Automatic Uplink Power Control; Introduction; Configuring Aupc - Paradise Datacom Quantum Installation And Operating Handbook

Quantum and Evolution Series Installation and Operating Handbook

8.3 Automatic Uplink Power Control

Authorisation from the satellite operator should be sought before
AUPC is activated.
8.3.1

Introduction

Automatic Uplink Power Control (AUPC) provides a mechanism to counteract changes in
atmospheric conditions, such as rain, that degrade the performance of satellite links. It
does this by monitoring the distant-end signal to noise ratio (Eb/No) and automatically
adjusting the local power output of the satellite link to maintain the specified distant-end
Eb/No.
Distant Eb/No monitoring is performed by sending messages through the asynchronous
ESC channel (which is carried over the satellite multiplexed with the main data channel).
An asynchronous ESC channel is available in Closed Network (Minimum Overhead),
IBS/SMS and IDR modes. AUPC requires dedicated use of the ESC channel and while
the ESC channel is being used for AUPC then it is not available for other purposes.
The modem can be set to either just monitor the distant Eb/No or to maintain it at a
specified level. As well as being able to view the distant Eb/No and BER estimate, a
deferred alarm can be set to activate if the distant Eb/No falls below a user-set threshold
and the distant-end Eb/No can be recorded regularly in the local-end traffic log.
To maintain the distant Eb/No, a target Eb/No level has to be set along with a maximum
transmit power level for the local end. When the target Eb/No is exceeded by more than a
pre-defined tolerance, the transmit power is adjusted to bring the distant Eb/No back to
the target value. The power will continue to be adjusted automatically until the Eb/No
settles on the target value. The use of a tolerance value prevents continual transmit
power variations under normal minor thermal noise variations. The rate at which
adjustments are made is automatically controlled in such a way as to prevent rapid power
variations. If the satellite link is lost, then the transmit power will freeze at its current level
until the link is restored.
8.3.2

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 basic satellite link is operating correctly.
2. Set the transmit power to achieve the distant Eb/No expected under clear-sky
conditions. The ESC channel is automatically configured during AUPC operation
and any user ESC channel settings are ignored. However, use of the ESC
channel by the AUPC function will change the bandwidth of the signal and may
have a slight affect on the Eb/No. To counteract this, configure the ESC channel
to a nominal baud rate of 2400 when setting up.
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