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By Alvin Lim
7 March 2023
Alvin Lim, part of the ETSI Technical Committee TCCE (TETRA and Critical Communications Evolution), explains the increasing relevance of TETRA in the rail industry.
TETRA has been successfully installed on Taiwan’s high-speed rail network.
For more than two decades the global TETRA communications standard by ETSI has experienced widespread adoption into the transportation sector including rail networks. London Underground was one of the early adopters, along with metros in Paris, Madrid, and Copenhagen. Outside of Europe, TETRA has been implemented successfully in light-rail, heavy metro, high-speed rail, mainline railways, freight, and mining rail networks. While commercial 2G technologies have largely been superseded, private mission-critical land mobile radio (LMR) networks like TETRA are still being deployed, upgraded, and expanded, even at state-wide and nationwide levels. Through ongoing investment, including enhanced security and resilience, through to the introduction of new air interface encryption algorithms with the ETSI standard, TETRA has become even more relevant and necessary for the rail sector. This is helping to ensure that TETRA continues to meet needs for the rail sector today and well into the foreseeable future.
TETRA (Terrestrial Trunked Radio) technology is used throughout the world every day for secure, reliable, and robust critical communication. The TETRA standard was first released by the European Telecommunications Standards Institute (ETSI) in the mid-1990s. It was the first European standard developed for a digital trunked radio scheme to address the needs of both mission critical and business critical users. The TETRA standard includes a suite of standards covering different technology aspects, for example, air interfaces, network interfaces and services and facilities.
Today, key markets for TETRA include the public safety sector, air, rail, road and water transport, utilities, mining, manufacturing and other mission critical verticals.
The mission critical features inherent in the TETRA standard are well known in the public safety sector. These include very fast call setup times, group communications, emergency and priority calls, dispatch functionality, dynamic group number assignment, direct mode of operation and more. All of these features are well suited for railway operations because rail is another sector where safety, security and operational efficiency are all essential needs.
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Railway and customer specific features can be implemented through open interfaces including dispatcher consoles, mobile radios, and other points of interface. These interfaces allow different suppliers to build their own train dispatching and control applications on top of the underlying TETRA network and terminal infrastructure.
TETRA equipment can also be integrated with on-board train control and signalling systems to provide location monitoring and control information including GPS coordinates and live status updates.
One commonly used voice application in the rail sector are public announcements made to passengers on-board trains. This requires the TETRA system to interface with the train’s public address system and it can be done on a single train or multiple trains simultaneously. Another voice application that leverages TETRA are passenger emergency calls. This requires the TETRA system to establish a full-duplex audio path to the designated dispatch controller in the control centre. TETRA’s high performance group calls, with very fast call set-up times (usually quoted as 300 msec for efficient communications) as well as its efficient use of radio channels, means that emergency calls on train systems can always be made quickly and reliably.
Another area where TETRA works particularly well for rail is train telemetry. TETRA allows for simultaneous transmissions of voice and data through the same radio. As such, telemetry can be reported to control and maintenance systems without interrupting other voice calls being made at the same time by the train driver or via the control room. TETRA can also be used to provide some data services for passenger information systems and to update on-train information systems.
TETRA equipment can also be integrated with on-board train control and signalling systems to provide location monitoring and control information including GPS coordinates and live status updates. These voice and data applications need to interface with external systems which are normally located at a central point such as the main control centre’s equipment room used by a railway.
As some of these features provide for safety, it is important that TETRA systems meet the desired software safety integrity levels (SIL) based on the EN 50128 standard. This is especially important for driverless trains. TETRA has also been implemented in metro rail systems with a GOA (grade of automation) Level 4 for unattended train operation.
TETRA mobile radios are normally designed to meet both military and vehicular standards for ruggedness. Therefore, they typically meet railway specific requirements too (e.g., EN50155).
In addition, the TETRA base stations deployed in stations are normally certified to meet the strict EMC standards (e.g., EN50121) required for rail.
TETRA has been deployed for train control for Kazakhstan Railways (KTZ).
It is now a reality that critical infrastructures are among the potential targets for malicious cyber actors. That’s why cyber-vigilance is now a key design consideration and feature on many new rail implementations. Consequently, we are seeing tighter cyber-security requirements for TETRA systems, including Air Interface Encryption (AIE) for both trunked mode and fallback (local trunking and direct) mode of operations.
Authentication and key management are also an integral part of the architecture and should be centrally controlled for better security and efficient operations.
