TErrestrial Trunked RAdio (TETRA) is an open digital trunked radio standard defined by the European Telecommunications Standardization institute (ETSI) to meet the needs of the most demanding Private Mobile Radio users such as Police, Emergency Services, Energy Distributors, Manufacturing, Petro-Chemical, fire department etc.
TETRA is a professional mobile radio and two-way transceiver (colloquially known as a walkie talkie) specification.
ETSI has developed this standard in co-operation with leading manufacturers, system operators and users. The main purpose of this standard was to define a series of open interfaces, services and facilities, in sufficient detail to enable independent manufacturers to develop infrastructure and terminal products that would fully interoperate with each other.
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.
This means excellent efficiency of frequency spectrum.
In addition to voice and dispatch services, the TETRA system supports several types of data communication. Sending text messages, Status messages and short data services (SDS) are provided over the system's main control channel.
For protection against eavesdropping; air interface encryption and end-to-end encryption is available.
The common mode of operation is in a group calling mode in which a single button push will connect the user to the users in a selected call group and/or a dispatcher.
TETRA terminals can act as mobile phones(cell phones), with a full-duplex direct connection to other TETRA Users or the PSTN.
Emergency buttons, provided on the terminals, enable the users to transmit emergency signals, to the dispatcher, overriding any other activity taking place at the same time.
The frequency range for public safety systems are from 380-400 MHz and for the commercial applications are from 410-430 MHz & and from 870-876 MHz.
..Facilities of TETRA..
•Pre-emptive priority call (Emergency Call)
•Direct Mode Operation (DMO)
•Dynamic Group Number Assignment (DGNA)