Appendix C: Power Consumption - Iridium SHOUT nano User Manual

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Appendix C: Power Consumption

The SHOUT nano has an internal 1.95 A-Hr Li-Ion rechargeable battery. When
both the Iridium and GPS antennas have clear view of the sky and the battery is
fully charged, the nano is capable of sending more than 1,200 tracking reports
with the following settings: (1) report rate of less than two hours, (2) mailbox
check rate and the report rate are the same and (3) Standard Accuracy. Blocked
or partially blocked antennas will force the nano to retry multiple SBD
transmissions for each report and, as a result, can significantly reduce the overall
number of reporting cycles.
The nano saves valid ephemeris data after each 3-D fix. The data is used to
reduce acquisition time in the next reporting cycle from cold-start to hot-start. If
the ephemeris data is older than two hours (time between reports is set for more
than two hours), the GPS receiver will go through cold-start each time it wakes up
to send a report. As a result, the nano configured for report rate of more than two
hours and Standard Accuracy can only send ~750 tracking reports. Setting the
Accuracy to Best also reduces the number of tracking reports to ~750 regardless
of the report rate setting.
IMPORTANT: Data presented here are only estimates and are highly dependent
on the operating environment, accuracy setting and antenna type. Data are based
on measurements made with multiple nano devices placed on the roof of NAL
Research's facility with no blockage.
Each time the nano wakes up to send a report, it has two minutes to acquire a
GPS fix and send an Iridium SBD message. Assuming the ephemeris data is valid
(less than two hours old or time-between-reports is less than two hours) and the
Accuracy option is set to Standard, the GPS receiver takes about 10 seconds for a
position fix drawing approximately 55mA. The Iridium transceiver takes about 10
seconds to transmit an SBD message drawing an average current of 110mA. The
nano circuit draws about 125mA during 25-second reporting cycle. The entire
reporting cycle consumes ~1.32 mA-Hr of battery power. If the Iridium antenna is
blocked or an overhead Iridium satellite is not available, the Iridium transceiver
can potentially stay on for another 100 seconds in attempting to send a report.
This results in additional consumption of 9.7 mA-Hr or 11 mA-Hr total. A missed
report consumes ~8.5 times more power than a ‗normal' transmitted report.
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