Terrestrial Trunked Radio

Terrestrial Trunked Radio^[1] (TETRA; formerly known as Trans-European Trunked Radio), a European standard for a trunked radio system, is a professional mobile radio^[2] and two-way transceiver specification. TETRA was specifically designed for use by government agencies, emergency services, (police forces, fire departments, ambulance) for public safety networks, rail transport staff for train radios, transport services and the military.^[3]

TETRA is a European Telecommunications Standards Institute (ETSI) standard, first version published 1995; it is mentioned by the European Radiocommunications Committee (ERC).^[4]

Description

TETRA uses Time Division Multiple Access (TDMA) with four user channels on one radio carrier and 25 kHz spacing between carriers. Both point-to-point and point-to-multipoint transfer can be used. Digital data transmission is also included in the standard though at a low data rate.

TETRA Mobile Stations (MS) can communicate direct-mode operation (DMO) or using trunked-mode operation (TMO) using switching and management infrastructure (SwMI) made of TETRA base stations (TBS). As well as allowing direct communications in situations where network coverage is not available, DMO also includes the possibility of using a sequence of one or more TETRA terminals as relays. This functionality is called DMO gateway (from DMO to TMO) or DMO repeater (from DMO to DMO). In emergency situations this feature allows direct communications underground or in areas of bad coverage.

In addition to voice and dispatch services, the TETRA system supports several types of data communication. Status messages and short data services (SDS) are provided over the system's main control channel, while packet-switched data or circuit-switched data communication uses specifically assigned channels.

TETRA provides for authentication of terminals towards infrastructure and vice versa. For protection against eavesdropping, air interface encryption and end-to-end encryption is available.

The common mode of operation is in a group calling mode in which a single button push will connect the user to the users in a selected call group and/or a dispatcher. It is also possible for the terminal to act as a one-to-one walkie talkie but without the normal range limitation since the call still uses the network. TETRA terminals can act as mobile phones (cell phones), with a full-duplex direct connection to other TETRA Users or the PSTN. Emergency buttons, provided on the terminals, enable the users to transmit emergency signals, to the dispatcher, overriding any other activity taking place at the same time.

Advantages

The main advantages of TETRA over other technologies (such as GSM) are:

• The much lower frequency used gives longer range, which in turn permits very high levels of geographic coverage with a smaller number of transmitters, thus cutting infrastructure costs.
• During a voice call, the communications are not interrupted when moving to another network site. This is a unique feature, which dPMR networks typically provide, that allows a number of fall-back modes such as the ability for a base station to process local calls. So called 'mission critical' networks can be built with TETRA where all aspects are fail-safe/multiple-redundant.
• In the absence of a network, mobiles/portables can use 'direct mode' whereby they share channels directly (walkie-talkie mode).
• Gateway mode - where a single mobile with connection to the network can act as a relay for other nearby mobiles that are out of range of the infrastructure.
• TETRA also provides a point-to-point function that traditional analogue emergency services radio systems did not provide. This enables users to have a one-to-one trunked 'radio' link between sets without the need for the direct involvement of a control room operator/dispatcher.
• Unlike cellular technologies, which connect one subscriber to one other subscriber (one-to-one), TETRA is built to do one-to-one, one-to-many and many-to-many. These operational modes are directly relevant to the public safety and professional users.
• Security TETRA supports terminal registration, authentication, air-interface encryption and end-to-end encryption.
• Rapid deployment (transportable) network solutions are available for disaster relief and temporary capacity provision.
• Network solutions are available in both reliable circuit-switched (telephone like) architectures and flat, IP architectures with soft (software) switches.

Further information is available from the TETRA Association (formerly TETRA MoU) and the standards can be downloaded for free from ETSI.

Disadvantages

Its main disadvantages are:

• Requires a linear amplifier to meet the stringent RF specifications that allow it to exist alongside other radio services.
• Data transfer is slow by modern standards.

Up to 7.2 kbit/s per timeslot, in the case of point-to-point connections, and 3.5 kbit/s per timeslot in case of IP encapsulation. Both options permit the use of between one and four timeslots. Different implementations include one of the previous connectivity capabilities, both, or none, and one timeslot or more. These rates are ostensibly faster than the competing technologies DMR, dPMR, and P25 are capable of). Latest version of standard supports 115.2 kbit/s in 25 kHz or up to 691.2 kbit/s in an expanded 150 kHz channel. To overcome the limitations many software vendors have begun to consider hybrid solutions where TETRA is used for critical signalling while large data synchronization and transfer of images and video is done over 3G / LTE.^[5]

TETRA usage

At the end of 2009 there were 114 countries using TETRA systems in Europe, Middle East, Africa, Asia Pacific, Caribbean and Latin America.^[6]

The TETRA-system is in use by the public sector in the following countries. Only TETRA network infrastructure installations are listed. TETRA being an open standard, each of these networks can use any mix of TETRA mobile terminals from a wide range of suppliers.

