Waveforms

Contents

• Narrowband Data Modem Waveforms – HF
• Wideband Data Modem Waveforms – HF
• Typical Data Modem Capabilities – HF
• MIL-STD-188-141D 2G ALE Waveform – HF
• MIL-STD-188-141D / STANAG 4539 3G ALE Waveforms – HF
• Narrowband RapidM Proprietary SDV Waveforms – HF

Narrowband Data Modem Waveforms – HF

Table 4 below shows the more traditional HF data modem waveforms which have been around for quite a number of years. These waveforms find use in shore to ship and strategic broadcast systems. The STANAG waveforms are well suited to broadcast because of the built-in continuous synchronisation sequences. STANAG 4529 is employed but could be very where useful wherever channel availability is restricted.

The STANAG 4539 / MIL-STD-188-110B serial tone waveform is normally associated with the STANAG 5066 ARQ protocol to ensure error free delivery of data. The Autobaud capability of this waveform is suitable for the implementation of fast Data Rate Change (DRC) algorithms in the STANAG 5066 protocol, thereby allowing the communication link to adapt to changing ionospheric channel conditions or interference. The STANAG 4539 / MIL-STD-188-110B waveform is often coupled with 2nd or 3rd Generation Automatic Link Establishment (ALE) capability to allow HF multi-channel operation. This is a crucial capability to achieve wide geographic coverage of Beyond Line-of-Sight (BLOS) communications. This is due to the varying nature of ionospheric propagation and its strong dependence of the radio frequency used.

The STANAG 4539 TDMA is for use in older Link 22 systems, whilst STANAG 5065 is for LF-band (90 kHz) submarine communications.

Table 4: Narrowband HF Data Modem Waveforms

A summary of the provided Narrowband HF Modem Waveforms and Data Rates is given below.

Notes:

1. According to STANAG 4415 (NATO robust: 75 bps)
2. MIL-STD-188-110D 'serial tone' modem and the STANAG 4539 modem is the same waveform. Also referred to as '110B', when it originally appeared.
3. The MIL-STD-188-110D Appendix F 'ISB modem' uses upper and lower sideband independently (ISB capable transceiver required)
4. 'ACF' is a RapidM proprietary waveform mode that offers '110' SSB and '110 App. F' ISB modes in combination. This is supported by the RapidM STANAG 5066 Narrowband Automatic Repeat Request (ARQ) Protocol's Data Rate Change (DRC) Function. Note that the Single Sideband (SSB) (and ALE) modes use the Upper Sideband (USB).
5. This is the '110B' version of the 9600 bps modem (SSB not ISB)

All the narrowband HF PSK-based waveforms, except for STANAG 4529, have a single carrier centered at 1800 Hz with a symbol rate of 2400 symbols per second. All coded waveforms use standard rate 1/2, (K=7 constraint length) convolutional encoding. The 2/3 and 3/4 rate codes are obtained by puncturing the 1/2 code. The lower rates of 1/4 and 1/8 are obtained by repetition coding.

The symbols sent over the air contain segments of known data (synchronization sequences and channel probes). This information is used by the receiver to lock onto the signal and to estimate the distortion of the HF sky-wave channel in real-time. Powerful adaptive equalization techniques are employed to mitigate the effect of this channel distortion.

Wideband Data Modem Waveform – HF

The Wideband HF (WBHF) serial tone modem waveforms (w/f) specified in MIL-STD-188-110D Appendix D and STANAG 5069 provide for the following Blocks of capability depending on the bandwidth (b/w):

• Block 1 W/f in 3 kHz b/w with data rates up to 16 000 bps
• Block 2 W/f in 3, 6, 9 and 12 kHz b/w with data rates up to 64 000 bps
• Block 3 W/f in 3, 6, 9, 12, 15, 18, 21 and 24 kHz b/w with data rates up to 120 000 bps
• Block 4 W/f in 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42 and 48 kHz b/w with data rates up to 240 000 bps

Note that in addition, Blocks 1 and 2 provide for Forward Error Correction (FEC) with constraint length 7 convolutional codes, whilst Blocks 3 and 4 support FEC modems with constraint length 7 and 9 codes. These data rates per modulation and bandwidth are shown in the table below.

The RM10 comes standard with the option to activate MIL-STD-188-110D up to Block 3 capability. Note that MIL-STD-188-110C is equivalent to MIL-STD-188-110D Block 3 capability.

Comparison: MIL-STD-188-110D / STANAG 5069 versus 110C versus 110B versus 110A

The relationships between MIL-STD-188-110D (MS110D) and its previous versions of the specification is given in the table below. Parts of the MS110D standard are identified as follows:

