CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Appendix D
MN-CDM750
D–8
D.4.1 DoubleTalk Carrier-in-Carrier Cancellation Process
The
state
‐
of
‐
the
‐
art
signal
processing
technology
employed
via
CnC
continually
estimates
and
tracks
all
parametric
differences
between
the
local
uplink
signal
and
its
image
within
the
downlink.
Through
advanced
adaptive
filtering
and
phase
locked
loop
implementations,
it
dynamically
compensates
for
these
differences
by
appropriately
adjusting
the
delay,
frequency,
phase
and
amplitude
of
the
sampled
uplink
signal,
resulting
in
excellent
cancellation
performance.
When
a
conventional
full
duplex
satellite
connection
is
established
between
two
sites,
separate
satellite
channels
are
allocated
for
each
direction.
If
both
directions
transmitted
on
the
same
channel,
each
side
would
normally
find
it
impossible
to
extract
the
desired
signal
from
the
aggregate
due
to
interference
originating
from
its
local
modulator.
However
since
this
interference
is
produced
locally,
it
is
possible
to
estimate
and
remove
its
influence
prior
to
demodulation
of
the
data
transmitted
from
the
remote
location.
For
the
CnC
cancellation,
it
is
necessary
to
provide
each
demodulator
with
a
copy
of
its
local
modulator’s
output.
Figure D-5. DoubleTalk Carrier-in-Carrier Signals
Referring
to
Modem
1
and
Modem
2
transmit
signals
S1
and
S2
respectively.
The
satellite
receives,
translates,
and
retransmits
the
composite
signal.
The
composite
downlink
signal
S1*
+
S2*
is
received
at
Modem
1
and
Modem
2.
The
modem’s
returned
image
of
the
uplink
signal
(not
including
the
desired
carrier)
differs
from
the
originally
‐
transmitted
signal
primarily
in
terms
of
phase,
frequency,
and
delay
offsets.
Referring
to
For
round
trip
delay
estimation,
a
search
algorithm
is
utilized
that
correlates
the
received
satellite
signal
to
a
stored
copy
of
the
local
modulator’s
transmitted
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...
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