Continent	Country	Supplier	Name	Agency	Status
Asia	China mainland	EADS / Cassidian	Shenyang Metro	Transport	In use: Line 1 Rolling out: Line 2[7]
		DAMM TetraFlex	Guangzhou Electric Power	Utility - GuangZhou Electric Power Emergency Communication	In Use 2010
		EADS / Cassidian	Shenzhen Metro	Transport	Ordered 5/2010[8]
		EADS / Cassidian	Guangzhou	16th Asian Games in 2010	Ordered 2010[8]
	Hong Kong	EADS / Cassidian[9]	Hong Kong International Airport (HKIA)	2008 Beijing Olympics and Paralympic Games (Hong Kong Equestrian Event)	Used from July 2008 to October 2008
		EADS / Cassidian	Hong Kong Fire Services Department	Fire service and ambulance	In use
		Motorola / Dimetra	Hong Kong Police Force	Police	In use
		Artevea	Mass Transit Railway (MTR)[10]	Transport	In use
		Motorola / Dimetra	Hong Kong International Airport (HKIA)	Transport	In use since Feb 2009[11]
	India	Artevea	Military College of Telecommunication Engineering (MCTE)	Indian Army	In use since 2004 at Mhow, Indore, Madhya Pradesh
		Motorola / Dimetra	Delhi Metro Rail Corporation Ltd.	Transport	The First TETRA in India, in use since 2002
		DAMM TetraFlex / Consort Digital Pvt Ltd	Mumbai Mono Rail, Mumbai Metropolitan Region Development Authority (MMRDA)	Mass Transport - Indias first Monorail Project - Mumbai	Awarded 2010[12]
		C-DAC	TETRA with Automatic Dial 100 (AD100)	Kerala police	In use by police, Trivandrum city, since 2008
		DAMM TetraFlex / Consort Digital Pvt Ltd	Tamil Nadu police	Police and internal security and safety	Awarded 2011[13]
		HCL & Motorola	Secure Communication Network	Delhi government	Integrated Communication System used by various departments under government of Delhi and Delhi police since 2010.
		DAMM TetraFlex / Consort Digital Pvt Ltd	Gas Authority of India Limited (GAIL)	Gas Pipeline - Safety, Telemetry and Security	Awarded 2011[14]
		THALES Portugal S A & Motorola	With PSTN call integration designed by Thales Group for BMRCL	BMRCL Bangalore Metro Corporation Limited	Transport, in use since March 2011
		Sepura & Rohde and Schwarz	TETRA with Automatic Dial 100 (AD100)	Gurgaon police	In use by police, Gurgaon city[15] Since 2009. In Salem from August 2011.
		Sepura & Rohde and Schwarz	TETRA with Automatic Dial 100 (AD100)	Faridabad police	In use by police, Faridabad city, since 2012
	Indonesia	Motorola / Dimetra, installed & maintained by PT. Mobilkom Telekomindo	SCADA PT. Chevron Pacific Indonesia	HOOU	In use since 2009 at Duri, Riau, Indonesia.
		Rohde & Schwarz / Accessnet - T	Anti Corruption Agency	Anti Corruption Agency	Operational
		Rohde & Schwarz / Accessnet-T	Jakarta State Government Network	Jakarta Capital City Jakarta	Operational, Installed since 2007
	Macao	Artevea	Melco-Crown Entertainment	Casino-Hotels: Altira (formerly Crown Macau),[16] and City of Dreams	In use since 2007
			Forças de Segurança de Macau	All emergency services	In use
	Malaysia	EADS	Segi Maju (SEGI)	Public operator	In use[17]
	Maldives	Motorola / Dimetra	Maldives Police Service (MPS)	Police	In use
	Pakistan	Motorola / Dimetra	NITRS Nationwide Integrated Trunk Radio System Project for Police under Ministry of Interior, Government of Pakistan	Police	In use Since 2009
	Philippines	Motorola Dimetra/GA Technology and Systems Inc.	Shell Exploration	Oil and Gas	In use October 2013, Phase 2 On Shore Gas Plant for Implementation
		Motorola Dimetra/GA Technology and Systems Inc.	Globe Telecom	Telecommunications Carrier	Implementation on Going Project Finish Dec 2013
		Rohill (TetraNode) SynTech Systems Inc.	Meralco	Electric Company	Implemented Nov 2014
		Rohill (TetraNode) SynTech Systems Inc.	LRT-2	Transport (Manila Light Rail Transit System Line 2)	Implemented Oct 2015
	South Korea	EADS	Korea Electric Power Corporation (KEPCO)	Electricity	In use[18]
	Taiwan		Taiwan Railways Administration	Transport	In use
			Taiwan High Speed Rail	Transport	In use
			Taipei Metro	Transport	In use
			Kaohsiung Mass Rapid Transit	Transport	In use
			Coast Guard Administration (Taiwan)	Republic of China Armed Forces	In use
Africa	Algeria	Rohde & Schwarz	Sonatrach	Oil & Gas company	In use since 2003.
