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TETRA Terrestrial trunked radio
Joe Nielson
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outline Radio Terminology/Basics What is “trunked radio” TETRA
Technology Standards Features TETRA today
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Radio terminology Base Station – Tower site “repeater” radio
Portable Radio – Hand held, lower power, when compared to Mobile Mobile Radio – High power when compared to portable radio (larger antenna) PMR – Professional Mobile Radio, radio systems that are used by public safety, and other organizations that use the above equipment. Base station is used to re-transmit messages across the known radio network to other registered users Portable radio is the walkie-talkie style used for its small size Mobile radio is the kind in a squad car or mobile vehicle, higher power and a larger antenna Professional (Private) Mobile Radio – radio users who need large coverage areas, instant communications
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radio basics The PMR market requires constant reliable communication and needs to allow for capacity increases during major incidents This makes it necessary to have tower sites to increase the range of communication for portable and mobile radios Along the M5 motorway in England Cannot have “no service” areas or dropped calls High Congestion, service almost unusable Cannot be in control of tower sites
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Radio basics A radio channel is a single band of frequency that can successfully deliver radio communications Either voice or data The size of the channel, or bandwidth is determined by the channels frequency tolerance and the type of transmission Cannot have channels interfering with each other Channel – a defined frequency used for a single line or channel of communication Bandwidth – the amount of range that the defined frequency is allowed to travel into
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bandwidth Ex: Center frequency = 150 kHz (f0)
bandwidth allocation = 50 kHz Then the 150 kHz frequency cannot be modulated above 175 (f2) kHz, or below 125 (f1) kHz
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Radio basics The channel is identified by a distinct frequency, and has to be modulated in order to transport a message across the channel Some types are frequency, amplitude, phase modulation and pi/4 DQPSK (Differential Quaternary Phase Shift Keying) Due to technology improvements, it is now possible to have the same amount of channels with less bandwidth If someone were to purchase a frequency, the frequency purchased would be the “center” frequency. Frequencies can be purchased through periodic auctions put on by the FCC Example: AM radio stations typically have better quality than FM stations 50 years ago only VHF band of spectrum was usable for PMR users due to unstable hardware
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Spectrum overview TETRA in Europe - 380-385/390-395 MHz
The radio spectrum is regulated by the FCC and has well-defined rules for bandwidth utilization. i.e. how efficient a radio system uses the spectrum that it has available TETRA in Europe / MHz Asia Pacific and South America: frequencies // MHz Able to operate between 300 to 1000 MHz
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Analog vs digital Digital systems use binary numbers and have to encode and decode a voice signal by using a voice codec The voice signal is translated in a way so that it best represents a voice signal in the codecs reference table Since something like background noise cannot be translated in the reference table, it makes digital systems good at filtering background noise CODEC = voice coder/decoder
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Analog vs digital Threshold = point at which communication is lost Note: the digital voice quality is significantly higher for the most part when compared to analog Many other factors can determine the voice quality such as antenna spacing, transmitted RF power, receiver sensitivity,… Note: Just for an overall picture, other factors can effect the voice quality as well
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Analog vs digital Security is easier to implement on a digital system because encryption algorithms are generally digital themselves Non-voice services in an analog system would need an entirely separate method, whereas it can be built into digital Digital radios are much more expensive Really depends on the type of user and what they need The best security algorithms are digital Digital radios are currently more expensive but will change over time A small police department of 4 officers will not need a multi-million dollar communications system
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Conventional radio Only a single channel of frequency is used for each communication path - predetermined Not very efficient, especially for critical communications A pair of frequencies can be used in the same way, (one for North, one for south) Manual switching One communication channel is used and it is predetermined what frequency will be used to transmit the message If the channel is being used and someone else wants to use it, they have to wait for it to open up
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Conventional radio The frequency carrier itself defines who the message gets sent out to Doesn’t mean a single radio can be programmed to listen to all channels or have all of them programmed in their radio…
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Trunked radio Multiple channels are pooled together and used as a shared resource A trunking controller is used to locate an open channel in the pool of channels and uses it to repeat the message across the system Unknown what frequency will be used A talkgroup is used to keep track of who needs to hear what messages Why the name “Trunked”? The term trunking refers back to old telephone networks, the connections between them were thick hard lines, and were often covered in lead to reduce interference, thus resembling an elephant trunk It is unknown at the time the button is pressed what frequency the message will be sent out on
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Trunked radio Fire: Using channel 1, only Talk Group 1 will hear it
