NextNav Says Z-Axis Technology Fully Tested, FCC Should Adopt 9-1-1 Indoor Location Accuracy Metric
Monday, August 27, 2018 | Comments

In an ex-parte filing with the FCC, 9-1-1 Z-axis location accuracy technology provider NextNav questioned CTIA’s characterization of the recent test results for Z-axis technology in a report to the commission. The technology supplier said the FCC should adopt a vertical location metric.

NextNav said the Z-axis test bed reaffirmed the accuracy of its Metropolitan Beacon System (MBS) technology, documenting vertical location accuracy of 1.8 meters or better for 80 percent of fixes and 3 meter or better accuracy for 94 percent of fixes or “floor level” accuracy.

NextNav addressed four CTIA concerns from the report. NextNav was not able to participate in the tests that were conducted in Chicago. A decision to locate the testing in the Chicago area was not announced until September 2017, with the testing then scheduled for November 2017, providing insufficient time for NextNav to deploy its network in that market, the company said.

One of the test environments included a 24-hour test to determine variability on a time-of-day basis as heating, ventilation and air conditioning (HVAC) systems cycle to retain stable indoor temperature with varying outdoor environments. “CTIA noted these modest variations and speculates that those variations should potentially be additive to the test results,” NextNav said. “However, the normal test process itself involved various times of the day, in differing HVAC cycles and weather and temperature conditions, and most time-of-day and weather fluctuation is already captured within the body of the test results. The modest time-of-day fluctuation that was exhibited can reasonably be contained within a vertical error budget of 3 meters for 80 percent of fixes, as the FCC and the public-safety community originally proposed.”

NextNav’s MBS technology is not available in rural areas and wasn’t tested, but the company said Z-axis location is not essential in rural areas. “NextNav’s MBS technology was tested for vertical accuracy in rural areas during the original CSRIC (Communications Security, Reliability and Interoperability Council) test bed conducted in the winter of 2012 and NextNav’s results from that testing fell well within an accuracy level of 3 meters for 80 percent of all calls,” the filing said. “It is also unclear what benefit would result from such testing. The commission’s location accuracy rules require wireless carriers to deploy Z-axis capabilities only in the top 50 CMAs (cellular market areas), outside of which the presence of high-rise structures is not significant, making a rural Z-axis solution arguably not as critical.”

Regarding the handsets used, CTIA argued that further investigation into the vertical location capabilities of older wireless handsets may be needed, arguing that the accuracy of barometric pressure sensors degrades with age. The recent Z-axis test process, however, employed both older and newer handsets and identified no degradation in location capabilities for the older devices, NextNav said.

CTIA said that although commercially available handsets were used in the test bed, they were supplemented with additional software to replicate the capabilities of the NextNav and Polaris Wireless solutions. NextNav said the appropriate signaling to support barometric-based altitude determination from the device to the network is already standardized in Third Generation Partnership Project (3GPP) Releases 13 and 14 and the Open Mobile Alliance (OMA).

“As such, all elements required to commercially scale either solution exist today and simply need carrier and device manufacturer support to include appropriate calibration software within new handsets,” the filing said.

“We are encouraged by the test bed’s results, which show that even the z-axis accuracy benchmarks proposed by the FCC in its 2014 third further notice can be achieved by techniques available today,” said a statement from the National Emergency Number Association (NENA). “These accuracy improvements — especially those that allow 9-1-1 to dispatch responders to a specific floor on a building — will save countless lives when implemented. However, as stakeholders have expressed the desire for additional testing, we hope that all parties can work together to conclude that testing in a timely fashion.”

The Association of Public-Safety Communications Officials (APCO) International and Polaris Wireless didn’t respond to requests for comments. The NextNav filing is here.

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