Automatic Link Establishment (4G ALE WALE)
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|---|---|
| Frequencies | 3 MHz,30 MHz |
| Frequency Range | 3 MHz - 30 MHz |
| Mode | USB |
| Modulation | PSK |
| ACF | Capture probe block: 40 ms, TLC block: 13.33 ms |
| Emission Designator | — |
| Bandwidth | 3 kHz |
| Location | Worldwide |
| Short Description | 4G ALE (Wideband ALE, WALE), defined by MIL-STD-188-141D Appendices G and H. The link-setup handshake runs on a 3 kHz channel using the Deep WALE and Fast WALE 8PSK burst waveforms (1800 Hz subcarrier, 2400 Bd), while a contiguous wideband HF traffic channel of up to 48 kHz is dynamically negotiated for a MIL-STD-188-110D Appendix D modem. Backward compatible with 2G ALE and 3G FLSU, with optional HALFLOOP linking protection. |
| I/Q Raw Recording | — |
| Audio Sample | |
Fourth-generation ALEAutomatic Link Establishment (4G ALEAutomatic Link Establishment), also known as Wideband ALEAutomatic Link Establishment (WALE), is the wideband HFHigh Frequency (3-30 MHz) automatic link establishment system defined by MIL-STD-188-141D, Appendix G (waveforms, signal structures, protocols and performance requirements) and Appendix H (the HALFLOOP linking-protection algorithm). It extends the ALEAutomatic Link Establishment concept to Wideband HFHigh Frequency (3-30 MHz) (WBHF): the link-setup handshake is performed on an ordinary 3 kHzKiloHertz (kHz) 10^3 Hz channel, but the protocol negotiates a contiguous traffic channel of up to 48 kHzKiloHertz (kHz) 10^3 Hz which is then used by a wideband traffic modem (MIL-STD-188-110C/D Appendix D). 4G ALEAutomatic Link Establishment borrows protocol ideas from both 2G and 3G ALEAutomatic Link Establishment and adds a formal traffic-bandwidth negotiation, integrated messaging, and two new burst waveforms: Deep WALE (robust) and Fast WALE (fast).
Description[edit]
4G ALEAutomatic Link Establishment / WALE conveys fixed-size, 96-bit Protocol Data Units (PDUs) over an HFHigh Frequency (3-30 MHz) channel. Exchanging these PDUs according to the defined protocols supports channel evaluation, selective calling, automatic answering, traffic-bandwidth negotiation, and the passing of text and binary messages. Two 8PSK8-Phase Phase-Shift Keying (3 bits per symbol) burst waveforms are used: the robust Deep WALE waveform for challenging channels and the Fast WALE waveform for relatively benign (voice-quality or better) channels. Either waveform may be used in a given transmission, but a single transmission uses only one of them; the two are distinguished by the final four symbols of the preamble.
Wideband channels of up to 48 kHzKiloHertz (kHz) 10^3 Hz are described in the PDUs using 16-element "sub-channel" vectors, where each bit marks a 1.5 kHzKiloHertz (kHz) 10^3 Hz or 3 kHzKiloHertz (kHz) 10^3 Hz sub-channel as assigned/occupied/usable. During the handshake the caller and responder each report the spectrum available to them, and the usable traffic channel is computed independently for each direction of the link. This lets the system route around localised interference and adapt the occupied bandwidth to channel conditions and to the requested traffic type.
Two forms of addressing are used: alphanumeric User Process addresses (3 to 15 printable ASCII characters) presented to the operator, and 16-bit binary PDU addresses carried on the air. An individual address refers to exactly one Participating Unit (PU); a multipoint address refers to a pre-programmed group of PUs, analogous to a 2G net address. In NATONorth Atlantic Treaty Organization applications a 16-bit network number is associated with each address.
