Public Safety Needs Indoor Wireless 9-1-1 Accuracy Standards
May 09, 2012
Charts courtesy NENA
In July 2011, the FCC took its first step toward addressing indoor 9-1-1 wireless location accuracy with a ruling that established the Communications Security, Reliability and Interoperability Council (CSRIC), tasked to research possible indoor solution requirements. The public-safety community hopes that the research will be presented and action will follow sometime in 2012.
The FCC mandated wireless carriers to meet standards for locating outdoor wireless 9-1-1 phone calls — within 50 meters 67 percent of the time and within 150 meter 95 percent of the time (by 2019) — but the standard applies exclusively to outdoor calls. No standards have been established for locating wireless 9-1-1 calls indoors.
Several myths regarding the challenges of locating indoor wireless calls have helped stall the process. Misconceptions include the view that assisted-GPS (A-GPS) is sufficient for indoor locations, that no technology is available to solve the problem, and that indoor testing is too expensive and time intensive, said Sara Kaufman, analyst, telco strategy, Ovum. But in reality, “the lack of indoor standards represents a huge gap,” she said.
Through testing performed by TruePosition and Ovum, an independent research company, a hybrid solution that deployed both the predominate technologies used for outdoor location findings — A-GPS and uplink time difference of arrival (U-TDOA) —provided the most accurate findings in indoor and outdoor tests.
The National Emergency Number Association (NENA), Ovum and TruePosition hosted a webinar focused on raising awareness about the importance of locating wireless 9-1-1 calls indoors. Ovum also released a white paper
detailing the test and findings.
With the goal of testing the real-world accuracy of U-TDOA and A-GPS technologies, TruePosition and Ovum conducted a five-day test in Wilmington, Del., with test points inside and outside of 11 buildings, and 50 test calls made at each point. The tests dialed 9-1-1 and the calls were treated as normal 9-1-1 calls by the system, except a provisionary switch in routing routed the calls to a message bank rather than a public-safety answering point (PSAP).
The tests tried A-GPS, U-TDOA and two types of hybrids. One hybrid first looked for A-GPS, and if that was unavailable, fell back to U-TDOA.
The optimal hybrid option is the weighted hybrid, used when both technologies can function. Both technologies search for the location and the results are combined and weighted. “The accuracy of the hybrid is better than either of the technologies used alone,” said Brian Varano, director of marketing, TruePosition.
The indoor test results are plotted in the chart above. When all points, indoor and outdoors, were shown together (more than 1,300 calls), the hybrid solution far exceeded A-GPS and was more accurate than U-TDOA.
“The hybrid had significant gains from either technology by itself,” said Dr. Rash Mia, vice president of technology and chief scientist, TruePosition. “The hybrid offers better performance than either on their own. We’ve done several tests, and the results seem to be fairly consistent.”
Outdoor Location Findings
The FCC set standards for outdoor wireless location accuracy in 2001. In July 2011, in addition to establishing CSRIC, the FCC amended the outdoor standards. The new rule stopped carriers from conducting nationwide averaging when calculating if they were meeting the acceptable location findings. Now the averages must be based on countywide results to ensure carriers meet the standard everywhere. The commission also eliminated different location accuracy standards based on the type of technology. Originally, two separate sets of standards were established for handset-based and network-based location findings. With this proposed rule, regardless of which technology carriers deploy, they all must meet the same standard.
The two technologies deployed by carriers to achieve outdoor locations are A-GPS and U-TDOA. Major CDMA carriers chose the handset-based solution (A-GPS) while major TDMA/GSM carriers chose the network-based solution (U-TDOA).
A-GPS has proven to be accurate outdoors, but the technology requires a clear line of sight (LOS) to make contact with the nearest satellites. The technology can struggle if the device is in a building or in a dense city with lots of high-rises, where there is not clear LOS.
Comparatively, U-TDOA uses location measurement units (LMUs) to calculate the location. In highly populated cities where LMUs are numerous, the technology can provide very accurate results. However, as the number of LMUs available diminishes, the calculation can become less accurate. It can be especially difficult in some rural areas that deploy towers in a straight line along a highway as the geometric calculation is limited, Varano said.
“This is why a hybrid solution is such a compelling option,” Varano said. “The technologies are so complementary to one another.”
As wireless cell phone use continues to increase at a rapid rate, NENA officials urge users to contact the FCC to address the indoor location issue. The public can file comments in the FCC electronic comment filing system (ECFS) with reference to the docket number 07-114.