has changed by some hundred kilometres since last operation,
the satellites´ real elevation and Doppler might not match those values expected by the
receiver thus forcing the receiver to start scanning for satellites. This mode is called
Warm Boot because the receiver can obtain ID numbers of existing satellites from the
valid almanac. When the receiver has found four satellites in view it can update its new
position and switch to Normal Operation. If the almanac has been lost because the
battery had been disconnected the receiver has to scan for a satellite and read in the
current almanacs. This mode is called Cold Boot. It takes 12 minutes until the new
almanac is complete and the system switches to Warm Boot mode scanning for other
satellites.
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