CDM-570A/570AL Satellite Modem with Optional Packet Processor
Revision 5
DoubleTalk Carrier-in-Carrier Option G–9 MN-CDM570A
Figure G-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.
G.4.2 Margin Requirements
Typical interfering signal cancellation is 28 to 35 dB (depending on the product). The residual
interfering signal appears as noise causing a slight degradation of the Eb/No. To compensate for
the residual noise, a small amount of additional link margin is required to maintain the BER.
Margin requirements depend on the product, modulation and power ratios:
For the CDM-570A/AL, the additional margin requirements are as follows:
Modulation Nominal Margin*
BPSK 0.3 dB
QPSK/OQPSK 0.3 dB
8-PSK 0.5 dB
8-QAM 0.4 dB
16-QAM 0.6 dB
8-ARY 0.6 dB
16-ARY 0.8 dB
32-ARY 1.0 dB
* Equal power and equal symbol rate for the interfering carrier and the desired carrier, i.e., 0 dB PSD ratio. Measured
at IF with AWGN, +10 dBc Adjacent Carriers, 1.3 spacing.
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