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8–1
Chapter 8. AUTOMATIC UPLINK
POWER CONTROL
8.1 Introduction
Automatic Uplink Power Control (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 SHALL 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, the framed (EDMAC) mode of operation must be used. 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, and hence, a closed-loop feedback system is created 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 also that AUPC can be used simultaneously with
EDMAC.