Automatic
Link Establishment (ALE)
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Harris RF-7210A Autolink II ALE Controller (NSN 5895-01-357-1966) |
General Overview
Automatic Link Establishment (ALE) is the principle where a
specialized radio modem, known as an ALE adaptive controller, is assigned the
task of automatically controlling an HF receiver and transmitter in order to
establish the highest quality communication link with 1 or multiple HF radio
stations.
ALE controllers can be found as external devices (such as pictured above, the
Harris RF-7210A) or as imbedded options in modern HF radio equipment.
Link establishment is dependent on many factors and is fully optimized by the
use of a micro computer in the ALE controller. What follows is a basic
description of how ALE functions as the in-depth workings of ALE can be
elaborate and complicated to illustrate.
ALE controllers function on the basic principles of LQA (Link
Quality Analysis) and SOUNDing. These tasks are
accomplished using the following common elements.
When a station desires to place a call, the ALE controller attempts to
LINK
to the outstation using the data collected during ALE and SOUNDing activities.
If the outstation's data has not been collected by the sending ALE, the
controller will seek the station and attempt to LINK using all programmed
channels.
Upon a successful LINK, the ALE controllers will cease the channel scanning
process and alert the operators that the system has establish a connection and
that stations should now exchange traffic. Upon completion of a LINK
session, the ALE controllers will send a LINK TERMINATION
command and the ALE units will return to the scanning mode awaiting further
traffic. Built-in safeguards also insure that ALE controllers will return
to the SCAN mode in the event of loss-of-contact.
As well as being capable of LQA and Optimum Working Frequency channel selection,
modern ALE controllers are also capable of sending short (87 ASCII characters
long) orderwire digital messages known as Automatic Message Display (AMD)
to ANY or ALL members on the network. ALE controllers can contact
individual stations by their call sign, ALL stations, or
ANY stations on the NETwork or GROUP. ALL call and ANY call make
use of wildcard characters in substitution for individual call sings such as @?@
(ALL) and @@? (ANY). NULL
Address Calls are used for system maintenance and are sent as @@@.
Waveform
ALE controllers conform to MIL-STD-188-141A link establishment functions and
perform encoding and decoding of data by the use of an 8-ARY binary FSK
modulator/demodulator.
Compatibility
Not all ALE controllers are compatible. Further developments have now
produced 2 generations of link controllers mainly referred to AUTOLINK I
and AUTOLINK II. The second generation controller is both
downwards and upwards compatible with the first generation controllers as long
as the compatibility features are enabled in the system software.
The basic difference between the first and second generation units is in the
type of addressing utilized. Call signs in the generation 1 controllers
are limited to numerical digits (i.e. 112358) and call signs in the generation 2
controllers can employ up to 15 alphanumerical identifiers (i.e. UUT or UNIT1
etc...).
Reliability
Research indicates that equipment employing ALE technology over a set of 10 to
20 HF frequencies dispersed across the spectrum can raise the probability of
communication (above 95%) to a distant station several thousand kilometres away
to nearly that of SATCOM systems.
Note: You will require aPlayer®
plug-in in order to listen to the sample files.
Sample Audio
ALE modem performing a SOUNDing transmission
(36k).
ALE modem performing and ANY CALL transmission
(42k).
ALE modem sending a AMD transmission to 1
outstation (39k).
Spectrum view of the ALE Waveform
Revised: June 08, 2017
(C) 1999-2023, Richard Lacroix. All rights reserved.