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Feature Descriptions MDM6000 Satellite Modem
14.8.3 AUPC Approaches
14.8.3.1 Beacon Based
For non ALC transponders, a possible implementation of AUPC is to use a dedicated beacon
receiver that measures the level of a beacon signal on the transponder. Variations in the beacon
level can only be created by fading that is present between the satellite and the uplink station where
the beacon receiver is located. The level of the beacon is then used to adjust the uplink power to
compensate for uplink fading.
A beacon receiver based AUPC mechanism requires additional hardware at the power control site.
This additional hardware allows however to distinguish between uplink and downlink fading as well.
This mode of AUPC can be operated in combination with transponders in FGM or
ALC mode.
14.8.3.2 Simple Implementation of AUPC
Another simple implementation of AUPC on modems which does not require additional hardware, is
to measure the Es/No (or Eb/No) on the receiving side and communicating it to the sending side
(over a return link) such that if the Es/No decreases, the output power of the sending side is
increased.
This works fine if the fade indeed occurs at the uplink. For interference or fades on the downlink this
may have the effect of increasing the power of the carrier without improving the receive level and
potentially violate the satellite operator defined power density ratios.
These mechanisms are only rarely used in practice and are often limited to a small range of uplink
power changes (2~3 dB) due to the difficult control of input power at satellite level.
For this reason the gain of this Es/No based AUPC is typically limited to a few dB in order to avoid
too much quality loss in the case of downlink fading, and also to protect the other carriers on the
transponders.
Most satellite operators don't allow AUPC on their transponders to assure that the bandwidth
equivalent power requirements are respected at all times.
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