Radyne DMD20 LBST, Инструкция по установке и эксплуатации

Страница: 276 / 306

DMD20/20LBST Universal Satellite Modem AUPC Operation
MN-DMD20-20LBST Revision 14 G–2
G.1.2 EF AUPC
In EF AUPC mode, the Target E
b
/N
o
indicates the local unit wants the remote unit to maintain a
power level sufficient to provide the local E
b
/N
o
value.
EF 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 EF AUPC Operations are 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.
The local modem is transmitting to modem at a remote locale under normal conditions. The
remote modem has a receive E
b
/N
o
of 7.5 dB. The local modem has been set with a Target E
b
/N
o
of 7.5 dB, and has a current power output of –15 dBm.
It begins to rain at the local site, and the E
b
/N
o
drops to –7.0 then –6.8 dB. The local modem is
constantly sending update messages of its E
b
/N
o
to the remote modem. When the remote
modem sees the drop in the E
b
/N
o
, it slowly begins to raise its output power, and will continue to
do so until the Target E
b
/N
o
is restored at the local site.
When the rain diminishes, the local modem’s E
b
/N
o
will begin to increase. The remote modem
will now lower its power level to restore the target value. The operation is therefore a feedback
control loop with the added complication of a significant time delay.
G.1.3 Near Side AUPC
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 E
b
/N
o.
, is
used for feedback. This creates a Tx-Satellite-Rx control loop.
Near Side AUPC is primarily used for broadcast applications since the modem cannot expect to
receive data from a distant location. Near Side AUPC can be utilized with any satellite framing or
Network 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 should be set to a level high enough to re-establish communications regardless of
rain fade.
EF AUPC, also provides some control over the rate of power change; while the Radyne and Near
Side AUPC use a optimized rate for rain fade compensation.