Mobile networking technology, including push-to-talk (PTT), has never been more critical. From first-responder communications during an emergency to essential field operations management for transportation systems, utilities, farming or sports arenas, reliable connectivity for voice, even in remote or harsh environments, can be the difference between mission success and failure – sometimes, between life or death. 

The standard approach for PTT has been Land Mobile Radio (LMR) systems, either simple analog channels or computer-controlled trunked systems. However, with the emergence of new 4G LTE mobile broadband technology capabilities and the launch of the First Responder Network Authority (FirstNet™), a dedicated 4G LTE network for first responders in the United States, many public safety and industry verticals are increasingly considering if and how they might want to begin using LTE for mission-critical (MC) or business-critical (BC) communications. Making this determination regarding what infrastructure they should use for MC or BC communications – one that will serve both immediate and future needs – demands a careful assessment of evolving requirements, current and emerging technologies, the solutions on the market and the vendors supporting them, and, of course, costs.

The first step in this process is understanding the requirements, and the first question to ask: do the objectives of the operation call for mission-critical (MC) or business-critical (BC) communications support? 

Mission-Critical Communications

MC communications typically refers to communications operations – largely push-to-talk – supporting operations involving high risk to life and property. In short, the public safety use cases. Firefighters battling a blaze that presents an immediate danger to life and health (IDLH) environment – to citizens or the firefighters themselves – require a communications infrastructure that works without failure. A paramedic assisting a victim of violence or a car accident must have constant, reliable communications both at the scene – even in remote rural locations where cell phone service may not make business sense – and during transport in an ambulance to a medical facility.

This is why the MC communications ecosystem used for LMR is built using public safety-grade infrastructure. For example, MC LMR Base stations are hardened against failure from high winds or heavy ice loads, shielded from vandals and other bad actors and supplied with power generation to handle prolonged loss of the electric grid. In addition, this infrastructure includes multiple, independent transport links to the network, so if, for example, a copper link is severed, a microwave link can immediately take over.

An MC communications ecosystem also has key architectural requirements, such as support for multiple levels of fault tolerance. For example, if the network fails, despite all the hardening, the radios must still continue to operate. This is achieved through a device-to-device communications capability build into the devices themselves. Known around the world as “Talk Around,” “Direct Mode” or “Back-to-Back,” this capability enables radios within a relatively short distance to communicate with each other even when no network connection is available. 

This is an essential capability in firefighting, for example, where it is common for firefighters to find themselves in deep areas of a building where a connection to a radio tower is impossible. When this happens, the firefighting team can simply switch their radios to the Talk Around frequency and keep communicating. Meanwhile, a team member outside the building can remain on the network and relay information as necessary.

Business-Critical Communications

A BC communications ecosystem shares similarities with the MC ecosystem. These are typically trunked systems and generally use the Digital Mobile Radio (DMR) protocol, which is less expensive than a system based on the hardened mission-critical P25 or TETRA protocols. They also provide a Talk Around capability to communicate if the network goes down.

But these systems lack some of the resilience and robustness built into the MC standards and deployments. Instead of relying on multiple hardened sites, there may be just one site providing service where the BC communications are needed, such as at an airport or sports arena. The towers and hand-held devices may not be as full-featured and fully hardened, leaving the system more vulnerable to failure. This means each business must weigh the cost of potential downtime against the cost of a more expensive P25 or TETRA-based, MC system.

The Emergence of LTE to Support MC and BC Voice Communications

Mission-critical LTE (MC-LTE) has been made possible by advancements in 3GPP Releases 12 and 13 that improve on the quality of service (QoS) mechanisms that have supported LTE voice calls and provide new capabilities. Network traffic is now graded to ensure that if there is network congestion due to overutilization by users, a “scheduler” ensures higher priority MC traffic will enjoy a higher quality of service than the lower priority traffic.

Further, Access Barring, based on “access classes” that are provisioned on the device SIM by the network provider, provides a mechanism in the cellular network that actually prevents users not engaged in MC communications (say, large numbers of witnesses to an event who want to call friends or live-stream what they are seeing and are therefore threatening to overwhelm the system) from establishing a network connection, leaving the network free for emergency workers engaging in MC communications.

