Terrestrial Trunked Radio
Terrestrial Trunked Radio ( TETRA ), originally Trans European Trunked Radio with the same abbreviation, is a standard for digital trunked radio . It is standardized as a universal platform for different cellular services (ETSI, EN 300). With TETRA, universal networks can be set up, over which the entire corporate mobile network can be handled by users such as authorities, industrial or local transport companies.
history
Official radio was operated worldwide with analog radio until the end of the 1980s. The TETRA standard developed in the mid-1990s is used by various users in several European and non-European countries in the form of national BOS networks or with local coverage. TETRA was originally an initiative of network operators in response to a serious competitive threat posed by GSM against their analog networks. In addition, the second digital radio standard Tetrapol from EADS, which was originally developed for the French BOS and is now used in the same spectrum as TETRA.
technology
TETRA is specified as a time division multiplex system (TDMA) with four time slots, each 14.167 ms long per carrier frequency. The distance between the individual carrier frequencies is 25, 50, 100 or 150 kHz , depending on the type of modulation selected . TETRA uses frequency division multiplexing by dividing each communication channel into an uplink and a downlink frequency .
The frequency economy is essentially determined by:
- the gross data rate of the transmission channel,
- the frequency repetition distance (distance between two base stations using the same frequency) and
- the co-channel signal-to-noise ratio (difference in level between two signals with the same frequency from two different base stations, at which interference-free operation is possible).
Taking these factors into account, a study by the CEPT has shown the same capacity and frequency economy for GSM and TETRA, since both systems work close to the theoretical limit, which is determined by the energy per bit and the interference level .
The possible modulation types for 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, the following gross bit rates result per carrier frequency:
| modulation | 25 kHz | 50 kHz | 100 kHz | 150 kHz |
|---|---|---|---|---|
| π / 4-DQPSK | 36.0 | |||
| π / 8-DQPSK | 54.0 | |||
| 4-QAM | 38.4 | 76.8 | 153.6 | 230.4 |
| 16-QAM | 76.8 | 153.6 | 307.2 | 460.8 |
| 64-QAM | 115.2 | 230.4 | 460.8 | 691.2 |
A time slot of a phase-modulated carrier frequency can have net bit rates of 2.4 kbit / s, 4.8 kbit / s and 7.2 kbit / s when using π / 4-DQPSK and 10.8 kbit / s when using π / 8- Make DQPSK available. Speech is transmitted in one channel at 7.2 kbit / s.
Speech is transmitted either with a special TETRA- CODEC or an AMR codec with a bit rate of 4.75 kbit / s. The TETRA codec is a specially parameterized ACELP codec, the AMR codec corresponds to the codec specified for GSM and UMTS.
The TETRA standard enables the following operating modes:
TMO
Trunked Mode Operation (network mode, two-way communication ) in which two or more radio devices communicate via the infrastructure . The range is not bound to the site, all participants can, within the network, possibly even nationwide move .
There are two modes of transport in the TMO:
- Two-way communication ( duplex operation), two participants talk to each other as in the telephone network. This demands a lot of the resources of the radio network, since each participant needs its own time slot.
- Conditional two-way communication, all participants in a radio circuit speak to one another as usual. A talk group occupies a time slot during a transmission, comparable to an analog radio channel.
DMO
Direct Mode Operation , in which two or more radio devices can communicate with each other without using a base station and independently of the network, comparable to the two-way communication in emergency station radio according to the conventional designation.
This is of interest on two points:
- when setting up the network in locations with a dead zone.
- for indoor use in buildings without a building radio system.
It is possible to use a single radio device as a mobile relay station ( repeater ) for other devices. For example, a device in the vehicle can act as a relay to ensure the radio supply to the handheld radio devices at a deployment location, similar to the previous use of the FuG-9c with RS-1 circuit.
It is also possible to use a terminal device as a gateway , so that a vehicle radio device at a remote location with poor radio coverage establishes a connection for local handheld radio devices in the DMO to the remote radio tower in TMO. In this way, the on-site operations manager can still reach the control center, comparable to a large relay station in RS-2 circuit.
