Critics Claim Interference in 5G-as-Alternative-GPS Proposal

A proposed GPS-replacement system designed to use existing 5G mobile phone networks could interfere with the functioning of billions of everyday Internet of Things (IoT) devices, according to an alliance of industry groups.

The GPS-replacement system, proposed by the Reston, Va.-based company NextNav, could affect critical security and public safety technologies such as fire and carbon monoxide alarms, flood sensors, motion sensors, and security cameras, according to an alliance of groups representing the affected industries. NextNav disputes the criticism, however, pointing to results of lab tests, which they say rule out excessive interference.

The NextNav technology relies on the 900 MHz frequency band to pinpoint users with respect to the position of mobile cell towers. The company is currently petitioning the Federal Communications Commission (FCC) to reconfigure the 900 MHz band to enable widespread adoption of their technology as part of the existing 5G network infrastructure.

The company says the system would provide a low-cost and reliable alternative to the Global Positioning System (GPS) at a time when the cornerstone navigation technology is facing growing challenges due to jamming and interference from space weather. (While the current solar cycle peaked last year, some of the worst solar storms come during a cycle’s declining phase.)

According to the NextNav proposal submitted to the FCC, 5G operators would be able to use parts of the band, too, to feed their growing hunger for bandwidth.

IoT and Security Tech Square Off With 5G and GPS

In its proposal, NextNav describes the 900 MHz band as “underutilized.” However, this opinion is being challenged by stakeholders from the IoT, smart tech, and security industries, whose technologies use this band.

The Z-Wave Alliance, an association representing manufacturers of smart home IoT devices, says NextNav’s technology could overpower billions of critically important IoT sensors, making them unreliable. Z-Wave is among a group of critics that have joined forces to challenge the NextNav proposal alongside the Wi-Sun Alliance, and the Security Industry Association (SIA).

“The lower 900 [MHz spectrum band] is a really heavily used band of public RF white space,” Z-Wave Alliance chair Avi Rosenthal told IEEE Spectrum in an email. “A spectrum reallocation would impact everything from smart home devices, security sensors, and cameras to life safety devices, tolling devices, and transportation infrastructure.”

Moreover, Rosenthal says, even devices that are using the same communications channel as NextNav transmissions could stop working properly. Tests show the issue could harm the proper functioning of other connected devices, he says, not just those using Z-Wave technology.

“In essence, we expect that low power device reliability would be severely degraded,” Rosenthal said.

Any disruption to GPS, underpinning no small portion of present day technologies and the global economy, could cost billions of dollars.

But the devices possibly affected by the NextNav system are also widespread. Rosenthal estimates that “billions” of panic buttons, fire and carbon monoxide alarms, doorbell cameras, security cameras, infrared sensors, motion sensors, traffic cameras, CCTV cameras, smart meters and other technologies are distributed across American homes and cities.

Debate Swirls Around Unlicensed Spectrum

Regulated by the FCC under the Part 15 regulation, these devices don’t require a license as they only emit low-power radio signals to send reports to nearby smart hubs. But the Pericle Communications study found that to safely operate alongside the NextNav system, these hubs would have to be over 500 times more sensitive to overcome the expected interference.

“A high-power application wouldn’t need to completely smother Part 15 devices to cause a serious failure,” said Rosenthal. “If communications are interrupted in the moment a security sensor detects an intruder, the alarm won’t go off. It won’t help if communications resume a few moments later—the bad guys are already in the house.”

According to the Pericle Communications report, the Nextnav technology, if widely rolled out, would have “devastating impacts on outdoor public safety for things like traffic monitoring, gunshot detection and monitoring of public spaces.”

NextNav, however, disputes this criticism. A NextNav spokesperson told IEEE Spectrum in an email that the report by its opponents contains “significant errors that undermine its validity.” The company also said that the “assumptions” of the report “appear to be specifically invented to create the appearance of interference.”

In a blog post published on the company’s website on Nov. 11, NextNav’s Senior Vice President for Technology Development John Kim wrote that “Pericle exaggerated the maximum 5G channel power by at least 16 times, leading to unrealistic and greatly exaggerated levels of interference to Part 15 devices.”

Rosenthal, on the other hand, describes NextNav’s tests as being “based on highly optimistic assumptions,” using “idealized conditions, limited measurement points” and only testing “low-density device performance.”

“We’d like to see robust, real-world testing using dense deployments, as you’d encounter in any urban environment,” he wrote. “The risks involved here are severe: we’ve cautioned the FCC against moving forward without genuine evidence demonstrating successful co-existence.”

IEEE’s 802 LAN/MAN Standards Committee also issued a public notice on NextNav’s petition, stating that granting the changes requested by NextNav might “potentially disrupt the operation of the millions of currently deployed IoT devices.” The Committee wrote that it would cost millions to replace the devices, adding that for some of these technologies “there may be no viable alternatives.”

“NextNav completely failed to demonstrate how coexistence with millions of Part 15 devices can be achieved,” the Committee wrote.

NextNav filed its Petition for Rulemaking to the FCC in April last year. As of mid-November, there are no clear indications when the FCC’s decision will be made.

Regardless, the agency will be choosing between a 5G-based GPS back-up and (as Z-Wave Alliance states) the proper functioning of a large number of IoT and smart home and security devices.

Other GPS alternatives are currently being studied, including new, low-Earth-orbit satellite constellations that would be harder to jam. NextNav argues that their system, using existing 5G infrastructure, requires only software-based tweaks to work and would save taxpayers’ money. NextNav’s critics say the equation is more complex.

“We all want to see the U.S. develop a secure complement to GPS, but it doesn’t make sense to do so at the cost of bulldozing multiple device ecosystems Americans already rely on,” said Rosenthal.