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CDM-Qx Satellite Modem Revision 5
CnCPerformance Characterization MN/CDMQx.IOM
D–7
The following CDM-Qx configurations were tested for Eb/No degradation as a function
of CnC ratio:
Modulation Forward Error
Correction
Reference Eb/No
At BER ≈ 10
-6
C/N
QPSK 21/44 Turbo 2.6 dB 2.4 dB
QPSK 3/4 Turbo 3.7 dB 5.5 dB
QPSK 7/8 Turbo 4.3 dB 6.7 dB
QPSK 17/18 Turbo 6.5 dB 9.3 dB
8-PSK 2/3 TCM 5.3 dB 7.9 dB
8-PSK 3/4 Turbo 6.1 dB 9.6 dB
8-PSK 7/8 Turbo 7.1 dB 11.3 dB
8-PSK 17/18 Turbo 9.0 dB 13.5 dB
16-QAM 3/4 Turbo 7.2 dB 12.0 dB
16-QAM 7/8 Turbo 8.1 dB 13.5 dB
The Eb/No degradation is the difference between the reference Eb/No with no interfering
carrier present and the Eb/No reported by the modem at a given CnC ratio.
Figure D- plots the impact of CnC ratio on QPSK and 8-PSK constellations, and Figure
D-8 shows 16-QAM. In general, the higher the operating C/N of a carrier, the more
sensitive it is to degradation. QPSK is the least sensitive to CnC ratio followed by 8-PSK
and 16-QAM.
Figure D-7. CnC Ratio For QPSK and 8-PSK
Eb/No Degradation vs CnC Ratio (QPSK)
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
-10 -5 0 5 10
CnC Ratio (dB)
Eb/No Degradation (dB
)
QPSK 17/18 Turbo
QPSK 3/4 Turbo
QPSK 21/44 Turbo
QPSK 7/8 Turbo
Eb/No Degradation vs CnC Ratio (8-PSK)
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
-10 -5 0 5 10
CnC Ratio (dB)
Eb/No Degradation (dB)
8-PSK 2/3 TCM
8-PSK 7/8 Turbo
8-PSK 3/4 Turbo
8-PSK 17/18 Turbo