Model: MTS200 (1U)
Doc. Ref. no. : m08/om/201
Issue no. : 03
User’s Manual
Page 36 of 195
Page 36 of 195
8 Start-Up Operation
8.1 Receiver Boot-up mode
When
mas
TER
T-Sync
Model MTS200 unit is power up, the time of unit depends on the GPS receiver
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 UNLOCK 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 information 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 information,
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 position in Cold start is
less than <45 seconds (when GPS Antenna is placed in open sky conditions without any obstacle
interference)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
almanac data is transmitted by satellite in 12.5 minutes. So, in order to have very highly accurate position
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 current
almanac satellite data, time which receiver knows is within 20 seconds from the satellite time, receiver
position to within 100 kms 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 (when GPS Antenna is placed in open sky conditions without any obstacle interference)
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.
