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A Hybrid Wireless Location Solution Could Potentially Save More Lives

Author: Brian Varano, Director of Marketing for TruePosition

Copyright: 9-1-1 Magazine, Feature Content

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At first glance, the 9-1-1 system may seem straightforward: dial 9-1-1 when an emergency occurs and wait for first responders to arrive and provide assistance. For those who are familiar with 9-1-1 technology, the reality is not quite that simple, especially as it relates to locating 9-1-1 calls that originate from cell phones.  With the increased pervasiveness of cell phones, wireless carriers and public safety answering points (PSAPs) have had to utilize cutting-edge solutions to find and assist 9-1-1 callers more effectively.

9-1-1 Magazine file photo

A challenge that continues to face PSAPs is locating 9-1-1 calls from cell phones. With the inherent portability of cell phones, a 9-1-1 caller could literally be located anywhere in the U.S. In addition, the number of 9-1-1 calls coming from cell phones is increasing, as more and more people abandon fixed-line telephone service and rely solely on their cell phones for all communication.

When cell phones initially reached the mass market in the 1990s, the Federal Communications Commission (FCC) mandated that all wireless 9-1-1 calls be quickly and accurately located. To meet the stringent E9-1-1 location regulations, U.S. wireless carriers turned to one of two technologies: either network-based or handset-based. Network-based technologies use equipment that is installed in the wireless carrier’s network to calculate the location of the cell phone. Handset-based approaches require technology in the cell phone to make the calculation.


The Two Technologies: Network-based and Handset-based

Uplink Time Difference of Arrival (U-TDOA), the most widely deployed network-based technology, works by measuring and comparing the times at which a cell phone’s signal reaches several cell towers, which is a process called multilateration. Since U-TDOA is network-based, there is no need for handset manufacturers to install any additional hardware or software into the phone for it to work, which means that it can locate any phone regardless of its age or sophistication.

Assisted GPS (A-GPS), the most widely deployed handset-based technology, uses orbiting global positioning system (GPS) satellites to triangulate a caller’s location. A-GPS is accurate, but the chance of getting a location fix is not 100 percent, since it requires a clear line-of-sight with the orbiting GPS satellites. This means that if a caller is indoors or in a city with tall buildings, A-GPS’s ability to locate a cell phone will be negatively affected.

Currently, the FCC requires that network-based technologies locate 67 percent of 9-1-1 calls within 100 meters and 95 percent of calls within 300 meters. Handset-based technologies must locate 67 percent of 9-1-1 calls within 50 meters and 95 percent of calls within 150 meters; however, there is currently no mandate that specifically addresses accuracy for wireless 9-1-1 calls that are made indoors.


In July 2011, the FCC released a Notice of Proposed Rulemaking (NPRM) that addresses three areas related to E9-1-1 location: county-wide averaging, simplifying performance requirements, and an indoor location requirement. The NPRM will put a bright spotlight on the limitations of A-GPS. Before the FCC officially put the new rules in place, the FCC has initiated a nine-month-long assessment of the performance of A-GPS in various environment and conditions. It should be completed later in 2012. If the FCC votes for stricter indoor location requirements based on its findings on A-GPS technology, then wireless carriers will need to implement solution that meets the performance requirements that are specified in the ruling.


Hybrid Technologies

Because U-TDOA has demonstrated greater reliability and accuracy in locating cell phones indoors during testing, industry experts and key influencers in the emergency response sector are beginning to discuss a hybrid location solution that incorporates both technologies, U-TDOA and A-GPS, to improve the ability to calculate a location, regardless of where the 9-1-1 caller is.

In fact, during a recent webinar entitled The Importance of Locating Wireless 9-1-1 Calls Indoors, which was sponsored by the National Emergency Number Association (NENA), Trey Forgety, NENA’s Government Affairs Director, stated that “the optimum location solution would be one that uses multiple techniques to provide the best accuracy in locating callers in all environments.”

Utilizing a combination of U-TDOA and A-GPS technologies, wireless carriers could provide the most precise location regardless of whether a caller was indoors or in an urban environment surrounded by skyscrapers. The system would attempt an A-GPS location calculation, using the GPS satellites to try to get a location fix. If A-GPS did not work due to a blocked line-of-sight, the system would fall back to U-TDOA. Interestingly enough, in circumstances where A-GPS and U-TDOA could both perform calculations, the results could be combined to achieve better accuracy than either location technique would be able to achieve on its own.

A primary reason to consider a hybrid technology solution for indoor E9-1-1 location is that the strengths and weaknesses of U-TDOA and A-GPS are remarkably complementary: A-GPS works best in rural and remote areas, while U-TDOA works best in suburban and urban environments. Working together, both technologies create the optimum solution for locating wireless 9-1-1 calls.


What Now?

As with any public policy decision, cost must be taken into consideration. But the incremental cost of a hybrid solution surely is outweighed by the value of affording indoor and urban wireless callers the same high degree of confidence in the 9-1-1 location system afforded to other callers. Surely their lives are no less valuable.

Later in 2012, the FCC will rule on the issue of indoor location for mobile 9-1-1 callers. Although the primary consideration should be the safety and wellbeing of U.S. citizens who make indoor 9-1-1 calls from their cell phones, money and politics tend to play roles in these types of decisions. However, you can have a voice in the FCC’s decision process. You can visit the FCC’s Electronic Comment Filing System ( to make a comment about the importance of accurately and reliably locating wireless 9-1-1 calls that are made indoors (reference Docket Number  07-114).

With a hybrid wireless location approach, PSAPs will always receive high-accuracy location information regardless of whether the caller dials 9-1-1 indoors or outdoors. As a result, first responders will be empowered to potentially save more lives.


With nearly 20 years in wireless and information technology, Brian Varano brings substantial management and marketing experience to TruePosition. Prior to joining TruePosition, Varano served as the head of marketing for Advanced Management Group. He has also served as the head of analyst relations for the Commerce Internet Division of Sterling Commerce, an IBM Company. Varano is a graduate of Villanova University, where he earned a Bachelor of Science degree in Marketing.  For more information, see



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