		Sepura	Sonelgaz	Power utility	In use.
	Morocco	Rohill	ADM	Highway authority	Rolling out / Almost completed.
	Nigeria	Dizengoff/Motorola IL (Dimetra IP)	Nigeria LNG	Oil & Gas	Since 2006
		Cisan International Limited/Rohill (TetraNode)	Mobil Ng	Oil	Since 2014
		Dizengoff/Motorola IL (Compact-Tetra IP)	Shell Ng	Oil	Since 2010
		Satcomm Integrated Resources LLC SatCom IRL/EADS	[19]	Nigerian Ports Authority, Nigeria (Rolling Out)	Rolling out
		Rohill (TetraNode)	Bayelsa State	Government	Since June 2012
		Briscoe Technologies[20] / Artevea	Lagos / Abuja / Port Harcourt	Oil industry / Airports / security companies	In use Since 2006
	Namibia	Artevea	Namibian Police Force[21]	Police	In use, nationwide
	South Africa		Police, traffic police	SAPS Gauteng	Gauteng province
			Municipality, fire, and ambulance.	City of Cape Town	Cape Peninsula
		Rohill (TetraNode)	Mbombela Local Municipality	Nelspruit, Mpumalanga	Complete
		Rohill (TetraNode)	City Power	Johannesburg, Gauteng	Complete
		Rohill (TetraNode)	City of Tshwane Municipality	Pretoria, Gauteng	Complete
		Rohill (TetraNode)	Rustenburg Platinum Mine	Potgietersrus, Limpopo	Complete
	Sudan	Artevea	Ministry of Interior	Police	In use, nationwide
Europe	Austria	Motorola / Dimetra	TETRON	Police, fire, ambulance, and local train company.	In use, in all states except Tyrol and Vorarlberg (still rolling out).
	Belgium	EADS/Since 1998	A.S.T.R.I.D.	Police, fire, ambulance, customs, coast guard, hospitals, Red Cross, department of Justice, utility companies, airports, ports, lifeguard service, military.	Nationwide network
		Motorola 2010/ DIMETRA	ENTROPIA DIGITAL	Commercial & Private Security users.[22]	Antwerp, Belgium / Roaming with Entropia Digital in The Netherlands
		Rohde & Schwarz since 2011/ ACCESSNET-T	ENTROPIA DIGITAL	Commercial & Private Security users.[22]	Flanders & Brussels/Roaming with Nationwide The Netherlands
	Croatia	Motorola / Dimetra	MUPNet	Police, Fire Brigades, Ambulance Service	Nationwide coverage (99,5%) in use
	Denmark	DAMM TetraFlex	DONG Energy Power Plants - 11 Power Plants across Denmark	Utilities - Safety, Security, Telemetry	Awarded 2009[23]
		Motorola / Dimetra	SINE[24]	All emergency authorities, incl. police, fire, and ambulance.	Nationwide coverage (99,5%) in use
	Estonia			Police, fire, ambulance, and customs	Rolling out
	Finland	Nokia; now EADS	VIRVE	Police, fire, ambulance, customs, defence forces, and border guard	Nationwide network
			HelenNet	Energy company Helsingin Energia, tram operator HKL-Raitioliikenne, and several bus operators on HRTA's lines. Also used by some security guard companies, mostly securing HRTA's transport. Available for lease for various short-term uses.	In use, covers greater Helsinki region
	Germany	EADS	BOSNET	Police, fire, ambulance, customs, and coast guard.	Nationwide
		DAMM TetraFlex	Global Tech 1 Offshore Wind GmbH.	Utility Windfarm - Telemetry, Security and Safety Critical communications	Awarded 2012[25]
	Greece	Motorola / Dimetra	COSMOTE TETRA Services Formerly branded OTElink (2009).	Business Critical and PPDR communications, public utility and oil-gas companies, seaports, airports, public and private transportation companies, public and private sector security personnel, other. Data applications nationwide including SCADA, AVL, M2M.	Extensive nationwide footprint, 70% population coverage in 2014, in use since 2002
	Hungary	Pro-M Ltd.	EDR (acronym for Unified Digital Radiosystem)	Ambulance, army, Central Office for Administrative and Electronic Public Services, Civil Defence, Hungarian Prison Service, Hungarian Customs and Finance Guard, Disaster Management, fire, Hungarian Secret Services, Ministry of Environment and Water, and police	In-use
	Iceland		TETRA Iceland	All emergency services, most utility companies, and private users	In-use
	Ireland	Motorola / Dimetra	TETRA Ireland	An Garda Siochana, HSE National Ambulance Service, Irish Prison Service, Irish Naval Service, Customs & Excise, Civil Defence (Only A Few Units), Irish Coast Guard, Mountain Rescue (Only A Few Units), Order of Malta Ambulance Corps, Irish Red Cross, St John Ambulance, National Emergency Office, Port of Cork, Revenue Commissioners and Office of Public Works.	Nationwide roll-out network complete. The fire services are planning to implement in the coming years. As of July 2011, TETRA Ireland now operates the national Paging System.
