User`s manual

100-M0074X1 5 of 24
www.cobham.com/gms
2.0 Introduction
GMS’ Messenger Digital Transmitter with ASI option (MDT-A) accepts DVB compliant
MPEG-2 Transport Streams (TS) via an Asynchronous Serial Interface (ASI). The stream
can be scrambled with an AES scrambling algorithm to provide protection in sensitive
applications prior to the final step of DVB-T compliant FEC coding and C-OFDM modulation. The
transmitter provides automatic zero stuffing when the TS rate is less than the channel rate. Data rates
from 100 Kbps to 30 Mbps can be supported. However, the system is optimized for high rate
transmission above 5 Mbps. This transmitter is compatible with GMS’ MSR receiver, which outputs the
recovered ASI stream. When the AES scrambling option is chosen, the MSR must be configured with
the Digital Data Processor Card (DDPC). The DDPC accepts the ASI signal from the MSR and performs
the de-scrambling operation and then outputs the transport stream to an ASI output port.
The MDT-A will transmit any data that is formatted into a DVB compliant MPEG-2 TS per ETSI TBD for
Audio/Video (A/V) data and ETSI EN 301 192 for generic digital data transmission. Other A/V
compression formats such as H.264 and WM-9 can be transmitted provided that the TS structure
follows the TS specification.
The MDT-A can be used as part of a cost effective repeater system by combining it with an MSR,
antennas, down-converters, and optional Power Amplifiers (PAs) The ASI output of the MSR can be
fed directly into the MDT-A’s ASI input port.
GMS’ C-OFDM equipment uses a robust digital modulation system known as Coded Orthogonal
Frequency Division Multiplexed (COFDM) that provides frequency diversity and powerful Forward
Error Correction (FEC) algorithms. The Messenger receiver include an option for Spatial Maximal Ratio
Pre-Detect Diversity Combining to combat short delay spread multipath reflections found in indoor
environments. A Messenger Digital Link (MDL)
provides a robust wireless link that is effective against the multipath interference experienced by
analog systems and provides reliable data transmission in the most difficult of terrains.
This manual provides information on how to operate the MDT-A model as well as pertinent technical
information related to the overall system. Also, refer to model identifier (on-line document, 100-
MNI0042) at GMS website, www.cobham.com/gms, for available frequency and power configurations
along with available options.
2.1 Key System Features
• ASI Only Interface
• Coded Orthogonal Frequency Division Multiplexed (COFDM) Modulation
• Output Frequency 0.36 to 6 GHz (In-Bands)
• Low Power Consumption
• Local and Remote Control Interfaces
• Rugged and Compact Portable Design