Table of Contents
Advertisement
CDM-Qx Satellite Modem
CnCPerformance Characterization
Referring back to Figure D-9, the degradation due to adjacent carrier spacing is negligible
when spacing is 1.3 x Symbol Rate and 0 db is allocated for adjacent carrier degradation.
Initially the CnC ratio is 0 dB, and the desired and interfering carriers are operating at the
same power level. At one end of the link (Site A), a downlink fade of 4 dB is expected
and an uplink fade of 6 dB. The other end of the link (Site B) is allocated 2 dB for
downlink and 3 dB for the uplink:
When a rain fade occurs at one site, the effect is felt at both sites as outlined in
Figure D-10, which diagrams the worst case fade at Site A. The interfering carrier at Site
A is attenuated twice, once due to the uplink and the second time due to the downlink on
the return path. The carrier transmitted from Site B sees only the downlink fade when it is
received at Site A. The resulting power level changes at each site due to the rain fade and
the resulting CnC ratio and Eb/No degradation is summarized in the following table:
Parameter
Relative Level of
Carrier A @ Site A
Relative Level of
Carrier B @ Site A
CnC Ratio At
Site A
Degradation At
Site A
Desired
Carrier(s)
Carrier
Spacing
Figure D-9. CnC Example
DL Fade
Site A
4 dB
Site B
2 dB
Site A
dB
Comment
-10
Due to fade at
A
-4
Due to fade at
A
-6
-0.1
Per Figure D-10
8-PSK
D–9
UL Fade
6 dB
3 dB
Site B
Parameter
dB
Relative Level of
0
Carrier B @ Site B
Relative Level of
-6
Carrier A @ Site B
CnC Ratio At
+6
Site B
Degradation At
-0.3
Site B
Revision 6
MN/CDMQx.IOM
Comment
Due to fade at A
Due to fade at A
Per Figure D-10
8-PSK
Advertisement
Table of Contents
