Standardized by ETSI, TETRA shares many basic technological elements with cellular mobile telephony, but with added unique mission-critical features such as instant connection, push-to-talk, direct mode, and group calling. TETRA is constantly evolving, with a rich array of additional capabilities to meet the growing needs of its users. Just as cellular systems have developed to add higher-speed data services, TETRA has evolved with the introduction of TEDS (TETRA Enhanced Data Service), providing a significant increase in broadband data capacity.
During this time, cellular systems have moved through two generational shifts, from 2G to 3G/HSDPA and now to 4G/LTE. With each step, data speeds have increased and are now much faster than were possible with TETRA, even with TEDS. Although nothing on the horizon can compete with TETRA voice services, some operators and potential TETRA customers are wondering if they should migrate to LTE for broadband services now.

This article analyzes the potential of migrating to a broadband data service that will still provide the necessary capabilities for public safety and critical users, working with TETRA's unparalleled voice capabilities.

Essential Mission-Critical Communications Capabilities - Back to Basics
The specification for the TETRA standard was developed under a set of fundamental requirements that still hold true today:

• Prioritization and preference, allowing the most important calls to be connected during times of congestion.

• Emergency calls, prioritized over other traffic, are made even if the network is busy, and controllers are automatically alerted.
• Wide area, "fast-call" configuration, and "network-informed" group calls.
• Direct Mode Operation (DMO) enabling back-to-back communication between network-independent radio terminals.
• High level of voice encryption to meet the security needs of public safety organizations.
• Full-duplex voice for PABX and PSTN telephony communications.

Furthermore, TETRA networks are specified to operate at frequencies that allow for long-range coverage for base stations. They are designed to provide high levels of coverage and availability, and include much higher levels of security than public cellular networks.

Public Cellular Performance in Emergency Situations:
Public cellular mobile networks experience considerable stress during emergencies, or even during significant incidents such as traffic jams on busy highways. Numerous examples of network congestion exist during these times. The most concerning examples occur during major emergencies, when public safety and other critical user communications are most critical. Furthermore, well-documented local and regional outages of public networks due to technical issues continue to occur. This is why dedicated public safety and other mission-critical networks are considered essential. Many public safety officers and other critical personnel are known to use the public mobile communications system during their workday. Engineers, detectives, and senior staff use mobile phones, and with 3G or even 4G available in some areas, this works well for voice and data calls under normal circumstances. However, during critical moments, the networks cannot provide
the resilience, speed, and special features truly essential for emergency responders to perform their jobs effectively. Time and again, TETRA demonstrates its ability to connect the initial response in high-stress environments when they have to perform to the limit of their capacity.

Built for the Environment:
TETRA terminals, whether handheld or vehicle-mounted, are designed to standards far exceeding those used in the development of consumer mobile phones. All "standard" TETRA terminals are rugged and durable. Furthermore, there is a range of enhanced models designed to continue working in the most challenging situations, including fire, flood, and dusty and gaseous environments.
TETRA terminals continue to operate well beyond the normal lifespan of a mobile phone, ensuring an excellent return on investment. A wide range of accessories enhances these radios for different types of end users. These accessories are designed to operate successfully in the harsh environments encountered daily, where cell phones would not survive.
The emergency button is now a standard feature on most TETRA radios. This immediately alerts colleagues and supervisory personnel if a user is in distress. The GPS receiver automatically informs control room personnel of the individual's location, providing greater user safety.
Radios are constantly being enhanced with additional capabilities, including secure Bluetooth, web browsers, larger screens, and cameras to increase user efficiency and effectiveness.
Bluetooth offers exciting possibilities for connecting the TETRA radio to other devices, such as PDAs, laptops, or even body sensors that monitor vital signs.

At all times, the reliable and secure TETRA radio system ensures that communications are maintained under the most severe conditions.

Working together, the best of both worlds.
A combination of TETRA and LTE can be considered a medium-term migration strategy for many mission-critical users. This solution could be designed using either the public LTE solutions being deployed in many countries worldwide or a dedicated LTE data network for mission-critical users. There are advantages and disadvantages to both, which are discussed in the TCCA article: "Mobile Broadband for Critical Communications Users - A review of options for delivering Mission Critical Solutions." This document can be downloaded from the TCCA website at:
www.tandcca.com/Library/Documents/Broadband/MCMBB%20Delivery%20Options%20v1.0.pdf

In both cases, TETRA remains the "safety net" to ensure the availability of resilient and reliable voice and data communications under all conditions.

