CDM-Qx Satellite Modem

Revision 5

CnCPerformance Characterization

MN/CDMQx.IOM

Other QPSK turbo code rates have similar performance and the QPSK plots above are

used to estimate their performance. The degradation plots above are also used for other

turbo 8-PSK and 16-QAM code rates. A good practice for carrier spacing is to operate

the links with sufficient spacing so there is no degradation.

 

D.3 Selecting The Adjacent Carrier Curve

The information presented earlier characterizes the case for one or two adjacent carriers relative to the desired carrier. The desired and adjacent carriers may also be CnC carriers occupying the adjacent slots. These cases are summarized by several variants shown in Figure D-5. Understanding the relationship between these assists in selection of the correct adjacent carrier degradation curve.

Case A in Figure D-5illustrates the way the adjacent carrier testing is conducted. It shows a single adjacent carrier 3 dB higher than the desired carrier, equivalent to two like-modulated adjacent carriers on either side of the desired carrier, each at the same level as the desired (0 dB higher). Case B shows two adjacent carriers each 3 dB higher than the desired.

Case C illustrates a CnC with a pair of co-located desired carriers (CnC ratio is 0) and a single adjacent slot with pair of CnC carriers whose total composite power is 3 dB higher than the desired pair. The total adjacent power to one of the CnC carriers is 6 dB, or the equivalent of two single adjacent carriers (one on each side of the desired) each 3 dB higher than “one” of the desired CnC carriers. It does not matter whether the adjacent carrier is a pair of CnC carriers or a standard carrier. It is based on the power.

Adjacent

 

 

 

Carrier

 

 

 

Level

Desired

Adjacent

 

 

 

 

Carrier

Carrier

R = +3 dB

R = +3 dB

Desired

Adjacent

Carrier

Carrier(s)

 

A

 

 

Carrier

 

 

C

 

 

 

Spacing

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Desired

R = +3 dB

 

 

 

 

Carrier(s)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R = +3 dB

Desired

Carrier

B

D

Figure D-5. Adjacent Carrier Cases

D–5

Page 247
Image 247
Mocomtech CDM-QX operation manual Selecting The Adjacent Carrier Curve, Figure D-5. Adjacent Carrier Cases