Hub Cancellation - Teledyne QMultiFlex-400 Installation And Operating Handbook

QMultiFlex-400™ Installation and Operating Handbook

8.3 Hub Cancellation

Using advanced Paired Carrier™ technology, it is possible to create a system where the
outbound carrier shares the same space segment as the return carriers. With careful
system planning, the remote modems will not require any delay cancellation, which is a
huge cost saving for any sized system.
Figure 8-5 Hub Canceller Spectra
This section describes the operation and configuration of a QMultiFlex-400™ DVBS2(X)
hub modem incorporating a hub canceller, operating in a star network configuration. This
section will also explain the expected additional system losses, due in part, to the self-
interference by the return carriers being located under the larger hub outbound carrier and
ways of mitigating this additional system loss.
The Hub Canceller allows satellite carriers in a point-to-multipoint system to operate in the
same satellite bandwidth providing satellite BW savings of up to 50%. The Hub Canceller
uses adaptive self-interference cancellation to remove the uplink signal, which is present
within the downlink signals. The resulting canceller output is the desired return signals from
the remote terminals.
A single Modem containing a Hub Canceller is used at the hub, and no additional equipment
is required at the remotes. The hub transmits the broadcast carrier and simultaneously
receives its own transmission back from the satellite. The remote terminals receive the
broadcast carrier and transmit their return signals in a managed fashion in the same carrier
space as the hub broadcast carrier. The canceller at the hub removes the broadcast carrier
from the composite receive signals enabling the hub to demodulate the return links.
In this broadcast network, the remote terminals use much smaller antennas than the hub.
The asymmetry in the broadcast carrier to return channel data rates and hub-to-remote
antenna size results in an asymmetry in the satellite EIRP. With proper system design, the
satellite EIRP for all return channels can be kept sufficiently below the satellite EIRP on the
8-5