Report Finds 9-1-1 Altitude Location Not Ready for Live Environments
Tuesday, August 14, 2018 | Comments
Determining the altitude of a 9-1-1 caller is proving difficult with a recent report finding significant questions remain about the performance and scalability of Z-axis technology — which could locate a caller in a high-rise for example — for live 9-1-1 call environments.

Only two vendors and two carriers — AT&T and Verizon — participated in a Z-axis technology test to assess vertical location solutions for 9-1-1 calls. The 9-1-1 Location Technologies Test Bed, an independent entity established by CTIA, conducted the Z-axis tests.

The test bed was formed after the FCC in 2015 adopted rules requiring wireless service providers to improve 9-1-1 indoor location accuracy.

NextNav and Polaris Wireless participated in Stage Z testing after an open call to vendors.

NextNav’s technology uses its Metropolitan Beacon System (MBS), a wireless network deployed using Part 90 Multilateration Location and Monitoring Service (MLMS) licenses. NextNav beacons, where deployed, broadcast information required for the 9-1-1 caller’s device to compute a precise location estimate. Polaris Wireless’s Hybrid Location Engine (HLE) technology is a software-based solution that collects data from the 9-1-1- caller’s device and applies proprietary algorithms to generate a Z-axis location estimate.

Following Alliance for Telecommunications Industry Solutions (ATIS) standards, Stage Z testing was conducted in the dense urban, urban, suburban and rural morphologies of the Atlanta, San Francisco and Chicago regions. Testing was conducted in 48 buildings using 312 test points. ATIS manages the test bed.

Testing involved 30 smartphone devices, including 12 different handset models, and produced more than 100,000 location estimates However, NextNav’s testing didn’t include the Chicago region or rural areas because NextNav has not deployed its MBS network in Chicago or rural areas. Chicago was selected for extreme weather conditions.

NextNav’s testing produced 80 percent of fixes at 1.8 meters or less in the two areas tested. Polaris Wireless covered all three test regions and produced 80 percent of fixes at 4.8 meters or less. Polaris Wireless' testing did not include Apple’s iPhone.

One question following the testing surrounds barometric sensor bias. The results reflect that sensor bias is the dominant error source for estimating altitude. Each mobile device is subject to its own unique sensor bias and thus requires individualized active barometric sensor bias calibration. Adjusting for sensor bias on an individualized device-by-device basis proved manageable when dealing with dedicated apps running on six test handsets, but the calibration capability would need to be built into live production solutions, with signaling based on standards and retested at scale to fully assess performance. Therefore, it is unclear whether the Stage Z performance results would be replicated in a live 9-1-1 calling environment, the report said.

In addition, the testing did not include a variety of device types or extreme weather. Only relatively new headsets were tested. In addition, the tests were proof of concept, and no actual calls were placed to produce Z-axis fixes, and standardized 9-1-1 signaling was not used.

“For these reasons, barometric pressure sensor-based Z-axis solutions require further development, potentially including further standardization efforts, implementation into wireless network systems and production mobile devices, and then re-testing in a production configuration to determine whether the Stage Z results can be replicated and deployed ubiquitously in real-world production and live wireless 9-1-1 call environments,” the report said. “Further, additional factors are likely to limit the availability of barometric pressure sensor based Z-axis solutions, including lack of support for existing mobile wireless devices.”

A report from AT&T said it is implementing uncompensated barometric pressure (UBP) for new voice over Long Term Evolution (LTE) handsets. Both AT&T and Verizon said they are updating their networks to support delivery of UBP.

The test bed report said other approaches to X-axis location estimates, such as enhanced Wi-Fi positioning technologies, are emerging. Handset-based emergency location technologies are gaining traction and undergoing separate testing.

CTIA said further testing is needed to validate and confirm performance expectations for live wireless 9-1-1 calling environments. Verizon said it supports additional testing in the next 12 months, both to enable NextNav and Polaris Wireless to participate more comprehensively, and to test other emerging Z-axis solutions that rely primarily on enhanced Wi-Fi positioning technologies, such as 3D Wi-Fi. A few vendors of the 3D Wi-Fi positioning approach have indicated the availability of their solutions for testing within the next 12 months, Verizon said.

"NextNav believes that although the tests were conducted in a technically accurate manner, the broad interpretation and conclusions drawn by CTIA in the report are inaccurate," said Ganesh Pattabiraman, CEO and co-founder of NextNav. "As the report itself acknowledges, a reasonably comprehensive set of regions, buildings and diverse environment conditions were tested and the use of the most popular off-the-shelf mass-market phones such as the iPhone and Samsung Galaxy make the technology representative of real-world conditions and performance. NextNav has demonstrated consistent floor-level accuracy since 2012 in various blind tests conducted by CSRIC (Communications Security, Reliability and Interoperability Council) and CTIA. The NextNav technology as tested is fully ready for commercial service and capable of meeting public safety’s needs today."

The full Stage Z report is here. A letter from CTIA about the report is here.

The AT&T location accuracy report is here, and the Verizon report is here.

Would you like to comment on this story? Find our comments system below. 

Post a comment
Name: *
Email: *
Title: *
Comment: *

On 8/15/18, Arthur Miller said:
NextNav was clearly the top performer here. This author's opinion on the results is a clear example of how the power players in the wireless industry including Qualcomm and such are trying to keep NextNav down. People are dying as a result of poor 9-1-1 location and the industry is slow rolling the improvements to save a few bucks.

Site Navigation