TETRA and Public LTE:
This can be an economically attractive solution, leveraging the investments made by public companies in their commercial networks while continuing to utilize existing TETRA infrastructure. Both networks could "do what they do best," with LTE offering fast data service in densely populated urban areas, where it is likely to be deployed more quickly. Because TETRA provides a high level of geographic coverage, the public operator will not need to replicate this coverage and may be able to offer service to users at a similar price point to that offered to the general public. TETRA will continue to offer secure and resilient voice and some data services over a wide area. It is worth noting that upgrading a TETRA network to TEDS will provide increased data speeds and, to a large extent, deliver many of the applications offered by LTE in a conveniently modified form. This option is the natural first step in a migration path for mission-critical communications.
One variation of this approach would be to establish an MVNO (Mobile Virtual Network Operator), which would contract with critical service agencies and the public operator(s) to ensure a high level of LTE service availability, even during times of congestion and/or emergency. The MVNO would be able to integrate services such as location tracking, device management, and command and control over both LTE and TETRA networks.

TETRA and Private LTE:
In this scenario, a separate LTE network is deployed on its own frequencies and managed entirely separately from the public LTE network. This would also work alongside TETRA until nationwide coverage is achieved and the features integrated into TETRA are fully replicated in LTE. Since both will take many years (and significant cost) to achieve, this "overlap" will take many years to materialize. This solution will require frequency allocation by regulators in each administration and considerable investment unless LTE coverage is limited to specific high-value areas.
On the positive side, this system could maintain the high levels of security that some TETRA operators insist on, and service integration could be simpler.
This option could be a second step after the TETRA/Public LTE step.
The TETRA-only network without a base layer faces significant challenges at present. Public LTE networks might be required to offer guaranteed service levels, coverage, and resilience, which will be costly and difficult for commercial operators to provide. These unique features in TETRA, which mission-critical users rely on—such as group calling and direct mode—will take years to replicate in LTE. While these have emerged as working elements of standards bodies, they remain quiet, a long way from becoming a reality for users.
Critical communications users need a network to meet their needs now. In the immediate future, that network is TETRA.

Proprietary Solutions:
A small number of manufacturers are proposing broadband solutions that are positioning themselves as suitable for public safety and critical communications. These solutions will face significant adoption challenges. Operators choosing these technologies will need to consider the risks of adopting non-standardized solutions and the potential long-term price penalties resulting from being locked into a single manufacturer. History shows that standards-based technologies force manufacturers to compete and innovate, keep prices under control, and foster a rich ecosystem of products, applications, and services. TETRA's success is based on the industry-leading interoperability testing program developed by the TCCA in conjunction with all leading manufacturers. This program ensures that all certified products and systems work together seamlessly, regardless of the number of vendors contributing equipment to a network.

Summary:
It is clear that TETRA continues to meet all the voice and data requirements for many existing and future critical communications users. This will remain the case for many years to come.
A migration path toward public safety and critical broadband services can begin today by combining TETRA/TEDS and commercial LTE. This will provide mission-critical voice and data services, as well as existing voice and broadband services, to meet the needs of critical users.

Once broadband services become established as essential elements of daily operations, the pressure to ensure constant availability, even during critical emergencies, will lead to a need for guaranteed access and high-quality service.
These services are likely to require dedicated spectrum to ensure that public safety and other critical communications users continue to have access, even during periods of high network load, on both publicly provided and privately owned LTE networks. Since LTE standards do not yet include the TETRA features essential for critical communications users, even a private LTE network will have to work alongside TETRA for many years to come.

More information
TCCA website http://www.tandcca.com/assoc/page/18100
"The Strategic Case for Mission Critical Broadband"
http://www.tandcca.com/Library/Documents/Broadband/MCMBB%20Strategic%20Case%20v1_0.pdf
"Mission Critical Mobile Broadband: Practical standardization and roadmap considerations" http://www.tandcca.com/Library/Documents/CCBGMissionCriticalMobileBroadbandwhitepaper2013.pdf