CiM-550 IP Enabled Satellite Modem

Rev. 2

Theory of Operation

CD/CIM550.IOM

6.4AUPC (AUTOMATIC UPLINK POWER CONTROL)

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.

6.4.1SETTING AUPC PARAMETERS

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:

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