Trimble Outdoors Part Number 45005-00-ENG, AcutimeTM2000 Synchronization Kit manual Warm Start

Theory of Operation F

F.2.2 Warm Start

In a warm start condition, the receiver has a current almanac, an initial position (within 3,000 km) and current time (within five minutes) stored in memory. Although the smart antenna does not have an onboard battery for preserving memory, it can be initialized using the TSIP protocol. To force a warm start, the almanac, time, and initial position must be uploaded to the receiver.

During a warm start, the smart antenna identifies the satellites that are expected to be in view, given the system almanac, the initial position and the time. The receiver calculates the elevation and expected Doppler shift for each satellite in this expected set and directs the eight tracking channels in a parallel search for these satellites. If the internal oscillator error is known, the smart antenna compensates for the offset to optimize the search. If the offset is not known, the search algorithms are set wide enough to allow for oscillator tolerance, aging, and temperature errors.

If the receiver has an almanac and an initial position, but does not have the current time, it executes a cold start search until the first satellite is acquired. Once this first satellite is acquired, the receiver can obtain an approximate time and will convert to warm start mode to acquire additional satellites. Although the time to first fix is slightly longer in this case, it is significantly shorter than a complete cold start.

The warm start time to first fix is usually less than 50 seconds (40 seconds is typical).

F-4 Acutime 2000 Synchronization Kit User Guide