CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Appendix D
MN-CDM750
D–2
CnC
was
first
introduced
in
Comtech
EF
Data
products
such
as
the
CDM
‐
Qx
Satellite
Modem,
CLO
‐
10
Link
Optimizer,
and
CDM
‐
625
Advanced
Satellite
Modem.
The
implementation
of
DoubleTalk
Carrier
‐
in
‐
Carrier
in
the
CDM
‐
750
has
been
further
refined,
and
some
of
the
limitations
that
existed
in
the
prior
offerings
have
been
overcome.
CnC
technology
provides
a
significant
improvement
in
bandwidth
and
power
utilization,
beyond
what
is
possible
with
FEC
and
modulation
alone,
allowing
users
to
achieve
unprecedented
savings.
When
combined
with
advanced
modulation
and
FEC,
it
allows
for
multi
‐
dimensional
optimization:
•
Reduced
operating
expense
(OPEX)
–
e.g.,
Occupied
Bandwidth
&
Transponder
Power;
•
Reduced
capital
expenditure
(CAPEX)
–
e.g.,
Block
Up
Converter/High
‐
Power
Amplifier
(BUC/HPA)
size
and/or
antenna
size;
•
Increased
throughput
without
using
additional
transponder
resources;
•
Increased
link
availability
(margin)
without
using
additional
transponder
resources;
•
A
combination
of
any
of
the
above
to
meet
different
objectives.
Conclusion:
When
using
the
DoubleTalk
Carrier
‐
in
‐
Carrier
(CnC)
option,
up
to
50%
savings
in
transponder
utilization
is
possible
when
carriers
share
common
bandwidth.
D.2
Application Requirements
The
following
conditions
are
necessary
in
order
to
operate
DoubleTalk
Carrier
‐
in
‐
Carrier:
•
Link
must
be
full
duplex.
•
A
CDM
‐
750
must
be
used
at
the
end
of
the
link
where
the
cancellation
needs
to
take
place.
Normally,
this
is
both
ends
of
the
link.
•
The
transponder
is
operated
as
Loopback.
That
is,
each
end
of
the
link
must
be
able
to
see
a
copy
of
its
own
signal
in
the
downlink
path
from
the
satellite.
The
looped
back
signal
is
then
subtracted,
which
leaves
the
signal
from
the
distant
end
of
the
link.
DoubleTalk
Carrier
‐
in
‐
Carrier
cannot
be
used
in
spot
beam
systems.
•
The
transponder
needs
to
be
“bent
‐
pipe”
–
meaning
no
on
‐
board
processing,
demodulation,
regeneration
can
be
employed.
Demodulation/remodulation
does
not
preserve
the
linear
combination
of
the
forward
and
return
signals
and
the
resulting
reconstituted
waveform
prevents
recovery
of
the
original
constituent
signals.
shows
a
simplified
conceptual
block
diagram
of
CnC
processing.
The
two
ends
of
the
link
are
denoted
'
A
'
and
'
B
'
and
the
uplink
and
downlink
are
shown.
Summary of Contents for CDM-750
Page 76: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Updating Firmware MN CDM750 4 12 Notes...
Page 224: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix A MN CDM750 A 4 Notes...
Page 234: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix B MN CDM750 B 10 Notes...
Page 256: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix C MN CDM750 C 22 Notes...
Page 280: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix D MN CDM750 D 24 Notes...
Page 300: ...2114 WEST 7TH STREET TEMPE ARIZONA 85281 USA 480 333 2200 PHONE 480 333 2161 FAX...
