Model: MC-1-DE
Doc Ref. No:-m05dom102
Issue No:-00
User’s Manual
Page 28 of 76
7. GPS TIME SYNC UNIT MC-1-DE
Power ON
7.1 Receiver Boot-up mode
When GPS TIME SYNC UNIT MC-1-DE unit is power up, the time of unit depends on the GPS re-
ceiver RTC data. At every Power ON, unit is in UNLOCK mode initially. If GPS antenna is connected
after Power ON or was already connected while powering up the unit, the time to getting unit LOCK
depends on the duration for which the unit was in Power OFF condition. Also, if the unit was in UN-
LOCK condition during the normal operation of unit, the time taken by unit to get LOCK after antenna
is connected depends on the duration for which unit was in UNLOCK condition.
Refer below explanation for time taken by unit to get LOCK after Power off or UNLOCK condition.
For a receiver to obtain a position fix, it must download the almanac and ephemeris information from
the satellite through a satellite frame
.
The receiver must download almanac and ephemeris informa-
tion to achieve a position fix. Depending on the parameters such as valid almanac, ephemeris data of
previous visible satellites, last position of receiver and time stored, the boot process (Cold start /
Warm start / Hot start) mode is determined.
Cold start: If the GPS receiver does not have any initial data regarding current almanac, ephemeris
data (case when backup battery is discharged) or it has invalid data for almanac and ephemeris in-
formation, on boot up the receiver will enter in Cold start mode. In order to get current almanac data,
GPS receiver should receive at least one satellite frame. Typically, TTFF (Time to First Fix) for posi-
tion in Cold start is less than < 45 seconds because each GPS receiver may take few seconds time to
get initialized on boot up and as each satellite frame takes 30 seconds to transmit single frame.
Since each satellite transmits total 25 frames as satellite complete broadcast message, complete al-
manac data is transmitted by satellite in 12.5 minutes. So, in order to have very highly accurate posi-
tion and time data, to reach 90% confidence level after acquiring complete almanac data from each
satellite, Cold start for TTFF (Time to First Fix) can be < 15 minutes, it will acquire almanac and
ephemeris data for visible satellites and thereafter receiver will enter in its normal operation mode. In
this case, it is necessary that antenna should be located in open environment having no immediate
obstacles.
If the device is moved to very far location in hundreds of kilometers from its last operation position
and system is made ON, then receiver will try to identify visible satellites data and compare it with
previously stored almanac data. If this does not match, receiver will start as in Cold start mode.
Warm or Normal start: In the warm start mode, when the receiver boots and if the information of cur-
rent almanac satellite data, time which receiver knows is within 20 seconds from the satellite time, re-
ceiver position to within 100 km, but do not have ephemeris information or ephemeris information
may be invalid, the receiver enters Warm start mode. Typically, time required for position fix in Warm
mode is less than 38 seconds as each satellite transmits its ephemeris data at every 30 seconds.
If the receiver does not have valid almanac data, it enters the Cold start mode.
Hot start: When receiver boots up, if the information/data of current almanac, position, current time is
stored and are valid, receiver enter Hot start mode and provides accurate time within few tens of
seconds.