Simultaneously Police sends a message Trunking controller automatically allocates another channel for TG 2 to use -Could be a different channel every time -Each time a user is essentially sending a request to use the system, vs. the actual message In a trunking system, it is unknown at call set-up time which exact frequency will be used. The trunking controller picks an available channel and then assigns the talk group to it so the message can retransmitted In most situations of public safety systems, most radios have all talk groups programmed into their radios
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Trunking benefits The main advantage to trunking is that it factors in that not everyone will need channel access at the same time Therefore, fewer channels are required for the same amount of users Likewise, with the same number of radio channels, more users can be brought in A voter can seamlessly transfer an ongoing call to another site if a user is mobile and suddenly goes out of range of a certain site
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Trunking benefits TETRA at 4 channels per 25 kHz bandwidth
TETRA system utilizing a 25 kHz bandwidth has 4 communication channels, considered narrowband by FCC TETRA at 4 channels per 25 kHz bandwidth
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Trunking benefits Trunking does not increase the amount of simultaneous conversations per channel, it only utilizes the channels more efficiently If a channel goes down, it can be (almost) seamlessly transferred to another channel
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Trunking downfalls Problems with the channel controller could mean problems for everyone A slightly longer delay for communication set up Trunking radios are more expensive Central controller controls everything, fix = have a backup! Delay caused by the controller searching for an available channel, Not by much, hardly noticed Expensive due to the lack of competition
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Tetra introduction Schengen Agreement An agreement to lessen
TETRA is an open standard developed by the European Telecommunications Standards Institute It was developed for the PMR market in order to solve the problems of congestion and a growing demand for data services Schengen Agreement An agreement to lessen border controls between distinct countries (1985) TETRA was originally designed to solve the Schengen agreement which sought to have cross-border communications between certain European countries and also allow citizens to cross borders more freely
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Tetra introduction TETRA is in use throughout the world and is considered the first truly open digital private mobile radio standard The openness allows different equipment from different manufacturers to be able to fully communicate with each other. It is currently not allowed in the US for multiple reasons, some of which there is debate over, but will be allowed soon Others: P25, DMR Other examples in the United States are: P25 – a digital trunking method (expensive), DMR – not fully functional yet Opposite example: Apple products, only Apple software runs on Apple hardware
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Tetra introduction TETRA is currently not fully compliant with certain FCC rules dealing with frequency allocation The TETRA Association has already requested that the rules be waived and the waivers are currently in progress with some of them already waived In the future it is likely that the FCC will follow the waivers with a rule-making process to allow TETRA equipment in the US permanently
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Tetra introduction Motorola Inc. has many intellectual property rights on TETRA due to the companies effort in developing the standard The company claims that it would support the use of TETRA in the US, if there is evidence that enough people have a need for it There are many in the industry that believe Motorola is protecting its P25 business
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Tetra technology TETRA uses Time Division Multiple Access (TDMA) in order to increase the number of channels on a given frequency It can divide one 25 kHz channel into four separate communication channels This creates both a cost savings in frequency needed and the amount of hardware needed per system
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Tetra technology 1 time slot = 14.167 ms
1 TDMA frame = 4 time slots = ms 1 muliframe = 18 TDMA frames = 1.02 s Circuit mode compresses the data frames down to 17 to allow the 18th to be a control frame
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Tetra technology Channels in TETRA can be designated for any combination of voice and data
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Tetra technology pi/4 DQPSK – pi/4 Differential Quaternary Phase Shift Keying is what TETRA uses for its common TETRA V+D and TEDS control channel Phase shift keying relies on shifts of the phase of the signal to transmit data, versus shifting the frequency or amplitude In pi/4 there are four possible phase shifts: -3π/4, +3π/4, +π/4, -π/4
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Tetra technology Example, not actually what TETRA uses
Bit value Amount of shift 00 None /4 /2 /4 Correct Pattern:
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Tetra technology Quadrature Amplitude Modulation (QAM) is a combination of amplitude modulation and PSK If two different amplitudes are used, along with 4 different phases, that equates to a total of 8 different possible combinations QAM is used in Release 2 where TEDS is defined
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Tetra technology Bit value Amplitude Phase shift 000 1 None 001 2 010
1/4 011 100 1/2 101 110 3/4 111 Each wave gets shifted from the wave before it
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Tetra technology Also require better signal to noise ratio, and error rates also increase In general, the higher order modulations provide higher data rates, but are more prone to error ** The three different levels of 64-QAM refer to the amount of interference protection against noise used
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Tetra technology 16-QAM equates to 16 possible bit values: 0000, 0001 …. 1110, 1111 64-QAM equates to 64 possible bit values: , , … The higher the amount of possible values, the more chance there is for error since the shifts are closer together QoS attributes can also be negotiated such as; throughput, delay, priority and reliability.
