Q-Lite Satellite Modem Installation and Operating Handbook
7-38
A. Yes, bandwidth savings can be made with existing networks, but a link budget analysis
must be made to assess the suitability and benefits.
Q. Surely there is some disadvantage in using
Paired Carrier™
?
A.
Paired Carrier™
has a minimal impact on Eb/No for a desired BER but typically
between 0.15dB and 0.5dB extra carrier power is required to be transmitted on satellite to
overcome the imperfections in the signal cancellation process. Also, of course, power is
needed for the second carrier.
Q. What prerequisites exist for using
Paired Carrier™
?
A. It requires a full-duplex link where you must be able to receive your own uplink signal
off satellite. It works only with ‘bent-pipe’ transponders where there is no
demodulation/remodulation or cross-strapping between transponders. The transponder
must do no more than filter, frequency convert and amplify the signal.
Q. Is it difficult and time consuming to install and set up
Paired Carrier™
?
A. No. The operator sets the satellite delay or alternatively the modem and satellite
positions to allow the satellite signal to be acquired. A few other parameters specific to
Paired Carrier™
need to be set up. Set up takes less than five minutes in total.
Q. Is
Paired Carrier™
available as a field upgrade?
A. Yes. All
Q-Lite™
modems can be field upgraded to support
Paired Carrier™
operation to the desired cancellation bandwidth.
Q. Is
Paired Carrier™
affected by spectral inversions?
A. Yes.
Paired Carrier™
will operate correctly if the following simple spectral inversion
rules are observed:
a. Try to keep the signals in the space segment non-inverted. This keeps
everything conceptually straightforward. If the ground-segment
uplink
equipment contains a spectral inversion then you should put a
Tx
spectral
inversion in the modem to correct for it. This ensures that the signals in the
space segment are spectrally non-inverted.
b. If the ground segment
downlink
equipment contains a spectral inversion
(e.g., due to an inverting LNB) then you should put an
Rx
spectral inversion in
the modem to correct for it.