HF Radio Communication Across Desolate Landscape

Decoding HF Radio: How Automatic Link Establishment (ALE) Keeps You Connected

Mira Elwood in Tech & Innovation June 2025 • 4 min read.

"Discover how ALE technology ensures reliable communication in high-frequency radio networks, even when conditions are tough."

Imagine a world where staying connected isn't as simple as pulling out your smartphone. In areas with minimal infrastructure or during critical situations, high-frequency (HF) radio communications step in as a reliable solution. But HF radio isn't always easy; its propagation channel can be highly variable and error-prone, making connections unreliable. That's where Automatic Link Establishment (ALE) comes in, automating the process of finding and maintaining the best possible connection.

Automatic Link Establishment (ALE) has revolutionized HF communications. ALE allows radios to automatically scan frequencies and establish links, ensuring reliable communication without the need for extensive technical expertise. The technology has been standardized into two main generations: 2G and 3G ALE which are now being looked at again due to new wideband HF waveforms. In this article, we will focus on the 2G ALE procedure, since it is still widely used because it can operate asynchronously.

This article explores the design and capabilities of Automatic Link Establishment (ALE) in high-frequency (HF) networks. Understanding these models can help in planning and optimizing HF network deployments, ensuring reliable communication in challenging environments.

Understanding 2G ALE: The Workhorse of HF Communication

HF Radio Communication Across Desolate Landscape

The 2G ALE system, defined by the MIL-STD-188-141A standard, is popular because it is asynchronous. This means that radios can connect with each other without needing to be precisely synchronized in time. The system uses an 8-ary FSK (Frequency Shift Keying) modulation at the physical layer, transmitting data at 375 bits per second. Each radio scans a set of predefined frequencies,

When a radio wants to make a call, it goes through a series of steps to find a good channel:

Listening: The radio listens to available channels to determine if anyone else is transmitting.
Calling: If a free channel is found, the radio sends out a call request that includes the address of the receiving radio.
Handshake: If the receiving radio hears the call and recognizes its address, it sends back a confirmation. The two radios then enter a linked state for communication.
Linked: Once the communication is done, both radios go back to listening.

Scanning: Radios continuously scan available frequencies, awaiting call requests.
Calling: Initiating a call involves testing channels and sending a request to the receiver.
Linked: Successful handshakes lead to the linked state, maintaining connection through communication.

The 2G ALE system includes a special frame structure that helps radios synchronize, even if they start receiving a message in the middle. The calling radio repeats key information, so the receiving radio has multiple chances to lock onto the signal. To avoid constant collisions, the duration of each call request varies, reducing the need for complex backoff procedures.

The Future of Staying Connected

Automatic Link Establishment (ALE) continues to be a vital technology for maintaining communication in challenging environments. Ongoing research and development aim to enhance ALE systems, making them more robust and efficient. As technology advances, ALE will adapt to meet the evolving needs of wireless communication, ensuring that reliable connections remain within reach.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.15803/ijnc.7.2_419, Alternate LINK

Title: On The Design Of Automatic Link Establishment In High Frequency Networks

Subject: General Medicine

Journal: International Journal of Networking and Computing

Publisher: IJNC Editorial Committee

Authors: Bruno Baynat, Hicham Khalife, Vania Conan, Catherine Lamy-Bergot, Romain Pouvez

Published: 2017-01-01

Everything You Need To Know

What is Automatic Link Establishment (ALE) and why is it important for high-frequency radio communication?

Automatic Link Establishment (ALE) is a technology used in high-frequency (HF) radio communications to automatically find and maintain the best possible connection. It allows radios to scan frequencies and establish links, ensuring reliable communication without needing extensive technical expertise. This is particularly useful in environments where traditional communication methods are unreliable or unavailable.

What are the key differences between 2G ALE and 3G ALE, and why does the document focus mainly on 2G ALE?

The main difference between 2G ALE and 3G ALE lies in their technical specifications and capabilities. 2G ALE, based on the MIL-STD-188-141A standard, is asynchronous and uses 8-ary FSK modulation. The article primarily discusses 2G ALE due to its widespread use and asynchronous nature, which allows radios to connect without precise time synchronization. The newer 3G ALE and wideband HF waveforms, while more advanced, are not detailed within this document.

Can you describe the step-by-step process of how a radio makes a call using 2G ALE?

In 2G ALE, the process of making a call involves several steps. First, a radio listens to available channels. If a free channel is found, the radio sends out a call request that includes the address of the receiving radio. If the receiving radio hears the call and recognizes its address, it sends back a confirmation. The two radios then enter a linked state for communication. Once communication is complete, both radios return to listening.

What does it mean that 2G ALE is 'asynchronous,' and how does this characteristic contribute to its functionality?

The asynchronous nature of 2G ALE, as defined by the MIL-STD-188-141A standard, means that radios do not need to be precisely synchronized in time to establish a connection. This is beneficial because it simplifies the communication process and makes it more robust in challenging environments. The 2G ALE system uses an 8-ary FSK (Frequency Shift Keying) modulation at the physical layer, transmitting data at 375 bits per second.

How does Automatic Link Establishment (ALE) help overcome the challenges associated with using high-frequency (HF) radio?

Automatic Link Establishment (ALE) addresses the variability and unreliability of high-frequency (HF) radio communication by automating the process of finding and maintaining the best possible connection. It allows radios to automatically scan frequencies and establish links, ensuring reliable communication without the need for extensive technical expertise. Ongoing research and development aim to enhance ALE systems, making them more robust and efficient.