	Italy	DAMM TetraFlex	Lombardi Ambulance Emergency Services	Ambulance - Security, Safety, Communication	Awarded 2010[26]
		SELEX ELSAG	Rete Interpolizie	Polizia di Stato (Italian state police), Carabinieri (military police), Guardia di Finanza (financial police), Polizia Penitenziaria (prison police), and Corpo Forestale Italiano (Italian forest brigades)	Rolling out
		DAMM TetraFlex	Rome International Airport	Airport - Security, Safety, Commercial, Fire, Customs, Police	Awarded 2009[27]
	Latvia	Artevea	Ventamonjaks Serviss Ltd, Ventspils[28]	Oil and gas	In use since 2007
	Luxembourg	Motorola / Dimetra	Renita[29]	Government; Police, Fire Brigade, Ambulance services and others	Start building 2014, Operational since 2015
		Motorola / Dimetra	ConnectCom[30]	Commercial network	Operational
		Motorola / Dimetra	ConnectCom[30]	Public Transport, city of Luxembourg	Operational
		Motorola / Dimetra	ConnectCom[30]	European Union	Operational
	Malta	Marconi		Civil Protection Force[31]	July 2001
	Montenegro	Motorola / Dimetra	Wireless Montenegro d.o.o.	Police, Military, Firebrigade, Ambulance	In use since November 2012 Podgorica area only. Rolling out elsewhere.
	Netherlands	Motorola / Dimetra	C2000[32]	Police, fire, and ambulance	Nationwide network
		Motorola since 2007/ Dimetra	ENTROPIA DIGITAL	Commercial users.[22]	Nationwide network /Roaming with Entropia Digital in Belgium
		Rohde & Schwarz since 2010/ ACCESSNET-T	ENTROPIA DIGITAL	Cityguards and commercial use[22]	Rotterdam area network / Roaming with Entropia Digital in Belgium
		Motorola/ Dimetra	HTM	Public transport The Hague	Regional network
	Norway	Motorola / Dimetra	Norwegian Public Safety Radio	Police, fire, ambulance, civil defense and search and rescue	Nationwide rollout completed September 2015 And Metro and Tram in Oslo completed 2002. Sporveien Metro and Sporveien Tram. On Norway Sporveien T-Banen og Sporveien Trikken
	Portugal	Motorola	SIRESP	Police, fire, and ambulance	Nationwide roll-out, in use since 2007
	Poland	Motorola	Ministry of Interior, Polish army, and Warsaw police	Police, fire, public transport, airports, and army.[33]	Local TETRA Networks in use since 2000; national roll-out expected to start in 2011.
		Rohill (TetraNode)	Szczecin, Warsaw and Kraków police	Roll-out ongoing.	Modern IP based TETRA solution for 3 cities
	Romania	Motorola / Dimetra	Special Telecommunications Service (STS)	Police, fire, and search and rescue	Nationwide
		Motorola	Dimetra	Ministry of Administration and Interior (MAI) / Romanian Border Police (RBP)	In use since 2008 for police, emergency and search and rescue agencies from Romanian border counties-wide
		Cassidian	TETRA EADS	Ministry of Administration and Interior (MAI) / Romanian Border Police (RBP)	In use since 2010 for police, emergency and search and rescue agencies from Romanian border counties-wide
	Russia	DAMM TetraFlex	Moscow Metro (second most heavily used rapid transport system in the world)	Transport - Rail - Telemetry, Safety, Security, Police, Ambulance, Fire	Awarded 2011[34]
		Sepura	Unified system of operational trunking radio (Единая Система Оперативной Транкинговой Радиосвязи)	Fire, ambulance and partially, police	Launched in 2008
		DAMM TetraFlex	Russias Kaliningrad Power Plant.	Utility Power Plant - Safety and Security - Telemetry and Commercial agents	Awarded 2009[35]
		DAMM TetraFlex	St Petersburg and North West Russia.	Government - Ambulance and Emergency services, Police, Healthcare facilities, Utility services, St. Petersburg Authorities and the regional Civil Defence	Awarded 2011[36]
	Serbia	Motorola / Dimetra	Ministry of Interior	Police, Fire Brigades, Ambulance	Fully rolled out as of 2009
	Slovenia	Selex/OTE/Marconi	Ministry of Interior	Police	In central Slovenia
	Spain	Motorola	Basque Country	Mainly police	In use since 2006
		Teltronic	Basque Country	Mainly municipalities and public services	In use since 2009
