This section is designed to help you to carry out your own assessment before investing in TETRA, whether this investment is as a potential user organisation, operator, manufacturer, supplier, applications developer or other type of investor.

To assist with this assessment a range of TETRA specific and TETRA related aspects are described in detail.  Included as part of these descriptions are the advantages and benefits relating to each subject area. 

For ease of description and understanding each subject area is provided with its own sub-section under the following headings.  Links to these subject areas can be achieved by either clicking the subject area highlighted below or by clicking the relevant subject area on the left hand menu.

• Markets & Applications
• Markets & Applications
• TETRA Standard
• Technology Benefits
• Key Services
• References

Markets & Applications
In this section the positioning of TETRA is described with regard to markets served and other technologies.  Also, the interface specifications used by Application Developers to enhance the capabilities of TETRA are described.  In addition, some of the applications available on TETRA that use these interfaces are listed. Besides these applications, TETRA specific applications such as Public Protection & Disaster Relief (PPDR) and operation in hazardous environments are covered.

TETRA Standard
The areas covered in this section relate to several specific and related aspects of the TETRA standard, which inherently provide numerous advantages and benefits. For example, benefits relating to the ETSI TETRA Standard itself and its use of Digital, Trunking and Time Division Multiple Access (TDMA) technologies. In addition, this section provides details on the planned evolution of the TETRA standard within the ETSI Technical Committee (TC) TETRA and factors indicating the expected longevity of TETRA.

Technology Benefits
The core technologies used in the TETRA standard, such as Digital, Trunking and Time Division Multiple Access (TDMA) provide a number of inherent advantages and benefits. This section describes these benefits and also provides a downloadable pdf document containing more detailed information.

Key Services
The services and facilities supported on TETRA are numerous (see "About TETRA" page). However, this section describes the key services and facilities that are specifically designed to meet traditional PMR user requirements.  Some of the key TETRA services and facilities described are those that cannot be adequately provided on other wireless communication technologies such as GSM and UMTS/3G.

References
This section provides a list of references relating to TETRA.

Markets
TETRA networks are already operational in all the traditional PMR market segments listed below:

• Public Safety
• Transportation
• Utilities
• Government
• Military
• PAMR
• Commercial & Industry
• Oil & Gas

By far the largest market is that of public safety, where the trend is for the deployment of nationwide networks shared by all public safety organisations for reasons of economics (sharing), autonomy of operation for routine communications and the ability to fully interoperate with other services during emergency situations and disasters. 

The transportation market is the next fastest growing market, especially for Mass Rapid Transport systems and major Airports.  Interestingly, TETRA is also used by the military for non-tactical operations, a market application not originally anticipated for TETRA.

Because TETRA has been specifically developed to serve traditional PMR users and is optimised for medium to high capacity applications by utilising Time Division Multiple Access (TDMA) technology, TETRA is also used for Public Access Mobile Radio (PAMR) applications.

The success and market uptake of TETRA has also created a strong base of application developers who are able to provide a wide variety of applications for use with TETRA.

TETRA Applications
An important advantage of the TETRA standard is that it has a number of open interface specifications that can be used by application developers to further enhance the capabilities of TETRA.  Similarly, manufacturers are able to provide (under license) details of their proprietary interface specifications in support of specific applications.  Figure 1 shows all the interfaces on TETRA, some of which can be used by application developers. 

Figure 1: TETRA Standard Interfaces

The interface specifications that are commonly used by application developers are described as follows.

Air Interfaces (1 & 2)
To utilise the air interface, application developers often use the Peripheral Equipment Interface (PEI) (described later) or a manufacturer specific interface on radio terminals for applications.

Peripheral Equipment Interface (4)
This interface standardises the connection of the radio terminal to an external device, and supports data transmission between applications resident in the device and the connected TETRA radio terminal. The PEI also supports certain elements of control within the radio terminal from the external device and/or applications such as:

• Alarm Reporting
• Telemetry
• Ticketing machines for Bus Transportation
• Bespoke control heads for train borne installations
• Automatic Vehicle Location (AVL)
• Mobile Data Terminals
• Fixed Mobile Remote Control Desktop Consoles
• Command & Control

Remote Dispatcher Interface (5)
As this interface has not been standardised only TETRA manufacturer specific interface specifications are available to support the many voice and data applications requiring access to TETRA infrastructures.

