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Dec 11, 2018 | In the News

Solving the e911 problem: Locating emergency callers accurately

Nearly 80 percent of all 911 calls originate from a wireless device. This is not surprising, given that over half of households in the U.S. have given up landline phones and rely solely on wireless devices. This is a rapid increase from 15 percent in 2006 and shows no signs of slowing. However, only a fraction of wireless 911 calls can be located with pinpoint accuracy. The system, originally designed for an analog landline network, has struggled to keep pace with the massive shift to wireless devices and is facing pressure from government regulators, public safety advocates, and consumers to solve the problem of how to quickly and accurately locate emergency callers.

FCC demands accuracy

Over the past two decades, the FCC has issued increasingly stringent requirements on wireless providers to provide PSAPs (Public Safety Answering Points) with detailed location information of emergency callers:

  • 1998 – Enhanced 911 (E911) Phase I – Wireless providers must provide the PSAP with the telephone number of the originating device and the location of the transmitting cell site.
  • 2001 – E911 Phase II – Wireless providers must provide the PSAP the precise latitude and longitude of the originating device, with location accuracy ranging between 50 and 300 meters depending on the type of technology being used. In 2010, these rules were adjusted tightening the geographic areas for compliance and increasing the percentile of calls covered at the higher accuracy metric.
  • 2015 – Increased Horizontal Accuracy and Indoor Location – The FCC requires horizontal location accuracy to within 50 meters, regardless of location technology used, for an increasing percentage of 911 calls (from 40% of calls in 2017 up to 80% of calls by 2021). The Commission also called for ‘measures that will significantly enhance’ the ability of PSAPs to identify emergency calls originating indoors and required that compliance testing include indoor location.
  • 2018 – Vertical Location – Wireless providers must provide the vertical location in the 25 largest metropolitan areas by 2021, and in the 50 largest by 2023. The FCC has not yet specified a vertical location metric but is currently considering a recommendation made by wireless industry groups in August 2018, with a proposed ruling expected in late 2018 or early 2019.

Evaluating location technologies

Wireless providers have sometimes struggled to keep pace with these E911 requirements, with one major hurdle being the choice of location technology.  As the scorecard below illustrates, the most commonly-available location technologies differ significantly across several factors:

Location technology scorecard




Network-Based Software-based Hybrid
Horizontal Accuracy üü üüü üüü
Vertical Accuracy ü üüü üüü
Indoor Accuracy üü üü üüü
Publicly Disclosed Performance ü üüü üüü
Deployment Time üüü ü üüü
Deployment Cost üüü ü üüü
Universality üü ü üüü
Commercial Applicability üüü üü üüü


  • Device-based hybrid technologies work only on a specific operating system, such as Apple or Android. No device-based location capability has been delivered that is publicly proven to meet the needs of public safety agencies.  This past June, Apple announced it would automatically share location information with first responders by the end of this year, and other device companies are working on similar developments.  Even as device capabilities improve, they only work with one brand of devices (and typically only with newer generation versions of that brand).  They will not locate emergency callers universally across a given area, so a wireless provider must adopt multiple systems or risk being unable to meet the FCC’s accuracy requirements.
  • Network-based technologies are device-agnostic, so do not have the limitations of device platform-specific solutions. They offer more control for wireless providers but require the deployment of specialized network hardware.  This is time-consuming, costly, and limits E911 coverage to wherever the hardware has been deployed.  In addition, some hardware solutions also require specific changes to devices operating on these networks, which further exacerbates the deployment time and cost factor.
  • Software-based hybrid technology does not rely solely on device capabilities and does not require the deployment of specialized hardware or devices. Because it incorporates inputs from a wide variety of sources using multiple location techniques, it is the most adaptable to today’s evolving wireless networks. Hybrid technology incorporates GPS, Wi-Fi, cellular signals, and device sensors to increase accuracy indoors and outdoors, and can be deployed network-wide without the delay, cost, and complexity of network hardware.

Attaining the new horizontal location accuracy requirement is proving to be no small feat for wireless providers, and indoor and vertical accuracy promises to be similarly difficult.  Many location technologies are available, yet they differ significantly across several factors, and wireless providers must balance the FCC’s accuracy regulations and timetables with their own desire to deploy these capabilities in a non-disruptive and cost-efficient manner.  An additional consideration is the ability to adapt any public safety-focused location technology for commercial use to satisfy consumers’ demand and open new revenue streams.  In the end, one objective overrides all others – the need to locate emergency callers accurately, and in any environment, must not be sidetracked by lingering technology evaluations and funding considerations.


About the author

Dr. Tarun K. Bhattacharya serves as the Chief Technology Officer of Polaris Wireless Inc.   Dr.  Bhattacharya has over 25 years’ experience in the design and development of advanced signal processing systems for commercial and military applications. Dr. Bhattacharya’s areas of expertise include spatiotemporal filtering, neural networks, pattern recognition, time-frequency distributions, geolocation, and multi-target tracking with data fusion. Dr. Bhattacharya earned the Ph.D. degree in Electrical Engineering from Indian Institute of Science.  He has more than 20 issued patents.

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