TETRA (Terrestrial Trunked Radio) is a professional mobile radio and two-way transceiver specification. TETRA networks were designed to be used by government agencies, emergency services (police forces, fire departments, ambulance), public safety networks, rail transport staff for train radios, transport services and the armed forces. They use it to communicate using their radios as both mobile phones and walkie-talkies, depending on the type of the network coverage available.
TETRA networks support voice and dispatch services, as well as, several types of data communication. These include status messages, short data services (SDS) and packet-switched data or circuit-switched data communication via specifically assigned channels. To provide security against eavesdropping, there is air interface encryption and end-to-end encryption.
Three advantages of TETRA networks over other technologies (such as GSM) are:
- The geographic coverage is high as the lower frequency used gives a longer range. This means that a smaller number of transmitters is needed, which cuts infrastructure costs.
- Mobile communications, such as voice calls, are not interrupted when moving from one network site to another network site.
- If there is no mobile network reception, the radio devices can use ‘direct mode’ to share channels directly, acting as walkie-talkies.
These benefits mean that TETRA networks can therefore also provide additional radio coverage for railway organisations in the same way. For example, The lower frequency used by TETRA gives a longer range, which is particularly useful for locations where there is potentially no GSM-R or other telecoms coverage, such as inside tunnels.