Automatic Link Establishment.doc

Automatic Link Establishment, commonly known as ALE, is the worldwide de facto standard for digitally initiating and sustaining HF radio communications.[1] ALE is a feature in an HF communications radio transceiver system, that enables the radio station to make contact, or initiate a circuit, between itself and another HF radio station or network of stations. The purpose is to provide a reliable rapid method of calling and connecting during constantly changing HF ionospheric propagation, reception interference, and shared spectrum use of busy or congested HF channels.Contents[hide]  1 Mechanism 2 Operator skill 3 Common applications 4 Techniques 5 History and precedentso 5.1 Reliability 6 Standards and protocolso 6.1 2G technical characteristicso 6.2 3G technical characteristics 7 Basis for HF interoperable communicationso 7.1 Tactical communication and resource managemento 7.2 Emergency / disaster relief or extraordinary situation response communicationso 7.3 International HF telecommunications for disaster relief 8 Use in amateur radioo 8.1 Amateur radio interoperability adaptationso 8.2 Disaster relief HF networko 8.3 International coordination 8.3.1 International channels 8.3.2 Standard configurations 8.3.3 International nets 9 See also 10 References[edit]MechanismA standalone ALE radio combines an HF SSB radio transceiver with an internal microprocessor and MFSK modem. It is programmed with a unique ALE Address, similar to a phone number (or on newer generations, a username). When not actively in contact with another station, the HF SSB transceiver constantly scans through a list of HF frequencies called channels, listening for any ALE signals transmitted by other radio stations. It decodes calls and soundings sent by other stations and uses the Bit error rate to store a quality score for that frequency and sender-address.To reach a specific station, the caller enters the ALE Address. On many ALE radios this is similar to dialing a phone number. The ALE controller selects the best available idle channel for that destination address. After confirming the channel is indeed idle, it then sends a brief selective calling signal identifying the intended recipient. When the distant scanning station detects ALE activity, it stops scanning and stays on that channel until it can confirm whether or not the call is for it. The two stations' ALE controllers automaticallyhandshake to confirm that a link of sufficient quality has been established, then notify the operators that the link is up. If the callee fails to respond or the handshaking fails, the originating ALE node usually selects another frequency either at random or by making a guess of varying sophistication.Upon successful linking, the receiving station generally emits an audible alarm and shows a visual alert to the operator, thus indicating the incoming call. It also indicates the callsign or other identifying information of the linked station, similar to Caller ID. The operator then un-mutes the radio and answers the call then can talk in a regular conversation or negotiates a data link using voice or the ALE built-in short text message format. Alternatively, digital data can be exchanged via a built-in or external modem (such as a STANAG 5066 orMIL-STD-188-110B serial tone modem) depending on needs and availability. The ALE built-in text messaging facility can be used to transfer short text messages as an "orderwire" to allow operators to coordinate external equipment such as phone patches or non-embedded digital links, or for short tactical messages.[2][3][edit]Operator skillDue to the vagaries of ionospheric communications, HF radio as used by large governmental organizations in the mid-20th century was traditionally the domain of highly skilled and trained radio operators. One of the new characteristics that embedded microprocessors and computers brought to HF radio via ALE, was alleviation of the need for the radio operator to constantly monitor and change the radio frequency manually to compensate for ionospheric conditions or interference. For the average user of ALE, after learning how to work the basic functions of the HF transceiver, it became similar to operating a cellular mobile phone. For more advanced functions and programming of ALE controllers and networks, it became similar to the use of menu-enabledconsumer equipment or the optional features typically encountered in software. In a professional or military organization, this does not eliminate the need for skilled and trained communicators to coordinate the per-unit authorized frequency lists and node addresses - it merely allows the deployment of relatively unskilled technicians as "field communicators" and end-users of the existing coordinated architecture.[edit]Common applicationsAn ALE radio system enables connection for voice conversation, alerting, data exchange, texting, instant messaging, email, file transfer, image, geo-position tracking, or telemetry.。