Comtech EF Data CDD-880, Инструкция по установке и эксплуатации

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CDD-880 Multi Receiver Router MN-CDD880
Appendix G Revision 2
G–14
G.3.2.3 Hub Fade Control
The hub attenuation information fully optimizes power control, allowing the remote terminal to
use all of available amplifier power to sustain data throughput without jeopardizing SLA.
However, it can be difficult to determine if the hub downlink is in a fade condition. The problem
involves measuring link quality variations from clear-sky to degraded performance, if the hub
cannot receive its own uplink carrier or if the servicing satellite does not provide a beacon
signal.
Hub downlinks with satellite beacon signals provide the most reliable and accurate reference for
realizing if the carriers from the satellite to the hub are being attenuated. A beacon receiver can
measure the satellite signal and provide C/N; by reading this level, the system can set a
reference of clear-sky. With a reference point established, any reduction of that signal is
distributed to all receiving remotes in the service area network.
To accomplish this control, the CTOG-250 sets up SNMP polling to the beacon receiver that is
measuring the satellite’s downlink carrier for C/N. The periodic polled value is first stored in the
CTOG-250’s reference snapshot of clear-sky condition, which sets the minimum attenuation in
the UA messaging. From that “zero point” reference, any variation is updated and broadcast to
all receiving remotes, providing an additional backoff value from terminal maximum.
An alternate method is a collaborative approach, whereby outbound ACM remote LQRMs are
collected at the corresponding CTOG-250 and stored in a table that is periodically updated. The
link quality values formulate a variation in power using a statistical averaging algorithm, which
the system uses to determine hub downlink fade.
G.3.2.4 Roaming with DPC
The Roaming Oceanic Satellite Server (ROSS) is an integrated location server that works in
conjunction with Comtech EF Data’s Vipersat Management System (VMS) to facilitate on-the-
move satellite communications for oceanic vessels. With the support of ROSS, the modem
power margin is modified depending on the Effective Isotropic Radiated Power (EIRP) value.
ROSS stores multiple contours per service area, with each beam contour assigned a number (0
to 255) in order of power, high to lower gain.
Roaming DPC provides additional control within a service area with multiple beam contours. As
the vessel roams between beam contours, the power difference from beam-to-beam is applied
to the CDM-840 DPC beam offset control, adjusting the terminal’s power margin by adding or
subtracting the beam power differences. The net effect on power is that the maximum power
scale is increased or decreased, depending on the vessel’s location within that satellite service
area.
The beam offset plays a very important role in maintaining power during beam contour
transitioning. If the power control is operated without this additional adjustment, the uplink
power may exceed budget, or the vessel could drop communication all together because of
insufficient margins.