PTT over FirstNet still needs to clear multiple barriers for mass adoption, 5×5 attendees say

FirstNet’s overall adoption rate has been impressive, but most of public safety still is not enthralled by the idea of using push-to-talk services over the nationwide public-safety broadband network (NPSBN) for a variety of reasons, according to attendees of the recent 5×5: The Public Safety Innovation Summit in San Diego.

AT&T has reported that FirstNet supports 4.7 million public-safety broadband connections, but push-to-talk (PTT) offering on the NPSBN—from over-the-top applications to 3GPP-standard mission-critical push to talk (MCPTT)—is used by a “far smaller number,” according to Jennifer Harder, director of roadmap domains for the FirstNet Authority,

“We didn’t have a lot of adoption nationwide, although we do have a couple-hundred thousand users across the country using various different forms of push to talk,” Harder said. “And we have different push-to-talk products, so what may be an issue for one product might not be an issue for another.”

Harder made the statement while moderating a session designed to identify the primary reasons why public-safety agencies are not using push-to-talk solutions on FirstNet more.

Interestingly, none of the participants—including a significant number of public-safety leaders—mentioned any shortcomings in the performance of existing PTT offering. This would seem to reinforce the notion that PTT works well—in fact, most believe the audio quality to be superior to LMR—when there is a good connection to a broadband network, particularly one that provide public safety with prioritized and preemptive access.

But there are several other issues limiting the usage of PTT across LTE networks like FirstNet, such as ensuring that the device and accessory ecosystems meet the needs of public safety.

In the U.S., one of the issues is that the vast majority of public-safety personnel prefer to connect to broadband via iOS devices, which do not include a push-to-talk button in the hardware and do not support tethered remote speaker microphones.

“The responders in the field need that simplicity of being able to push a button on the side of a device and know that it’s going to talk, versus trying to swipe up, get an app, push a button, and that kind of thing,” said one session participant.

Red Grasso with the state of North Carolina noted that Apple has established a “push-to-talk framework” that is designed to allow quick access to PTT via a button on a remote speaker microphone.

But the inability to use a tethered speaker mic with Apple devices undermines the benefits, according to one session participant.

“Then you’re relying on a Bluetooth device that’s connecting to the phone, which is bad for public safety and first responders,” according to the session participants.

“I can’t put an iPhone in one of my responders’ hands with an type of accessory on it and depend on it to work every single time, because that is a computer, not a radio.”

Harald Ludwig, chair of the TCCA Technical Forum, echoed the concerns with using a Bluetooth-connected remote speaker mic.

“Bluetooth uses an unlicensed frequency, so it can never be mission-critical,” Ludwig said.

Harder noted that there is some disagreement in the public-safety community about the value of tethered microphone solutions, noting that some officers complain that the wiring can get caught on door handles and other objects, particularly when the user is trying to move quickly, such as during the pursuit of a suspect.

Multiple session attendees that even standards-compliant MCPTT clients are only as mission-critical as the network and ecosystems they operate on. For instance, MCPTT can support communications to users on a Wi-Fi system, but most Wi-Fi systems do not provide the quality-of-service guarantees needed to reach mission-critical status.

Meanwhile, one of the most-discussed shortcomings of PTT over LTE is the lack of ability to communicate when an LTE user is beyond the range of a terrestrial broadband network. This is particularly important to public safety, which often has to respond in remote areas without coverage or after network infrastructure has been compromised by a natural or man-made disaster.

The LTE standard included a direct-mode solution—one that would let one device to communicate with another without going through a network—known as Proximity Serves (ProSe), but the technology has not gained traction in the marketplace or with chipmakers like Qualcomm.

The development of 5G includes an evolution of the ProSe standard that is known as Sidelink, and Qualcomm officials have expressed optimism about the technology during the 5×5 Summit and in other venues.

While Sidelink is expected to encounter some of the same physics challenges associated with ProSe—limited range, based on the low power levels used by LTE devices—it is designed to support a relay function that could allow greater effective range, if devices are deployed properly.

FirstNet Authority CTO Jeff Bratcher said that attendees in another 5×5 session declared that direct-mode functionality is a “minimum requirement” to adopt cellular PTT for mission-critical uses.

Recently, there has been some discussion that satellite-direct-to-phone solutions being development by companies like AST SpaceMobile and Lynk Global could provide off-network communications support when users are outdoors and beyond the coverage footprint of terrestrial networks.

Many public-safety leaders acknowledge that full deployments of such systems—in which LEO satellites effectively act as 4G/5G roaming towers for terrestrial carriers—could dramatically alter public-safety need for direct-mode communications outdoors. However, the satellite-direct-to-phone systems are still in their nascent stages of development, and they would not address the need for direct-mode functionality when users are indoors.

Meanwhile, at least one session participant was bullish on the notion of using PTT over FirstNet for voice communications.

Joe Duvall, police chief for the city of Dallas, Ga., said his agency is “100% broadband” after shuttering its end-of-life DMR system from Motorola Solutions and turning to PTT over FirstNet for its mission-critical voice needs. The move to PTT over LTE cost the city of Dallas, Ga., about $500,000—a fraction of the estimated $4 million it would have cost to fund the necessary LMR upgrades.

“The technology is there, and making the jump to it—from a management standpoint—just made so much sense,” Duvall said. “You can’t even compare the costs; it’s like apples and oranges with this. And the technology’s never going back.”

Indeed, Duvall said he noticed a change in the use of communications at incident scenes while working in a metro Atlanta police department years ago.

“When you’re out at a big scene, everybody’s on cell phones,” Duvall said. “The only people who might be on LMR are the people inside who are clearing a building. Everybody else is on cell phones.”

But Harder said that not as many of these public-safety officers are using PTT over FirstNet as could be, which means that first-responder-specific enhancements are needed in multiple areas.

“The synopsis here is that [PTT-over-FirstNet solutions] are not working as well as they could, and we need to get that whole ecosystem to some level of parity,” Harder said.