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QMultiFlex-400™ Installation and Operating Handbook
8.1 Automatic Uplink Power Control
Authorisation from the satellite operator should be sought before
AUPC is activated.
8.1.1
Introduction
Automatic Uplink Power Control (AUPC) provides a mechanism to counteract changes in
atmospheric conditions, such as rain or snow, that degrade the performance of satellite
links. It does this by monitoring the remote-end signal-to-noise ratio (Eb/No) and
automatically adjusting the local power output of the satellite link in order to maintain the
specified remote-end Eb/No. Note that if the rain is falling at the local end of the link then
the power seen at the satellite will be unchanged. However, if the rain is falling at the
remote end of the link, then the power seen by the satellite will increase, which if not
controlled carefully has the potential to affect other carriers or saturate the transponder.
Carrier power must be kept to the levels agreed with the satellite operator.
Remote Eb/No monitoring is performed by sending Eb/No messages via the return IP
channels. The AUPC implementation has an extremely low overhead.
The modem can be set to simply monitor the remote Eb/No, or to maintain it at a specified
level. A deferred alarm can be set to activate if the remote Eb/No falls below a user-set
threshold.
A target Eb/No level has to be set along with a maximum transmit power level for the local
end. The transmit power is adjusted to keep the remote Eb/No at the target value. If the
satellite link is lost, then the transmit power can be frozen at its current level until the link
is restored, or it can be returned to its nominal value.
8.1.2
Configuring AUPC
To use the AUPC function, the following procedure should be followed:
1. Prior to switching on AUPC, configure the modems at both ends of the link and
ensure the satellite link is operating correctly.
2. Set the transmit power to achieve the remote Eb/No expected under clear-sky
conditions.
3. To receive an indication of when the remote Eb/No falls below a defined threshold,
set a target Eb/No minimum threshold (which will cause a backward alarm to be
generated under these conditions).
4. Set the AUPC mode to monitor the remote Eb/No in order to determine if it is
working correctly. If the remote-end Eb/No is not available on the Status screen,
then the modems are not configured correctly.
Chapter 8 System Considerations
8-1
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