ALE and ALE400
General : Automatic Link Establishment (ALE) was developed to automatically select a frequency that will support automatic linking between stations in a network or point-to-point communication.without operator assistance.
In high-frequency (HF) radio, ALE makes possible for a station to make contact, or initiate a circuit, between itself and another specified radio station, without human intervention and usually under processor control.
Allowed functions : ALE techniques include automatic signaling, selective calling, and automatic handshaking. Other automatic techniques that are related to ALE are automatic channel scanning, link quality analysis (LQA), polling, sounding, message store-and-forward, address protection, exchange of orderwire commands and messages.
Description (standard) :
Baud rate : 125 bauds
Speed : about 76 wpm
Modulation : FSK 8 tones (3 bits)
Reception mode : only one side (USB or LSB), USB is recommended
Character set : ASCII characters
Shape of pulse : rectangular
Space between tones : 250 Hz,
Bandwidth : 2000 Hz,
Demodulation : non-coherent,
Synchronization : automatic using the signal
Coding : Golay and average on 3 frames (with a 2/3 voting logic)
Interleaving : yes (within a block of 48 bits)
Drift tolerance : 10 à 20 Hz/mn according to signal-to-noise ratio,
Pmean/Ppeak : 1
Lowest S/N : -4 dB
ARQ FAE mode :
This new ARQ mode is located, for the modulation, between the FS1045A DTM and DBM ARQ modes. For the protocol it is located between the FS1045A DTM and DBM modes and PAX/PAX2 modes.
"ARQ" is worth for "Automatic Repetition reQuest" and "FAE" for "Fast Acknowledged Exchange".
It is a bilateral mode, which means that messages can be transmitted from A to B and from B to A, in full duplex (protocol one, not physical one). The ACK or NAK answer can be accompanied or not by a message (as in PAX/PAX2).
The characters exchanged are 8 bits length so as to permit exchange in all ASCII-ANSI languages (English, French, German, Russian...), but not those with ideograms (as Japonese).
Contrary to DBM mode, the length of the frame is variable and depends of the message length (as in DTM mode). But as DBM mode, the blocks are not redundantly repeated and there is a global message interleaving (but with a variable ID).
ARQ FAE modulation description :
Baud rate : 125
Rough speed : maximum: 148 wpm (for 30 characters length message) or 184 wpm (for 63 characters length message)
Use speed : maximum in unilateral: 88 wpm (for 30 characters length message) and 125 wpm (for 63 characters length message)
: maximum in bilateral: 120 wpm (for 30 characters length message) and 164 wpm (for 63 characters length message)
Modulation : FSK 8 tones (3 bits)
Reception mode : only one side (USB or LSB), USB is recommended
Character set : ASCII +ANSI characters (8 bits)
Shape of pulse : rectangular
Space between tones : 250 Hz,
Bandwidth : 2000 Hz,
Demodulation : non-coherent,
Synchronization : automatic using the signal
Coding : Golay
Interleaving : yes (global within a block of data (message + CRC))
Drift tolerance : 10 to 20 Hz/mn according to signal-to-noise ratio,
Pmean/Ppeak : 1
Lowest S/N : - 6.5 dB (- 8.5 dB with many repetitions)
A "soft decision" Memory Arq is implemented. It makes the transmission more reliable (see details in the ARQ FAE protocol).
Differences between ALE (standard) and ALE400 (non standard)
The ALE400 system has exactly the same functions as the ones of the "141A" of Multipsk except that:
* the bandwidth is 400 Hz instead of 2000 Hz as in standard ALE (so ALE400 can be transmitted anywhere where 500 Hz digital modes are authorized),
* the modulation speed (50 bauds instead of 125 bauds) and consequently the text throughput are 2.5 slower,
* no fix frequency (as in MFSK16...), the automatic tuning being able to be done thanks to the RS/ID transmission,
* the S/N is 5 dB better:
- 9 dB for sounding, AMD messages and Unproto mode,
- 11.5 dB (- 13.5 dB with many repetitions) for ARQ FAE.
