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CDM-740 Advanced Satellite Modem
Introduction
The platform includes support for constant coding and modulation (CCM) and variable coding and
modulation (VCM) operation. VCM allows operators to define groups of remotes that can have
different modulation and coding parameters to improve efficiency on existing satellite capacity.
The CDM-740 supports reception and transmission of IP data over satellite links via two
fundamentally different types of interface – IF and data:
•
The IF interface provides a bidirectional link with the satellite via the uplink and downlink
equipment.
•
The data interface is a bidirectional path, which connects with the customer's equipment
(assumed to be the DTE) and the modem (assumed to be the DCE). All terrestrial data is
connected using up to two (2) available 10/100/100 BaseT Ethernet interfaces.
On the transmit side: The return modulator transmits IP datagrams and is compatible with the
Comtech EF Data's CDM-570/L modems and CDD-562L/564/564L demodulators located at a
hub site.
Transmit data is received by the terrestrial interface where line receivers convert the data signals to
CMOS levels for further processing. A small FIFO follows the terrestrial interface to facilitate the
various framing options.
In the FEC encoder, the data is differentially encoded, scrambled, and then TPC-encoded.
Following the encoder, the data is fed to the transmit digital filters, which perform spectral shaping
on the data signals. The resultant I and Q signals are then fed to the QPSK, 8-QAM, or 16-QAM
modulator. The carrier is generated by a frequency synthesizer, and the I and Q signals directly
modulate this carrier to produce an IF output signal.
Turbo Product Codec (TPC) Return Modulator Hardware Option: The CDM-740 has an optional
return modulator providing a very low latency SCPC return link with data rates from 16Kbps to
9.98Mbps. Available modulations are QPSK, 8-PSK and 16-QAM with FEC rates of 21/44, 3/4,
7/8 and 0.95 providing numerous options to balance power and bandwidth on duplex circuits.
On the receive side: The DVB-S / DVB-S2 demodulator supports MPE/IP Decapsulation (ETSI
EN 301 192 Multi-Protocol Encapsulation) and Program Identifier (PID) filtering for up to 256
unique PIDs.
DVB-S and DVB-S2 Receiver: The CDM-740's demodulator supports DVB-S QPSK up to
45Msps, DVB-S2 QPSK, 8-PSK and 16-APSK demodulation up to 62 Msps with receive data rates
up to 167 Mbps depending on the modulation type and code rate. In DVB-S2 operation, the receiver
operates in the CCM and VCM modes. The receiver automatically detects for pilots ON/OFF and
supports spectral rolloff of 20%, 25% or 35%.
1–3
Revision 0
MN-CDM740
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