There are many reasons why Land Mobile Radio (LMR) can’t hold a candle to smartphones for first responder communications. But one area where LMR does have an advantage is in its ability to support direct device-to-device communications between radio users in close proximity to each other, without the need to go through a central hub like Dispatch.

Thankfully, this capability may soon come to 5G smartphone users, according to a posting on Qualcomm’s OnQ Blog. Entitled How will sidelink bring a new level of 5G versatility?, this blog delves into the promise of ‘sidelink’. It is a feature of the 5G platform that enables device-to-device communications between ‘side-by-side’ 5G smartphones; aka ‘sidelinks’. (Qualcomm’s electronics are used in 5G smartphones.)

If sidelink works as Qualcomm suggests it could, it could address “one of the big fears associated with using cellular, which is what happens if the network goes down?” said retired NYPD Assistant Police Chief Chuck Dowd, who spent the last 12 years of his career in charge of New York City’s 911 systems. “That’s the one thing that Land Mobile Radio still has over smartphones, namely the ability to support device-to-device communications.”

What sidelink Is

According to Qualcomm’s OnQ blog, current 5G systems operate primarily on a network-to-device communication model. In other words, all data transmissions flow between the network (i.e., the base station) and devices (e.g., smartphones).

“However, to fully deliver on the original 5G vision of supporting a wide range of devices, services, and deployment scenarios, expanding the 5G topology is essential to reach new levels of performance and efficiency,” the blog said. “That is why sidelink device-to-device communication (as opposed to the traditional downlink and uplink communications) — designed to facilitate direct communication between devices independent of connectivity via the cellular infrastructure — was introduced in 3GPP standards.” Short for 3rd Generation Partnership Project, 3GPP is an engineering organization that develops technical specifications.

According to Qualcomm, the device-to-device communications enabled by sidelink “enhances many 5G use cases, such as IoT (Internet of Things, or machines sharing data with each other), mobile broadband, public safety, and more.” Interoperability is a key feature of sidelink: It supports “device-to-device communication for disaster scenarios when multiple agencies need to communicate with each other with and without the cellular infrastructure,” the OnQ Blog said.

What sidelink Could Mean for Public Safety

The introduction of 5G smartphone-to-smartphone communications could provide numerous benefits to public safety agencies.

One of these benefits could be enhanced in-building communications, particularly in multi-level basements. Concrete reinforced with steel rebar, and steel structures overhead, can degrade the signal strength of cellular transmissions trying to penetrate from the outside. But smartphones within these envelopes should be able to communicate directly with each other, as long as they have an enabling device-to-device connection technology such as sidelink. If this proves to be the case, “the ability to establish such device-to-device networks could facilitate public safety operations in these kinds of environments,” said Chief Dowd.

Tactical communications is another area where sidelink device-to-device communications could make a difference, such as hostage rescue situations. “Again, if these were to occur in areas where cellular signals from outside had difficulty penetrating, being able to set up device-to-device networks on site could be a great advantage,” Chief Dowd said.

Finally, should cellular network access be compromised due to man-made/natural disasters — a problem that FirstNet is designed to mitigate by providing priority access to first responders  — sidelink could provide them with the kind of backup device-to-device communications that LMR provided to its users. “It would certainly provide police, fire and EMS with an additional option,” said Chief Dowd.

Worth Watching Out For

It remains to be seen if 5G sidelink will actually end up providing the device-to-device communications that Qualcomm talks about in its OnQ Blog. But one thing is certain: Now is the time for first responders to pay attention to the development of this technology and have a say in its direction/deployment should sidelink prove itself.

“Sidelink is a technology that public safety should start taking a look at and kicking the tires on, so to speak, to see what advantages it could potentially bring to them,” Chief Dowd said. “The only way to do that is for us to test sidelink in pilot trials, to see what it can do.”