Mocomtech CDM-QX Carrier-in-Carrier Ratio CnC Ratio, Case Desired Adjacent Carrier

CDM-Qx Satellite Modem	Revision 5
CnCPerformance Characterization	MN/CDMQx.IOM

Case D shows two desired CnC carriers accompanied by a CnC carrier on each side. Again, it does not matter whether the adjacent carriers are CnC or conventional carriers, just the total power. This situation is equivalent to adjacent carriers each 6 dB greater than the one desired CnC carrier. The following table summarizes which adjacent carrier plot to select for this particular example, and which ones to use with a ratio, R, between the composite adjacent and composite desired carriers.

Case	Desired	Adjacent Carrier
(Figure D-5)	Carrier	(See Note)
A	1 Carrier	1 Adjacent Carrier
B	1 Carrier	2 Adjacent Carriers
C	1 CnC Carrier	1 Adjacent Carrier
D	1 CnC Carrier	2 Adjacent Carriers

Curve To Use In Figure D-2, Error!

Reference source not

found., or D-4

0dB

+3 dB

+3 dB

+6 dB

Curve To Use

For Any Ratio

R (dB)

R - 3 dB

R + 0 dB

R + 0 dB

R + 3 dB

Note: The adjacent carrier is the composite power for either a conventional carrier or CnC. carrier.

D.4	Carrier-in-Carrier Ratio (CnC Ratio)
	The CnC Ratio represents the difference in power between the co-located interfering
	carrier and the desired carrier in dB.
	CnC Ratio = Interferer Power - Desired Carrier
	During CnC operation, the interfering carrier is removed by the CDM-Qx using a stored
	version of the transmitted carrier to adaptively cancel it from the composite received
	signal. The desired carrier remaining after the cancellation process is delivered to the
	demodulator and decoder to recover the data.
	When the CnC ratio increases, the level of the interferer rises relative to the desired
	carrier and degradation grows. As the CnC ratio decreases, the desired carrier dominates
	and degradation becomes negligible. Figure D-6represents two cases of the CnC Ratio
	when the interfering and desired carriers are equal, and when the interferer is 6 dB
	stronger than the desired carrier. This representation is artificial because a real spectral
	plot displays only the composite power of the combined carriers and is unable to
	distinguish two carriers, but it is instructive to describe the underlying principle.
		+6 dB
	CnC Ratio = 0 dB	CnC Ratio = 6 dB
	Equal Interfering And	Interferer >
	Desired Carriers	Desired Carrier

A

B

Figure D-6. CnC Ratio

D–6