		EADS	Catalonia	Mainly police	In use since 2006
	Sweden	SAAB, Cassidian, Eltel Networks	RAKEL	Managed by the Civil Contingencies Agency for use by the emergency services and others in the fields of civil protection, public safety and security, emergency medical services and healthcare.	In operation, covering 99.8% of Sweden's population and 95% of its territory
		Motorola	Tetra	Stockholm Public Transport: Used by Transport Security Officers for dispatch internal communications, Transport Police ("Tunnelbanepolisen") and other police forces for liaison with transport officials. Roll-out stage for train operations on underground.	In operation / roll-out
		Swedish Radio Supply	Got1	Got1 is a modern IP based Tetra network used in the west parts of Sweden.	In operation / roll-out
	United Kingdom	Motorola / Dimetra / Sepura	Airwave	Police, fire, NHS ambulance services, Border Force, Immigration Enforcement, some armed forces, Highways Agency Traffic Officers, Civil Contingency Services, HM Coastguard, British Red Cross, Highland Council, and misc. emergency services.	Full emergency service roll out complete
		Motorola / Dimetra	CONNECT	Transport for London (London Underground)	Used by all Tube staff and relaying Airwave for BTP when underground
		AirRadio AR-en	Use by some services at some major airports	(Heathrow, Birmingham, Manchester, Glasgow, Aberdeen)
Middle East	Israel	Motorola[37]	Mountain Rose	Israel Defense Forces (IDF)	In use by IDF, country-wide
	Turkey	DAMM TetraFlex	Alacer Gold Mine	Mining - Safety and Security Critical Communications	Awarded 2012[38]
	United Arab Emirates	EADS/Cassidian	Nedaa	Police, emergency services, and professional communications	Dubai, Sharjah, Ajman, Umm Al-Qaiwain, Ras Al-Khaimah, and Fujairah operational
		EADS/Cassidian	Polikom	Police, emergency services, and professional communications	Abu Dhabi
	Qatar	EADS/Cassidian		Ministry of Interior, Army, Police, Air Force Search and Rescue, EMS (Medical).	Initial use for the 15th Asian Games all games venues inclusive of transportation routes for "blue light" services, later extended to cover the State of Qatar, in use since 2006, national roll out complete by 2008. Known as Qatar Secure TETRA Radio System (QSTRS).
Latin America	Mexico	Rohde & Schwarz / Sepura	Mazatlán, Sinaloa Police & Emergency Services	Police, Emergency Services operational	Operational
South America	Brazil	Motorola	América Latina Logística	Railroad, communication and licensing.	Operational
		Teltronic / Motorola	Polícia Rodoviária Federal	Road patrol, country-wide	In operation / national roll-out in progress
Caribbean	Windward Islands and Leeward Islands	Rohill	Zenitel	Police, emergency services, oil and professional communications	Aruba, Bonaire, Curaçao, Sint Maarten, Saint Martin, Saba, Sint Eustatius, and Anguilla operational
Oceania	Australia	DAMM TetraFlex	BHP Billiton	Temco Smeltering Tasmania - Mining, Commercial, Safety, Security	Awarded 2011
		DAMM TetraFlex	Rio Tinting Mining group	Western Australia Mining	Awarded 2009[39]
		Damm TetraFlex	Origin Energy (APLNG)[40]	Kordia Solutions	Australian Pacific Project
		DAMM TetraFlex	Fortescue Metals group	Open Cut Mining	Awarded 2011[41]
		DAMM TetraFlex	Gorgon LNG Project, Chevron, Australia	Gas and Pipelines	Awarded 2011[42]
		Motorola	Zeon	Local government	Operational across Brisbane City Council, including the Brisbane State Emergency Service Unit
		DAMM TetraFlex	Australian Submarine Co	Military, Defence, Comms, Safety, Security	Awarded 2012
		Motorola	Zeon	Tertiary education	Used by Queensland University of Technology security staff.
		Sepura			Being used by several Mining Operations throughout Western Australia and Queensland - Terminals only - No Infrastructure.
	New Zealand	DAMM TetraFlex	BHP One Steel	Aluminium Smelter - Ore production - Safety, Security, Operations	Awarded 2012
		Kordia	KorKor	Airports	Used by Wellington International Airport, Air New Zealand
		Kordia	KorKor	Councils	Used by Hutt City, Auckland Transport
		Teltronic	Widarcom	Commercial Network launched 2008	Used by University of Auckland, Westpac

