User guide

MS-DMT Guide v1.04
Released 05-30-2014
14
complex Military serial tone PSK waveforms being supported by this software have much higher
symbol rates, wider bandwidth and higher data rates than do the Amateur Radio, Commercial
and Military FSK (RTTY) digital modes commonly used by MARS in the past and implemented on
the PC Sound Device as the modem. Much more care must be taken in the initial configuration
and the configuration management of the PC operating system and the radio configuration for
the best and consistent results when using this software.
The standard Military serial tone waveforms utilize either a constant 1200bps or the more
common 2400bps symbol rate where the design of the IF passband filtering and radio receiver
dynamic range determines how faithfully the radio reproduces these complex signals. The MIL-
STD/STANAG serial tone signals contain information in both phase state and amplitude value
and occupy an instantaneous bandwidth as wide as 3kHz at the 2400 baud symbol rate,
requiring a minimum of 2.75Khz of IF filtering for optimal results. As the passband response of
radio IF filtering alters both phase and amplitude of a complex signal, any marginal radio design
considerations can cause degraded performance of these complex waveform signals. In
transmitting these complex waveforms radio linearity is more critical as well where only full
STANAG 4203
[8]
compliant filtering provides for the best results.
The use of the 110A ST waveform for FEC only peer-to-peer, broadcast and multicast
communications can most closely be compared to the use of MT-63 from a MARS user’s
perspective. They both make use of robust FEC and some common features from outward
appearance in application, such as operation at different data rates and interleaver settings.
However they also differ greatly in numerous ways, where MT-63 although influenced by
various Military standards, MT-63 does not adhere to any Military standards. In addition the
author of MT-63 developed the protocol to take into account all of the negative issues of
implementing the protocol as a software modem running within the MS-Windows environment
and on Ham radio equipments with narrow voice grade filters. The same is true of most other
sound device protocols such as WINMOR, where even the use of VOX PTT and its latency was
taken into account in designing the waveform protocol. This software however, attempts to
meet the rigid requirements of the Military standards within a general computer and
operating system environment that is just not suited to doing so without additional effort
made on the part of the end user to mitigate known issues that impact modem performance,
such as latency.
In keeping with the requirements of MIL-STD-188-110B, Appendix E, a Rockwell MDM-3001
single channel modem with a two path HF channel simulator per CCIR-549-3
[10]
is used to verify
the MS-DMT’s MIL-STD-188-110A modem compliance with the minimum serial tone modem
performance requirements in a 3kHz AWGN channel. At present the software comes close to
meeting the minimum performance requirements in testing with a single sound device looping
back through the MDM-3001 to eliminate sound device sample clock error and phase distortion