Microwave Radio Communications SCM4000, Техническое справочное руководство

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Theory of Operation 8-2 SCM4000 Technical Reference Manual
8.3 Operation
The SCM4000 can be comprised of one or more of the following
primary components:
• Single Carrier Modulator Module
• Single Carrier Demodulator Module
• MPEG Encoder Module
• MPEG Decoder Module
Combinations of these components may be included in an
SCM4000, depending upon your applications.
8.3.1 Description
The SCM4000 is a multi-functional platform for the transmission
of video, audio, and high-speed data. The 1 rack unit (1RU) can
be ordered in different configurations to meet changing operating
conditions.
Available in duplex and simplex configurations and with internal
encoders and decoders, the unit can be optioned with up to four
industry standard interfaces in different combinations plus AC or
DC prime power.
The fully functioned SCM4000 includes a data multiplexer/
demultiplexer for interfacing to multiple data sources, a
Modulator, and a Demodulator. The SCM4000 is capable of data
rates up to 110 Mb/s at any of four different Quadrature
Amplitude Modulation (QAM) schemes, including QPSK,
16QAM, 32QAM, and 64QAM.
The Modulator and Demodulator setup must be identical for the
signal to pass. The demux removes the overhead and sends
the appropriate data to the appropriate interface as identified by
its unique Packet Identifier (PID).
The single carrier modulation/demodulation scheme uses
symbol rates up to 20Ms/s. An extremely powerful equalizer
removes multipath and is coupled with a Reed Soloman Noise
Reduction System to form a robust, reliable communications link.
Careful attention is made to the maximum data rate and its
relationship to bandwidth to achieve a reliably designed
microwave system.
8.3.2 Interfaces
The transmit and receive data interface consists of from one to
four interface types as follows:
• ASI 1, ASI 2, and ASI 3 (1 to 100 Mb/s)
• DS3/E3 1 and DS3/E3 2
• T1/E1 1 and T1/E1 2
• RS232/RS485
• Ethernet 10/100 1 and 10/100 2
8.3.3 Data Mux
The multiplexer works on a constant output data rate. The data
rate is directly related to the symbol rate used by the Modulators.
The symbol rate is directly related to the bandwidth of the IF
carrier. The output of the multiplexer contains Reed Solomon
overhead and mux/demux overhead.
To accommodate changes in the data rate supplied by the
source and the constant output of the mux, the gaps are filled
with null data that is later removed by the demux. Therefore,
data is completely variable up to the point where the mux
overflows. Variable interfaces like the DVB ASI can take full
advantage of this feature.