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Acutime 2000 Synchronization Kit User Guide F-9
F Theory of Operation
If ephemeris or almanac data is available for the lost satellite, then the
satellite's velocity is factored into the center frequency calculation.
The diminished accuracy of an older almanac is accounted for in the
width of the search range. If neither the ephemeris nor almanac is
available, then the Doppler frequency at last lock is searched for two
minutes. If the satellite has not been re-acquired after two minutes,
then the maximum expected Doppler frequency, based on satellite
dynamics, is searched.
If the current position is not accurately known, the search width is
increased. If the smart antenna is computing velocity or velocity
aiding is provided, then the receiver's motion is also factored into the
Doppler frequency. If velocity information is not available, then the
dynamics code is used to determine the maximum expected Doppler
frequency.
The re-acquisition time for momentary signal blockages is typically
under two seconds.