The TETRA logo

TErrestrial Trunked RAdio (TETRA) (formerly known as Trans European Trunked RAdio) is a specialist Professional Mobile Radio and walkie talkie standard used by police departments, fire departments, ambulance services and the military. Image File history File links Tetralogo. ... Professional Mobile Radio (also known as Private Mobile Radio (PMR) in the UK and Land Mobile Radio (LMR) in North America) are field radio communications systems which use portable, mobile, base station, and dispatch console radios and are sometimes based on such standards as MPT1327, TETRA and APCO 25 which... Recreational, toy and amateur radio walkie talkies A walkie-talkie or two-way radio is a hand-held portable, bi-directional radio transceiver. ... The word standard has several meanings: Originally, standard referred to a conspicuous object used as a rallying point in battle. ... Wikipedia does not yet have an article with this exact name. ... An ambulance in San Jose Del Cabo, Mexico A Helicopter used as an Ambulance. ...

TETRA is an ETSI standard, first version published 1995. TETRA is endorsed by the European Radio Communications Committee (ERC). The European Telecommunications Standards Institute (ETSI) is a standardization organization of the telecommunications industry (equipment makers and network operators) in Europe, with worldwide projection. ...

Description

TETRA terminals can act as mobile phones (cell phones), with a direct connection to the PSTN. It is common also for them to operate in a group calling mode in which a single button push will connect the user to a dispatcher and all the other users in a group. Also possible is for the terminal to act as a one to one walkie talkie but without the normal range limitation since the call still uses the network. 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. Motorola T2288 mobile phone A mobile phone is a portable electronic device which behaves as a normal telephone whilst being able to move over a wide area (compare cordless phone which acts as a telephone only within a limited range). ... The public switched telephone network (PSTN) is the concatenation of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concatenation of the worlds public IP-based packet-switched networks. ... A dispatcher can mean different things (with related meanings). ... A dispatcher can mean different things (with related meanings). ...

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. Digital data transmission is also included in the standard though at a low data rate. Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. ... A carrier wave, or carrier is a waveform (usually sinusoidal) that is modulated (modified) to represent the information to be transmitted. ...

TETRA Mobile Stations (MS) can communicate Direct Mode or using Trunked infrastructure (Switching and Management Infrastructure or SwMI) made of TETRA Base Stations (TBS). As well as allowing direct communications in situations where network coverage has been lost, Direct Mode or DMO also includes the possibility of using one (or a chain) of TETRA terminals as relays for a signal. This functionality is called DMO gateway (from DMO to TMO) or DMO Repeater (DMO to DMO). In rescue situations this feature could allow direct communications underground or in areas of bad coverage.

In addition to voice and dispatch services, the TETRA system supports several types of data communication. Status messages and short data services (SDS) are provided over the system's main control channel, while Packet Data or Circuit switched data communication uses specifically assigned traffic channels.

All traffic is normally encrypted. TETRA provides both over the air encryption and end-to-end encryption. The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write) is the study of message secrecy. ...

Advantages

The main advantages of TETRA over other technologies (such as GSM) are: Not to be confused with Get Some Mates The Global System for Mobile Communications (GSM) is the most popular standard for mobile phones in the world. ...

• the much lower frequency used, which permits very high levels of geographic coverage with a smaller number of transmitters, cutting infrastructure cost.
• fast call set-up - a one to many group call is generally set-up within 0.5 seconds (typical less than 250 msec for a single node call) compared with the many seconds that are required for a GSM network.
• the fact that its infrastructure can be separated from that of the public mobile phone network, and made substantially more diverse and resilient by the fact that base stations can be some distance from the area served.
• unlike most cellular technologies, TETRA networks typically provide a number of fall-back modes such as the ability for a base station to process local calls in the absence of the rest of the network, and for 'direct mode' where mobiles can continue to share channels directly if the infrastructure fails or is out-of-reach.
• gateway mode - where a single mobile with connection to the network can act as a relay for other nearby mobiles that are out of contact with the infrastructure.
• TETRA also provides a point-to-point function that traditional analogue emergency services radio systems didn't provide. This enables users to have a one-to-one trunked 'radio' link between sets without the need for the direct involvement of a control room operator/dispatcher.
• unlike the cellular technologies, which connect one subscriber to one other subscriber (one-to-one) then TETRA is built to do one-to-one, one-to-many and many-to-many. These operational modes are directly relevant to the public safety and professional users.

