Terrestrial Trunked Radio

TETRA ( terrestrial trunked radio, originally trans -European trunked radio) is a standard for digital trunked radio. It is intended as a universal platform for various mobile services. TETRA is universal networks can be set up through which the entire company of mobile users such as government, industry or transport operations can be handled.

History

Public safety radio was operated until the late 1980s the world with analog radio. The developed mid-1990s TETRA standard is used in several European and non-European countries in the form of a nationwide public safety networks or in local coverage by different users. TETRA originally represented an initiative of network operators in response to a serious competitive threat from GSM to their analog networks dar. addition, there is a second digital radio standard Tetrapol of EADS, which was originally developed for the French BOS and today is in the same range as TETRA in use.

Technology

TETRA is a time division multiplex (TDMA) system with four time slots, length of each of 14.167 ms per carrier frequency specified. The distance between the individual carrier frequencies is depending on the chosen modulation, 25, 50, 100 or 150 kHz. TETRA utilizes, by the division of each communication channel in an uplink and a downlink frequency, the frequency division multiplexing method.

The spectral efficiency is essentially determined by:

  • The gross data rate of the transmission channel,
  • The frequency repetition (distance between two base stations which use the same frequency ), and
  • The Gleichkanalstörabstand ( level difference between two signals with the same frequency of two different base stations in the fault-free operation is possible).

Taking into account these factors, a study of the CEPT has the same capacity and spectrum efficiency for GSM and TETRA result, since both systems operate close to the theoretical limit, which is determined by the energy per bit and the noise level.

The possible types of modulation of the carrier frequency are π/4-DQPSK or π/8-DQPSK when using phase modulation 4- QAM, 16- QAM or 64- QAM when using quadrature amplitude modulation. Depending on the type of modulation and the channel bandwidth leads to the following gross bit rate per carrier frequency:

A time slot of a phase-modulated carrier frequency can net bit rates of 2.4 kbit / s, 4.8 kbit / s and 7.2 kbit / s by using π/4-DQPSK and 10.8 kbit / s when using π/8- DQPSK provide. Speech is transmitted in a channel at 7.2 kbit / s.

Language is transmitted either with a special TETRA CODEC or an AMR codec with a bit rate of 4.75 kbit / s. In the TETRA codec is a specially configured ACELP codec, the AMR codec corresponding to the specified for GSM and UMTS codec.

The TETRA standard enables the following modes:

TMO

Trunked Mode Operation (network mode, intercom ), in which two or more wireless devices to communicate with the infrastructure. The range is not bound to the site, all participants are able to move within the network, possibly even nationwide.

In TMO, there are two types of traffic:

  • Intercom ( duplex operation), two participants talk to each other as in the telephone network. This significant burden on the resources of the radio network, since each participant needs its own time slot.
  • Conditional intercom, all participants of a radio circuit speak as usual with one another. A talkgroup occupied during transmission a time slot, similar to an analog radio channel.

Help

Direct Mode Operation ( direct mode or simplex operation ), which can communicate with two or more wireless devices without using a base station and network independent of each other, comparable to the change in use Talk radio sites after conventional designation.

This is at two points of interest:

  • The construction of the network in places with still existing radio hole.
  • For internal operations in buildings without building radio communication system.

It is possible to use a single radio device as a mobile relay station ( repeater) for other devices. Thus, a device in the car to make sure as a relay the radio coverage of portable radios at a work site, similar to the previous use of the FuG - 9c with RS-1 circuit.

It is also possible to use a device as a gateway, so that a vehicle radio with poor radio coverage makes in a remote location using a connection for local handheld radios in DMO for remote radio tower in TMO. Thus, the operations manager on site still reach the control center, comparable to a large relay station in RS- 2 circuit

Disadvantage of the DMO is the relatively long set-up times of a call. Spontaneous, fast known as radio traffic from analog, is only possible with DMO, after a call has been established. There is also no information as to whether the receiving station has been reached, as is the case in TMO. The device that initiates a communication, you must first check if the channel is vacant. If this is the case, he is seized and sent a preamble to ' awaken ' other wireless devices. This figure includes the information of the selected talk group and the separate identifier is transmitted. Finally, after one or two seconds, the acceptance tone occurs at the radio that started the conversation. Now dictating the users. If a connection can be spoken quickly and alternately. Once the lag time (the time after the last transmitter keying a participant ) has expired, the entire call setup starts all over again. This call set-up extended again with the use of a gateway, since this additional testing and signaling must make in the radio network. DMO can be considered as emergency or transitional solution or as a solution for conversations in which the time factor is irrelevant.