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Tetra technology the decision boundaries of lower order schemes are much larger The difference in phase is known as “phase jitter”
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Tetra standards TETRA Release 1:
The original release of TETRA occurred, previously known as the TETRA V & D or voice and data. Defined the original functionality such as the interfaces, voice and basic (slow) data services < 20 k bit/s throughput…
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Tetra Standards DMO – Direct Mode Operation AIR IF – Air Interface
TEI – Terminal Equipment Interface ISI – Inter-System Interface AIR IF, and DMO – most complicated and most complex TEI- facilitates the independent development of mobile data applications.
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Tetra Standards Also can interface to:
PSTN/ISDN/PABX, WAN/LAN, and internet
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Tetra Voice and data Group Call – Not unique to TETRA
TETRA provides very fast call set-up time of 300 ms This would be very difficult to do on a cellular network, since they were primarily designed for one-to-one calls Pre-Emptive Priority Call (Emergency Call) Call Retention – protects users from being forced off the network Pre-Emptive Priority Call – In emergency situations, a user can push a predefined button to give them highest priority access to the network resources. It will even drop current calls on the network if need be.
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Tetra Voice and data Priority Call – allows 16 different resource access levels Dynamic Group Number Assignment (DGNA) – creating talkgroups “on the fly” Ambience Listening Busy Queuing Full-Duplex phone calls: Basically anything that you can do with a regular phone – caller ID, block call, call forward, call hold… Eliminates the need for a cell phone Priority Call – Provides different GoS to different users. Ex: Front-line officers DGNA – Ex. Creating a group for select police, fire and EMS users during a major incident where close coordination is needed Ambience Listening – ability to place a radio in listen-only mode, without any notification that it is in the mode. Also brings up questions of invasion on privacy. Busy Queuing – If the network is at full capacity, then a new call will be placed in a queue to later have the request fulfilled in a FIFO manner
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Tetra Voice and data Data Services :
Short Data Service – Implemented on the TETRA control channel, only can support up to 256 bytes per message Packet Data Service – Both connection-oriented and connection-less configurations Data Rate (bit/s) No. Time Slots High Protection* Protected Not Protected 1 2400 4800 7200 2 9600 14400 3 21600 4 19200 28800 TETRA also supports Data services on top of the voice services. *Protection – protection against data corruption due to noise, or other environmental factors
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Why not use gsm or 3g? Many organizations are looking at using cellular based services due to the data rates available Technology Unit Narrow Band Wide Band Broadband TETRA 1 kbits/s 7.2 to 28.8 TETRA 2 28.8 to 384+ GSM 9.6 GPRS 115 EDGE 144 to 384 3G 384 to 2,000 One thing that many PMR users are considering is switcing over to a cellular service. From the table above it looks like a viable option, but data rates are on the lower priority side of things with most PMR users.
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Why not use gsm or 3g? Service TETRA GSM 3G Group call yes no No
Broadcast call End-to-End encryption DMO Gateways Transmit Inhibit Simultaneous V & D Receive only Access Priority Late Entry Discreet Listening Service TETRA GSM 3G Priority call yes no Ambience listening No Multiple key encryption Full duplex telephony Over air encryption Long range capability Area selection Other services, like the ones shown below are much more useful and important to most PMR users. Most companies or agencies do not want their employees to have the capabilities to go on facebook anyway. From the above charts it is apparent that TETRA offers the key services that PMR users want.
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Why not use gsm or 3g? TETRA was designed for PMR use, by PMR users
Cellular technologies were designed for one-one-communication primarily and therefore do not offer the services needed by PMR users The higher data rates offered are not of interest to the PMR market Other features are more important: Call setup time, (6-9 seconds versus 300 ms) Reliability, security, must be highly available
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Tetra DMO Direct Mode Operation – Allowing TETRA radio terminals to communicate directly with one another while outside of the TETRA network Allows for local communications when the entire group does not need to be notified - “Back-to-Back mode” Allows for Trunked Mode Operation extension or “Gateway mode”, an extension back to the network to out-of-range terminals
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Tetra DMO “Back-to-Back” – normal DMO operation (nearby communications) “Gateway Mode” – special equipment can provide communications between both networks “Dual Watch” – Also allows communication between both networks
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TETRA ISI Allows a TETRA terminal to access another TETRA network other than the one it is registered on Assignment of talk groups needs to be defined Billing of telephony calls Encryption schemes used must be released No need for extra hardware Only a few systems currently using ISI Talk Groups – does the roaming user still need to communicate with the original talk groups? Telephony calls – who should be billed? Releasing the encryption scheme becomes a security risk
