Mocomtech CDM-570 Manuel D’Utilisation

CDM-570/570L Satellite Modem with Optional IP Module 

Revision 4 

Automatic Uplink Power Control 

MN/CDM570L.IOM 

The Alarm parameter defines how the user wants the modem to act if, under AUPC 
control, the maximum power limit is reached.  
 
The two choices are: 
•  None (no action) 
•  Tx-Alarm (generate a TX alarm) 
 
The default setting is None. 

This defines the action the modem will take if the remote demodulator loses lock. 
 
The two choices are: 
•  Nom-Pwr (reduce the Tx Output Power to the nominal value) 

•  Max-Pwr (increase the Tx Output Power to the maximum value permitted by the 

parameter Max-Range) 

 
The default setting is Nom-Pwr. 
 
(Note: If the local demod loses lock, the modem will automatically move its output 
power to the nominal value.) 

As with any closed-loop control system, the loop parameters must be chosen to ensure 
stability at all times. Several features have been incorporated to ensure that the AUPC 
system does overshoot, or oscillate. 
 

•  First, the rate at which corrections to the output power can be made is fixed at 

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, the first correction made will be 80% of the calculated 
step. This avoids the possibility of overshoot. 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. 

 
 

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