Hughes HX System System Overview page 75

Beam edge
most robust
coding/modulation
QPSK rate 1/2
Beam center
m ost andwidth fficient b e
c oding/ odulation m
8PSK ate 9/10 r
G-28732 C
08/22/06
Figure 12: Using ACM to optimize the link budget
satellite routers at beam center can be configured for the most
bandwidth efficient coding/modulation combination (8PSK Rate
9/10). The ability to customize the outbound channel per satellite
router allows an operator to realize additional bandwidth
efficiencies of up to 30% over and above the 30% gain from
8PSK and BCH/LDPC coding. Thus, DVB-S2 with ACM can
provide an operator up to 60% bandwidth gain over DVB-S.
In the second application of the ACM feature, the HX system can
dynamically change the coding/modulation combination based on
changing received signal conditions, which occurs in the event of
a rain fade. In this mode, there is a closed loop control feedback
mechanism between the HX gateway and the satellite router,
whereby the satellite router can instruct the HX gateway to
change the coding/modulation combination to overcome rain
fade. The benefit for an operator is the ability to provide higher
availability to its customers. The ACM capability of the HX
System is shown in Figure 13.
Beam edge
Beam
center
Chapter 8 • Transmission features
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