The LTE cellular standard also now provides excellent support for group calling voice communications that mimic what happens with an LMR system, with these short LTE push-to-talk voice transmissions taking priority over “best-effort” data services. 

However, what’s missing in MC-LTE today compared to LMR is an effective mechanism for operating without a network – the Talk Around capability. The rigorous network-based scheduling of LTE, which allows the system to take maximum advantage of the network utilization of time and frequencies, does not support Talk Around. Interestingly, the 3GPP actually includes a specification for Proximity Service (ProSe) for enabling LTE devices to operate peer-to-peer without a network, thus emulating Talk Around, but device vendors have not implemented this specification in their devices.

Even if ProSe were to be broadly available in silicon, the challenge of interference may kill adoption. LTE radio systems are limited by interference, as noise in the radio spectrum degrades capacity, reducing efficiency. And because LTE is an example of an interference-limited system, modern LTE devices transmit at very low power compared to much higher-power LMR devices (around 100 milliwatts with LTE compared to 2 to 3 watts for LMR) – so even if ProSe is implemented, confidence in the ability of LTE devices to push the signal outside of large buildings is low. For these reasons, first responders are not expected to start using LTE in place of LMR for mission critical communications anytime soon.

An essential point, however, is that though MC-LTE will not be replacing LMR, it will be complementing it. New LTE-powered PTT over Cellular solutions can be integrated into LMR systems, providing supervisors with the ability to communicate with subordinates when they are out of LMR range. In addition, MC-LTE provides a communications alternative to LMR for first responders if they are in rural or other areas where there is no LMR coverage but LTE service is available and offers reliable and secure communications to law enforcement officers engaged in undercover operations who cannot use a LMR device. 

In addition, and most importantly, MC-LTE, unlike LMR, provides connectivity for a wide variety of high-speed data and other IoT applications. With LTE, for example, police officers can use a drone to capture crime scene video and then view that video on a mobile device, firefighters can access floor plans for a building before they enter it and EMS personnel can send and receive data on patients while they are being brought to a hospital – all applications that LMR cannot support. 

Today, MC-LTE is being implemented in LTE networks. One of the first MC-LTE networks is FirstNet, which has put into place the priority and preemption mechanisms required for MC PTT. Likewise, the UK is moving towards an MC-LTE network for its new Emergency Services Network (ESN) and Korea is building out its SafeNet network.

MC-LTE as a Foundation for BC Communications 

While MC-LTE will complement but not soon replace LMR for public safety MC voice communications, it has tremendous potential for both BC voice and data communications use cases. Using MC-LTE, it is possible for service providers to create additional QoS levels that give higher priority to business use cases than to consumers (though lower priority than emergency services), supporting BC mobile voice and cloud-first workflows that continue to work in the face of network congestion collapse.

Such services are already being made available by AT&T in the U.S. and Telstra in Australia. The capabilities of these services support PTT, as well as IoT control mechanisms, such as running an ATM at a large event so a bank can provide reliable cash services to customers or supporting operational workflows, such as a back-up to a field office fixed line to ensure operations should the fixed line fail and the cellular network is busy. It will also likely become a solution of choice for drone management. 

In the context of overall cellular usage, businesses adopting a BC communications solution can be confident their communications will enjoy the next level of priority below MC emergency services, ensuring they can continue operating the face of network congestion. In the past, to achieve this capability, businesses had to build their own expensive LMR network. With MC-LTE, they can now move from a CapEX-centric model to an OpEx-centric model where, thanks to the larger scale of the cellular equipment market, they can also significantly reduce device costs compared to LMR. Beyond the cost advantages, enterprises benefit as responsibility for complex radio system upgrades shifts to the service provider. 

As a reliable data network, MC-LTE also enables enterprises to leverage cloud access from all types of devices to create a unified communications network for business-critical operations. And as MC-LTE solutions and platforms mature, we will see interoperability built in that allows a combination of MC and BC use cases. For mission-critical and business-critical operations, the availability of reliable mobile broadband data capabilities creates a profoundly transformative opportunity holding promise for saved lives, reduced property loss and enhanced business operations.  

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