CDM-840 Remote Router MN-CDM840
Appendix M Revision 3
M–9
M.2.3.1.1 Closed Loop Mechanism
DPC is defined as a closed loop mechanism using an outer and inner feedback exchange
between CDD-880 lock quality and CDM-840 Tx power.
Figure M-3. Closed Loop Mechanism
As shown in the Figure M-3 diagram, the outer loop requires that each CDD-880 send an LQRM
(IP Packet) to a corresponding CDM-840 over the Management IP Network via the CTOG-250
Comtech Traffic Optimization Gateway w/CDM-800 Gateway Router WAN forwarding channel.
The LQRM contains the demodulator’s lock quality; unlocked/locked with current E
S
/N
0
value
and sanity check
1
conditions; threshold; Max ModCod; DPC enable/disable state; and current
symbol rate.
The inner loop is Tx power adjustment based on last reported LQRM with configured conditions.
The control loop is a constant handshake requiring certain conditions to be met before
modifying power. The CDD-880 is assigned the Management IP Address of the corresponding
CDM-840. Once assigned, the demodulator sends LQRM packets at either fast (500 ms) or slow
(60 sec) rate; this rate depends on target window, ModCod, and lock condition.
The decision to send the LQRM fast or slow is contingent on internal checks of E
S
/N
0
value and
current ModCod. These checks modify the timer to accelerate or slow down the send rate. The
main check is: If E
S
/N
0
is outside of the target window (± .5 dB), and/or the ModCod is not at
maximum; then the fast timer is invoked. If ModCod is not at maximum, the timer will remain at
fast rate.
1
The sanity check allows the CDM-840 to compare against configured parameters, sending adjustments
to the CDD-880 if mismatched. This exchange synchronizes modulator settings to demodulator checks.
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