ViaSat ArcLight, User Manual, Page: 42 / 368

ArcLight Hub User’s Guide
General System Description
1-6 1081006 Rev. 001
RtNMS
The Real-time Server (RtNMS) communicates with the NMS NRTS to
receive VMT configuration, and with the VMTs (using the FLM and
Forward Link) to log them on the network, distribute their network
access parameters, and adjust their transmit power and frequency,
based on information it receives from the MCD-II. The RtNMS server
contains algorithms that adjust the transmit power and frequency of all
the VMTs in the network. The VMT automatically adjusts frequency for
the mobile terminal application to compensate for the Doppler Effect.
Congestion control forces the terminal to transmit only a certain
percentage of data. The percentage is configurable using the NMS
NRTC.
The closed loop uplink power control algorithm implemented jointly by
RtNMS and the VMT controls the transmit power of the VMTs and
provides fair network access.
FLM
The transmit side of the Hub is provided by the FLM. The FLM
interfaces to the hub network using its 100baseT Ethernet port. In
addition to the HC, the FLM is also controllable via the SNMP. On the
satellite network side, packets are formatted and transmitted over the
satellite network to VMTs.
The ViaSat Forward Link Modulator (VFLM-70) delivers broadband IP
data to a collection of transceivers within a STAR satellite network. The
FLM interfaces to the network on the hub side over a 10/100 base-T
Ethernet interface and outputs an RF signal at a 70MHz IF. The FLM IF
output is connected to a PCMA Hub Canceller, in standard network
configuration, who simultaneously forwards that signal to the
appropriate band converters and cancels it to allow for the return link
signal recovery at the MCD-II. In a cross-strapped configuration the
FLM IF output signal is simply sent to the appropriate band converters.
MCD-II
The Multi-Channel Demodulator II (MCD-II) in many respects is the
heart of the ArcLight system. The MCD’s blade servers are located in
the ABS and it receives and demodulates the spread spectrum bursts
from the VMTs then re-assembles IP packets from the ATM cells it has
demodulated and decoded. Table 1-1 lists the MCD-II server set
installed in an ABS. The MCD-II has several Correlator-Demodulator-
Cards (CDCs) that receive, unspread and demodulate the incoming
traffic bursts from the VMTs. Each CDC has one correlator and twelve
Demodulators. All the CDCs communicate with the rest of the hub
equipment through a System Processor (SP). The SP implements the IP
packet reassembly and forwarding functions.