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Chapter 8. AUTOMATIC UPLINK
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
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.
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.
POWER CONTROL
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
8–1
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