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TETRA Release 2 Work started around 1999, and was released at the end of 2005 High Speed data with rates almost 10 times greater than that of Release 1 Expected rates of 30 – 400 kbits/s More voice codecs in order to improve communications with cellular systems Fully compatible with TETRA Release 1 TMO range extension Released around end of 2005, started in 1999
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TETRA Security 3 methods: Supports four AIE Algorithms
Authentication Used to make sure both the radio is allowed, and if the network is trusted Air Interface Encryption (AIE) Protects against eavesdropping End to End encryption Supports four AIE Algorithms TEA1, 2, 3, 4 which each have a specific area of use Enabling/Disabling of terminals
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TETRA Data applications
Custom Applications can be created for a TETRA system using SDS, Packet data service, or TEDS No generic “TETRA SDK” – systems differ on terminal and network side a lot The SDS on TETRA primarily would only be useful for status messaging or Automatic Vehicle Location, (AVL) due to the low data rate
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Tetra Data applications
The Packet data service allows for things such as: Database lookup, imaging, or slow scan video. High speed data could be used for things such as fingerprinting or real time video. The wide variety of data services offered by TETRA, along with over 350 companies offering solutions, make it an ideal choice for data applications in the PMR market
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Tetra users BMW’s plant in Dingolfing, Germany
Had multiple analog systems replaced by a single TETRA system SDS message is sent whenever there is a fault on the production line If no one accepts, the system re-sends the message up to three times, and then gets transferred to a manager If more than one person accepts, only one of them will be given instructions to attend the fault - If no team representative is able to accept, the system resends the SDS up to three times, after which the request is escalated to a supervisor who then makes the final decision with regards to job allocation. - If more than one operative accepts the repair job, only one of them will be automatically selected to receive instructions to attend the fault. -
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Tetra users 2008 Beijing Olympics Petrom S.A. Petrobrazi Oil Refinery
Handled 1.6 million calls a day, Asia's largest TETRA network 90,000 users Petrom S.A. Petrobrazi Oil Refinery Around 2,000 employees, using SDS for tracking of employees Doubled the previous systems capacity using the same amount of spectrum New system is also much more scalable
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Tetra in the us NYC Transit carried out a TETRA pilot in 2011, along with NJ Transit in 2010 Both pilots confirmed that TETRA meets and exceeds their requirements for voice and data communications TETRA pilot in Wisconsin Nielson Communications Inc. Green Bay, WI is comparing their current analog system to a TETRA system
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Tetra pilot in US Blue = Best Red = Weak Black = No signal
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Tetra pilot in US Connected the TETRA system to an IP-based phone system for full duplex phone calls, also had AVL capabilities In summary the results of signal coverage compared to other systems is about the same as TETRA Loud background noise is filtered out very well on a TETRA system Easy radio interface to train and use Busted the myth of needing more hardware for a TETRA system Clear audio and voice even in noisy environments Radio interfaces resemble a cell phone
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Tetra current market As of 2010, total TETRA contracts has grown to 465 TETRA is operating in over 125 countries Over the next four years, the Compound Annual Growth Rate of TETRA is expected to grow by 15%
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Tetra current market 2010 a record year for terminal shipments (IMS analysis) Deployment of new networks up 6% and extensions up 8% Source: TETRA MoU
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Tetra current market Source: TETRA MoU
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Video Examples
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Tetra summary Trunking Benefits TDMA benefits
Spectrum utilization, security, better coverage TDMA benefits less hardware = less cost, concurrent voice and data Unique TETRA services; ISI, DMO, security features, DGNA, full duplex phone calls.. Etc Increased competition due to openness means cheaper products and solutions
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Questions
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Sources References Is TETRA on its way to North America? - Urgent Communications article. (n.d.). Urgent Communications magazine online | Formerly MRT magazine. Retrieved March 25, 2012, from Phase Shift Keying. (n.d.). Home - University of Delaware Dept. of Physics & Astronomy. Retrieved March 27, 2012, from Unrequited love | Many in the U.S. are smitten with TETRA, and they don’t understand why they can’t have it. (n.d.). Urgent Communications magazine online | Formerly MRT magazine. Retrieved March 25, 2012, from Signal Harbor. (2005). Understanding trunking. Retrieved from Hayes, W. (2003, May 29). What is trunking. Retrieved from
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Sources TETRA Association. (n.d.). Tetra. Retrieved from TETRA Association. (2006, January). Tetra technology advantages & benefits. Retrieved from Benefits.pdf Krishna, S. (2012, April 12). Non coherent demodulation of pi/4 dqpsk (tetra). Retrieved from Barrus, J. (2012, March 5). Fresh ideas in two-way communications. Retrieved from Charan, L. (2006). Complex technology made real. Retrieved from ETSI. (2007, October). Etsi TR v Retrieved from University of California, Berkeley. (Producer). (2000). The radio spectrum. [Print Photo]. Retrieved from Ascom. (n.d.). Tetra - terrestrial trunked radio. Retrieved from
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