PSTN/ISDN/PABX (6)
This standardised interface enables TETRA to interface with the PSTN, the ISDN and/or PABXs as required by both user organisations and application developers.

Inter-System Interface (7)
This standardised Inter-System Interface (ISI) allows infrastructures supplied by different TETRA manufacturers to inter-operate with each other allowing interoperability between two or more networks.  There are two methods of interconnection in the standard, one covering information transfer using circuit mode and the other using packet mode.  Application developers are expected to utilise this interface when it becomes available on TETRA networks.

Network Management Interface (8)
As this interface has not been standardised only TETRA manufacturer specific interface specifications are available to support the many network management applications requiring access to TETRA networks.

Application developers
Because of the size and success of TETRA, as well as the many applications required by traditional PMR user organisations, there are a wide variety of applications available from numerous application providers. Further details can be found on the TETRA Association member’s page (members). Once the membership list has been accessed, use the left hand menu to link to application providers.

Other Applications
With the traditional PMR market segments TETRA is often used for specialist applications such as operation of terminals in Hazardous Environments and Public Protection & Disaster Relief (PPDR).  More information on these special applications can be found by clicking the highlighted links.

TETRA Standard

TETRA is an open standard developed by the European Telecommunications Standards Institute (ETSI).  The main purpose of the TETRA standard was to define a series of open interfaces, as well as services and facilities, in sufficient detail to enable independent manufacturers to develop infrastructure and terminal products that would fully interoperate with each other as well as meet the needs of traditional PMR user organisations.

The initial responsibility of ETSI Project TETRA (now known as ETSI Technical Committee (TC) TETRA) was to deliver as set of standards, under a mandate from the European Commission, for a Digital Trunked PMR communications system that could be deployed in Western Europe.  As well as producing these mandatory ETSI deliverables (now completed), TC TETRA’s responsibility was, and still is, to make sure that the portfolio of standards continue to be developed in accordance with user needs and priorities.

The technology solutions chosen to meet user requirements contained in the TETRA standards have been, and continue to be, developed primarily by well know and respected manufacturers who have been serving the PMR market with products and services for several decades.  This combined “Know How” ensures that optimum technology solutions are chosen to meet user requirements.  Details of manufacturers can be viewed on the member’s page of the TETRA Association by clicking on the left hand menu under core products.

Although the prime responsibility of ETSI is to develop standards for Europe, many of its standards are also adopted world-wide, as evidenced by the uptake of GSM, the first wireless technology standard to be developed by ETSI.  Similarly, TETRA has already been deployed in many regions and nations outside Europe, resulting in TETRA becoming a truly global standard.

There is no doubt that a proprietary technology solution can be brought to market in less time than a solution conforming to a recognised open standard.  However, large user organisations, especially those in the public sector, have recognised that some proprietary solutions can meet their needs but the ‘tie in’ to a single supplier can have significant disadvantages.  Even though there are some disadvantages, the main advantages and benefits of adopting an open standard are:

• Economies of scale provided by a large harmonised market served by several independent manufacturers and suppliers competing for the same business resulting in competitively priced solutions
• Second source security if existing suppliers exit the market
• Evolution (instead of revolution) of the technology standard ensuring longevity and good return on investment for both users and suppliers
• Choice of manufacturers for new products keeping prices down
• Greater choice of products for specialised applications
• Greater responsiveness to future needs by existing suppliers because of competition

Because there are several independent manufacturers of both TETRA network infrastructure and radio terminals all the benefits of standardisation listed also apply to the TETRA market.

Evolution & Longevity
The ETSI TETRA standard will continue to evolve beyond Release 1 and Release 2 to provide additional enhancements as driven by user needs, technology innovations and other parallel standard developments.  As a consequence, ETSI has no plans to develop a new technology standard for use by large traditional PMR user organisations.  Similarly, other technology standards being developed and/or available outside Europe offer little or no benefit over what TETRA already provides.

This planned evolution of TETRA can be appreciated when considering that traditional PMR user organisations will always require private PMR networks because public networks cannot adequately provide the required RF coverage, Grade of Service (GoS) during busy periods and high levels of reliability.  Besides these basic needs, public networks will not be able to provide the specialised voice services such as wide area fast call-set up all informed nets (group calls), Direct Mode Operation (DMO) and high levels of secure encryption for voice and data.

