Radio frequencies in industrial environments

In 1838, Cooke and Wheatstone sent information for the first time through a telegraph system between London and West Drayton (21 km). Since then, sending signals has been evolving until today, when radio communications are used for, among other things, exchanging information with cars, sensor measurements that make possible to optimize processes, medical applications for patient readings, etc.

The world of radio frequency (RF) refers to signals transmitted through electromagnetic waves ranging from 3Hz to 300GHz.

Among all the radio frequency bands in the electromagnetic spectrum, this article will focus both on communications in a low frequency (LF) range from 30 to 300 kHz, and whose wavelength is between 1 and 10km of space, as in the high frequency (HF) that goes from 3 to 30 MHz and whose wavelength is between 10 and 100 metres of space.

- Existing radio frequency (RF) ranges -

High and low frequence communications in Industrial Control Systems

Within radio communications, we have to consider the following concepts:

• Radio waves spread spherically and equitably through the sender as light does.
• When talking about the attenuation of a wave, it refers to the reduction in the amplitude that it has in the medium when it is transmitted by the sender.
• The unit of measurement that allows to know the attenuation that these waves may have is the decibel (dB), used to dimension the attenuation of the signals.

The use of radio communications in industrial environments is marked by different factors that affect the propagation of waves and influence their attenuation, including:

• Distance: space that separates the sender from the receiver. Commonly, in industrial environments there are usually cases in which the sender and receiver are many kilometres away.
• Physical medium: this factor refers to the quantity of obstacles that will exist between the sender and the receiver. Since in the industry deployments can be made in places such as tunnels, underground passages, building walls, etc., it is important to take this into account when designing the communications infrastructure to be deployed.
• Meteorological and environmental phenomena: atmospheric conditions such as rain, snow, storms, etc., along with the possible dust or pollution that may be recorded in the atmosphere, are also factors to consider when using radio communications. Much of the infrastructure that industrial companies possess is usually located in outdoor environments so, in addition to having ruggedised devices, their communications must also withstand adverse conditions to preserve service availability.
• Antennae: key elements for communication between sender and receiver. The stability of radio communications will depend directly on the gain they have. Typically, in the industry antennae are used that are specially designed and built to operate in harsh and industrial environments with levels of IP protection.
• Fresnel zone: volume of space that exists between the sender and the receiver of a wave.

Some examples in the industrial world that use low and high frequency radio communications can be seen in:

• The collection of information on sensors deployed throughout a factory.
• Labels for reading information (health sector).
• Manufacturing tracking.
• Obtaining data for the IoT world and industry 4.0.
• Etc.

Cases of low and high frequency attacks in Industrial Control Systems

There are possible attacks against radio frequency communications that affect the availability, confidentiality and integrity of radio communications. Among the most common are:

• Signal inhibitions: the use of this technique has a strong impact on availability, the most important factor in the industry. The attacks that originate denials of service are not very complex to reproduce for the attackers and usually cause a great impact on the processes.
• Authentication evasion: these types of attacks can lead to command execution, process anomalies and even denials of service in the event of uploading a constant "stop" state. Some real examples are the authentication evasion on the Ewon web server or the authentication evasion in Hetronic products.
• Traffic reinjections: the use of this technique in certain environments can lead to an impact that evolves from the logical to the physical world. For example, some valves within the water treatment sector are regulated via radio communications, which allow them to be opened and closed. A capture by an attacker that reproduces the same signal at a correct distance from the valve would allow it to interact with it by changing the state at will.

In addition to these generic attacks, there are others more specific for RFID technology (Radio Frequency Identification), which is increasingly widespread in industrial environments, and which relies on electric or magnetic radio frequency fields to transmit information. Both the use of tags, and readers or management systems with related applications that have RFID technology, are used in the industrial world. Trucks that contain this technology so that, each time they pass through a specific area of the plant, a reader allows to know both the stock, the origin of the cargo, etc., thus improving the task of the operators, are a clear example of its use in industrial environments. RFID tags are also used for container protection, bag sealing, package management, etc.

Advantages of using radio frequency in industrial environments

These are some of the advantages that the use of radio communications in the industry provides:

• Versatility in terms of the terrain that radio communications can cover. For industrial companies that have a presence over a large land area and when, moreover, it is difficult to access, using this type of communications can be a good option.
• The cost savings is also a point to bear in mind, since a major investment in material is not necessary to give communication support to a large land area.
• Increase in the frequency and reliability of data collection.
• The radio frequency networks owned by industrial companies are private and, therefore, provide greater security in terms of privacy. It is also necessary to comply with a series of regulations when transmitting radio communications and the simple act of passive listening on certain frequencies is considered a crime.
• They allow the use of different protocols on the same communication layer, giving the user greater flexibility.
• Modems adapted to industrial environments. Industrial wireless modems usually have some type of UL certification, which allow radio operation in the presence of flammable or explosive gases, fluids or vapours. Having this certification is also beneficial because one type of device can be standardised and used for many applications, regardless of the environment.

Disadvantages of using radio frequency in industrial environments

These are some of the disadvantages that the use of radio communications in the industry provides:

• As with virtually all wireless communications, availability can be a big problem if the mitigating factors and possible situations in which malicious users can use different techniques to modify communication or to inhibit communication are not considered. These problems caused by attenuation or a possible attacker with specific devices to cut the signal, are one of the great disadvantages of the use of radio communications.
• In addition to these disadvantages, the use of devices that work at the same frequency and can be used by attackers with the aim of injecting commands, carrying out packet forwarding attacks, etc., is another of the weakness and disadvantages to take in account when protecting this type of communications and deploying them in a production environment.

Good practices and lessons learned

Some of the good practices that can be applied in securing radio communications in industrial environments are:

• Having a secure procedure in which phases such as pairing between devices are carried out with all the activated security measures that the devices have. In addition, and if possible, it is advisable to modify the identification code in the pairing to prevent malicious impersonations of devices.
• Use anti-tampering mechanisms in the devices to prevent unauthorised modifications and firmware uploads that cause abnormal behaviour. In this regard, it is advisable to always use the latest official firmware provided by the manufacturer, if possible.
• Use robust protocols that have been tried, tested and correctly implemented avoiding security through obscurity.
• Use of perimeter measures to prevent possible attackers from approaching the radius of action of the communications and can somehow inhibit or modify them.