Glossary; Doubletalk Carrier-In-Carrier Specifications; Carrier-In-Carrier Summary - Radyne DMD20 Installation And Operation Manual

DMD20/20LBST Universal Satellite Modem
3.15.14

DoubleTalk Carrier-in-Carrier Specifications

Operating Mode
Power Spectral Density Ratio
and CnC Ratio
Maximum Symbol Rate Ratio
Inbound/Outbound frequency
uncertainty
Delay range
Eb/No Degradation
(equal Inbound/Outbound
power spectral density)
Monitor Functions
3.15.15

Carrier-in-Carrier Summary

Comtech EF Data's DoubleTalk Carrier-in-Carrier can provide significant savings in operational
expenses. Considerations include:
• DoubleTalk Carrier-in-Carrier can only be used for full duplex links where the transmitting
earth station is able to receive itself.
• DoubleTalk Carrier-in-Carrier can be used in both bandwidth- and power-limited
situations.
• The maximum savings is achieved when the original link is symmetric in data rate.
3.15.16

Glossary

Allocated Bandwidth
Bandwidth or Allocated Bandwidth or Occupied Bandwidth is the frequency space required by a
carrier on a transponder.
For example, a Duplex E1 (2.048 Mbps) Circuit with 8-PSK Modulation, FEC Rate 3/4 and 1.4
Spacing requires:
2.548 MHz = 2.048 / (3 * 0.75) * 1.4 * 2
For a 36 MHz transponder, 2.548 MHz corresponds to 7.078% Bandwidth Utilization.
MN-DMD20-20LBST Revision 14
Requires the two links to share a common carrier frequency (Outbound and Inbound
symbol rates do not have to be equal)
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
3:1 (TX:RX or RX:TX)
Within the normal acquisition range of the demod, as follows:
Below 32 ksymbols/sec: ±1 to ± (Rs/2) 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
0-330 ms
BPSK = 0.3dB QPSK = 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
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)
OQPSK = 0.3dB
Theory of Operation
3–44