Comtech EF Data SLM-5650A - Manual (Page 318)

SLM5650A_CDM625 Satellite Modem Revision 8
DoubleTalk Carrier-in-Carrier Option MN-SLM5650A
15–20
15.6 DoubleTalk Carrier-in-Carrier Specifications
Operating Mode Requires the two links to share a common carrier frequency (Outbound and Inbound symbol
rates do not have to be equal)
Power Spectral Density Ratio
and CnC Ratio
BSPK/QPSK/8-PSK/8-QAM: –7 dB to +11 dB (ratio of power spectral density, outbound
interferer to desired inbound)
16-QAM: –7 dB to +7 dB (ratio of power spectral density, outbound interferer to desired
inbound)
Note: With asymmetric carriers the absolute power ratio (or CnC ratio) would be different,
depending on the ratio of the symbol rates.
Example:
Outbound interferer = 1 Msymbols/sec
Desired Inbound = 500 ksymbols/sec
Ratio of power spectral density = +7 dB
Absolute power ratio (CnC Ratio) = +7dB + (10 log Outbound/desired symbol rate) = +10 dB
Maximum Symbol Rate Ratio 3:1 (TX:RX or RX:TX)
Inbound/Outbound
frequency uncertainty
Within the normal acquisition range of the demod, as follows:
Below 64 ksymbols/sec: ±1 to ±(Rs/2) kHz, where Rs = symbol rate in ksymbols/sec
Between 64 and 389 ksymbols/sec: ± 1up to a maximum of ± 32kHz
Above 389 ksymbols/sec: ±1 to ± (0.1Rs) kHz, up to a maximum of ± 200 kHz
Delay range 0-330 ms
Eb/No Degradation
(equal Inbound/Outbound
power spectral density)
BPSK = 0.3dB QPSK = 0.3dB OQPSK = 0.3dB
8-PSK = 0.5dB 8-QAM = 0.4dB 16-QAM = 0.6dB
For +10 dB power spectral density ratio (outbound interferer 10 dB higher than desired
inbound) add an additional 0.3 dB
Monitor Functions Delay, in milliseconds
Frequency offset (between outbound interferer and desired inbound). 100 Hz resolution
CnC ratio, in dB (ratio of absolute power, outbound interferer to desired inbound)
CnC Monitor Accuracy ±1.0 dB for symmetric symbol rate
15.7 Carrier-in-Carrier Summary
Comtech EF Data’s DoubleTalk Carrier-in-Carrier can provide significant savings in operational
expenses. The following should be considered when evaluating CnC:
• CnC can only be used for full duplex links where the transmitting earth station is able to
receive itself.
• CnC can be used in both bandwidth limited and power limited situations.
• The maximum savings is generally achieved when the original link is symmetric in data
rate.