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Standardization Offers High Efficiency

March 2002
By Lt. Col. Ilkka J. Korkiamaki, FDF

Emergency services communications approach presents alternative for military operations.

A globally adopted standard and technology developed for public safety organizations could support multinational military operations by providing international interoperability. The high-level commercial technology product offers various data applications that meet the communications needs of international peace support operations.

Terrestrial trunked radio (TETRA), an open digital professional mobile radio standard and technology, is designed to support public safety organizations. Products that employ the standard currently are available, and a growing number of networks that incorporate the technology have been or shortly will be used worldwide.

The European Telecommunications Standards Institute defined the standard with the support of network operators, national administrators and equipment manufacturers. The essential parts of the TETRA standard were approved in national votes at the end of 1995. Users, particularly those working in emergency services, influenced the development of the standard and have contributed significantly to its creation.

A fully digital system, TETRA provides consistent voice quality and low-bit-error rate for data. It supports circuit-switched data, packet-switched data services and voice communications with a wide selection of data transmission rates and error protection levels.

TETRA uses time division multiple access technology with four user channels interwoven into one carrier with 25 kilohertz of carrier spacing. This enables efficient use of frequency spectrum and cost savings in base stations because a single radio unit offers four user channels. Higher data transfer rates of up to 28.8 kilobits per second are implemented by reserving up to four channels for the same user connection. Bandwidth allocation is determined by demand.

The technology has been designed as a trunked system that supports shared usage of the network by several organizations, while maintaining privacy and mutual security. Virtual networking enables each organization to operate independently, yet take advantage of the benefits of a large, highly functional system with efficient use of resources.

The technology features a very fast call set-up time, which is crucial for public safety and emergency services. It supports both semi-duplex operations for efficient group communications and duplex operations for individual telephone calls. Advanced group and announcement call features and multiple call priority schemes also are included. Multiple data services enable TETRA to be used as a platform for data applications.

TETRA also includes a direct mode operation between mobile radios, allowing communication without using the network infrastructure. Repeater and gateway functions are defined, extending the coverage of handheld radios in both direct mode and network operation. A terminal operating in direct mode also can operate in dual watch, periodically checking for signaling messages from a base station.

The high-security technology includes encryption of voice, data, signaling and user identities. The TETRA standard defines familiar security features but uses much longer encryption keys. The technology offers special features, including encryption of group traffic, mutual authentication, remote disabling and an end-to-end encryption capability.

To promote an open multivendor market, TETRA specifies essential interfaces. An air interface ensures that terminal equipment items from different manufacturers are compatible. A peripheral equipment interface facilitates the independent development of mobile data applications. An intersystem interface allows TETRA networks to interconnect with networks from different manufacturers. Direct mode operation guarantees communication between terminals even when they are out of network coverage range.

The interfaces inside the switching and management infrastructure are not standardized; consequently, manufacturers can implement the most cost-effective network solutions.

The connectivity between networks of different types was addressed in the development of TETRA technology. For example, a network can be connected to public and private telephone networks, different types of data networks, and large command and control systems.

The largest network deployments to date have been by European public safety and security organizations that are building nationwide shared networks to cover most of western and central Europe, and commercial network operators building “Pan-European” radio network coverage to sell services to mobile business work forces.

Vital to this development is the European harmonization of the TETRA radio spectrum, completed in cooperation with the NATO. In Europe, the 380- to 400-megahertz frequency band is reserved for TETRA for public safety and security use. The 410- to 430-megahertz band is reserved for TETRA commercial use. Outside Europe, the 800-megahertz band has become a dominant frequency band for TETRA.

The largest network projects to date are in Belgium, Finland, France, Germany, the Netherlands, Spain and the United Kingdom. Several system suppliers, such as Nokia, Motorola, Marconi, Simoco and Rohde & Schwarz, are producing TETRA network equipment and radios. A test program initiated and facilitated by the TETRA Memorandum of Understanding Association ensures compatibility among these manufacturers’ equipment. The association has almost 100 member organizations.

The TETRA standard and technology were designed for the demanding use of public safety organizations and not as a military standard, which is a factor in evaluating the military uses of the technology. In addition, major differences exist between a TETRA network owned and managed by the military and a single network shared with different organizations.

TETRA technology could improve military communications that support command and control. However, every system brought into operation must be studied very critically because the design of military communications systems differs from those required for civilian products. Existing military and nonmilitary systems must be integrated. Managing armed forces’ networks demands special requirements. The network must be flexible enough to address the specific military situation. In some cases, the network must be able to survive both electronic and physical attacks. Finally, efficient information security features are needed in critical applications.

Despite these challenges, TETRA meets several of the military’s special requirements. The technology features a wide selection of services, efficient use of capacity, short call set-up time, direct mode operation and base station stand-alone capabilities, a high level of integration and international interoperability, security and the option to use transportable network elements. On the other hand, TETRA responds poorly against electronic attack. It is mainly based on fixed network sites and elements, and it offers only centralized database solutions.

A system implementation that will meet military requirements must be defined. TETRA’s shortfalls can be improved to meet the requirements. System-level issues, such as survivability and physical and logical dispersion, are strongly dependent on a manufacturer’s network solution and the number of different elements in the network.

TETRA can replace old systems in operation with military police, security units, military fire brigades and logistics services and provide communications for peace support operations and exercises. In addition, it can support civil-military cooperation in civic actions and in peacekeeping operations or be used when training military troops.

Although it may not be suitable as the main means of communication for military troops on the front line, TETRA could support rear area communications during wartime for data applications and act as an additional means of communication for military troops on the battlefield.

Additional information on TETRA is available on the World Wide Web at http://www.tetramou.comm and www.nokia.com/networks/pmr.

Lt. Col. Ilkka J. Korkiamaki, Finnish Defense Forces (FDF), is chief of the communications and information systems division, Western Command Headquarters, Finnish Defense Forces.