For Intercom ( duplex operation) the " Time Division Duplex" method is used in TETRA. In this case the speech is compressed in time such that a continuous two-way communication via two staggered time slots on the same frequency is possible. In parallel, the usual in trunking mode TMO frequency division multiplexing comes to fruition; a TETRA terminal transmits normally on the lower frequency, and receives at the higher frequency of the channel pair. The need for a duplexer is avoided by the above-mentioned time shift of the time slots for transmission and reception at the terminal.

The digital radio is distinguished from the analog radio by the fact that it can be encoded and therefore designed to be relatively bug-proof. The achieved here security against eavesdropping is used by the encryption process and the security of the cryptographic key used in this case dependent.

The redundant components in some system features, in comparison to GSM, an improved reliability.

Data transmission

For data transmission in TETRA network can be summarized by a four time slots ( multi- slot packet data). This data transfer is up to 28.8 kbit / s ( gross data rate ). In practice, data rates can be achieved up to ten kbit / s at the application level. This allows direct access to applications such as the Central Traffic Register.

The thus achieved bandwidths are now out of date; in the definition of the standards advertised in the 1990s fast access to image and video data via TETRA has significantly mitigated by the development of other mobile data transmission methods such as EDGE, UMTS, WLAN and especially LTE and the achievable with these transfer rates.

The currently probably the most promising way to increase the data transfer rate is developed by EADS TETRA Enhanced Data Service ( TEDS). With this system, up to 300 kbit / s are possible, which means about a tenfold increase in speed. This also visual information such as maps, digital images or video sequences could be transferred, which should speed up the response time of police, fire or ambulance services. Current trends go but to couple in the direction of TETRA systems with LTE networks.

Structure of the TETRA radio network

The TETRA network is technologically cellular, cellular changes and thus call transfer is possible across the network. The actual admissibility of the cell use is regulated to connect network - level, here are among others also the control centers into play. The TETRA network is designed to operate as an IT network, with user authorizations and exclusions as well as opportunities for interconnection of user groups and functions. The air interface, ie the actual wireless network, then only provides the access ( neudeutsch " Access Network" ) on it. This power mode is then called a "trunked mode" in switched mode. The capabilities of TETRA terminals to the " direct mode " and " relay mode " must be taken into account by appropriate frequency planning and channel assignment in the network. This is done by holding the free channels that are provided for DMO communications. Since a large number of channels in the border area of ​​a frequency coordination is subject to our neighboring countries, reduces the number of usable channels in these areas.

Addressing the terminal

Each TETRA terminal has a TETRA Subscriber Identity (TSI ), similar to a MAC address for a network card. Thus, the TSI is unique worldwide, is this divided into three areas (see figure):

  • Mobile Country Code (MCC). The Mobile Country Code consists of 10 bits, featuring the world's countries, such as Germany 262
  • Mobile Network Code (MNC ). The Mobile Network Code consists of 14 bits, featuring networks within a country.
  • Short Subscriber Identity ( SSI). The Short Subscriber Identity consists of 24 bits, featuring participants and system components within a network. There are four different types of SSIs: The ISSI (Individual Short Subscriber Identity ) indicates a terminal within a radio network clearly. (eg TETRA Meldeemfänger (TME ) )
  • The GSSI (Group Short Subscriber Identity ) denotes a discussion group within a radio network.
  • The ASSI ( alias Short Subscriber Identity) is used for the addressing of other network participants.
  • The fourth group represent the TETRA system addresses

Security

By TSI, it is possible to identify each terminal. To log in to the TETRA network, the TSI must be valid in this network. If it is not, the participant has no access to the TETRA network. This is similar to a whitelist of MAC addresses in a router.

Depending on the user various encryptions are used, the hardware is the same. There are only different algorithms in the device used. There are three different classes in the encryption TETRA Encryption Algorithms (TEA )

  • Class 1, unencrypted
  • Class 2, encrypted with static keys (SCK -Static Cipher Keys)
  • Class 3, encrypted using dynamic keys ( DCK - Dynamic Cipher Keys)

Can then apply the following encryption algorithms for security -class 2 3:

  • TEA -1, industrial encryption for EU countries
  • TEA -2, authorities encryption for EU countries
  • TEA -3, authorities encryption for third countries
  • TEA -4, industrial encryption for third countries

TEA -2 may only be used for security and military tasks within Schengen countries, an export to third countries is prohibited.