In summary, TETRA will evolve in a similar way to GSM, which evolved from providing a basic V+D “one to one” telephony service (via GSM II+, GPRS, EDGE, etc.) to UMTS/3G supporting powerful multimedia applications and High Speed Data.  Also, the focus and technology solution for Next Generation Networks (NGN) will primarily be for public networks.

Taking these previous factors into consideration and the fact that analogue MPT 1327 trunking networks are still being deployed across the world more than 28 years after the technology was first developed, TETRA networks are expected to be available for at least another 25 years, thereby ensuring a very good return on investment for user organisations as well as manufacturers and suppliers.

Technology Benefits

The core technologies used in the TETRA standard, such as Digital, Trunking and Time Division Multiple Access (TDMA) also provide a number of inherent advantages and benefits as follows: 

Digital
Nowadays, practically everything electronic uses digital technology and wireless communications are no exception.  Even though analogue FM PMR communications will remain a viable option for several years, digital radio provides relative advantages and disadvantages in the important performance areas of:

• Voice Quality
• RF Coverage
• Non-Voice Services
• Security
• Cost

Trunking
Trunking techniques have been used for many years in switched telephone networks.  The first trunked mobile radio communication systems were deployed as early the 70's in North America with proprietary signalling protocols and shortly afterwards in Europe using analogue MPT1327 technology. The main benefit of trunking is normally seen as spectrum efficiency, or more radio users per RF channel compared with a conventional radio channel for a given Grade of Service (GoS), brought about by the automatic and dynamic assignment of a small number of communication channels shared amongst a relatively large number of users. 

Because trunking systems support more radio users than conventional systems, national administrations actively support the deployment of trunking systems as this helps reduce pressure on meeting PMR spectrum demands.  However, from a radio users operational point of view, spectrum efficiency does not really mean anything. What users want is to solve all the operational problems associated with conventional PMR, yet still retain the simplicity of conventional open channel ‘all informed net’ operation.  The fundamental element of trunking that solves these conventional PMR problems is the use of a control channel. Table 1 below lists the operational problems of conventional PMR and also lists how the use of trunking solves these problems.

Table 1: Conventional PMR problems solved by Trunking

It is important to note that the operational simplicity of conventional PMR ‘all informed net’ talk group communications is still retained by employing fast call set-up “Push To Talk” (PTT) operation on radio terminals.

Additional Services and Facilities
As the control channel acts as a signalling communications link between the Trunking Controller and all mobile radio terminals operating on the system, the Trunking Controller knows the status of the system at any moment in time as well as its historic usage, which is stored in its memory.  For example, the Trunking Controller knows:

• The individual and group identity of all radio units registered on the system
• The individual identity and time radio units registered on the system
• The individual identity and time radio units de-registered from the system
• The individual and group identity, time and duration of all messages

With additional intelligence in both the radio terminals and the trunking controller the advantages and benefits of trunking can be increased.  For example, the length of the control channel signalling messages can be increased by a set amount to accommodate a variety of new services and facilities.  Also, the trunking controller can be programmed to handle calls in a variety of ways as required by the operator of the system. 

Time Division Multiple Access (TDMA)
A four time slot TDMA technology was adopted in TETRA as it offered the optimum solution to balance the cost of equipment with that of supporting the services and facilities required by user organisations for a medium to high capacity network providing single site local RF coverage and/or multiple site wide area RF coverage. 

RF Spectrum efficiency is a combination of three main factors being the occupied bandwidth per communication channel, the frequency re-use factor determined by the Carrier to Interference protection ratio C/I in dB’s and the trunking technology used.  As previously mentioned TETRA utilises the latest in trunking technology.  Also, the TDMA technology used in TETRA provides 4 independent communications channels in a 25 kHz RF bandwidth Channel, making it twice as efficient in occupied bandwidth terms as a traditional 12.5 kHz RF bandwidth FDMA channel.  Although FDMA technologies tend to have a better C/I performance than TDMA TETRA, the overall spectrum efficiency advantage lies with TETRA, especially for medium to high capacity networks.

