ViaSat ArcLight, Руководство пользователя, Страница: 38 / 368

ArcLight Hub User’s Guide
General System Description
1-2 1081006 Rev. 001
The ArcLight features include:
•
Forward link that supports 500Kbps to 10 Mbps data rates
•
Return link CRMA data rates from 32Kbps to 512 kbps
•
No frequency or time coordination required for transmission in
either direction
•
Uplink power control to combat link fading
•
Congestion control to increase system availability
•
Efficient spectrum use using A-PCMA
•
Basic design leverages third party commodity products to
reduce cost
•
Network management that is based on proprietary UDP
messaging to manage the VMT network and Hub components
anas well as the industry standard Simple Network Management
Protocol (SNMP)
Asymmetric Paired Carrier Multiple-Access
The bandwidth capacity of a satellite system can be doubled using A-
PCMA. This is accomplished by having the outbound high-speed hub
transmit signal and the return low-speed VMT signals occupy the same
frequency spectrum on the satellite simultaneously. This is illustrated
in Figure 1-1.
Figure 1-1. A-PCMA Bandwidth Reuse.
The Hub transmit signal is a high-power signal while the VMT
transmitted CRMA signal is low-powered and spread over the same
spectrum as the Hub transmit signal. When the signal is received by
the VMT, the receiver is unaffected by the low-level interference
introduced by the CRMA signals, so there is no performance impact or
cost at the VMT, i.e., the S/N ratio at the VMT receiver is good, as
shown in Figure 1-2.