Hughes HX System, System Overview

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Chapter 8 • Transmission features
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Closed loop control
The Hughes HX System has a closed loop power control between
the HX gateway and satellite routers so that there is a continuous
monitoring of the outbound and inbound channels. As shown in
Figure 15, the closed loop control provides for the HX gateway to
continuously monitor the received signal quality of transmissions
from each satellite router while each satellite router continuously
monitors the received signal quality of the transmission from the
HX gateway. As atmospheric conditions affect the link quality,
each component is able to request changes to overcome fade
conditions.
At the gateway, the outbound channel coding and modulation can
be varied dynamically, while at the satellite router the forward
error correction (FEC) coding can be varied dynamically to
improve link availability. If the satellite router needs a more
robust link performance for the inbound transmissions, it has the
ability to shift to a different inroute group supporting a lower
symbol rate. Note that the latter capability does not exist when
operating with CBR IQoS plans. Additionally, the satellite router
can dynamically change its local uplink power control to
overcome fade conditions.
Closed Loop Timing As part of the closed loop control implementation, the HX
System also supports closed loop timing (CLT) which allows for
both mobility of operation as well as
spot beam satellite
operation.
Figure 15: HX System closed loop power control
HX GTWY measures received
s
s b
t o r
r
ignal trength and urst
iming ffset eceived
from emote
GTWY sends
adjustments to
HX remote
HX remote
continually
measures
received
signal quality
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08/22/06