Establishing Z-axis location information has been an ongoing part of an effort by the Federal Communications Commission to improve the location data available to first responders when a wireless user calls 911. Here are the basics to know:
What is Z-axis location information and why is it important?
Z-axis location is the vertical location of a wireless 911 caller. According to the National Emergency Number Assocation, consumers make 240 million calls to 911 each year, and in many areas 80% or more of these calls are from wireless phones. Locating a caller who is indoors is complicated in multi-story buildings and can increase response time; with better information on the location of wireless 911 callers, dispatchers and first responders can more quickly respond, find and assist them. Knowing which floor a caller is on — especially in a high-rise — is vital information, particularly when a caller cannot give that information themselves, either because they do not know or are not in a position to give the information clearly, as in the case of a child or an injured person.
What is the FCC doing in this area?
Back in 2014, the FCC gave the four national mobile network operators the task of establishing an independently administered test bed and proposing a metric to improve the vertical location information that they could provide, with test data to be submitted by August 3, 2018. The FCC put forth the possibility that Z-axis information should be provided from MNOs that was accurate to within 3 meters of the handset. On Aug. 3, 2018, CTIA submitted the results of testing conducted in the summer of 2018 by its independent test bed that involved two companies, NextNav and Polaris Wireless, which both relied on barometer sensors inside smartphones to provide information that could be used to calculate a caller’s vertical location. CTIA proposed a z-axis metric of plus or minus 5 meters for 80% of fixes from mobile devices capable of delivering barometric pressure sensor-based altitude estimates, and said that “further testing of vertical location technologies could yield results to validate adoption of a more accurate z-axis metric.” Public safety agencies, meanwhile, have expressed support for a plus-or-minus two-meter rule, which would more accurately place a caller on a specific floor.
What did the testing show?
The test results showed that in 80% of NextNav test calls, vertical location was identified to a range of 1.8 meters or less, while 80% of Polaris test calls yielded a vertical accuracy range of 4.8 meters or less; both companies, the FCC noted, have asserted that they could meet the commission’s requirements within its proposed timeframe. The report noted that Polaris’ performance “could likely be significantly improved should a more robust handset barometric sensor calibration approach [than that used in the test bed]be applied.” CTIA, however, has told the FCC that “z-axis solutions must be further evaluated to determine whether, as the proposed rule requires, the solution can deliver ± 3 meter vertical location accuracy for 80% of wireless calls in the test bed” and that “further technology development and testing remains necessary to validate the accuracy of vertical location technology solutions to meet the FCC’s proposed metric … across regions, weather conditions and devices.”
What happens now?
Now that the testing is complete, the FCC has formally proposed the plus-or-minus-three-meter rule for mobile network operators and is taking public comment on it, as well as on whether it should instead adopt a two-meter rule or a five-meter rule, and the timelines which it should require and other details. The proposed rulemaking released in mid-March has an April 3, 2021 deadline for nationwide carriers to deploy the capability in the top 25 cellular markets and cover 80% of the population, with those requirements expanded to the top 50 markets by 2023. Smaller carriers would get an additional year to meet the benchmarks. Once the comment process on the z-axis location information is complete, the FCC can move ahead with approving a final z-axis location information metric. (More timeline information on vertical and horizontal location information to be provided by MNOs to public safety agencies is available here.)
CTIA’s independent test bed on the vertical location metric has also opened up another round of testing, Stage Za, and invited vendors to participate; Stage Za will begin in July.
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