Technical details

Radio aspects

For its modulation TETRA, uses  ^π⁄₄ differential quadrature phase-shift keying. The symbol (baud) rate is 18,000 symbols per second, and each symbol maps to 2 bits, thus resulting in 36,000 bit/s gross.

As a form of phase shift keying is used to transmit data during each burst, it would seem reasonable to expect the transmit power to be constant. However it is not. This is because the sidebands, which are essentially a repetition of the data in the main carrier's modulation, are filtered off with a sharp filter so that unnecessary spectrum is not used up. This results in an amplitude modulation and is why TETRA requires linear amplifiers. The resulting ratio of peak to mean (RMS) power is 3.65 dB. If non-linear (or not-linear enough) amplifiers are used, the sidebands re-appear and cause interference on adjacent channels. Commonly used techniques for achieving the necessary linearity include Cartesian loops, and adaptive predistortion.

The base stations normally transmit continuously and (simultaneously) receive continuously from various mobiles on different carrier frequencies; hence the TETRA system is a frequency-division duplex (FDD) system. TETRA also uses FDMA/TDMA (see above) like GSM. The mobiles normally only transmit on 1 slot/4 and receive on 1 slot/4 (instead of 1 slot/8 for GSM).

Speech signals in TETRA are sampled at 8 kHz and then compressed with a vocoder using algebraic code-excited linear prediction (ACELP). This creates a data stream of 4.567 kbit/s. This data stream is error-protection encoded before transmission to allow correct decoding even in noisy (erroneous) channels. The data rate after coding is 7.2 kbit/s. The capacity of a single traffic slot when used 17/18 frames.

A single slot consists of 255 usable symbols, the remaining time is used up with synchronisation sequences and turning on/off, etc. A single frame consists of 4 slots, and a multiframe (whose duration is 1.02 seconds) consists of 18 frames. Hyperframes also exist, but are mostly used for providing synchronisation to encryption algorithms.

The downlink (i.e., the output of the base station) is normally a continuous transmission consisting of either specific communications with mobile(s), synchronisation or other general broadcasts. All slots are usually filled with a burst even if idle (continuous mode). Although the system uses 18 frames per second only 17 of these are used for traffic channels, with the 18th frame reserved for signalling, Short Data Service messages (like SMS in GSM) or synchronisation. The frame structure in TETRA (17.65 frames per second), consists of 18,000 symbols/s; 255 symbols/slot; 4 slots/frame, and is the cause of the perceived "amplitude modulation" at 17 Hz and is especially apparent in mobiles/portables which only transmit on one slot/4. They use the remaining three slots to switch frequency to receive a burst from the base station two slots later and then return to their transmit frequency (TDMA).

Radio frequencies

TETRA frequencies in South America

Number	Frequency pair (MHz)
	Band 1	Band 2
Emergency systems
1	380–383	390–393
2	383–385	393–395
Civil systems
1	410–420	420–430
2	870–876	915–921
3	450–460	460–470
4	385–390	395–399.9

TETRA frequencies in other countries

Country	Allocation	Frequency pairs (MHz)
France	Civilian/private	410–430
	Emergency services	380–400
Belgium	Emergency services/civilian	380–385, 390-395
Germany	Emergency services	380–385, 390–395, 406 - 410 for DMO
Ireland[43]	Civilian/private	385–389.9, 395–399.9
	Emergency services	380–385, 390–395
Italy	Emergency services / armed forces	380–390
	Civilian/private	462
Norway[44]	Emergency services	380–385, 390–395, 406.1–426, 870–876
South Africa	TBD	TBD
UK	Airwave	390.0125–394.9875, 380.0125–384.9875
	AirRadio	454, 464 or 460
Saudi Arabia		350–370, 380–395, 385–399.99, 410–430, 450–470, 870–921

Air interface encryption

To provide confidentiality the TETRA air interface is encrypted using one of the TETRA Encryption Algorithm (TEA) ciphers. The encryption provides confidentiality (protect against eavesdropping) as well as protection of signalling.

Currently 4 different ciphers are defined. These TEA ciphers should not be confused with the block cipher Tiny Encryption Algorithm. The TEA ciphers have different availability due to export and use restrictions. Few details are published concerning these proprietary ciphers. Riess^[45] mentions in early TETRA design documents that encryption should be done with a stream cipher, due to the property of not propagating transmission errors. Parkinson^[46] later confirms this and explains that TEA is a stream cipher with 80-bit keys. TEA1 and TEA4 provide basic level security, and are meant for commercial use.^[47] The TEA2 cipher is restricted to European public safety organisations. The TEA3 cipher is for situations where TEA2 is suitable but not available.^[48]

Additional information

• Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 7: Security^[49]

Cell selection

Cell re-selection (or hand-over) in images

This first representation demonstrates where the slow reselect threshold (SRT), the fast reselect threshold (FRT), and propagation delay exceed parameters are most likely to be. These are represented in association with the decaying radio carrier as the distance increases from the TETRA Base Station.