... Many-to-many is a term that describes the third major Internet computing paradigm. ...

Disadvantages

Its main disadvantages are:

• it can only support a much lower teledensity in a given area, compared to GSM and similar technologies (which is not a problem in the applications for which it is used, but mostly limits it to these applications).
• handsets are more expensive (about 750 EUR in 2003, about 600 EUR in 2006), due to the reduced economies of scale, different business model when compared to mass-market mobile phones, need for security evaluation, and robustness.
• data transfer is slow at 7.2 kbit/s per timeslot (3.5 kbit/s net packet data throughput), although up to 4 timeslots can be combined into a single data channel to achieve higher rates, due to need to fit into 25kHz bandwidth channel plans.
• due to the pulsed nature of TDMA employed by the protocol, handsets can interfere with sensitive electronic devices such as heart pacemakers and defibrillators, as can other RF transmitting equipment when used in close proximity (e.g. < 1 metre distance.)

The heart and lungs, from an older edition of Grays Anatomy. ... The term pacemaker has multiple meanings: In sports, a pacemaker or pacer is a competitor who enters an athletics race with little or no intention of winning, but purely to set a fast pace for other competitors to follow. ... This article or section does not adequately cite its references or sources. ...

Radio Frequencies

In Europe, TETRA uses frequencies:

In Britain the public sector TETRA system operates under the name 'Airwave'. In Belgium, the 'A.S.T.R.I.D' system uses TETRA. In the Netherlands, the TETRA system is called 'C2000'. In Sweden the RAKEL system uses TETRA. In Finland the VIRVE (short for VIRanomaisVErkko, loosely translated: "official network") network uses TETRA. VIRVE and C2000 are currently the only TETRA networks that covers an entire country. VIRVE (short for VIRanomaisVErkko, loosely translated: authority network) is the Finnish authorities telecommunications network. ...

Radio aspects

TETRA uses a digital modulation scheme known as π/4 DQPSK which is a form of phase shift keying. TETRA uses TDMA (see above). The symbol rate is 18,000 symbols per second, and each symbol maps to 2 bits. A single slot consists of 255 symbols, a single frame consist of 4 slots, and a multiframe (whose duration is approximately 1 second) consists of 18 frames. As a form of phase shift keying the downlink power is constant. The downlink (i.e. the output of the basestation) is a continuous transmission consisting of either specific communications with mobiles, synchronisation or other general broadcasts. Although the system uses 18 frames per second only 17 of these are used for traffic channel, with the 18th frame reserved for signalling or synchronisation. TETRA does not employ amplitude modulation. However, TETRA has 17.65 frames per second (18000 symbols/sec / 255 symbols/slot / 4 slots/frame), which is the cause of the PERCEIVED "amplitude modulation" at 17Hz. Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). ...

See also

• P25, a standard used in North America for similar purposes. P25 equipment is considerably more expensive than TETRA.

P25 (Project 25) (also APCO-25) is a standard for digital radio communications for use by federal, state/province and local public safety agencies in North America to enable them to communicate with other agencies and mutual aid response teams in emergencies. ...

External links

• TETRA Memorandum of Understanding - TETRA Facts
• The Trower Report and study about TETRA commision for by The Police Federation for England and Wales
• report on health effects of TETRA
• Powerwatch Report on health effects of TETRA
• COST281 - Potential Health Implications from Mobile Communication Systems