Comtech EF Data MM200 - Manual (Page 19)

MM200 High-Speed Microwave Modem Theory of Operation
TM086 - Rev. 4.1 3-1
Theory of Operation
3
3.0 Theory of Operation
The MM200 Microwave Modem is a highly flexible platform for the transmission of high-speed
data across links such as microwave and cable. The 2 RU-rack mount unit can be supplied in
many different configurations and was designed to be expanded in the field to meet new and
changing operating conditions. Available in Duplex and Simplex Configurations, the unit can be
optioned with up to four industry standard interfaces in any combination, Diversity (requires two
chassis), maximum rates of 50, 100, 150, 175, and 200 Mbps, and world standard AC or DC
prime power.
The fully configured MM200 includes a data multiplexer/demultiplexer for interfacing to multiple
data sources, a modulator, and a demodulator. The MM200 is capable of data rates up to
200 Mbps at any of six different Quadrature Amplitude Modulation (QAM) schemes including
QAM256 (optional). The unique modulation/demodulation scheme uses multiple carriers to slow
the modulated symbol rate to up to four times slower than conventional modems. The lower
symbol rate is inherently more resilient to the multipath environment common to microwave
systems. An extremely powerful equalizer, working at the lower symbol rate, removes multipath
and is coupled with Reed Solomon Noise Reduction System to form a robust, reliable
communications link. Additionally, two receivers can be optioned with diversity cards. The two
chassis are then coupled via a high-speed data link to allow the automatic hitless switching to the
receiver with no errors. This feature can be used for standard path redundancy on long links or to
improve the capacity (via an increase in modulation mode) of an existing link. Refer to Figure 3-1
for operational block diagram.
3.1 Signal Flow
3.1.1 Interfaces
The transmit customer data interface consists of four “slots”. Each slot can accept one of a range
of industry standard interface cards including:
 DVB ASI (1 to 160 Mbps)
 DVB SPI (1 to 160 Mbps)
 G.703 E3/DS3/STS-1
 G.703 T1/E1
 G.703 E2
 OC3/STM-1 optical/electrical
 Orderwire, 8 synchronous, 64 Kbps, RS-422 (one channel can be switched to ADPCM)
 10Base T Ethernet
Data between interface slots can be Asynchronous and in any combination. Careful attention to
the maximum data rate and its relationship to bandwidth are required for the correct operating
conditions.
Some Interface Cards are capable of multiple standards such as the DS3,E3 or STS-1. These
cards can operate in any one of the standards listed. Changing to another standard simply
requires a change in the front panel configuration.