In this article we will review the capacity of current communication systems based on the TETRA standard to provide coverage in confined spaces such as tunnels where this service becomes even more essential.
What is the TETRA standard?
Today, a large number of devices use radio signals to communicate with each other: television, mobile phones, Wi-Fi, satellite, and more. The problem with such a diverse range of applications is the need to standardize transmissions so that equipment from different manufacturers can communicate without causing interference.
This led to the creation of the TETRA standard, defined by the European Telecommunications Standards Institute (ETSI) and established by the European Union to unify various digital radio interface alternatives for communication between government agencies, emergency services, public safety networks, railway personnel, transport services, and the military.
The bands used for this service are 380-400 MHz (security forces) and 410-430 MHz (commercial use).
TETRA Coverage in Tunnels:
Due to the frequencies used and the high-power transmitters employed in these systems, outdoor coverage is usually not a problem when base stations are strategically placed.
However, coverage in confined spaces like tunnels is more challenging due to the specific characteristics of these environments. Therefore, the ideal passive element for providing coverage in these locations is the radiating cable.
The radiating cable has the same structure as a traditional coaxial cable used in telecommunications, with an inner and outer conductor that allows the various electromagnetic waves to be projected along its length, but with one key difference. By applying openings to the outer conductor of the cable, some of the energy from inside the cable is transferred to the surrounding outer part, providing coverage along its entire length. Thus, because the cable adapts to the shape of the tunnel, it prevents the formation of black spots after bends or turns, which would be problematic for communication between security teams in the event of an emergency in these areas.
In addition to the advantage described above over other radiating systems such as antennas, EUPEN (distributed in Spain by Telecom Business Solutions) manufactures a radiating cable optimized for different operating bands, including one specifically for TETRA. This reduces coupling and attenuation losses at these frequencies. It achieves this by modifying the distance between periodic apertures, which is always comparable to the operating wavelength (λc).
But what good would it do for the cable to function perfectly in an emergency if it falls to the ground due to a fire or the suction created in the tunnel? To prevent this, FIMO provides special fixings for the radiating cable that have been tested to withstand loads similar to those generated by a train traveling through a tunnel at 300 km/h. Furthermore, with proper installation, placing a plastic clamp every meter and inserting a metal one every 10 meters, the cable will not fall in case of fire.
Finally, and continuing with the issue of the variety of tunnel shapes, Telecom Business Solutions also distributes the most versatile, modular, and flexible repeaters on the market, manufactured by JMA/TEKO TELECOM. These repeaters can be adapted to any system configuration to provide TETRA service to the tunnel, whether with a direct connection to the base station, receiving the external signal via a donor antenna, including remote units with fiber optics, modules of varying power, multi-operator capability, etc.
In short, Telecom Business Solutions provides all the necessary equipment to provide TETRA coverage to various locations such as tunnels where safety is and must be a priority.
