Introduction To Terrestrial Trunked Radio (TETRA)

TETRA Communications System
TETRA Communications

Terrestrial Trunked Radio (TETRA) is a wireless communications standard for Professional Mobile Radio (PMR) and Private Access Mobile Radio (PAMR) applications that is used in over 140 countries, including Western Europe, Eastern Europe, Middle East, Africa, Asia Pacific, Caribbean and Latin America. In the United States, this is commonly referred to as “walkie talkie” communications.

Initially called the Trans-European Trunked Radio, TETRA is a two way digital communications protocol developed by the European Telecommunications Standardization Institute (ETSI)  for government agencies, first responders and emergency services. Its use was expanded to include railway, marine and some military organizations, in addition to the fire, ambulance and police.

The communications technology, originally deployed in the early 1980′, is based on Time Division Multiple Access (TDMA). There are four user channels multiplexed over a single radio carrier frequency. The protocol supports both point-to-point as well as point-to-multipoint communications. There are three different modes of operation in which TETRA radios can operate:

  • Voice plus Data (V+D)
  • Direct Mode Operation (DMO)
  • Packet Data Optimized (PDO)

In the most commonly used ” Voice plus Data ” mode, a full duplex communications channel is initialized which allows for multiplexing of both voice and data over the same channel by packetizing the information into different time slots.

The ” Direct Mode Operation” configuration does not support full duplex, but using simplex communications for both voice and data. The advantage is that DMO can bypass using a base station and initiate direct communications between two mobile units.

When voice is not needed, and high bandwidth data transmission is required, the ” Packet Data Optimized ” mode is used. This is the least commonly used of the three modes and was developed for the protocol in anticipation of future needs and applications.

Private Mobile Radio (PMR) and Public Access Mobile Radio (PAMR) are digital communications protocols that provide for very fast call initiations. Unlike standard cellular communications and existing POTS (Plain Old Telephone Service), PMR and PAMR do not rely on a relatively time consuming process of establishing a caller channel, routing through towers and central office, and call tear downs. While this may only take seconds for personal calls, the call set-up  time delays as well as potential for call drop-out,  are not acceptable for emergency services. This advantage, along with extreme flexibility in deployment and security encryption, makes TETRA ideal for civil, government and business applications.

For agencies that are deploying TETRA communications based infrastructures, it’s important to know what  are the typical coverage areas and quality of service (QOS) metrics. In order to discover dead spots and potential handover issues, as well as monitor radio communications, specialized test equipment is usually required. Aeroflex (which acquired Wiltek) offers the ” 8140 TETRA AirAnalyzer ” to test for coverage, network performance, voice  and data communications loads and other signaling conditions.

Aeroflex / Wiltek also provides an excellent in-depth explanation of the Terrestrial Trunked Radio (TETRA) protocol.

(Image Credit -TETRA.org )

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