From this illustration, these SRT and FRT triggering points are associated to the decaying radio signal strength of the respective cell carriers. The thresholds are situated so that the cell reselection procedures occur on time and assure communication continuity for on-going communication calls.

Initial cell selection

The next diagram illustrates where a given TETRA radio cell initial selection. The initial cell selection is performed by procedures located in the MLE and in the MAC. When the cell selection is made, and possible registration is performed, the mobile station (MS) is said to be attached to the cell. The mobile is allowed to initially select any suitable cell that has a positive C1 value; i.e., the received signal level is greater than the minimum receive level for access parameter.

The initial cell selection procedure shall ensure that the MS selects a cell in which it can reliably decode downlink data (i.e., on a main control channel/MCCH), and which has a high probability of uplink communication. The minimum conditions that shall have to be met are that C1 > 0. Access to the network shall be conditional on the successful selection of a cell.

At mobile switch on, the mobile makes its initial cell selection of one of the base stations, which indicates the initial exchanges at activation.

• Refer to EN 300 392 2 16.3.1 Activation and control of underlying MLE Service
• Note 18.5.12 Minimum RX access level

The minimum receive access level information element shall indicate the minimum received signal level required at the SwMI in a cell, either the serving cell or a neighbour cell as defined in table 18.24.

Cell improvable

The next diagram illustrates where a given TETRA radio cell becomes improvable. The serving cell becomes improvable when the following occurs: the C1 of the serving cell is below the value defined in the radio network parameter cell reselection parameters, slow reselect threshold for a period of 5 seconds, and the C1 or C2 of a neighbour cell exceeds the C1 of the serving cell by the value defined in the radio network parameter cell reselection parameters, slow reselect hysteresis for a period of 5 seconds.

Cell usable

The next diagram illustrates where a given TETRA radio cell becomes usable. A neighbour cell becomes radio usable when the cell has a downlink radio connection of sufficient quality.

The following conditions must be met in order to declare a neighbour cell radio usable: The neighbour cell has a path loss parameter C1 or C2 that is, for a period of 5 seconds, greater than the fast reselect threshold plus the fast reselect threshold, and the service level provided by the neighbour cell is higher than that of the serving cell. No successful cell reselection shall have taken place within the previous 15 seconds unless MM requests a cell reselection. The MS-MLE shall check the criterion for serving cell relinquishment as often as one neighbour cell is scanned or monitored.

The following conditions will cause the MS to rate the neighbour cell to have higher service level than the current serving cell:

• The MS subscriber class is supported on the neighbour cell but not on the serving cell.
• The neighbour cell is a priority cell and the serving cell is not.
• The neighbour cell supports a service (that is, TETRA standard speech, packet data, or encryption) that is not supported by the serving cell and the MS requires that service to be available.
• The cell service level indicates that the neighbour cell is less loaded than the serving cell.

Cell relinquishable (abandonable)

The next diagram illustrates where a given TETRA radio cell becomes relinquishable (abandonable). The serving cell becomes relinquishable when the following occurs: the C1 of the serving cell is below the value defined in the radio network parameter cell reselection parameters, fast reselect threshold, for a period of 5 seconds, and the C1 or C2 of a neighbour cell exceeds the C1 of the serving cell by the value defined in the radio network parameter cell reselection parameters, fast reselect hysteresis, for a period of 5 seconds.

No successful cell reselection shall have taken place within the previous 15 seconds unless Mobility Management (MM) requests a cell reselection. The MS-MLE shall check the criterion for serving cell relinquishment as often as one neighbour cell is scanned or monitored.

Radio down-link failure

When the FRT threshold is breached, the MS is in a situation where it is essential to relinquish (or abandon) the serving cell and obtain another of at least usable quality. That is to say, the mobile station is aware that the radio signal is decaying rapidly, and must cell reselect rapidly, before communications are terminated because of radio link failure. When the mobile station radio-signal breaches the minimum receive level, the radio is no longer in a position to maintain acceptable communications for the user, and the radio link is broken.

Radio link failure: (C1 < 0). Using the suggested values, this would be satisfied with the serving cell level below −105 dBm. Cell reselection procedures are then activated in order to find a suitable radio base station.

Infrastructure TETRA parameters guide^{[lower-alpha 1]}

Coverage	Parameter	Distance (km)	Type of communication
City	< 4	< 8	Pedestrian/metro
Sub-urban	10–18	20–36	Bus/train
Countryside	18–31	36–62	Inter-regional train
In Air	> 32	> 64	In flight
↑ Data to be verified

Man-machine interface (MMI)

Virtual MMI for TETRA radio terminals

Any given TETRA radio terminal using Java (Java ME/CLDC) based technology, provides the end user with the communication rights necessary to fulfil his or her work role on any short duration assignment.

