Chapter 8 • Transmission features
1037852-0001 Revision A
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Chapter 8
Transmission features
This chapter introduces HX System transmission function
elements and explains the features and advantages of the HX
System transmission implementation.
This chapter discusses the following topics:
• Outbound channel: DVB-S2 on page 61
• Inbound channel: adaptive coding on page 64
• Closed loop control on page 65
• Inroutes and inroute groups on page 66
Outbound channel:
DVB-S2
All of the Hughes satellite IP broadband systems use the DVB
standards for the outbound transmission channel. The use of DVB
for the outbound channel provides the following significant
advantage for an operator:
• DVB scales efficiently
The HX System also supports the DVB-S2 standard to provide
the following advantages:
• Improved spectral efficiency
• Outbound adaptive coding and modulation (ACM)
These features are described in the following sections.
DVB scaling
DVB channels are designed to scale effectively to large
carriers—the HX System can support carriers as large as 45 Msps
on the outbound channel. This contrasts sharply with non-DVB
systems, in which the maximum outbound channel capacity in
some instances is limited to 10 Msps. Uplinking multiple
outbound channels incurs an efficiency penalty as each additional
carrier requires channel spacing. In addition, the advantage of
satellite multicast is reduced as each outbound carrier must
replicate every multicast message.
With the Hughes HX system, an operator can use a single
outbound channel to support hundreds of satellite routers.
DVB and multiplexing
Another important advantage of DVB systems is their ability to
multiplex two or more DVB-S channels together into a single
carrier. For operators who already broadcast a DVB video carrier,
the addition of data capacity is easily achieved by multiplexing
DVB video streams with a Hughes DVB data stream. With larger
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