Comtech EF Data CDD-880, Инструкция по установке и эксплуатации

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CDD-880 Multi Receiver Router MN-CDD880
Appendix G Revision 2
G–2
the clear sky quality reading as a zero reference, then disseminating the offset to all listening
remotes.
The Dynamic Power Control (DPC) feature as available with Comtech EF Data’s Advanced VSAT
products provides a mechanism whereby remote satellite uplinks have their transmit power
levels adjusted in order to optimize the receive signal quality as measured by the corresponding
demodulator E
S
/N
0
(the ratio of energy per symbol to noise density). This optimization process
acts to either increase or decrease transmitted signal levels in order to:
•
Achieve a minimum level of received E
S
/N
0
consistent with providing an error free link or set
margin.
•
Reduce transmit power where sufficient link margin exists in order to optimize group station
uplink saturation and/or satellite transponder power usage reducing costs.
• Increase link availability when margins apply (typically Ku-Band or Ka-Band).
• Maintain proper power backoff to eliminate high power amplifier saturation and carrier
distortion.
G.2 Dynamic Power Control
G.2.1 About DPC
DPC is a selectable software feature operating independently on CDM-840s exchanging a UDP
message between the receiving unit (where the signal quality is being measured) and the
transmitting unit (where the power level is to be adjusted). This message contains link quality
status, which is directed to the transmit site on timed intervals, updating the link state.
DPC is divided into two segments: return path remote to hub/forward path hub to remote.
On the return path, power adjustments can interoperate with Adaptive Coding and Modulation
(ACM) by combining modulator output power adjustments with ACM step points. This exchange
allows the transmit power level to try and compensate for fade before it is necessary to
decrease data link capacity. The fade reporting adjustment is maintained by Adaptive Control
Loop (ACL), which reports receiving E
S
/N
0
using messages over the LAN/WAN data transmission
segments. The ACL continuously updates the link conditions for each active receiving
demodulator.
The CDM-840 takes receipt of these messages via the outbound channel in order to take the
appropriate actions. Thus, depending on the link estimation compared to internal power curves,
the link is adaptive through configuration limits that maintain power budgets on the satellite.