Comtech EF Data CDM-Qx Installation And Operation Manual page 211

CDM-Qx Satellite Modem
CnCPerformance Characterization
The following table contains the CDM-Qx configurations tested:
Modulation Forward Error
QPSK
8-PSK
16-QAM
The results are plotted for Eb/No degradation versus relative carrier spacing where:
•
•
There are two sets of adjacent carrier plots representing operation with 20% and 35%
rolloff (α). When α is 20%, the spectrum is narrower than it is for 35%. The effect of this
is noticed in the adjacent carrier plots. The 20% plots are displaced slightly to the left of
those for 35%. This makes it possible to space carriers slightly closer when the rolloff is
20%. The table below generalizes degradation (≤ 0.5 dB) for all modulation and coding
combinations when there are two adjacent carriers:
Degradation ≤ 0.5 dB
Some caution is required because carriers with 20% rolloff are more sensitive to
impairments and non-linearity in the link.
Reference Eb/No
Correction At BER ≈ 10
3/4 Turbo 3.9 dB
3/4 Turbo 6.3 dB
3/4 Turbo 7.7 dB
Eb/No degradation is the difference between the reference Eb/No and the Eb/No
read from the modem in the presence of the interfering adjacent carrier.
Relative Carrier Spacing is the distance between the centers of the desired and
adjacent carriers divided by the symbol rate.
Carrier Spacing For
20% Rolloff
≥ 1.1 x Symbol Rate
Symbol
-8
Rate
1000 ksps
1000 ksps
1000 ksps
Carrier Spacing For
35% Rolloff
≥ 1.2 x Symbol Rate
D–3
Revision 6
MN/CDMQx.IOM
Data Rate Rolloff
(α)
1500 kbps 20 and 35%
2250 kbps 20 and 35%
3000 kbps 20 and 35%