Comtech EF Data CDD-880, Installation And Operation Manual

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CDD-880 Multi Receiver Router MN-CDD880
Appendix G Revision 2
G–7
G.3 DPC Operation
Dynamic Power Control operates independently from any upper Network Management System
(NMS), relying solely on a peer-to-peer exchange between the transmitting and receiving
terminals. This means that the logic control is embedded into each unit and requires no
interaction from any external process.
At a very basic level, the receiving demodulator is configured and assigned the Management IP
Address of the corresponding remote modulator; the demodulator then starts sending an IP
Packet (Link Quality Report Message, or LQRM) on varying timed intervals, depending on
measured signal quality. The modulator receiving the LQRM compares the signal quality to
target quality value, and adjusts its output power level accordingly.
DPC requires a power reference value in order to operate properly. While this value should be
determined during clear-sky operation, the Adaptive Control Loop (ACL) will work either way.
The power reference value should equal the sum of the symbol rate, MODCOD, and target
E
S
/N
0
. This value becomes the mathematical pivot point from which all other power is
calculated. For example, if the power reference measurement was taken during a 6 dB rain fade
with terminal margin of 5 dB, the power control algorithm would re-adjust as the fade clears
(leaving a –6 dB power delta) but the overall terminal margin is not affected, still providing fade
increase of up to –1 dB. The only notable problem with calibrating during a fade is that the DPC
delta reading is always at some offset from 0 dB, which represents clear-sky.
Power Reference also provides the point from which all dSCPC switch commands are calculated
for new power adjustments. Without DPC, the VMS switching engine uses home state values to
determine the power value to send to the modulator during a symbol rate/MODCOD change.
When using DPC, the power reference value is used to determine the modulator power, instead.
In this case, VMS power is ignored and internal power calculation uses the following:
Calculate Power:
•
Power Reference Base = Tx Power, MODCOD, and Symbol Rate
•
Target
•
DPC Delta
•
Switched Symbol Rate, and Switch-Point
•
Beam Offset (if roaming)
Reference Error Check (not to exceed maximum power):
•
Equal or less than Tx Margin
• Equal or less than Rate Maximum Power
• Equal or less than Terminal Maximum Power (if known)
When you enable DPC, the CDM-840 waits for first or next LQRM before performing any power
adjustment. Upon receipt, the CDM-840 internal Link Adaptation Manager acts in response to
incoming messages, storing the data from the last LQRM. If this message contains an E
S
/N
0
value
greater than or less than target, power is adjusted accordingly.