Stations repeatedly scan a list of calling channels (a "scan set") listening for calls and soundings. Both synchronous scanning (dwell periods aligned to the GPS epoch) and asynchronous scanning are supported, and stations capable of monitoring several channels at once may "stare" instead of scanning. While scanning, a PU measures the SNR of every WALE PDU it processes (whether addressed to it or not) and records channel occupancy, building the link-quality picture used for channel selection.
For interoperability, a WALE station operating in 4G mode can still accept and place 2G ALEAutomatic Link Establishment calls (MIL-STD-188-141D Appendix A, including individual/net calls and AMD messages) and 3G Fast Link Set-Up (FLSU, STANAGNATO Standardization Agreement (STANAG), defines processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the North Atlantic Treaty Organization (NATO). 4538) calls; support for 3G wideband extensions (3GWB) is optional. When linking protection is enabled, 4G PDUs are encrypted with the HALFLOOP-96 algorithm (Appendix H) before coding; the capture probe, which carries no PDU, is left unencrypted.
Characteristics[edit]
All WALE waveforms use 8PSK8-Phase Phase-Shift Keying (3 bits per symbol) modulation of an 1800 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). subcarrier at 2400 symbols per second (the same serial-tone core used by the MIL-STD-188-110A waveform and by 3G ALEAutomatic Link Establishment), designed to pass through the audio passband of a standard SSBSingle-sideband modulation radio. The link-setup handshake itself occupies a 3 kHzKiloHertz (kHz) 10^3 Hz channel; only the subsequently negotiated traffic channel is wideband.
Each 96-bit PDU is protected by a constraint-length 9, rate-1/2 convolutional code with full tail-biting, producing a 192-bit coded block which is then interleaved (load step of 25, modulo 192). A 16-bit CRC (STANAGNATO Standardization Agreement (STANAG), defines processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the North Atlantic Treaty Organization (NATO). 5066 polynomial) covers the PDU. The two waveforms differ in how those coded bits are carried:
- Deep WALE uses a 240 msmilliseconds (.001 of a second) acquisition preamble of 18 orthogonal Walsh-modulated, scrambled channel symbols. Data is carried four coded bits at a time: each "quad-bit" selects one of sixteen 16-element Walsh sequences, repeated four times to a 64-element symbol and scrambled by a 159-bit shift register (single tap after bit 31, iterated 16 times per symbol). This makes Deep WALE very robust but slow at roughly 1.28 s per PDU. The first of the final four preamble di-bits is 0, identifying the Deep waveform.
- Fast WALE uses a 120 msmilliseconds (.001 of a second) acquisition preamble of 9 Walsh-modulated symbols. Data is sent as BPSKBinary Phase-Shift Keying (1 bit per symbol) transcoded to 8PSK8-Phase Phase-Shift Keying (3 bits per symbol) (bit 0 -> symbol 0, bit 1 -> symbol 4), scrambled by an x9+x4+1 generator, in two 96-symbol blocks separated and bracketed by 32-symbol known "probe" sequences for channel tracking. One PDU takes about 120 msmilliseconds (.001 of a second). The first of the final four preamble di-bits is 1, identifying the Fast waveform.
The asynchronous-mode capture probe is the leading section of an asynchronous call or termination: a repeated block of 96 known 8PSK8-Phase Phase-Shift Keying (3 bits per symbol) symbols (40 msmilliseconds (.001 of a second) per block) that scanning receivers recognise so they stop scanning to receive the following PDU. It is the 4G equivalent of the 2G/3G scanning call, and its length is at least dmin x (C+2), where dmin is the minimum dwell time and C is the number of channels in the scan set. The optional TLC section (one or more 32-symbol known blocks, 13.33 msmilliseconds (.001 of a second) each) precedes non-asynchronous transmissions to let AGC and level control settle.
