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CDM-625A Advanced Satellite Modem
Appendix D
location of the transmission source; the time and costs associated with such methods are
significant.
By contrast, Comtech EF Data's CID products provide the operator with the interference
source's identification information within seconds. Once the offending carrier is identified, the
uplinking station may be contacted and the request made to shut down or otherwise remove
the identified transmission from service.
The MCED-100's combined carrier (transmission carrier + embedded MetaCarrier) creates a
composite carrier that results in scalable identification system that requires minimal power
(typically less than 0.1 dB) from the transmission carrier.
D.3
Functional Description
In a typical network, there can be many CDM-625s with MetaCarrier, and one (or more) MCDD-
100s to verify the presence of the MetaCarrier on each carrier. In an interference situation, the
MCDD-100 may be used to decode the MetaCarrier of an interfering carrier that may not be part
of one's own transmission network, as long as the interfering carrier has an embedded
MetaCarrier.
The CDM-625A creates a composite carrier by first sizing the appropriate MetaCarrier, and then
by adding the spread spectrum CID (with power spectral density approximately 22 dB below the
transmission carrier's spectral power density) to the transmission carrier.
The size of the MetaCarrier is determined based purely on symbol rate and is totally
independent of modulation and coding, resulting in three (3) discrete sizes of MetaCarrier being
combined with the transmission carrier. The available MetaCarrier sizes are as follows:
*
kchips per sec refers to the direct sequence spread spectrum chipping rate
As shown here, the MetaCarrier is sized to be no more than 87.5% of the bandwidth of the
transmission carrier. In all configurations of the combined carrier, the MetaCarrier raises the
transmission power less than 0.1 dB above the original carrier.
The CID message is composed of the following information:
•
CDM-625A MAC Address
•
Transmit carrier symbol rate
Original Carrier
≥256 ksps
128 ksps to < 256 ksps
64 ksps to < 128 ksps
32 ksps to < 64 ksps
< 32 ksps
Embedded MetaCarrier
224 kchips per sec *
112 kchips per sec
56 kchips per sec
28 kchips per sec
14 kchips per sec
•
Transmit carrier center frequency
•
Custom message
D–2
Revision 0
MN-CDM625A
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