CDM-Qx Satellite Modem

Revision 5

CnCPerformance Characterization

MN/CDMQx.IOM

Referring back to Error! Reference source not found., 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.

Desired

Carrier(s)

Carrier

Spacing

Figure D-9. CnC Example

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:

 

DL Fade

UL Fade

Site A

4 dB

6 dB

Site B

2 dB

3 dB

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:

 

Site A

 

 

Site B

 

Parameter

dB

Comment

Parameter

 

dB

Comment

Relative Level of

-10

Due to fade at A

Relative Level of

 

0

Due to fade at A

Carrier A @ Site A

 

 

Carrier B @ Site B

 

 

 

Relative Level of

-4

Due to fade at A

Relative Level of

 

-6

Due to fade at A

Carrier B @ Site A

 

 

Carrier A @ Site B

 

 

 

CnC Ratio At

-6

 

CnC Ratio At

 

+6

 

Site A

 

 

Site B

 

 

 

Degradation At

-0.1

Per Figure D-

Degradation At

 

-0.3

Per Figure D-

Site A

 

8-PSK

Site B

 

 

8-PSK

D–9

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Image 251
Mocomtech CDM-QX operation manual DL Fade UL Fade Site a Site B, Comment, Per Figure D