Frequency availability

The frequency availability in the ITU Region 1 ( Europe / Russia / Mongolia / Turkey / Arabian Peninsula / Africa ) is not uniform. As a result of the peace dividend after the dissolution of the Warsaw Pact parts of the mainly used by the military NATO harmonized UHF aeronautical radio bands could be OR ( 225-300 MHz) reorganized and approved for this particular bad radio application in NATO Europe. Other EU countries have decided that this initiative largely connected. Difficulties existed only in countries where the frequency bands in question have already been exploited commercially or vital security interests were affected. Regardless of a Europe-wide harmonized long-term solution is sought here. For cross-border BOS uses individual arrangements with neighboring frequency administrations concerned have been taken.

Examples frequency release BOS

  • Austria: 380-385 MHz ( uplink), 390-395 MHz ( downlink)
  • Germany: 380-385 MHz ( uplink), 390-395 MHz ( downlink). BOS radio

Other European frequency bands

  • 410-420 MHz ( uplink), 420-430 MHz ( downlink)
  • 450-460 MHz ( uplink), 460-470 MHz ( downlink)

Other frequency clearances

  • Russia: frequency ranges of 300 MHz
  • Asia ( ITU Region 3 ), 800 MHz band,

Frequency planning

The ability of TETRA terminals from the " relay mode " to switch to " Direct Mode " must be taken into account by appropriate frequency planning and channel assignment in the network. This is done by holding the free channels that are provided for DMO communications. Since a large number of channels in the border area of ​​a frequency coordination is subject to our neighboring countries, reduces the number of usable channels in these areas.

Use in the private sector

TETRA is in civilian or private sector for some time already in use: Straight industrial and transport companies have taken the digital trunked radio as a universal in-house communications medium that combines the functions of a radio and phone in itself, for itself in the surrounding application. In Germany the main companies in the auto industry, airports and major public transport company as a user are known, the latter especially in building of radio-based systems (Automatic Vehicle Location Systems, AVLS ). In Hamburg, for example, for many years, the port operator HHLA and operations of private health promotion. Some authorities of the federal and state governments operate their own first TETRA networks. The Cologne utilities Rheinenergie eg already adopted in 2004, the digital radio in operation. It is a network of 20 radio cells. Also, the clerk's office of the City of Cologne since 2005 uses the network of the Rhine energy.

The spatial extent may be limited to a building or terrain, but partly achieved even entire metropolitan areas and their hinterlands. Already in 2000, the company Dolphin Telecom began to build a nationwide network by TETRA standard, then interested users to sell digital trunked radio as a telecommunications service. This failed and the Dolphin Telecom had to file for bankruptcy in late 2005.

Use in the amateur radio service

Even in amateur radio TETRA is used. For commercial TETRA devices by radio amateurs be modified and reprogrammed them in the amateur band apply. So far, in Austria and Germany some TETRA relay, built in the 70 cm band and connected via IP Site Connect. There is also using VoIP and SIP technology to connect to other Internet- based digital Beriebsverfahren as DMR or D- STAR, as well as analog FM relay via EchoLink partly by means Hamnet.

Terminal provider

In contrast to the monopolistic Tetrapol, in which there is only one manufacturer, led the open standard TETRA to a variety of manufacturers.

  • EADS to date with bought- Nokia TETRA product line, now in-house production
  • Finmeccanica
  • Radio -Electronic Piciorgros GmbH, Germany
  • Funkwerk AG, Germany
  • Hytera Mobile GmbH, Germany
  • Motorola
  • Pontypool, United Kingdom
  • Rohde & Schwarz, Germany
  • Selex
  • Selkom GmbH Tetra control centers
  • Sepura
  • Team Simoco
  • Teltronic, Spain
  • Unimo, Korea

Infrastructure provider

  • 3T Communications AG, Vienna, Austria
  • Dam, Sønderborg, Denmark
  • EADS
  • Finmeccanica
  • Hytera Mobile GmbH, Germany
  • Motorola
  • Rohill, Netherlands
  • Selex
  • Teltronic TETRA, Spain

Norms and Standards

TETRA is an ETSI standard ( ETSI: European Telecommunications Standards Institute ). The first version of the standard was published in 1995.

The ETSI has tried together with the American TIA to develop a successor standard to broadband base. The project is called MESA ( Mobility for Emergency Broadband and Safety Applications). The MESA project was canceled on July 8, 2010 due to lack of progress.

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