Comtech EF Data DMD1050 - Manual (Page 48)

DMD1050 Satellite Modem Board Theory of Operation
MN-DMD1050 3–22
Revision 9
3.13 DMD1050 Automatic Uplink Power Control (AUPC Operation)
The modem has an optional built-in provision for Automatic Uplink Power Control, AUPC.
AUPC is useful when operating power levels are affected by environmental changes in the
atmosphere. AUPC attempts to adjust local power output to maintain a constant E
b
/N
o
at the
receiver location.
The modem supports three versions of AUPC. They include Radyne AUPC, EF AUPC and Near
Side AUPC. Radyne AUPC and EF AUPC use satellite overhead to send messages between the
local and remote ends of an SCPC link. The messaging is done with IBS 1/15 and EF AUPC
Framing messages.
3.13.1 Radyne AUPC
In this case, Target E
b
/N
o
indicates the remote value the local unit wants to maintain by adjusting
the local power level.
Radyne AUPC can be set to operate on either or both directions of a link but always require a bi-
directional channel. Enabling AUPC on one side of the link will activate AUPC on the distant
end of the link. It is necessary that both the Modulator and Demodulator be set to the appropriate
framing for AUPC options to be editable and for the AUPC function to operate properly.
Examples of the basic Radyne AUPC Operations are described as follows:
Assume that the two modems, one at each end of the link, are set to Radyne AUPC operation.
Only one direction is discussed, but the same functions could be occurring in both directions
simultaneously.
Local Modem is transmitting to Remote modem under normal conditions and the Remote modem
has a receive E
b
/N
o
of 7.5 dB. Local modem has been set to a Target E
b
/N
o
of 7.5 dB with an
output power level of -15 dBm.
It begins raining at Remote site and the E
b
/N
o
drops to –7.0 then –6.8 dB. Remote Modem is
constantly sending update messages of its E
b
/N
o
to Local modem. When Local modem sees the
drop in the remote E
b
/N
o
, it slowly begins to raise the output power, and will continue to adjust if
the remote E
b
/N
o
continues to drop. As the rain increases in intensity, the remote E
b
/N
o
decreases
but Local modem continues to increase its power level to compensate.
When the rain diminishes, Local modem will see the remote E
b
/N
o
begin to increase. Local
modem will lower its power level. The operation is therefore a feedback control loop with the
added complication of a significant time delay.
Implementing Strap Code 26 can set the following modem configuration.
Refer to Table 4-4 for an explanation and tabular listing of available
Strap Codes. The Frequency and Modulator Output Power are set
independently of the strap code.
IMPORTANT