Comtech EF Data CDM-425, Installation And Operation Manual

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CDM-425 Advanced Satellite Modem
Revision 0
Appendix C C–1 MN-CDM-425
Appendix C. AUPC (AUTOMATIC
UPLINK POWER CONTROL)
C.1 AUPC Overview
WARNING! YOU MUST OBTAIN PERMISSION FROM THE SATELLITE OPERATOR
TO USE THIS FEATURE. IMPROPER USE OF THIS FEATURE COULD RESULT IN
A TRANSMITTING TERMINAL SERIOUSLY EXCEEDING ITS ALLOCATED FLUX
DENSITY ON THE OPERATOR’S SATELLITE. THIS COULD PRODUCE
INTERFERENCE TO OTHER CARRIERS, AND COULD CAUSE TRANSPONDER
SATURATION PROBLEMS.
The Automatic Uplink Power Control (AUPC) permits a local modem to adjust its own output
power level in order to attempt to maintain the Eb/No at the remote modem. To accomplish this,
you must use one of the following framing types if not running in IP-ACM Mode:
•
EDMAC, EDMAC-2, or EDMAC-3
•
D&I++
•
ESC++
•
Framed QDI
If IP-ACM mode is selected, no additional framing is required.
The remote modem constantly sends back information about the demodulator Eb/No using
reserved bytes in the overhead structure. The local modem then compares this value of Eb/No
with a pre-defined target value. If the Remote Eb/No is below the target, the local modem will
increase its output power, creating a closed-loop feedback system over the satellite link. A
particularly attractive benefit of this feature is that, whenever framed operation is selected, the
remote demodulator’s Eb/No can be viewed from the front panel display of the local modem. Note
that both EDMAC and AUPC can be used simultaneously with either framing type.
There are several important parameters associated with this mode of operation. You must
understand how the AUPC feature works, and what the implications are for setting these
parameters.