AT&T officials outline current IoT capabilities over FirstNet, future considerations for LTE-M

FirstNet currently does not support the use of low-power, wide-area (LPWA) protocols like LTE-M, but the nationwide public-safety broadband network can be leveraged for low-bandwidth Internet of Things (IoT) use cases with quality of service, priority and preemption (QPP) on LTE, according to AT&T officials.

David Allen, director of IoT advanced product development for AT&T—the nationwide contractor charged with building and maintaining FirstNet—said that devices using LPWA technologies like LTE-M and NB-IoT can have very long battery life by transmitting small amounts of data and then entering extended “sleep” cycles. In addition, these devices can transmit data repeatedly until the message is received, which effectively result in extended coverage.

FirstNet currently does not support LTE-M—a technology that also has been referenced as CAT-M, CAT-M1—but AT&T is in the process of evaluating the LPWA technology to determine if they would be suitable for use over the FirstNet system, Allen said.

“The FirstNet network does not support LTE-M today,” Allen said during an interview with IWCE’s Urgent Communications. “I tend to agree … that it probably would be helpful to have support for LTE-M, … [but] we don’t like to make any types of assumptions that it would be supported.

“We are currently testing and evaluating the unique capabilities of LTE-M. We want to make sure that these unique capabilities of these LPWA technologies … are interoperable with the unique capabilities of FirstNet, like uplift, priority and preemption.”

FirstNet initially was proposed as a network that would support operations only on the 20 MHz of 700 MHz Band 14 spectrum that is licensed to the FirstNet Authority, but AT&T decided to provide FirstNet subscribers with (QPP) across all of its existing LTE spectrum bands. LPWA technologies operate within these LTE bands.

“They operate within a mobile operator’s existing wireless spectrum, but they are a separate and unique channel within our spectrum,” Allen said. “So, we will have a separate LTE-M carrier channel that’s out there, and we’ll have a separate carrier channel for narrowband IoT, as well.”

NB-IoT requires a channel size of 200 kHz—“very, very tiny by LTE standards; it’s about the size of an existing GSM channel,” Allen said. Still, the NB-IoT channel size is much larger than the 12.5 kHz or 25 kHz channel sizes utilized in land-mobile-radio (LMR) technologies that also bear the “narrowband” moniker.

In contrast, LTE-M operates on a channel width of 1.4 MHz, which is much smaller than the typical 5 MHz to 10 MHz of contiguous spectrum used by a typical LTE system, Allen said. LTE-M also can support some voice communications, according to industry sources.

A potential key advantage of LTE-M technology is cost. Based on publicly released figures, the lowest price for an LTE module is about $15, while the LTE-M modules offered by AT&T were almost 50% less—and the prices could drop rapidly as the IoT sector gains traction in the marketplace, Allen said.

Matt Walsh, AT&T’s director of IoT business development for smart cities/FirstNet/drones/utilities, acknowledged the potential for LTE-M technology operating with FirstNet QPP but noted that public-safety IoT use cases are already are being developed over traditional LTE connections.

“We see a great opportunity, even with LTE, in the lower-bandwidth use cases, for FirstNet use cases,” Walsh said during an interview with IWCE’s Urgent Communications. “The inability to deploy on LTE-M today does not mean that those low-bandwidth use cases aren’t available to FirstNet customers, because we’re finding ways to do that today with LTE.”

Even though these IoT use cases involve using a full-fledged LTE connection, the cost to link to a low-bandwidth IoT device is markedly different than the costs associated with smartphone or video-camera use, Walsh said.

“We’re pricing things specific to the amount of data they would consume,” he said. “So, they’re not signing up for what you see as a consumer rate plan. We have services and the flexibility in our billing to size rate plans specific to their use case.”

Both LTE-M and NB-IoT are designed for use on licensed broadband spectrum, which typically is controlled by a carrier like AT&T. Other technologies like LoRa and SigFox also serve the IoT space, but they are designed to operate on unlicensed spectrum.

Allen said that some enterprises may consider IoT solutions on unlicensed spectrum. However, unlicensed spectrum typically is subject to greater security risks and uncontrolled RF noise, making it impossible to offer service-level commitments, he said.

Walsh said that private unlicensed networks also can create an operational burden on the enterprise that does not exist with a carrier solution, particularly one involving FirstNet.

“Cities that have those networks deployed, in a sense, become a carrier themselves, so they then have that [responsibility for] management of the network,” Walsh said. “When that’s really important is when that network goes down. Think about a natural disaster and all of the speed and timeliness that AT&T and FirstNet have demonstrated as we go to get our networks back up, so they can operate.

“They [cities with private unlicensed networks] would then have that responsibility to re-establish those networks, and they probably won’t have anywhere near the resources that we apply to this space to get these folks back up and running.”