The US Moves Wireless 911 Requirements Indoors

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The US Moves Wireless 911 Requirements Indoors

Adrian Stimpson
| April 22, 2015
Industry Views
The US Moves Wireless 911 Requirements Indoors

The proliferation of GNSS equipped mobile phones has had a profound effect on society’s ability to respond to emergencies. The days of running to the nearest house or payphone to call 911 are now just a historical footnote.  In fact, 80% of 911 calls are now made from mobile phones.

Rx Networks is a major player in the wireless 911 market, supplying the GNSS assistance data used by all Canadian, and the majority of US, mobile subscribers.

The service has saved countless lives, however, the ability to determine the exact location of a caller who is indoors, outside the reach of normal GNSS coverage, has been a problem the companies like Rx Networks have been working hard to address.  Given that 64% of mobile calls are made from indoors, and many are from within multi-story buildings, there is a need to determine not just the building address (using an x, y coordinate), but also the floor the caller is on (altitude/z-axis).

Given the work that Rx Networks and other companies have done in recent years, the US Federal Communications Commission (FCC) recently asked companies to comment on proposed rules for mobile operators that would require them to accurately determine a wireless 911 caller’s location, even if indoors. The end goal is a “dispatchable address” where first responders know exactly where to go – address and floor.

Rx Networks provided a response to this request for comments (available at, highlighting some of the ways we could help mobile operators meet a potential mandate.

With much input from industry and other stakeholders, including first responders and the general public, the FCC adopted new rules on January 29, 2015, that set out the following timelines and accuracy requirements for the national mobile network operators (regional operators have slightly extended deadlines):

Either a dispatchable location or x, y accuracy of 50 meters or better must be achieved as follows:

  • Within 2 years, 40% of the time
  • Within 3 years, 50% of the time
  • Within 5 years, 70% of the time
  • Within 6 years, 80% of the time


In addition, the FCC set out progressive steps that will lead to the establishment of a vertical location requirement, as follows:

  • Within 3 years, all providers must make uncompensated barometric data available to public safety answering points, for handsets equipped with such sensors. Providers must also use an independently administered and transparent test bed process to develop a proposed z-axis accuracy metric.
  • Within 6 years, the wireless providers must be able to provide a dispatchable location or z-axis location that meets the FCC accuracy requirements that will be adopted. For determining a dispatchable address, the FCC will require the establishment of a National Emergency Address Database (NEAD) that will have dispatchable reference points that can be associated with signals such as Wi-Fi access points or Bluetooth beacons. The NEAD must initially cover the top 25 Cellular Market Areas (CMA) / Metropolitan Statistical Areas with a density of dispatchable references equal to at least one quarter of the population of each CMA. This will be expanded to 50 CMAs within 8 years.

So, how will this be done? Based on the comments the FCC received, it was acknowledged that no single technology could address all use-cases. In fact, unlike previous mandates, the FCC agreed with Rx Networks that simply setting an accuracy target made more sense than mandating a technology. After all, technology tends to advance faster than regulations.

It is Rx Networks’ view that to meet the mandate, a combination of GNSS, Wi-Fi/Bluetooth positioning, and sensor integration (notably barometric pressure), will be required. Yet, therein lies a range of challenges to make such an integrated system work well. Let’s look at them a little closer:

GNSS – Use of GPS has been the foundation of wireless 911 for several years. When Rx Networks opened for business in 2006, the use of assistance data on mobile phones was a relatively new idea. We now provide assistance data to over a billion mobile phones and it has become an expected feature on all phones, providing a 10-12 dB effective sensitivity improvement and facilitating fixes in a number of indoor environments. The addition of other constellations has further augmented the performance of GPS. Our data sources now include not only GPS, but also the Russian system “GLONASS”, the Chinese system “Beidou” and the European system “Galileo.” More satellites means a greater ability to get a fix, particularly in indoor and other weak-signal environments. For more on this, see our study of combined GPS/GLONASS/Galileo performance at

Wi-Fi/Bluetooth Positioning – Wi-Fi positioning is well developed, being used routinely in today’s smartphones for social media and other apps. However, we’ve all experienced situations where the location we are presented with is completely wrong. This simply can’t happen in life or death situations. Bluetooth presents a new range of challenges, particularly given that many Bluetooth beacons are mobile, or at least nomadic. To address this, Rx Networks has developed reliable methods for determining and verifying the location of these signal sources. In fact, we are currently conducting a trial with a carrier where the devices accurately self-locate and report their location into the database. Reliable results, no risk of human error, and moves or changes are automatically addressed.

Barometric Sensors – Increasingly smartphones are being equipped with barometric pressure sensors. They are amazingly sensitive, detecting a change in altitude of as little as 1 meter. Then there are manufacturing variances between sensors, which have to be normalized. Then there is the need to compensate the pressure reading for current weather conditions, something that can vary as often as every 15 minutes. To address this, Rx Networks has developed a service called simply “Zed™”.  Zed normalizes sensor behavior and compensates the pressure reading based on current weather conditions near the caller’s location. The result – an accurate z-axis fix within 1.5 meters…easily accurate enough to determine a floor level.

The next few years will be an exciting time as these technologies, and those from other industry experts, get tested and ultimately deployed. As with the previous wireless 911 mandate, the new one will inspire greater innovation, not only saving lives, but also improving the overall location experience for mobile users.