Equipment capability (EC) is signalled as one of four classes: 3 kHzKiloHertz (kHz) 10^3 Hz, up to 12 kHzKiloHertz (kHz) 10^3 Hz, up to 24 kHzKiloHertz (kHz) 10^3 Hz, and up to 48 kHzKiloHertz (kHz) 10^3 Hz (mapping to MIL-STD-188-110D Appendix D Blocks 1-4). Synchronous dwell speed (SDS) sets the dwell time: SDS 1 = 1.350 s (mixed 3G/4G), SDS 2 = 0.675 s (Fast and Deep WALE), SDS 3 = 0.450 s (Fast WALE only). A square-root raised-cosine transmit filter with 35% roll-off is recommended.
Features[edit]
New / wideband features in 4G ALEAutomatic Link Establishment (WALE):
- Wideband HFHigh Frequency (3-30 MHz) operation: contiguous traffic channels dynamically negotiated up to 48 kHzKiloHertz (kHz) 10^3 Hz
- Per-direction traffic-channel negotiation using 16-element sub-channel vectors
- Two complementary burst waveforms: Deep WALE (robust) and Fast WALE (fast)
- Synchronous (GPS-epoch aligned) and asynchronous scanning, plus optional staring
- Listen-before-transmit / listen-before-respond occupancy sensing with an operator override mode
- Point-to-point, point-to-multipoint, and one-way link setup, plus sounding and two-way LQA exchange
- Integrated unacknowledged text and binary messaging
- HALFLOOP-96 linking protection (Appendix H): 128-bit key, 64-bit (time/frequency dependent) seed
Improvements over 3G ALE:
- Much higher potential throughput by linking straight into a wideband (up to 48 kHzKiloHertz (kHz) 10^3 Hz) traffic channel
- Spectrum use adapted to interference and to the requested traffic type
- Backward compatible with both 2G ALEAutomatic Link Establishment (Appendix A) and 3G FLSU (STANAGNATO Standardization Agreement (STANAG), defines processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the North Atlantic Treaty Organization (NATO). 4538), able to scan and link 2G/3G/4G at the 3G scan rate
Waveforms[edit]
The 4G system uses two PDU-bearing burst waveforms (Deep WALE and Fast WALE) plus two known-symbol leading sections (the optional TLC section and the asynchronous-mode capture probe). All sections use 8PSK8-Phase Phase-Shift Keying (3 bits per symbol) serial-tone modulation of an 1800 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). carrier at 2400 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second..
| Waveform | Description | Burst Duration | Preamble | Payload |
|---|---|---|---|---|
| Capture Probe | Async-mode scanning call/termination; stops scanning receivers | 40 msmilliseconds (.001 of a second) per block, repeated | None | None (known symbols) |
| TLC Section | Optional AGC / level-control settling section | 13.33 msmilliseconds (.001 of a second) per block | None | None (known symbols) |
| Deep WALE | Robust link setup; 4-ary Walsh data modulation | 240 msmilliseconds (.001 of a second) + ~1.28 s / PDU | 240 msmilliseconds (.001 of a second) | 96-bit PDU |
| Fast WALE | Fast link setup; BPSKBinary Phase-Shift Keying (1 bit per symbol) data with probe blocks | 120 msmilliseconds (.001 of a second) + ~120 msmilliseconds (.001 of a second) / PDU | 120 msmilliseconds (.001 of a second) | 96-bit PDU |
Samples[edit]
A typical asynchronous two-way handshake is: capture probe (caller) → LSU_Req PDU (caller) → LSU_Conf PDU (responder, after the listen-before-respond delay). Either party may use Deep or Fast WALE.
| Async Call (Capture Probe + Deep WALE) | LSU Confirm (Fast WALE) |
|---|---|
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Decoding Software[edit]
Hobby Level Software
- Currently no hobby-level software is known to decode this mode
Professional Level Software
- go2SIGNALS (in MIL Decoder Package)
- Krypto500 (lists MIL-STD-188-141D 4G ALEAutomatic Link Establishment / WALE)
- RapidM (RM12 wideband modem implements WALE, MIL-STD-188-141D Appendices G & H)
