Comtech EF Data CIM-550, Installation And Operation Manual

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CiM-550 IP Enabled Satellite Modem Rev. 2
Theory of Operation CD/CIM550.IOM
88
6.4 AUPC (A
UTOMATIC
U
PLINK
P
OWER
C
ONTROL
)
Automatic Uplink Power Control (AUPC) is a feature whereby a local modem is
permitted to adjust its own output power level in order to attempt to maintain the Eb/No
at the remote modem.
IMPORTANT
NOTICE
The user MUST obtain permission from the Satellite Operator to use this feature.
Improper use of this feature could result in a transmitting terminal seriously
exceeding its allocated flux density on the Operator’s satellite. This could produce
interference to other carriers, and could cause transponder saturation problems.
To accomplish this, the framed (EDMAC) mode of operation must be used. The remote
modem constantly sends back information about the demodulator Eb/No using reserved
bytes in the overhead structure. The local modem then compares this value of Eb/No with
a pre-defined target value. If the Remote Eb/No is below the target, the local modem will
increase its output power, and hence, a closed-loop feedback system is created over the
satellite link. A particularly attractive benefit of this feature is that whenever framed
operation is selected, the remote demodulator’s Eb/No can be viewed from the front
panel display of the local modem. Note also that AUPC can be used simultaneously with
EDMAC.
There are several important parameters associated with this mode of operation, and the
user needs to understand how the AUPC feature works, and the implications of setting
these parameters.
6.4.1 S
ETTING
AUPC P
ARAMETERS
1. The user, under the menu (CONFIG, FRAME) first ensures that Framed mode is selected.
EDMAC may be disabled, or the unit may be defined as an EDMAC Master or Slave. The
important consideration is that Framing should be enabled.
2. The user should verify that the remote modem also has Framing enabled.
3. The user, under the menu (CONFIG, TX, PWR) sets the nominal output power of the
modem. This is done by selecting the MANUAL mode, then editing the TX output power
level displayed.
4. The user will then select AUPC as the operating mode. At this point the user will be
prompted to define four key parameters: