TETRA

Terrestrial Trunked Radio (TETRA) is an open digital radio standard for professional mobile radio. TETRA can be used by a company for the communication with the mobile work forces (Private Mobile Radio; PMR) as well as by an operator to offer the same services on a commercial basis (Public Access Mobile Radio; PAMR). A third group of users are the Emergency Services (such as police and fire departments). The TETRA radio standard is defined by ETSI.

TETRA is based on radio channels with a bandwidth of 25 kHz. Each channel is subdivided in 4 traffic channels using TDMA. The traffic channels can be used for both voice and data. The maximum bit rate is 28.8 kbps if all 4 traffic channels are joint together for one data connection.

Mainly the frequency band 410-430 MHz is used for civil systems in Europe. TETRA is used in the 380-385/390-395 MHz band for emergency services. In some countries civil systems use the whole or parts of the 380-400 MHz band.

ETSI has developed an enhanced family of TETRA standards generally referred to as TETRA Release 2. TETRA Release 2 provides solutions to increase the data rate. See TAPS and TEDS.

TETRA has two modes of operation. These modes are called trunked mode operation (TMO) and direct mode operation (DMO). The latter is available for users in direct radio range of each other, when they are out of reach of the network or when the network is down.