A3LA-R-MIL-MOD User Guide Version B
Document Number: 451-93156-001A
75 of 159
Iridium system time source: The system time is available and valid only after the A3LA-
R has registered with the network and has received the Iridium system time from the
network. Once the time is received, the A3LA-R uses its internal clock to increment
the counter. In addition, at least every 8 hours, or on location update or other event
that requires re-registration, the A3LA-R will obtain a new system time from the
network.
Time localization: None. The system time value is always expressed in GMT time.
Resolution and accuracy: The resolution of the system time is one Iridium frame tick,
or 90 ms. Accuracy as measured by the difference between the time reported and the
actual time this message is sent out of the A3LA-R’ serial port should not exceed 4
frame ticks (.36 seconds) and in most cases will be one frame tick (.09 seconds) or less.
B.75 –MSGEO
–
R
EQUEST
G
EOLOCATION
Exec Command: –MSGEO
Query the geolocation grid code received from the network in the last Access Decision
Notification message. The response is of the form:
–MSGEO: <x>,<y>,<z>,<time_stamp>
<x>, <y>, <z> is a geolocation grid code from an earth centered Cartesian coordinate
system, using dimensions, x, y, and z, to specify location. The coordinate system is
aligned such that the z-axis is aligned with the north and south poles, leaving the x-
axis and y-axis to lie in the plane containing the equator. The axes are aligned such
that at 0 degrees latitude and 0 degrees longitude, both y and z are zero and x is
positive (x = +6376, representing the nominal earth radius in kilometers). Each
dimension of the geolocation grid code is displayed in decimal form using units of
kilometers. Each dimension of the geolocation grid code has a minimum value of –
6376, a maximum value of +6376, and a resolution of 4. <time_stamp> is assigned by
the A3LA-R when the geolocation grid code received from the network is stored to
the A3LA-R internal memory. Current Iridium system time, which is a running count
of 90 millisecond intervals, is used for the time stamp. Time stamp is a 32-bit integer
displayed in hexadecimal form.