Iridium SHOUT nano User Manual page 24

Accuracy
Accuracy option allows user to select either Standard or Best accuracy when
acquires a 3-D GPS fix. For Standard setting, the nano acquires 3-D fix using
saved ephemeris data in its non-volatile memory. The ephemeris is updated only
when becomes invalid. For Best setting, the nano always updates the ephemeris
data first before attempting to obtain a 3-D fix. The Best setting takes longer for a
3-D fix. However, the probability of obtaining position accuracy to within 2.5
meters is much higher than for the Standard setting. Best setting is not
recommended when operated in environments with limited view of the sky such
as under heavy foliage. Choosing Best accuracy setting can significantly reduce
the total number of reports on a fully charged battery because of longer GPS
acquisition time. Choosing Best accuracy is the same as setting the report rate to
more than two hours. For both cases, the nano has to update the ephemeris data.
Again, as a reminder, user is encouraged to read the Power Consumption section.
Format
The SHOUT nano can transmit position reports in either 30-byte format or 10-byte
format. The 30-byte format includes UTC date, UTC time, latitude, longitude,
altitude, speed, course, vertical velocity, number of satellites used to obtain 3-D
fix, HDOP and VDOP. The latitude and longitude are recorded with ~0.18 meters
resolution.
The 10-byte format includes UTC time, latitude, longitude and PDOP. With UTC
date omitted, the nano relies on the NOC server to record the date. Encryption
cannot be used with the 10-byte format. Latitude and longitude are recorded with
~1.1 meters resolution. Even though the message length is shorter, a 10-byte
format message consumes the same amount of power to transmit as a 30-byte
format. It is to be selected strictly for the purpose of airtime cost-saving.
SHOUT nano User's Manual Version 1.0
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