CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Appendix D
MN-CDM750
D–9
signal.
The
interference
cancellation
algorithm
uses
the
composite
signal
and
the
local
copy
of
S1
to
estimate
the
necessary
parameters
of
scaling
(complex
gain/phase),
delay
offset
and
frequency
offset.
The
algorithm
continuously
tracks
changes
in
these
parameters
as
they
are
generally
time
‐
varying
in
a
satellite
link.
Figure D-6. Carrier-in-Carrier Signal Processing Block Diagram
The
resulting
estimate
of
the
unwanted
interfering
signal
is
then
subtracted
from
the
composite
signal.
In
practical
applications,
the
estimate
of
the
unwanted
signal
can
be
extremely
accurate.
Unwanted
interfering
signal
suppression
of
30
dB
or
more
has
been
achieved
in
commercial
products
with
minimal
degradation
of
the
demodulator
performance.
D.4.2 Margin Requirements
Depending
on
the
product,
typical
interfering
signal
cancellation
is
28
to
35
dB.
The
residual
interfering
signal
appears
as
noise,
causing
a
slight
degradation
in
received
Es/No.
To
compensate
for
the
residual
noise,
a
small
amount
of
additional
link
margin
is
required
to
improve
the
Es/No
and
maintain
the
QEF
performance.
Margin
requirements
depend
on
the
product,
modulation
and
power
ratios;
for
the
CDM
‐
750,
these
additional
margin
requirements
are
as
follows:
Modulation
Nominal Margin*
QPSK 0.3
dB
8PSK 0.3
dB
16APSK 0.6
dB
32APSK 1.0
dB
*
Equal
power
and
equal
symbol
rate
for
the
interfering
carrier
and
the
desired
carrier,
i.e.,
0
dB
CnC
ratio.
Measured
at
IF
with
AWGN,
+7
dBc
Adjacent
Carriers,
1.3
spacing.
D.4.3 Carrier-in-Carrier Latency
DoubleTalk
Carrier
‐
in
‐
Carrier
has
no
measurable
impact
on
circuit
latency.
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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