Decision makers need to consider many layers when determining future role of mission-critical voice over LTE

Mission-critical users—particularly public-safety personnel—only trust LMR technology. This may still be true in many cases, but it’s not as cut-and-dry as it used to be, particularly for younger-generation public-safety officers that have grown up with cellular technologies.

According to study cited by FirstNet officials a year ago, 94% of public-safety personnel say they already use commercial wireless technology to complete tasks for their job. At the Rose Parade on New Year’s Day, some officers opted to use only public-safety LTE devices on the new Los Angeles Regional Interoperable Communications System (LA-RICS) public-safety LTE network to talk with LMR-using cohorts while providing security for the high-profile event, LA-RICS Executive Director Pat Mallon said.

To paraphrase a statement from FirstNet President TJ Kennedy, public safety will use what works. If MCPTT over LTE works, then it will be used.

Push-to-talk (PTT) over LTE will never be mission critical. Actually, many have argued that several existing PTT applications already provide mission-critical performance and reliability, with one very significant caveat: the application is only as good as the network it uses. Because no LTE network today is considered mission critical, none of the current PTT offerings are deemed to be mission-critical services today.

However, this statement could be false in a few years, with the establishment of public-safety LTE systems like FirstNet throughout the world and equipment based on the MCPTT standard—approved by 3GPP in March—hitting the market.

LTE networks will never meet the “public-safety-grade” standard. Certainly today’s commercial networks do not meet the public-safety-grade standard (by the way, there are a lot of public-safety LMR networks that don’t meet the standard, either). FirstNet and other public-safety LTE initiatives plan to change that, but we won’t know if that goal is met until the systems are deployed.

LTE won’t work if the network base station is out of range or otherwise unavailable—the LTE device becomes a "brick" at that point, in terms of communicating with others. That used to be the case, but the most recent versions of the LTE standard—Releases 12 and 13—are designed to address this issue, primarily to meet the needs of public safety. As a result, during the next few years, we could see LTE devices that can provide the kind of off-network, direct-mode communications that LMR portables have provided for years.

LMR provides “graceful degradation,” meaning that each tower can act as a repeater if cut off from the rest of the network. LTE doesn’t do that. That is true today, but that is expected to change soon. The latest release of the LTE standard includes a feature known as isolated E-UTRAN operation for public safety (IOPS), which effectively provides the same functionality as “graceful degradation” does in an LMR system.

Releases 12 and 13 of the LTE standard were designed to ensure that MCPTT provided at least the same functionality as LMR systems do today, according to Andrew Thiessen, deputy program director for Public Safety Communications Research (PSCR). In fact, they include some features—for instance, presence information about other LTE devices within direct-mode signaling range—that are not available with LMR.