Comtech EF Data DMD1050TS, Installation And Operation Manual

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DMD1050TS Satellite Modem Board
Revision 1
Theory of Operation 3–26 MN-DMD1050TS
3.13.2 EF AUPC
In this case, Target Eb/No indicates the local unit wants the remote unit to maintain a power level
sufficient to provide the local Eb/No value.
The EF AUPC can be set to operate on either or both directions of a link, but always requires a
bi-directional channel. Enabling AUPC on one side of the link activates AUPC on the distant end
of the link. It is necessary that both the Modulator and Demodulator be set to the applicable
framing for AUPC options to be editable, and for the AUPC function to operate correctly.
Examples of the basic EF AUPC Operations:
•
Assume that the two modems, one at each end of the link, are set to AUPC operation.
Only one direction is discussed, but the same functions can occur in both directions
simultaneously.
•
The local modem is transmitting to a modem at a remote locale under normal conditions.
The remote modem has a receive Eb/No of 7.5 dB. The local modem has been set with a
Target Eb/No of 7.5 dB, and has a current power output of –15 dBm.
•
It starts to rain at the local site, and the Eb/No drops to –7.0 dB, then to –6.8 dB. The
local modem is sending update messages of its Eb/No to the remote modem constantly.
When the remote modem sees the drop in the Eb/No, it begins to raise its output power
slowly, and continues to do so until the Target Eb/No is restored at the local site.
•
When the rain decreases, the local modem’s Eb/No starts to increase. The remote
modem lowers its power level to restore the target value.
•
The operation is a feedback control loop, with the added complication of a significant time
delay.
3.13.3 Near Side AUPC
The Near Side AUPC is a loop back system that adjusts the broadcast uplink signal when local
conditions change. This is done by having the Near Side AUPC attempt to adjust the outbound
power to compensate for local weather.
The local receiver must be tuned and locked to the transmitter, and then the internal Eb/No is
used for feedback. This creates a Tx-Satellite-Rx control loop.
Near Side AUPC is used primarily for broadcast applications, because the modem cannot expect
to receive data from a distant location. Near Side AUPC can be used with any satellite framing
mode.
There are safeguards built into the AUPC System. First, the modulator has two parameters,
which allow control of the maximum and minimum output power Levels. Second, a nominal, or
default, power level is specified, which takes effect if the receive signal or messaging is lost. This
nominal power must be set to a level high enough to re-establish communications, regardless of
rain fade.