The disadvantage of the DMO is the relatively long setup times for a call. Spontaneous, fast radio communication, as is known from analog technology, is only possible to a limited extent with DMO after a call has been established. There is also no information as to whether the remote station was reached, as is the case with TMO. The device that starts a communication must first check whether the channel used is free. If this is the case, it is seized and a preamble is sent to 'wake up' other radio subscribers. Among other things, the information of the selected talkgroup and your own identifier are transmitted here. Finally, after a second or two, the radio that started the call will give the release tone. Now the user can speak. If there is a connection, you can speak quickly and alternately. As soon as the follow-up time (the time after a subscriber's transmitter was last pressed) has expired, the entire call setup starts all over again. These call setup times are lengthened again when a gateway is used, as this has to carry out additional tests and signaling in the radio network.
For two-way communication ( duplex operation ), TETRA uses the "Time Division Duplex" method. The language is compressed in time so that continuous two-way communication is possible over two offset time slots on the same frequency. At the same time, the frequency division multiplex commonly used in trunking mode TMO comes into play; a TETRA terminal generally transmits on the lower frequency and receives on the higher frequency of the channel pair. However, the need for a duplexer is avoided in the terminal by the mentioned time offset of the time slots for sending and receiving.
Digital radio is distinguished from analog radio in that it can be encrypted and thus designed to be relatively secure against eavesdropping. The security against eavesdropping achieved here depends on the encryption method used and the security of the cryptographic key used.
The system, which is redundant in some components, has improved reliability compared to GSM.
Data transfer
One to four time slots can be combined for data transmission in the TETRA network (multislot packet data). This enables data transmission of up to 28.8 kbit / s (gross data rate). In practice, data rates of up to 10 kbit / s are achieved at the application level. This enables direct access to applications such as the fitness to drive register .
The bandwidths achieved in this way are no longer up-to-date these days; The fast access to image and video data via TETRA advertised when the standard was defined in the 1990s has been put into perspective by the development of other mobile data transmission methods such as EDGE , UMTS , WLAN and, above all, LTE and the transmission rates that can be achieved with these.
Probably the most promising way to increase this data transmission rate at the moment is the TETRA Enhanced Data Service (TEDS) developed by EADS. With this system up to 300 kbit / s are possible, which means about ten times the speed. This could also be used to transmit visual information such as maps, digital images or video sequences, which should accelerate the response time of the police, fire brigade or rescue services. Current developments are also going in the direction of coupling TETRA systems with LTE networks.
Structure of the TETRA radio network
The TETRA radio network is technologically cellular, which means that calls are passed on throughout the network by switching between several cells. A cell change during a radio call is just as possible here as in the GSM network (hand-over). The actual permissibility of cell usage is regulated at the connection network level. a. the control centers also come into play. In principle, the TETRA network behaves like an IT network, with usage authorizations and exclusions as well as options for interconnecting user groups and functions. The air interface, i.e. the actual radio network, then only provides access to it (new German "Access Network"). This network mode is then called “trunked mode”, ie mediated mode.
Addressing the end devices
Every TETRA terminal has a TETRA Subscriber Identity ( TSI ), similar to a MAC address on a network card. So that the TSI is unique worldwide, it is divided into three areas (see figure):
- Mobile Country Code (MCC). The Mobile Country Code consists of 10 bits and identifies the countries of the world, e.g. B. Germany 262.
- Mobile Network Code (MNC). The Mobile Network Code consists of 14 bits and identifies networks within a country.
- Short Subscriber Identity (SSI). The Short Subscriber Identity consists of 24 bits and identifies participants and system components within a network. There are four different types of SSIs:
- The ISSI (Individual Short Subscriber Identity) uniquely identifies an end device within a radio network. (e.g. radio transmitter )
- The GSSI (Group Short Subscriber Identity) identifies a talk group within a radio network.
- The ASSI (Alias Short Subscriber Identity) is used to address external network participants.
- The fourth group are the TETRA system addresses.
safety
The TSI makes it possible to identify every terminal. In order to log into the TETRA network, the TSI must be valid in this network. If it is not, the subscriber has no access to the TETRA network. This is comparable to a whitelist of MAC addresses in a router.
Different encryptions are used depending on the user, with the hardware always being the same. Only different algorithms are used in the device. There are three different encryption classes in the TETRA Encryption Algorithms ( TEA ):
- Class 1, unencrypted
- Class 2, encrypted with static keys (SCK-Static Cipher Keys)
- Class 3, encrypted with dynamic keys (DCK-Dynamic Cipher Keys)
The following encryption algorithms can then be used for security class 2 + 3:
- TEA-1, industrial encryption for EU countries
- TEA-2, authority encryption for EU countries
- TEA-3, authority 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; export to third countries is prohibited.
