u-blox ANTARIS 4, Руководство по системной интеграции

Страница: 13 / 187

Warmstart
Warmstart is performed whenever the receiver has only access to valid almanac data, and has not significantly
moved since the last valid position calculation. This is typically the case, if the receiver has been shut off for more
than 2 hours, but still has knowledge of last position, time and almanac. This allows it to predict the current
visible SVs. However, since ephemeris data is not available or outdated, the receiver needs to wait for the
ephemeris broadcast to complete.
Hotstart
Hotstart is performed whenever the receiver still has access to valid ephemeris data and precise time. This is
typically the case if the receiver has been shut off for less than 2 hours and the RTC has been running during
that time. Furthermore, during the previous session, the receiver must have been navigating (to allow it to
decode and store ephemeris data).
In Hotstart, the receiver can predict the currently visible SVs, and is therefore able to quickly acquire and track
the signal. Because ephemeris is already known, there is no need to wait for the ephemeris broadcast to
complete.
Current Time
and last position
known?
Valid ephemeris
available?
Coldstart
Warmstart
Hotstart
No
Yes
Yes
No
startup
Figure 3: Decision Tree on Startup Mode
If external aiding information like ephemeris and/or precise position and time are provided to the receiver, the
Time To First Fix can be significantly improved. Refer to Section 4.5.4 for further information.
GPS Modules - System Integration Manual (SIM) (incl. Reference Design) GPS Fundamentals
GPS.G4-MS4-05007-A1 Page 13