Because of using TDMA technology, the cost and equipment space at base station sites can be significantly reduced compared with traditional FDMA technology trunking solutions. Another advantage of TDMA technology is that it enables new services and facilities to be supported with minimum cost.  Some examples are:

Higher Data Rates
The ‘laws of physics’ limits the maximum data rate in a given RF channel bandwidth.  Assuming the same modulation scheme, the wider the channel bandwidth the higher the data rate.  Because TDMA uses wider channels than FDMA, the combined data rate on a single RF carrier is greater.

Improved Data Throughput in Poor RF Signal Conditions
The net data rate in TDMA is better than FDMA in poor RF propagation conditions.  This is because Automatic Repeat Requests (ARQ’s) are required when received data is corrupted as a result of RF fading.  As TDMA terminal devices effectively operate in full duplex ARQ’s can be sent efficiently after each time slot transmission instead of waiting until the end of each voice transmission, as is usually the case with FDMA. 

Bandwidth on Demand
In TDMA any number of time slots up to the maximum limit of the technology being employed can be combined to increase data throughput as required for specific applications.

Concurrent Voice and Data
Because of the TDMA time slot structure it is possible to assign one time slot to support voice and the next time slot to support data in a two slot transmission from radio terminals.  This capability effectively allows a single radio terminal to concurrently transmit or receive voice and data at the same time.

Full duplex Voice Communications
TDMA technology inherently supports full duplex communications.  Although full duplex voice communications can be supported on FDMA systems the need for duplex operation requires RF screening between the transmitter and receiver and also a duplexer to allow single antenna working.  Because of this, duplex FDMA radio terminals are usually bulkier and more costly to produce than TDMA terminals, which do not need RF screening or antenna duplexers.

Additional Information
More information on the advantages and benefits of Digital, Trunking and FDMA technology is provided in the downloadable PDF document highlighted: Technology Benefits pdf

Key Services

In developing the TETRA standard to meet the needs of traditional PMR user organisations, numerous services and facilities have been provided.  Details of all the TETRA services and facilities can be found in the “About TETRA” Section under TETRA Release 1 and TETRA Release 2.  However, in this section it is considered appropriate to list some of the Key Services and Facilities, which clearly differentiate TETRA from other wireless technologies.

Key Voice Services and Facilities:           

• Group Call (commonly called ‘all in formed net’ and ‘talk group call’)
• Pre-Emptive Priority Call (Emergency Call)
• Call Retention
• Priority Call
• Busy Queuing
• Direct Mode Operation (DMO)
• Dynamic Group Number Assignment (DGNA)
• Ambience Listening
• Call Authorised by Dispatcher
• Area Selection
• Late Entry
• Voice Encryption

Group Call
This is probably the most basic voice service in TETRA but yet the most complex to support effectively and efficiently.  This is because group calls need to:

• Use simple “Push To Talk” operation to provide fast call set-up group communications
• Be operated and managed in particular ways to optimise network loading, some examples being:
• Operate in simplex
• Operate on a "preferred" site for optimum network loading
• Have a defined area of operation (Area selection)
• Have a very reliable call-set up signalling protocol to ensure all users in a group are connected together when a call is first initiated (call acknowledgment signalling is impractical for group calls)
• Have priority mechanisms to ensure that specified users in a wide area group call (spanning multiple base station sites) are connected together when a network is busy

It is this complexity needed to support group calls that makes public cellular networks unsuitable, simply because they were originally designed to support “One to One” calls, unlike TETRA which was primarily designed to support group calls at the outset.

Pre-emptive Priority Call
This call service, of which the highest priority is the emergency call, provides the highest uplink priority and highest priority access to network resources. If a network is busy, the lowest priority communication is dropped to handle the emergency call.  Unlike 911, 112 or 999 initiated public network emergency calls (which can also be supported on TETRA) the TETRA emergency call can be initiated by using a dedicated switch located on the terminal.  Activating the emergency call automatically alerts the affiliated control room dispatcher and other terminal users in that persons talk group.

Call Retention
This service protects selected radio terminal users from being forced off the network as a result of pre-emptive calls (emergency calls) during busy periods.  When emergency calls are supported in a network, it is essential that only a small number of radio terminal users are provided with this facility as the objective of retaining important calls during busy periods could be lost.