Frequency availability
The frequency availability is not uniform in ITU region 1 (Europe / Russia / Mongolia / Turkey / Arabian Peninsula / Africa). As a result of the peace dividend following the dissolution of the Warsaw Pact , parts of the predominantly military NATO-harmonized UHF aeronautical radio band OR (225 to 399 MHz) were reorganized in NATO Europe and released for this special BOS radio application. Other EU states have largely joined this initiative. Difficulties existed only in countries in which the frequency ranges concerned were already used commercially or vital security interests were affected. Regardless of this, a Europe-wide harmonized solution is sought in the long term. For cross-border BOS uses, individual regulations were made with the relevant neighboring frequency administrations .
Examples of frequency approval 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)
Further frequency releases
- Russia: frequency ranges around 300 MHz
- Asia (ITU region 3): 800 MHz band
Frequency planning
The ability of TETRA terminals to switch from “relay mode” to “direct mode” must be taken into account by appropriate frequency planning or channel allocation in the network. This is done by keeping the channels reserved for DMO communication free. Since a large number of channels in the border area are subject to frequency coordination with neighboring countries, the number of channels that can be used in these areas is reduced.
Use in the private sector
TETRA has been in use in the civil and private sector for some time: Industrial and transport companies in particular have used digital trunked radio as a universal internal communication medium that combines the functions of a radio and telephone. In Germany, companies in the automotive industry, airports and larger urban transport companies are known to be users, the latter especially when setting up radio-based systems ( Automatic Vehicle Location Systems , AVLS). In Hamburg, for example, the port operator HHLA and private health transport companies for many years . Some federal and state authorities are also operating their own TETRA networks. The Cologne energy supplier Rheinenergie z. B. started using digital radio in 2004. This is a network with 20 radio cells. The regulatory office of the city of Cologne has also been using the RheinEnergie network since 2005.
The spatial expansion can be limited to a building or site, but in some cases it can also reach entire conurbations and their surrounding area. As early as 2000, Dolphin Telecom began building a nationwide network based on the TETRA standard in order to then sell digital trunked radio as a telecommunications service to interested users. This failed and Dolphin Telecom had to file for bankruptcy at the end of 2005.
On the Wuppertal suspension railway , TETRA is used to transfer data from the ETCS train protection system .
Use in the amateur radio service
TETRA is also used in amateur radio . Commercially available TETRA devices are frequency range extended and programmed by radio amateurs to use them in the amateur band . So far, there are some DMO repeaters in Austria and Germany, built in a 70 cm band and connected via an Echolink conference server. In addition, there is a connection to other internet-based digital operating procedures such as DMR , D-STAR or APCO P25 as well as to analog FM relays via EchoLink , sometimes via HAMNET , using VoIP and SIP technology . A position report with the LIP protocol to the DMO repeater enables a position beacon to be transmitted to the APRS server when using GPS- enabled devices .
Terminal provider
In contrast to the monopolistic Tetrapol , where there is only one manufacturer, the open standard at TETRA led to a large number of manufacturers.
- EADS previously with purchased Nokia TETRA product range, meanwhile in-house production
- Leonardo
- Funk-Electronic Piciorgros GmbH, Germany
- Funktel GmbH , Germany
- Hytera Mobilfunk GmbH, Germany
- Motorola
- Pontypool, UK
- Rohde & Schwarz , Germany
- SELECTRIC Nachrichten-Systeme GmbH, Germany
- Selex
- Selkom GmbH Tetra control centers
- Sepura
- Team Simoco
- Teltronic, Spain
- Unimo, Korea
Infrastructure provider
- Dam, Sønderborg, Denmark
- EADS
- Leonardo
- Hytera Mobilfunk GmbH, Germany
- Motorola
- Rohill, Netherlands
- Selex
- Sepura , England (through the acquisition of 3T Communications AG, Vienna)
- Teltronic TETRA, Spain
Norms and standards
TETRA is an ETSI standard (ETSI: European Institute for Telecommunications Standards ). The first version of the standard was published in 1995.
Together with the American TIA, ETSI tried to develop a successor standard on a broadband basis. The project was called MESA (Broadband M obility for E mergency and S afety A pplications). The MESA project was canceled on July 8, 2010 due to a lack of progress.
As part of the ongoing standardization for LTE as part of the 3GPP, functions have been introduced under the name MCPTT (mission critical push to talk). These functions are designed as the successor standard for TETRA.
See also
literature
- Michael Marten: BOS radio 1 ; Vth; Edition: 5th, chang. New edition 2005, ISBN 3-88180-616-4
- Michael Marten: BOS radio 2 ; Vth; Edition: 11th, chang. New edition 2005, ISBN 3-88180-647-4
- Linde, Christof: Structure and technology of the digital BOS radio , Franzis Verlag, 2008 ISBN 3-7723-4216-7
Web links
Individual evidence
- ↑ Trans European Trunked Radio (TETRA) system; 1994. Retrieved March 12, 2016
- ↑ ETSI EN 300 392-2 V3.2.1: Terrestrial Trunked Radio (TETRA); Part 2: Air Interface (AI), chap. 4.5: Multiple access and time slot structure; As of September 2007. Available from http://pda.etsi.org/pda (accessed: December 10, 2009)
- ↑ ETSI EN 300 392-2 V3.2.1: Terrestrial Trunked Radio (TETRA); Part 2: Air Interface (AI), chap. 5: modulation; As of September 2007. Available from http://pda.etsi.org/pda (accessed: December 10, 2009)
- ↑ ETSI EN 300 392-2 V3.2.1: Terrestrial Trunked Radio (TETRA); Part 2: Air Interface (AI), chap. 9.2.1: Logical channels hierarchy; As of September 2007. Available from http://pda.etsi.org/pda (accessed: December 10, 2009)
- ↑ ETSI EN 300 395-2 V1.3.1: Terrestrial Trunked Radio (TETRA); Speech codec for full-rate traffic channel; Part 2: TETRA codec; As of January 2005. Available from http://pda.etsi.org/pda (accessed: December 10, 2009)
- ↑ Wireless - TWC 2012: Hytera demonstrates critical comms over broadband LTE ( English ) May 21, 2012. Archived from the original on May 27, 2012. Retrieved on January 12, 2013.
- ↑ An Overview of TETRA ( English , PDF; 262 KB) February 22, 2005. Archived from the original on September 27, 2011. Retrieved on August 4, 2010.
- ↑ Overview of Standard TETRA Cryptographic Algorithms and their rules for management and distribution ( English , PDF; 118 KB) May 1, 2008. Accessed on August 4, 2010. ( Page no longer available , search in web archives )
- ↑ RTR : 400 MHz spectrum - TETRA: Overview of the frequency range used for TETRA, November 19, 2007
- ↑ Peer Jacobsen: The Wuppertal suspension railway with ETCS Level 3 and TETRA . In: Railway technical review . No. 6 , 2014, ISSN 0013-2845 , p. 54-57 .
- ↑ TETRA-DMO converter DB0MOT Kleiner Feldberg. Taunus Relais Group, accessed on August 21, 2014 .
- ↑ a b Tino Neubauer, Andreas Bier: SvxLink with Tetra DMO repeater (Tetra in amateur radio) DM0SVX. (No longer available online.) Archived from the original on August 21, 2014 ; accessed on August 21, 2014 .
- ↑ TETRA Vienna Bisamberg OE1XAR. OE Wiki of the Austrian Association of Experimental Broadcasters, accessed on August 21, 2014 .
- ↑ MultiMode platform MMP . In: Österreichischer Experimentssenderverband (Hrsg.): QSP Amateurfunkjournal des Österreichischer Experimentssenderverband . December 2012, digital communication: SvxLink with Tetra DMO repeater (Tetra in amateur radio), p. 22–23 ( online ( memento of August 21, 2014 in the Internet Archive ) [PDF; accessed on August 21, 2014]). MultiModePlattform MMP ( Memento from August 21, 2014 in the Internet Archive )
- ↑ MESA # 19 Draft meeting Report ( English , DOC; 77 KB) July 8, 2010. Accessed on November 6, 2012. ( Page no longer available , search in web archives )
- ↑ Kevin Flynn: Mission Critical Services in 3GPP. Retrieved May 15, 2018 (UK English).