For dexterity, flexibility, and evolution ability, the public transportation radio engineering department, have chosen to use the open sources, Java language specification administered by Sun and the associated work groups in order to produce a transport application tool kit.

TETRA MMI

Service acquisition admits different authorised agents to establish communication channels between different services by calling the service identity, and without possessing the complete knowledge of the ISSI, GSSI, or any other TETRA related communication establishment numbering plan. Service acquisition is administered through a communication rights centralised service or roll allocation server, interfaced into the TETRA core network.

In summary, the TETRA MMI aims are to:

• Allow any given agent while in exercise, to exploit any given radio terminal without materiel constraint.
• Provide specific transportation application software to the end-user agents (service acquisition, fraud, and aggression control).

This transport application tool-kit has been produced successfully and with TETRA communication technology and assures for the public transport application requirements for the future mentioned hereafter.

The home (main) menu presents the end user with three possibilities:

1. Service acquisition,
2. Status SDS,
3. End-user parameters.

Service acquisition provides a means of virtually personalising the end user to any given radio terminal and onto TETRA network for the duration the end user conserves the terminal under his possession.

Status SDS provides the end user with a mechanism for generating a 440 Hz repeating tone that signals a fraud occurrence to members within the same (dynamic or static) Group Short Subscriber Identity (GSSI) or to a specific Individual Short Subscriber Identity (ISSI) for the duration of the assignment (an hour, a morning patrol or a given short period allocated to the assignment). The advantage being that each of the end users may attach themselves to any given terminal, and group for short durations without requiring any major reconfiguration by means of radio software programming tools. Similarly, the aggression feature functions, but with a higher tone frequency (880 Hz), and with a quicker repetitious nature, so to highlight the urgency of the alert.

The parameters tab provides an essential means to the terminal end-user allowing them to pre-configure the target (preprogrammed ISSI or GSSI ) destination communication number. With this pre-programmed destination number, the end-user shall liaise with the destination radio terminal or roll allocation server, and may communicate, in the group, or into a dedicated server to which the service acquisition requests are received, preprocessed, and ultimately dispatched though the TETRA core network. This simplifies the reconfiguration or recycling configuration process allowing flexibility on short assignments.

The parameters tab also provides a means of choosing between preselected tones to match the work group requirements for the purposes of fraud and aggression alerts. A possibility of selecting any given key available from the keypad to serve as an aggression or fraud quick key is also made possible though the transport application software tool kit. It is recommend to use the asterisk and the hash keys for the fraud and aggression quick keys respectively. For the fraud and aggression tones, it is also recommend to use 440 Hz slow repeating tone (blank space 500 milli-seconds) and 880 Hz fast repeating tone (blank space 250 milliseconds) respectively. The tone options are as follows: 440 Hz, 620 Hz, 880 Hz, and 1060 Hz.

The parameters page provides an aid or help menu and the last tab within parameters describes briefly the tool kit the version and the history of the transport application tool kit to date.

TETRA Enhanced Data Service (TEDS)

The TETRA Association, working with ETSI, developed the TEDS standard, a wideband data solution, which enhances TETRA with a much higher capacity and throughput for data. In addition to those provided by TETRA, TEDS uses a range of adaptive modulation schemes and a number of different carrier sizes from 25 kHz to 150 kHz. Initial implementations of TEDS will be in the existing TETRA radio spectrum, and will likely employ 50 kHz channel bandwidths as this enables an equivalent coverage footprint for voice and TEDS services. TEDS performance is optimised for wideband data rates, wide area coverage and spectrum efficiency.^[50]

Advances in DSP technology have led to the introduction of multi-carrier transmission standards employing QAM modulation. WiMAX, Wi-Fi and TEDS standards are part of this family.

Refer also to:

• JSR-118;
• Mobile Information Device Profile, JSR-37;
• Wireless Messaging API, JSR120;
• Connected Limited Device Configuration, JSR-139; and
• Technology for the Wireless Industry, JTWI-185.

See also

• Digital mobile radio, an TDMA digital radio standard from ETSI
• Digital private mobile radio, an FDMA digital radio standard from ETSI
• NXDN, a two-way FDMA digital radio protocol from Icom and JVC Kenwood
• P25, a TIA APCO standard
• TETRAPOL, (previously MATRA)

References

External links

• Report on the health effects of TETRA by NRPB
• TETRA in use by radio amateurs
• TETRA and Critical Communications Association (TCCA)

[[Category:Rail transport mobile telecommunications stand Tetra in Geary's 430.00MHZ 1525MHZ