After set up the software checks every 10 seconds that a valid satellite is allocated to every channel.
There are two modes of allocation WARM and COLD allocation, when the allocation function is entered a check is made that there is Almanac data for at least 24 satellites and that there has been a valid position fix within the last 10 seconds.
In warm allocation mode a check is then made for every channel that is NOT locked onto a satellite signal that the current satellite is still above the horizon.
In cold allocation mode for every channel that is NOT phase locked onto a satellite signal the doppler frequency will be changed to the next search bin, if the current search over all doppler offsets is complete the next satellite in a list will be allocated to the channel and the doppler frequency reset to 0 offset.
This is a simple list with the satellites ordered by a mix of orbital position and orbital slot.
WAAS satellites are also allocated differently depending on whether the receiver is in WARM or COLD WAAS allocation mode.
In COLD allocation mode the 20 PRN's allocated to SBAS geostationary correction satellites are allocated in turn to the last channel of the receiver until lock is acheived on one of the satellites, once locked the receiver will get a series of almanac messages from the satellite which contain rough position data forall the WAAS satellites operated by the FAA. In WARM mode only the satellites for which the receiver has almanac data are cyclde through.
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