ETSI recently announced new encryption algorithms to counter such threats in the post-quantum cryptography world. Besides encryption, TETRA systems must also be ‘hardened’, have up-to-date system patches and the latest anti-virus software with proper firewalls and intrusion protection systems in place, especially at system interface points.
Cyber-security is important for mobile networks too as they carry safety-related critical information such as train control data, alerts, instructions, and other information. Several rail operators have already implemented Air Interface Encryption, whereas previously this was only implemented by public safety agencies. The greater adoption of encryption will only continue to rise as our awareness and understanding of cyber-risks grows.
Mission critical users, including rail operators, need their radio systems to have high levels of availability and reliability. TETRA manufacturers have predominantly designed their systems with redundancies at both the core switch and base station levels. This allows systems to operate in full wide area trunking, regional fallback, and individual base station fallback modes, as well as in direct point-to-point mode between devices that do not require supporting infrastructure. That means that communications can continue during different levels of a system failure, helping to enhance safety for the communications systems overall.
TETRA has been successfully deployed on mainline railways such as the Taiwan Railway Administration, Malaysian Railways and on high-speed rail lines in Taiwan2 and Korea (which operate at speeds of up to 300km/h).
TETRA has been deployed in many metro and light-rail systems in Europe, Asia Pacific, Australia, the Middle East and Africa. More than 100 rail projects utilise TETRA in the Asia Pacific alone, and that number continues to grow.
Outside Europe, where there is no mandate to use the ETSI GSM-R standard and spectrum availability is constrained, TETRA has proven to be a viable solution for many main line and high-speed railway communications. TETRA has been successfully deployed on mainline railways such as the Taiwan Railway Administration, Malaysian Railways and on high-speed rail lines in Taiwan and Korea (which operate at speeds of up to 300km/h).
The introduction of ETCS (European Train Control System) over GPRS (General Packet Radio Service) has opened the possibility of ETCS being deployed over TETRA’s packet data service (PDS) and other wireless packet data networks. This has already been tested by vendors of ETCS and TETRA.
TETRA had also been deployed for train control for Kazakhstan Railways (KTZ), Ferrocarriles del Norte de Colombia (FENOCO), and on the Roy Hill pit-to-port rail network in Australia.
Great strides have been made in the 3GPP MCX (Mission Critical Services) standards, and early MCX systems have since been deployed in public safety environments. ETSI’s FRMCS (Future Railway Mobile Communication System) specifications have also progressed with the first generation of this technology expected to be a 5G system based on 3GPP R17.
Most mission critical organisations have adopted a hybrid network approach, operating their existing TETRA radio systems and continuing to upgrade them in parallel to implementing interoperable communications with MCX systems via gateways. This is the most likely scenario for MCX deployments for operators with existing TETRA systems, as well as those planning to deploy TETRA in the future. The most viable option for operators is to continue to rely on their TETRA systems for mission critical communications while leveraging 4G/5G to meet their broadband data needs.
Hence, both technologies will most likely be used side-by-side for the next 10 years or even longer. However, there have been several adopters of early versions of the MCX standard which continue to evolve.
Key markets for TETRA include air traffic control.
In the meantime, some operators have taken a more cautious and pragmatic step to continue using TETRA for their mission critical needs while using 4G/5G for other data-based applications.
The reality for most rail operators is that they will not have their own private 4G/5G spectrum, nor will they be able to justify the cost of private 4G/5G networks. The only exception to this is where the spectrum is reserved specifically for rail and can be transferred to 4G technology (as is planned in Europe). Many operators will have to leverage public cellular network infrastructure which requires careful consideration, planning and investment to ensure that operators have adequate levels of resilience and security in their communication systems.
As the 3GPP standard continues to evolve, eventually rail operators’ mobile communication needs will be met by broadband cellular networks. Then, the transition to 4G/5G networks will be dependent on ensuring cellular networks can match the levels of resilience, control, and spectrum availability that TETRA networks provide today, as well as having appropriate commercial contracts in place with the network providers.
Alvin Lim is Business Development Lead for the systems business of Motorola Solutions’ Asia Pacific transportation market. He has more than 25 years’ experience in the critical communications industry including pre-sales and project management for large infrastructure projects including many control systems and communication systems for MRTs, railways, highways, airports and seaports. His professional interests include mobile and broadband communications, and cyber-security. Alvin holds a Bachelor’s in Electrical & Electronics Engineering and a Master’s in Business Administration from the National University of Singapore.
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