Chapter 11. Automatic Uplink Power Control; Introduction - Comtech EF Data CDM-570L Installation And Operation Manual

Chapter 11. AUTOMATIC UPLINK
11.1

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, or EDMAC-2) 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.
11–1