Adjustment For Data Rate - Comtech EF Data Vipersat CDM-570 User Manual

2 dB). This prevents loss of the link due to power value changes based on
fade conditions.
This feature is automatic and requires no operator intervention.

Adjustment for Data Rate

The maximum output power level is scaled according to the data rate at which
the modulator is transmitting. Consider, for example, a system that normally
runs at a data rate of 512 kbps with a Nominal Power Level of -10 dBm and a
Maximum Power Level of -5 dBm. If a voice switch occurs that sets the data
rate to 32 kbps, the power requirements are much lower than the nominal -10
dBm level. With the above process, it is theoretically possible for the power to
be raised all the way to -5 dBm, which is past the saturation point for such a
small data rate. To prevent the use of excessive power that will drown out the
signal and cause damage to the satellite, the modulator calculates a maximum
power that is appropriate for its current data rate.
The net result of the DPC algorithm is that the transmit power of all video carri-
ers is adjusted such that the receiving modems see a constant Eb/No value. This
optimizes receive signal quality and use of system resources since it can lead to
a reduction in power amplifier intermodulation and also a conserving of satellite
transmit power.
A p p e n d i x D y n a m i c P o w e r C o n t r o l
C -
Description
C-5