CDM-625 Advanced Satellite Modem
Revision 1
Introduction
MN-0000036 (Ref MN/CDM625.IOM)
1.7.5
DoubleTalk
®
Carrier-in-Carrier
®
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
From –7 dB to +11 dB (ratio of power spectral density, outbound interferer to desired inbound)
Note:
With asymmetric carriers the absolute power ratio will be larger than this, depending on the ratio
of the symbol rates.
Example:
Outbound interferer = 1 Msymbols/sec Desired Inbound = 50 ksymbols/sec
Ratio of power spectral density = +10 dB
Absolute power ratio
(CnC Ratio)
= +10dB +(10 log Outbound/desired symbol rate) = +23 dB
Worst case example:
Outbound interferer = 12.5 Msymbols/sec Desired Inbound = 18 ksymbols/sec
Ratio of power spectral density = +11 dB
Absolute power ratio
(CnC Ratio)
= +11dB +(10 log Outbound/desired symbol rate) = +38.4 dB
Inbound/Outbound
frequency uncertainty
Within the normal acquisition range of the demod, as follows:
Below 32 ksymbols/sec: ±1 to ± (Rs) kHz, where Rs = symbol rate in ksymbols/sec
Between 32 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)
1–16
