Conventional radio communication requires the reservation of radio frequencies for each user group. The licensed radio frequencies are only used by one user group and each user group must license their own frequency. To deal with the increasing demand and the finite amount of available radio spectrum, trunked radio system use several frequencies which are allocated to individual users on demand. This allows for more efficient utilisation of limited frequencies because each user group does not require a dedicated channel.
TETRA (TErrestrial Trunked Radio), is a European standard for modern digital trunked radio defined by the European Telecommunications Standards Institute (ETSI). For civil systems in Europe the frequency bands 385-390 MHz, 395-399.9 MHz, 410-430 MHz, 450-470 MHz, 870-876 MHz, and 915-921 MHz, have been allocated for TETRA by ERC Decision (96)04. Data transfer with TETRA is at 7.2 kbps. Due to the low frequency used, high levels of geographic coverage can be achieved with a smaller number of transmitters. TETRA was developed to meet the needs of organisations and companies who need fast one-to-one and one-to-many voice and data communication in their daily work. Users of trunked radio communication are typically public safety and security organisations such as police, fire and rescue forces, but also other professional user groups such as commercial vehicle fleets.