Comtech EF Data CDM-570/570L Vipersat - Manual (Page 163)

Appendix C - Dynamic Power Control C-11
Configuration
carrier value. When this value is received by the transmitting modulator, it is
compared to the set value; if they are different, the modulator servos its output
power level to achieve the targeted E
b
/N
0
level.
The modulator DPC function can support multiple demodulators as assigned by
the system. As each active demodulator is assigned, a separate DPC message is
received invoking the modulator process to add the demodulator to a list, which
is then scanned to determine the worst case demodulator. After each scan, the
demodulator with the lowest E
b
/N
0
is posted for the next DPC power servo
cycle. This process is repeated upon reception of each demodulator DPC
message. The list is renewed every 65 seconds and if, for any reason, a demodu-
lator fails to respond during active cycles, it is removed from the list.
Speed Up Eb/No Range
Normally, the DPC message is sent every 30 seconds from the corresponding
receiving demodulator(s) in the network. The Speed Up Eb/No Range is a
window value centered on the modulator set Target Eb/No value. However, the
demodulator does not have a user settable target value; it would be impossible
to predetermine this value for active demodulators, as they are dynamically
assigned during switch setup. On the flipside, the modulator does have this
value and, upon reception of the first DPC message from the corresponding
demodulator(s), it sends a message back to the demodulator for setting the
Target Eb/No value.
Now, if the measured demodulator E
b
/N
0
value falls outside the window range,
the demodulator DPC process will increase the message interval rate to every 10
seconds until the measured value is back within the set range.
Target DPC (IP) Address
In a standard Vipersat network where the modems are being used as switched
InBands, the VMS handles the assignment of the target IP address for the
receive units. When a remote is switched into SCPC mode and DPC is enabled,
the VMS writes the corresponding modulator IP address into the allocated
demodulator, hub or remote. This particular control is reserved for Out-of-Band
devices only, because in this case the system does not automatically assign this
target address. This entry is left as default 0.0.0.0 for dynamic SCPC usage.
Calculate Max Power Menu
Using the CLI, selecting Calculate Max Power from the DPC Main menu will
present the Calculate Max Power menu, as shown in figure C-5. Note that the
Parameter Editor presents the calibrated values for visual reference only, as
shown in figure C-6, and does not provide the calculate function.