User guide

MS-DMT Guide v1.04
Released 05-30-2014
13
MIL-STD MODEM IMPLEMENTATION
A MIL-STD/STANAG modem has traditionally been implemented in hardware as an Embedded
System, designed specifically to perform its functions as a military data modem. Embedded
systems contain processing cores that are typically either Microcontrollers (MCU),
Microprocessors (CPU), Digital Signal Processors (DSP) or Field Programmable Gate Arrays
(FPGA) based or some combination of processors. The key characteristic being that hardware
based military modems have processing power dedicated to the processing requirements of the
modem and are not shared among non-related tasks. Since the embedded modems are
dedicated to the specific modem tasks, design engineers have an optimized environment for
consistent reliability and performance of their hardware modem firmware, not to mention
accurate and stable reference clocks.
The trend among some military hardware modem designers in the 21
st
century has been based
upon using a Unix or Linux embedded operating system due to low cost and ease of life cycle
maintenance and ability to provide Software Development Kit (SDK) offerings for end user
customization as an alternative to past embedded approaches. An example of a Linux based
modem is the Rockwell-Collins Q96xx family of modems which even support direct video,
keyboard and mouse for configuration setup and some user controlled operation without the
need of an external computer to provide such user tools as Constellation and Channel Impulse
Response displays and an SDK for additional user tool development that traditional military
modems do not provide. However, even with these types of modems, the only tasking taking
place by the embedded Linux OS is that dedicated to the modem use, thus we are still talking a
dedicated, optimized environment for consistent reliability and performance of these military
modems.
The software detailed herein represents a virtual MIL-STD data modem that does not benefit
from having a dedicated environment in any aspect for its operation and is thus presented with
a host of challenges to achieve the goal of meeting the minimum performance requirements as
detailed in the military standards and with consistent results. However with a clean native
Windows OS install, properly configured and maintained on a dedicated PC (or one setup for
bootable USB 2.0 or greater Flash drive or an external bootable USB hard drive or solid state
drive) for MARS communications use, this software comes very close meeting minimum MIL-
STD performance requirements across all data rates for the 110A modem on a system meeting
all specified configuration requirements herein.
This software is much more demanding of the PC Sound Device, operating system and radio
equipments vs. Amateur Radio digital communications applications which support the low
symbol rate data modes that make use of the PC Sound Device as the modem hardware. The