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CDM-600 Satellite Modem Revision 7
Introduction MN/CDM600.IOM
1–2
1.1 Standard Features
The CDM-600 provides a wealth of standard features which go far beyond the basic
requirements of the Intelsat specifications.
• Low rate variable data rates – 2.4 kbps to 5.0 Mbps
• Mid-rate variable data rates – 2.4 kbps to 10.0 Mbps
• High-rate variable data rates – 2.4 kbps to 20.0 Mbps
• Embedded Distant-end Monitor and Control (EDMAC) (see Note)
• Selectable 50Ω / 75Ω IF port impedance
• Asymmetric Loop Timing
• Automatic Uplink Power Control (AUPC)
• Software – Flash Upgrading
• Modulation Types –BPSK, QPSK, and OQPSK
• 1:1 and 1:10 redundancy switches
Note: In this mode, an additional 5% overhead is combined with the traffic data,
(1.5% in Turbo BPSK modes, Turbo Rate 1/2 QPSK/OQPSK, and all data rates greater
than 2 Mbps) which permits Monitor & Control (M&C) information to be added
(transparently to the user), allowing access to the distant-end modem. This mode does not
require any additional cabling at either the local or distant-end Modems - access to
EDMAC is via the standard M&C control port. Full M&C is possible, and importantly,
the on/off status of the carrier at the distant-end carrier can be controlled. In addition, for
firmware version 1.5.0 and higher, the proprietary D&I++ framing mode is available.
This combines Drop & Insert (D&I) operation with a similar EDMAC link and a 2.2%
overhead.
1.1.1 AUPC
An important innovation in the CDM-600 is the addition of Automatic Uplink Power
Control (AUPC). This feature enables the modem to automatically adjust its output
power to maintain the Eb/No of the remote end of the satellite link constant. This
provides protection against rain fading, a particularly severe problem with Ku-band links.
To accomplish this, either the EDMAC or D&I++ framing types may be used, and the
distant end modem constantly sends back information about the demodulator Eb/No
using reserved bytes in the overhead structure. Using the Eb/No, the local modem then
adjusts its output power, and hence, a closed-loop feedback system is created over the
satellite link.
A benefit of this feature is that whenever EDMAC or D&I++ with AUPC operation is
selected, the remote demodulator’s Eb/No can be viewed from the front panel display of
the local modem. Note that EDMAC and D&I++ can be used in conjunction with either
framing type.