Mission-Critical Push-to-Talk: Will Critical Communications World Show the Way?

Part 3 in a series of reflections in the lead-up to Critical Communications World 2018

As happens each year, Critical Communications World highlights the latest innovations that advance the state-of-the-art in mission-critical communications. This year will be no different, and LTE will surely be a focal point for much of what the ecosystem unveils in Berlin. But while these new mobile broadband data capabilities are top-of-mind, mission-critical voice radio transmissions remain the backbone for public safety operations. Unfortunately, widely anticipated LTE technology supporting mission-critical voice transmissions continue to lack needed mechanisms when users are beyond the network's reach. Will Critical Communications World shed some light on the missing gap?

As emergency services workers operate inside large structures, they frequently move to locations where a network radio signal is absent. Even when the network is not reachable, modern critical communications systems such as TETRA provide for direct mode operations that enable out-of-range devices to directly communicate in a back-to-back fashion or via a nearby unit that can relay signals. Though emergency services personnel handle this challenge as a matter-of-course during day-to-day operations, the loss of network access can also result from major disasters that destroy network infrastructure. Regardless of the cause or duration, mission-critical networks must have direct mode functionality. As suppliers and network operators evolve towards LTE-based mobile broadband networks for efficiency and rich communications functionality, the base requirement for direct mode connectivity remains a high priority.

Sadly, LTE-based mechanisms to replace back-to-back (or, in American parlance "talk-around") communications remain a work-in-progress. The latest LTE modems entering the market do not support 3GPP Proximity Services (ProSe) needed for operation in the absence of a network. Worse, LTE's wideband radio carriers and low transmission power limits make any LTE-based solution unlikely to match performance levels reached in today's widely available mission-critical handset devices used in TETRA or APCO Project 25 systems. Without the power to punch out of a large building structure, the LTE-only devices will not gain the confidence of police officers and firefighters. 

A way out of this quandary may have emerged with hybrid devices. Both Airbus SLC and Hytera have already brought combined TETRA/LTE handset devices to market. In the US, Harris Corporation has a combined APCO Project 25/LTE handset. And at Mobile World Congress in Barcelona, SK Telecom highlighted its research and development towards LTE devices with DMR-based back-to-back functionality aimed at Korea's SafeNet users. These approaches vary significantly but they all point towards a future with a hybrid functionality that brings together the best of non-LTE voice and LTE voice/data. 

We do not yet know what suppliers will launch at Critical Communications World in Berlin. But the UK Home Office pleas for solutions to the Direct Mode conundrum may have stimulated a round of needed innovation. If nothing else, the conversation has begun, and Critical Communications World will provide a tantalizing peek at our prospects for a long-term solution meeting the needs of emergency services workers around the globe.