The RapidM modems include the narrowband HF data modem waveforms, which are in compliance with MIL-STD-188-110A. This standard describes the Frequency Shift Keying (FSK), Serial Tone Mode (STM) and Parallel Tone Mode (PTM) modem waveforms.
The original MIL-STD-188-110 “Military Standard Interoperability and Performance Standards for Data Modems” was released in November 1980. It has since been superseded by later revisions, the current one being MIL-STD-188-110D (December 2017).
- 2-Tone FSK waveform modes providing data rates ranging from 50 to 1200 bps in a 3 kHz channel. Both narrow-shift and wide-shift FSK modems are specified. The FSK waveforms are required for backwards interoperability with legacy systems. For example: beacons or control channels offering data rates from 50 bps to 1200 bps in 3 kHz.
- Autobaud capable STM waveforms providing data rates ranging from 75 to 2400 bps coded, and 4800 bps uncoded, in a 3 kHz channel. The STM waveforms are recommended for backwards interoperability with legacy Automatic Repeat Request (ARQ) data and digital voice systems.
- PTM waveforms in the form of the 39-Tone Parallel Mode (39-TPM) modem providing data rates from 75 to 2400 bps in a 3 kHz channel. The 39-TPM modem is interoperable with the NATO STANAG 4197 waveform as used with the legacy NATO Narrowband Digital Voice Terminal (ANDVT) products for data and digital voice operation.
- The FSK waveforms are required for backwards interoperability with legacy data or beacon systems.
- The serial tone PSK waveforms’ autobaud capability and the inclusion of tone excision (RapidM implementations) at the modem receiver makes these modes very popular and in wide-use for their performance and robustness.
- The parallel tone modems are required for backwards interoperability with legacy digital voice systems.
Serial Tone Mode (STM):
The table below summarises the complete MIL-STD 188-110A STM waveform suite. Included in the table are the modulation, code rate and interleaver settings for each data rate. The MIL-STD 188-110A waveform includes tone excision whereby suppression of up to 4 tones is possible. The inclusion of tone excision improves the waveform resilience and performance in the presence of channel interference.
|Waveform||Data Rate (bps)||Modulation
|Coding Rate||Interleaver Settings||Tone Excision Capability|
|75 C||Walsh||1/2||Z, S, L||YES|
|2400 C DATA||8-PSK||1/2||YES|
|2400 C VOICE||8-PSK||1/2||Z, S||YES|
Table 1: MIL-STD-188-110A – STM Waveform Suite
The 75 bps data rate of MIL-STD-188-110A is interoperable with the NATO STANAG 4415 waveform known as the “Robust 75 bps” waveform. The STANAG 4415 specification has stricter performance requirements in degraded channels and interference.
The following table gives performance results for the RM Modems (HF Channel Simulator).
|MIL-STD-188-110A (Serial mode)|
|STANAG 4203 Filters excluded|
HF Channel Conditions
|RM Modem SNR
|Doppler Spread [Hz]||Amplitude Path 2 [dB]||Multi-Path Spread [ms]||BER||SNR
Table 16: Performance: MIL-STD-188-110A (Serial Tone Modem)
The figure below illustrates the Bit Error Rate (BER) performances of the RapidM MIL-STD 188-110A STM waveform suite as measured for ITU-R Poor Channels. Where applicable, the absolute specification points are indicated. The RapidM RS8 HF & V/UHF Channel Simulator was used to simulate the HF channel conditions.
Bit Error Rate (BER) Performance of MIL-STD-188-110A for ITU-R Poor Channels<s/small>
Parallel Tone Mode (PTM):
Appendix A of the MIL-STD 188-110A standard specifies the 16-Tone Differential Phase-Shift Keying (DPSK) modem. This modem waveform has been removed in versions “C” of the specification, i.e. MIL-STD 188-110C.
Appendix B of the MIL-STD 188-110A standard specifies the 39-Tone Parallel Mode (39-TPM) modem waveforms providing data rates from 75 to 2400 bps in a 3 kHz channel. The 39-TPM modem is interoperable with the NATO STANAG 4197 waveform as used in the legacy ‘NATO Narrowband Digital Voice Terminal’ (ANDVT) products for data and digital voice operation.
The 39-TPM waveform makes use of a Quadrature Differential Phase-Shift Keying (QDPSK) constellation to transmit the data. The data is encoded using a shortened (15,11) Reed Solomon in a GF (16) field.
The table below presents the complete 39-TPM suite of waveforms. Included in the table is the preamble mode, coding, in-band diversity, and interleaver settings for each data rate. For the lower rates, time-and-frequency diversity and frequency-only diversity is selectable.
|Waveform||Data Rate (bps)||Preamble||Coding||In Band Diversity||Interleaver Settings||TEX
|75||Normal / Extended||RS
|Time and Frequency,
Table 2: MIL-STD-188-110A Appendix B – 39-TPM Waveform Suite
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