Q-Flex Satellite Modem Installation and Operating Handbook
7-39
many-to-many), hybrid star mesh, Single Channel Per Carrier (SCPC) and Demand
Assigned Multiple Access (DAMA) voice and data networks.
Paired Carrier™
helps in the case of bandwidth-limited links. However, if a link is instead
power limited then its design can be changed to turn it into a bandwidth-limited link and
then
Paired Carrier™
can be used to improve the bandwidth utilisation.
Paired Carrier™
is waveform agnostic and will work with all modulation and FEC
schemes. It is used in addition to, not instead of, other bandwidth saving techniques.
Paired Carrier™
and DVB-S2 represent two of the most bandwidth-efficient technologies
available today and can be used together in the
Q-Flex™
modem.
Some frequently asked questions about
Paired Carrier™
operation along with answers
are provided below.
Q. Does
Paired Carrier™
require a particular modulation or FEC configuration?
A. No,
Paired Carrier™
imposes no special parameter limitations on the carriers
involved. However, sometimes it is advantageous to use the bandwidth savings to switch
to a more robust modulation and coding scheme - but this is application dependent.
Q. Can
Paired Carrier™
handle multiple transmit and receive carriers?
A. No, the separate Paradise PCMA-70 Satellite Bandwidth Extender should be used if
you require to cancel multiple carriers appearing within the cancellation bandwidth.
Q. Can
Paired Carrier™
handle asymmetric carriers, that is, carriers with different data
rates and/or different symbol rates on transmit and receive?
A. Yes, the
Paired Carrier™
can handle asymmetric carriers.
Q. My transmit and receive carrier levels off satellite are different, can I still use the
Paired Carrier™
satellite signal canceller?
A. Yes, however, the wanted and unwanted signal levels (power spectral density) should
normally be within 10dB of each other. Symbol rate asymmetry of up to 12:1 is supported.
It is sometimes possible to relax these conditions subject to the constraints of an overall
detailed link budget analysis. Power asymmetry must be kept between +10 to -10dB
using the equation
Power ratio (dB) = Near PSD – Far PSD + 10log(Near symbol rate/Far symbol rate)
Q. Does the modem redundancy configuration affect
Paired Carrier™
operation?
A. No,
Paired Carrier™
works equally as well in 1:1 and 1:N modem redundancy
systems. The standby modem will have to go through the normal acquisition process
when it comes on traffic. While it is in standby, it is not possible for the demodulator to
lock (it cannot cancel the unwanted carrier since in principle it can only cancel its own
transmission). Paradise has therefore muted various spurious alarms that would
otherwise be reported for the standby modem in this situation.