Specifications

XT55 Hardware Interface Description
Confidential / Preliminary
s
mo b i l e
XT55_hd_v00.02 Page 77 of 116 17.03.2004
4.10 Start-up procedures
The start-up strategy of the XT55 GPS part depends on the last position, current time and
ephemeris data, that the receiver has stored no-board SRAM memory. There are three
different start up procedures:
4.10.1 Coldstart
The Coldstart take place when the receiver has no knowledge of its last position or time. In
this case the GPS RTC has not been running and no valid ephemeris data or almanac data
is available (The receiver has never been navigating or no battery backup memory
available).
4.10.2 Warmstart
This start-up procedure Warmstart is performed whenever the receiver is able to use the
valid almanac data, and has not in an important manner moved since the last valid position
calculation. This procedure start if the receiver has been shut off for more than 2 hours, but
the last position, time and almanac are still acknowledged. This procedure allows it to
announce in advance the current visible satellites. However, since ephemeris data is not
available or no longer widely used, the receiver needs to wait for the ephemeris broadcast to
complete.
4.10.3 Hotstart
This procedure Hotstart is performed whenever the receiver still has access to valid
ephemeris data and exact time. This procedure start if the receiver has been shut off for less
than 2 hours and the GPS 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 announce in advance the currently visible satellites, and is
therefore able to quickly obtain and track the signal. Due to the fact that ephemeris is
already known, there is no need to wait for the ephemeris broadcast to complete.