ArcLight Hub User’s Guide
General System Description
1-20 1081006 Rev. 001
1.4.1 Satellite Transmission System
The satellite transmission system includes two types of satellite
channels:
An Outlink, transmitted from the HUB and received by all
VMTs; and
A number of individual Return Links, transmitted as required
from the VMTs and received at the HUB terminal.
1.4.2 Outlink Requirements
The system allows the signal parameters of the forward link waveform
to be set under control of the NMS.
1.4.2.1 Input data
Input data is in the form of IPv4 datagrams.
1.4.2.2 Data rates
The system supports the transmission of the Outlink over the following
range of information rates (data rate prior to forward error correction):
100k increments from 500 Kbps up to 1 Mbps
250K increments from 1 Mbps up to 3.5 Mbps
500K increments from 3.5 Mbps up to 5 Mbps
1M increments from 5 Mbps to 10 Mbps
1.4.2.3 IP packet framing
The IP datagram is framed to maintain packet boundaries with high-
level data link control (HDLC) protocol with the following exceptions:
the address field and control field is omitted.
Flag – IP datagram – CRC – flag
1.4.2.4 Channel coding
Forward error correction coding is applied after packet framing. The
FEC is a turbo product code, supporting rates .325, .495 and .783.
1.4.2.5 Spreading
The forward channel operates in spread or un-spread mode. The spread
mode shall use direct sequence spreading, and a single spreading
sequence shall be used for all forward channels. Un-spread (or non-
spread) mode does not spread the output signal over a larger frequency
spectrum.
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