TETRA
TErrestial Trunked RA (TETRA) is a wireless cell phone standard used by police, ambulance and military. Its main advantage over technologies such as GSM is the much lower frequency used, which permits very high levels of geographic coverage with a smaller number of transmitters, and the fact that its infrastructure can be separated from that of the public cellphone network.
TETRA uses Time Division Multiple Access (TDMA) with four user channels on one radio carrier and 25 kHz spacing between carriers. Both point-to-point and point-to-multipoint transfer can be used. Mobile Stations (MS) can communicate Direct Mode or using infrastructure made of TETRA Base Stations (TBS).
All traffic is normally encrypted. TETRA provides both transfer encryption and end-to-end encryption.
In Europe, TETRA uses frequencies:
- Emergency systems 380-383 MHz, 390-393 MHz (also 383-395 MHz and 393-395 MHz)
- Civil systems 410-430 MHz, 870-876 MHz / 915-921 MHz, 450-470 MHz, 385-390 MHz / 395-399,9 MHz,
TETRA is an ETSI standard, first version published 1995.