Chapter 8. AUTOMATIC UPLINK
POWER CONTROL
8.1
Introduction
A
utomatic
U
plink
P
ower
C
ontrol (AUPC) is a feature whereby a local modem is permitted to
adjust its own output power level in order to attempt to maintain the Eb/No at the remote modem.
WARNING
The user 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.
To accomplish this, one of the following types must be used:
•
EDMAC or EDMAC-2
•
D&I++
•
ESC++
•
E1 D&I with CCS
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, and the user needs
to understand how the AUPC feature works, and the implications of setting these parameters.
8–1
