Deluo TRISTAR25 - Manual (Page 6)

Deluo Electronics http://www.deluo.com
6
2 Receiver Operation
Upon power up, after initial self-test has completed, the TISTAR25 will begin satellite
acquisition and tracking process. Under normal open-sky condition, position-fix can be
achieved within approximately 45 seconds (within 15 seconds if valid ephemeris data is
already collected from recent use). After receiver position has been calculated, valid position,
velocity and time information are transmitted through the on board serial interface.
The receiver uses the latest stored position, satellite data, and current RTC time to achieve
rapid GPS signal acquisition and fast TTFF. If the receiver is transported over a large distance
across the globe, cold-start automatic-locate sequence is invoked. The first position fix may
take up to five minutes searching the sky for the GPS signal. The acquisition performance can
be improved significantly if the host initializes the receiver with a rough estimate of time and
user position.
As soon as GPS signal is acquired and tracked, the TISTAR25 will transmit valid navigation
information through its serial interface. The navigation data contains following information:
! Receiver position in latitude, longitude, and altitude
! Receiver velocity
! Time
! DOP error-magnification factor
! GPS signal tracking status
The TISTAR25 will perform 3D navigation when four or more satellites are tracked. When three
or fewer satellites are tracked, altitude-hold is enabled using the last computed altitude and 2D
navigation mode is entered.
With signal blockage or rising and setting of the satellites, where a change in satellite
constellation used for position fix occurred, large position error may result. The TISTAR25
incorporates a proprietary algorithm to compensate the effect of satellite constellation change,
and maintains an accurate smooth estimate of the receiver’s position, velocity, and heading.