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DMD15/DMD15L IBS/IDR Satellite Modem Operation
TM051 - Rev. 5.8 3-23
The IBS Async Framer Data Mode provides a service channel between the two sites of a link
permitting the modem processors to send messages and get responses over this channel. AUPC
can be set to operate on either or both directions of a link but always requires a bi-directional
channel. Therefore, both the Modulator and Demodulator interface mode must be set to IBS
Async for the AUPC menus to be visible and for the AUPC function to operate properly. The
AUPC Functions and their descriptions are shown on Table 3-2.
Table 3-2. AUPC Functions
Function Description
AUPC ENABLE/DISABLE Enables/Disables the AUPC to function locally
AUPC Eb/No Desired E
b
/N
0
of remote modem
AUPC MIN LVL Sets minimum output power to be used
AUPC MAX LVL Sets maximum output power to be used
AUPC DEF LVL Sets default output power to be used
Note: The AUPC menus are located under the Modulator Menu as shown in Section 4.
The basic AUPC Operation is described as follows:
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 could be occurring in both directions
simultaneously. Modem “A” is transmitting to modem “B” under normal conditions and modem “B”
has a receive E
b
/N
o
of 7.5 dB. Modem “A” has been set to an AUPC E
b
/N
o
on the Front Panel of
7.5 dB, and is currently outputting –15 dBm. Next, it begins raining at location “B”, and the E
b
/N
o
drops to –7.0 then –6.8 dB. Modem “B” is constantly sending update messages to “A” and reports
the current E
b
/N
o
. When “A” sees the drop in E
b
/N
o
, it slowly begins to raise the output power, and
raises it again when it sees further drops. As the rain increases in intensity, and the E
b
/N
o
decreases again, “A” continues to increase its power level to compensate, and when the rain
diminishes and quits, it lowers its power level to compensate. The operation is therefore a
feedback control loop with the added complication of a significant time delay.
There are safeguards built into the AUPC System. First, the Modulator has two additional
parameters, which allow control of the Maximum and Minimum Power Output Levels. Second, a
default power level is specified which takes precedence over the output power level during signal
loss or loss of AUPC Channel Communication. The default power level should normally be set to
a high enough level to reestablish communication regardless of rain fade. The other controls are
built into the operating control software to limit response times and detect adverse operating
conditions.