TETRA: Terrestrial Trunked Radio System

- an overview, summary, or tutorial giving the basics of the way the TETRA mobile radio communications system works as a terrestrial trunked radio system in its application as a PMR, Private Mobile Radio system.

TETRA is a modern standard for digital Private Mobile Radio (PMR) and Public Access Mobile Radio (PAMR). It offers many advantages including flexibility, security, ease of use and offers fast call set-up times. This makes it an ideal choice for many business radio communications requirements.

The name TETRA stands for TErrestrial Trunked RAdio. It is aimed at a variety of mobile radio communications users including the police, ambulance and fire services, it is equally applicable for utilities, public access, fleet management, transport services, and many other users. It offers the advantages of digital radio whilst still maintaining the advantages of a PMR system.

TETRA radio beginnings

Work started on the development of the TETRA standards in 1990 and has relied on the support of the European Commission and the ETSI members. Experience gained in the development of the highly successful GSM cellular radio standard, as well as experience from the development and use of trunked radio systems has also been used to fashion the TETRA standard. In addition to this the process has gained from the co-operation of manufacturers, users, operators and industry experts. With this combined expertise the first standards for the new private mobile radio communications system were ready in 1995 to enable manufacturers to design their radio communications equipment to interoperate successfully.

TETRA Association

The industry organisation for TETRA radio is the TETRA Association (www.tetramou.org). The association was originally known as the TETRA MoU - Memorandum of Understanding and was formed in December 1994. The aim of the TETRA MoU was to create a forum that would act on behalf of all interested parties, i.e. users, manufacturers, application providers, integrators, operators, test houses and telecommunications agencies.

The TETRA Association represents more than 150 organisations and is continually growing as the TETRA standard is evolved and the uptake has increased..

The basic aims of the TETRA Association remain the same as that of the original TETRA MoU - providing a forum for all those interested in TETRA; to encourage adoption of the standard; and to support initiatives to obtain appropriate levels of spectrum to meet the growth in TETRA radio usage.

In view of its aims, the TETRA Association works closely with ETSI to maintain and advance the standards.

TETRA radio features

TETRA radio offers many new and valuable features and in this way it is a major step forwards over previous private mobile radio communications systems. These include a fast call set-up time, which is a particularly important requirement for the emergency services. It also has excellent group communication support, direct mode operation between individual radios, packet data and circuit data transfer services, better economy of frequency spectrum use than the previous PMR radio systems and in addition to this it provides advanced security features. The system also supports a number of other features including call hold, call barring, call diversion, and ambience listening.

The TETRA radio standard has undergone an evolutionary development to ensure that it is able to keep up with the needs of the users. There have been two releases of the TETRA radio standard.

  • TETRA Release 1:   As would be envisaged this was the first release of the TETRA radio standard which occurred
  • TETRA Release 2:   This release of the TETRA radio standard occurred in 2005 as a result of work dating back to 1999. It introduced a number of new features into the TETRA radio standard:

    • TETRA Enhanced Data Service (TEDS)
    • Mixed Excitation Liner Predictive, enhanced (MELPe) Voice Codec
    • Adaptive Multiple Rate (AMR) Voice Codec
    • Trunked Mode Operation (TMO) Range Extension
    Of these enhancements, it is the TETRA TEDS that has caught the headlines as the main enhanced feature, although the others all add to the overall package.

By Ian Poole

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