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CDM-625A Advanced Satellite Modem
Appendix C
C.2.3 Alarm
This defines modem behavior if the maximum power limit is reached while under AUPC control.
The two choices are:
•
NONE (no action) – default setting.
•
Tx ALARM (generate a Tx alarm).
C.2.4 Demod Unlock
This defines the action the modem will take if the remote demodulator loses lock. The two
choices are:
•
NOMINAL (reduce the Tx Output Power to the nominal value) – default setting.
•
MAXIMUM (increase the Tx Output Power to the maximum value permitted by the
parameter MAX RANGE).
If the local demod loses lock, then the modem automatically moves its output power
to the nominal value.
C.3
Compensation Rate
As with any closed-loop control system, you must choose loop parameters that ensure stability
at all times. Several features ensure that the AUPC system does overshoot, or oscillate:
•
First, corrections for which the output power can be made are fixed at the rate of once
every 4 seconds. This takes into account the round trip delay over the satellite link, the
time taken for a power change to be reflected in the remote demodulator's value of
Eb/No, and other processing delays in the modems.
•
Second, if the comparison of actual and target Eb/No yields a result that requires a
change in output power, to avoid the possibility of overshoot the first correction made
will be at 80% of the calculated step. Subsequent corrections are made until the
difference is less than 0.5 dB. At this point, the output power is only changed in
increments of 0.1 dB to avoid 'hunting' around the correct set point.
C–3
Revision 0
MN-CDM625A
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