For emergency services in Europe the frequency bands 380-383 MHz and 390-393 MHz have been allocated. These bands can be expanded to cover all or part of the spectrum from 383-395 MHz and 393-395 MHz should this be needed. For civil systems in Europe the frequency bands 410-430 MHz, 870-876 MHz / 915-921 MHz, 450-470 MHz, 385-390 MHz / 395-399,9 MHz, have been allocated.
TETRA radio trunking facility provides a pooling of all radio channels that are then allocated on demand to individual users, in both voice and data modes. By the provision of national and multi-national networks, national and international roaming can be supported, the user being in constant communication. TETRA supports point-to-point, and point-to-multipoint communications both by the use of the TETRA infrastructure and by the use of Direct Mode without infrastructure.
In addition to this it is possible for TETRA radio to operate in a secure format. The digital data can be encrypted before transmissions, making the system inherently secure. This may be required for some covert operations or for the police services.
The TETRA radio system uses Time Division Multiple Access (TDMA) technology with 4 user channels on one radio carrier and 25 kHz spacing between carriers. This makes it inherently more efficient than its predecessors in the way that it uses the frequency spectrum. Data can be transmitted at 7.2 kbits per second for a single channel. This can be increased four fold to 28.8 kbits per second when multi-slot operation is employed.
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