ViaSat ArcLight, User Manual, Page: 51 / 368

ArcLight Hub User’s Guide
General System Description
Rev. 001 1081006 1-15
Figure 1-9. Communications between RTNMS, MCD, and VMT.
1.2.5 Power control
A CDMA, and therefore a CRMA, network like ArcLight, must provide
power control for all the terminals in the network so that they function
well and efficiently together. ArcLight provides carrier power control via
two means; open loop control at the VMT and a closed loop algorithm
between the VMT and the hub. The closed loop control is an algorithm
operating in the real-time NMS (RtNMS) processor. The RtNMS receives
a summary IP packet for each incoming IP traffic packet that is received
from the multi-channel Demodulator. All CDCs that operate
concurrently with the same chip-rate and center frequency will be
maintaining Automatic Gain Control (AGC) on essentially the same
input energy. Even though the gain in the IF path for each CDC is
different, the matched-filter output will be driven to the same level on
each CDC which provides a common reference point.
1.2.6 Congestion control
Congestion control is essential for managing large networks or high
utilization networks. The ArcLight congestion control algorithm
attempts to drive the network-wide average number of simultaneous
accesses to a desired access level (DAL). Arclight return links may be
setup in homogeneous (uniform structure), and non-homogeneous
(non-uniform structure) configurations. Both of these may contain
multiple non-overlapping frequency channels. The congestion control
algorithm will treat each non-overlapping frequency channel as a
separate network called a congestion control group (CCG). The
homogeneous configuration requires that any overlapping access types
must share the same channel center frequency. A non-homogeneous
configuration may include overlapping access types that have different
channel center frequencies.