Priority Call
During network busy periods, that service allows access to network resources in order of user terminals call priority status.  As there are 16 levels of priority in TETRA, this service is very useful in providing different Grade of Service (GoS) levels (and tariff structures) during busy periods.  For example, front line officers would be provided with the highest priority levels in a Public Safety network to maintain the highest level of service access whilst routine users would be provided with lower priority levels.

Busy Queuing
In TETRA a queue is provided in the trunking controller during network busy periods to store and handle calls on a First In First Out (FIFO) basis in order of user priority level.  The advantage is that a user only has to initiate a call request once, knowing that even in busy periods the call will be automatically established once a traffic channel becomes free, thus reducing user stress and frustration when contending with other users on a busy network.

Direct Mode Operation (DMO)
Direct Mode Operation (DMO) provides the ability for TETRA radio terminals to communicate directly with each independent of the TETRA network infrastructure.  DMO is not new and has been a facility mandated and used by many traditional PMR user organisations for several decades.  The primary requirement for DMO has been brought about by the need to balance the RF Coverage, Grade of Service (GoS) and Reliability of a network with that of the network’s overall cost.  The requirement for DMO makes the use of public cellular networks unsuitable.

Dynamic Group Number Assignment (DGNA)
This service allows the creation of unique Groups of users to handle different communication needs and may also be used to group participants in an ongoing call.  This service is considered by many public safety organisations to be extremely useful in setting up a common talk group for incident communications.  For example, selected users from the Police, Fire and Ambulance could be brought together to manage a major emergency where close co-ordination between the three emergency services is required.  Similarly, DGNA is also considered useful for managing incidents by other user organisations such as Utilities and Transportation.

Ambience Listening
A Dispatcher may place a radio terminal into Ambience Listening mode without any indication being provided to the radio terminal user.  This remote controlled action allows the dispatcher to listen to background noises and conversations within range of the radio terminal’s microphone.  This is an important service to utilise for those persons transporting important, valuable and/or sensitive material that could be ‘hijack’ targets. Similarly, this is a useful service to have implemented in public service vehicles where a driver’s health and safety could be at risk. 

The number of user applications for the Ambience Listening service are numerous and in many cases application specific.  However, it is important to note that many users feel that this service invades a person’s privacy and for this reason only those users who need Ambience Listening as part of their work duties should be provided with this service. 

Call Authorised by Dispatcher
This services allows the dispatcher to verify call requests before calls are allowed to proceed.  This is a useful service to utilise when radio user discipline needs to be maintained.  This service also reduces the amount of radio traffic on a network as only essential work related calls are permitted.  However, the frequent need for all informed net group communications between terminal users and the time delay experienced in authorising calls can make this service unacceptable for some user organisations.

Area Selection
Area Selection defines areas of operation for users and can be chosen on a ‘call by call’ basis.  This service basically simulates the ability for a dispatcher to select different base stations to make a call as was possible in conventional networks.  This service also helps to improve network loading and overall spectrum efficiency by restricting the area of operation for selected group calls.

Late Entry
This service provides continuous call in progress updates to allow latecomers to join a communication channel.  This is not a service but an air interface feature that allows a trunked radio terminal to behave in a similar way to conventional PMR terminals.  For example, if a user turns on their TETRA terminal the control channel will automatically divert the user’s terminal to a talk group call, if a call is already in progress.  Similarly, if the user’s terminal has been outside radio coverage, for example in a tunnel, the control channel will also divert the user’s terminal to a talk group call assuming a call is already in progress.

Voice Encryption
The TETRA standard supports a number of over the air TETRA Encryption Algorithms (TEA’s), the differences being the types of users who are permitted to use them.  The main benefit of over the air encryption is that it can be implemented as software within radio terminals and base station equipment, instead of using encryption modules, which consume space and increase cost.  The TETRA standard also supports ‘end to end’ encryption using a variety of other encryption algorithms as deemed necessary by national security organisations.

References

This section will list references made in the ‘Why TETRA’ section as it expands with more information.  Where appropriate, web site links will be provided to the reference source.

References
TETRA Standard: Details of the latest published TETRA standards can be found at: http://pda.etsi.org/pda: