Functional Description - Comtec CDM-840 Installation And Operation Manual

CDM-840 Remote Router
Appendix F
of the transmission source in a densely populated area, you must dispatch a helicopter
equipped with a feed horn and spectrum analyzer; the time and cost associated with such
methods are significant.
By contrast, Comtech EF Data's DVB-CID provides you with the interference source's
identification information within seconds. Once you identify the offending carrier, you may then
contact the uplinking station and request that the station shut down or otherwise remove the
identified transmission from service.
F.1.2

Functional Description

In a typical network, there can be many CDM-840s with DVB-CID, and one (or more) MCDD-100
MetaCarrier Detection Devices to verify the presence of the DVB-CID on each carrier. In an
interference situation, the MCDD-100 may be used to decode the DVB-CID of an interfering
carrier that may not be part of one's own transmission network, as long as the interfering carrier
has an embedded DVB-CID.
The CDM-840 creates a composite carrier by first sizing the appropriate MetaCarrier, and then
by adding the spread spectrum CID (at a highly reduced power spectral density compared with
that of the host carrier).
The size of the MetaCarrier is determined based purely on symbol rate and is totally
independent of modulation and coding, resulting in two (2) discrete sizes of MetaCarrier being
combined with the host carrier. The MetaCarrier parameters are shown below:
Host Carrier
128 ksps to < 512 ksps
512 ksps to < 2048 ksps
2048 ksps to < 4096 ksps
4096 ksps to < 8192 ksps
8192 ksps to 12500 ksps
*kchips per sec refers to the direct sequence spread spectrum chipping rate
As shown here, the bandwidth of the host carrier is always wider than the MetaCarrier, the
worst case being a 112 kcps MetaCarrier underneath a 128 ksps host carrier. In all
configurations of the combined carrier, the MetaCarrier raises the transmission power less than
0.1 dB above the original carrier.
Note that in accordance with the DVB specification, Carrier ID is only available when
the Transmit symbol rate is greater than or equal to 128 ksps.
The CID message is composed of the following information:
•
CDM-840 MAC Address
• Contact Telephone number
Embedded DVB-CID MetaCarrier
112 kchips per sec *
224 kchips per sec
224 kchips per sec
224 kchips per sec
224 kchips per sec
•
Latitude and Longitude
• Custom message
F–2
MN-CDM840
DVB-CID psd Relative to Host Carrier psd
-27.5 dB
-27.5 dB
-24.5 dB
-21.5 dB
-18.5 dB
Revision 3