Tetra

Special radios help people talk.

These tools help the police and fire teams. They also help train workers.

Sometimes, there is no signal. The radios can talk directly to each other then. This helps people talk underground. One radio can even pass a message to another. This keeps everyone safe during an emergency. It is a smart way to stay connected.

TETRA is a special way for radios to work.

It was made for people with important jobs. This includes police, fire teams, and doctors. It also helps people who work on trains or in the military.

TETRA uses a system called TDMA. This stands for time-division multiple access. It means many people can share one radio signal. The system splits the signal into four parts. This lets four people talk at once on one carrier.

Sometimes, the main network signal is weak. TETRA has a way to fix this. It uses direct-mode operation, or DMO.

In DMO, radios talk directly to each other. This is like using a walkie-talkie. One radio can even act as a relay. A relay passes a message to another radio. This helps people talk underground or in bad areas.

Security is also very important. TETRA uses encryption to keep talks private. This stops people from listening in. The system also has emergency buttons. These buttons send a signal right away. This signal can even stop other work to get help.

TETRA is a special way for radios to work.

It stands for Terrestrial Trunked Radio. This system is built for people with very important jobs. It helps police, fire departments, and ambulance teams stay connected. It is also used by the military and people working on trains. This technology makes sure that emergency workers can always talk to each other. It is a professional tool used for public safety networks across many lands.

This system works using a method called time-division multiple access, or TDMA. This means many people can share one radio signal at the same time. The system splits a single radio carrier into four separate user channels. Each channel uses 25 kHz of spacing to keep the signals clear. Users can send voice or digital data through these channels. They can also send short messages called short data services. This allows the radios to do more than just talk.

The European Telecommunications Standards Institute, or ETSI, created this standard. They published the first version of TETRA in 1995. It was designed to be a European version of trunked radio. Other systems like Project 25 are similar to it. The European Radiocommunications Committee also mentions this standard. It has become a key way for many countries to run their emergency networks. It was built to be a reliable way for groups to communicate.

TETRA has many specific rules and numbers to keep it working. For example, the system uses a symbol rate of 18,000 symbols every second. This helps create a gross data rate of 36,000 bit/s. In some cases, the latest versions can reach much higher speeds. They can support up to 691.2 kbit/s in an expanded channel. Different countries use different frequency pairs for their systems. In France, civilian systems use 410 to 430 MHz. In the UK, the Airwave system uses specific bands like 390 MHz.

You can think of TETRA like a very smart walkie-talkie network. Most walkie-talkies only let you talk to one person at a time. But TETRA can connect one person to a whole group at once. It can also act like a mobile phone for direct calls. If the main network signal is weak, radios use direct-mode operation, or DMO.

In DMO, one radio can act as a relay for others. This helps people talk even when they are underground. This makes the system much stronger than a normal radio.

Terrestrial Trunked Radio, commonly known as TETRA, is a professional mobile radio standard.

It was developed by the European Telecommunications Standards Institute, or ETSI. This standard provides a specification for two-way transceivers and trunked radio systems. It is specifically designed for mission-critical communications. This means it is built for government agencies and emergency services. Police forces, fire departments, and ambulance services rely on these networks for public safety. It is also used by the military and rail transport staff.

The technical mechanism of TETRA relies on time-division multiple access, known as TDMA. This method allows multiple users to share the same radio frequency. Specifically, TETRA uses TDMA to create four user channels on a single radio carrier. These carriers are separated by 25 kHz of spacing. The system can handle both point-to-point and point-to-multipoint transfers. This means it can connect one person to one person, or one person to a large group.

TETRA users operate in two distinct modes: Trunked-mode operation (TMO) and Direct-mode operation (DMO). In TMO, mobile stations communicate through a switching and management infrastructure (SwMI). This infrastructure is made of TETRA base stations (TBS). However, if network coverage is unavailable, users can switch to DMO. In DMO, radios can communicate directly with each other like walkie-talkies. DMO also includes a special relay function. A terminal can act as a DMO gateway to connect to the TMO network. Alternatively, it can act as a DMO repeater to pass signals between two DMO radios. This is vital for communicating in underground areas or locations with poor coverage.

History shows that ETSI published the first version of the TETRA standard in 1995. It was created as the European version of trunked radio. It is often compared to the Project 25 standard used elsewhere. The European Radiocommunications Committee (ERC) also recognizes the standard. Over time, the technology has evolved to include more complex data capabilities. While early versions focused on voice, the system now supports various data types. These include status messages and short data services (SDS) sent over the main control channel. It also supports packet-switched or circuit-switched data on assigned channels.

The significance of TETRA lies in its reliability and coverage. Because it uses lower frequencies than technologies like GSM, it achieves a much longer range. This allows for high geographic coverage using fewer transmitters. This efficiency helps to reduce infrastructure costs. Furthermore, TETRA provides seamless transitions during voice calls. A user can move between different network sites without their communication being interrupted. This is a unique feature for mission-critical networks. The system is designed to be fail-safe and multiple-redundant.

Security is a major component of the TETRA standard. The system provides authentication to ensure only authorized terminals access the infrastructure. To prevent eavesdropping, it uses air interface encryption. It also offers end-to-end encryption for higher security. There are seven standardized ciphers known as the TETRA Encryption Algorithm (TEA). These are divided into TEA Set A (TEA1 to TEA4) and TEA Set B (TEA5 to TEA7). TEA2 is a specific cipher restricted to European public safety organizations. However, the standard has faced challenges. In the past, the TEA1 cipher was intentionally weakened to meet export control criteria. This allowed the cipher to be broken quickly on consumer hardware.

Data transfer speeds in TETRA are modest compared to modern cellular networks. In point-to-point connections, the rate is up to 7.2 kbit/s per timeslot. For IP encapsulation, the rate is 3.5 kbit/s per timeslot. These rates can vary depending on the number of timeslots used. However, the latest versions of the standard offer much higher speeds. They can support 115.2 kbit/s in a 25 kHz channel. In an expanded 150 kHz channel, speeds can reach up to 691.2 kbit/s. To handle larger files, some vendors use hybrid solutions. They use TETRA for critical signaling and 3G, LTE, or 5G for large data transfers like video.