• Section 5.3.2 of the MS110D standard specifying the HF Data Modems for data rates 75 to 2400 bps in 3 kHz is identical to the previous versions of the standard. This section is the original serial-tone modem standard, the so-called ‘110A’ mode.
• Appendix C of the MS110D standard specifying the HF Data Modems for data rates 3200 to 9600 bps in 3 kHz is identical to the previous versions of the standard. This is the next development in serial-tone modems and, taken together with the rates of ‘110A’, these rates comprise the so-called ‘110B’ mode.
• Appendix F of the MS110D standard specifying the HF Data Modems for multiple channel systems is identical to the previous versions of the standard. The rates specified in MS110D Appendix F are for ISB operation and require an ISB capable radio. This standard is an early design for wideband serial-tone modems and has been widely implemented in naval systems –the so called ‘110B ISB’ mode.
• Appendix D of MIL-STD-188-110C specifies the original Wideband HF (WBHF) Waveforms occupying bandwidths from 3 kHz to 24 kHz in increments of 3 kHz. These are the so-called ‘110C’ modes. The 110C 3 kHz modem effective replaces the 110A (75 – 2 400 bps) and 110b (3 200 – 9 600 bps) modems, the new design offering improved performance.
• Appendix D of MS110D and also STANAG 5069 specify the latest family of WBHF Waveforms. These comprise of the original ‘110C’ modes (unchanged) and, additionally, new WBHF waveforms occupying bandwidths from 24 kHz to 48 kHz in increments of 6 kHz. These modes taken together are the so-called ‘110D’ modes.

Table 5: Relationships between MS110C and MS110A, MS110B and some STANAG’s

#NOTE 1: STANAG 4415 (Robust 75 bps mode)
The 75 bps data rate of MS110A/B & C 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. It will operate effectively almost 11 dB below the noise floor in a noise dominated environment. This waveform can counter the effects of extreme multi-path delay (≤10 ms) and Doppler spread (≤50Hz). This mode is typically used to send ACKs and NACKs in ARQ systems.

#NOTE 2: STANAG 4539 (75 – 9600 bps mode)
The NATO STANAG 4539 specification specifying the HF Data Modems for data rates 75 to 9600 bps, includes the waveforms and associated data rates of the MS110A/B & C (section 5.3) and MS110 A/B & C Appendix C. STANAG 4539 is equivalent to the so-called ‘110B’ mode.

#NOTE 3: MIL-STD-188-110C (WB HF serial tone modems up to 120 000 bps in 24 kHz)
Note that MIL-STD-188-110C is equivalent to MIL-STD-188-110D Block 3 capability.

#NOTE 4: STANAG 5069
Note that STANAG 5069 is equivalent to MIL-STD-188-110D Block 4 capability.

Typical Data Modem Capabilities – HF

A summary of the capabilities included as part of the HF Narrowband Modem Waveforms is provided below.

Table 4: AutoBaud Waveforms

MIL-STD-188-141D 2G ALE Waveform – HF

Appendix A of the MIL-STD-188-141D standard specifies the Second Generation Automatic Link Establishment (2G ALE) waveform – physical layer and protocols.  The 2G ALE waveform is still widely deployed and an important capability for backwards compatibility for systems with multi-channel capability.

The 2G ALE waveforms used 8-FSK modulation and a Golay FEC as shown in the table below.

The ALE 2G Waveform functionality includes the capability to detect the presence of certain waveforms occupying a given channel in the scan list. This capability is referred to as Occupancy Detection and Listen-before-Transmit. The MIL-STD-188-141D Appendix A 2G ALE signal detection implementations include the capability to detect the presence of MIL-STD-188-110 A, MIL-STD-188-110 B and MIL-STD-188-110 C, STANAG 4285, STANAG 4529.

MIL-STD-188-141D / STANAG 4539 3G ALE Waveforms – HF

In Table 6 below the HF ALE related and RapidM proprietary data modem waveforms are listed.

The 3G ALE waveform has the significant advantage in that it can link in channels with SNR of -12 dB (6 dB lower than 2G ALE). This waveform also has a formal traffic management function and a very efficient set of packet data modems (xDL protocols). The original 3G ALE standard had the packet modem waveforms using the HDL+ protocol included, but they were removed in the latest version of the STANAG 4538 standardisation document. RapidM implemented a proprietary waveform (RDL) with similar functionality and not including the uncoded mode.  The RDL provides high channel throughput and can deal well with adverse and highly variable HF channel conditions.

Note: * These waveforms differ in a number of ways from the HDL+ waveforms originally in the standard

Table 6: Narrowband ALE and RapidM Proprietary HF Data Modem Waveforms

The 3G ALE waveforms have a wide variety of distinct modulations and require Viterbi FEC and decoding as shown in the table below.

Table 7: 3G ALE Waveform Modulations and Forward Error Correction

The ALE 3G Waveform functionality includes the capability to detect the presence of certain waveforms occupying a given channel in the scan list. This capability is referred to as Occupancy Detection and Listen-before-Transmit. The STANAG 4538 / MIL-STD-188-141D 3G ALE signal detection implementations include the capability to detect the presence of MIL-STD-188-110 A, MIL-STD-188-110 B and MIL-STD-188-110 C, STANAG 4285, STANAG 4529 and the Burst Waveforms (BW0 to BW4) of STANAG 4538 / MIL-STD-188-141D.

Narrowband RapidM Proprietary SDV Waveforms – HF

In Table 6 below the HF ALE related and RapidM proprietary Secure Digital Voice (SDV) modem waveforms are listed. The RapidM Secure Digital Voice (SDV) Waveform (W/F 11, SDV2) is a best-in-class digital waveform for high security and clear HF voice communications even in very adverse channel conditions where analog voice operation is not possible.

Table 6: Narrowband RapidM Proprietary HF Secure Digital Voice (SDV) Waveforms

From a communications assurance standpoint, we have indicated that the ALE functions provide Multi-channel capability which would be inherently more resistant to jamming than a single-channel system. ALE is thus a strategic necessity for the SDR multi-role platforms.