The Debate Over Accuracy Testing
Once the system is built, other daunting challenges will arise. Carriers, for example, will have to manage the accuracy of the system. Given the limitations of radio, wireless E911 is inherently inaccurate, especially compared to wire-line E911 systems, which trace phones connected to wires located at specific addresses.
According to Dale Hatfield, the FCC regulations governing accuracy recognized the
inherent inaccuracies of location technologies and allowed for a level of uncertainty. Carriers using network-based solutions must, on average, locate 95 percent of wireless calls to 911 within 300 meters and 67 percent of calls within 100 meters. For handset-based solutions, the rules require an average of 150
meters for 95 percent of calls and 50 meters for 67 percent.
“Accuracy varies with the environment and the type of system,” notes Hatfield.
“Network solutions tend to be more accurate where base stations are close together. In the country, where towers are farther apart and lined up, accuracy will suffer. The same is true of a handset solution when a caller is inside a building and the satellite can’t see the handset.”
The FCC’s averaging strategy aimed to solve this problem. But a debate has broken out over the proper geographical boundaries to be used for averaging. Should the geography be system-wide or national? Should it encompass a state? Should it be within the jurisdiction of each of 6171 PSAPs?
“It’s a very knotty problem,” Hatfield says.
Early this year, a focus group or subcommittee of the FCC-chartered Network
Reliability and Interoperability Council (NRIC) discovered just how knotty the issues surrounding accuracy testing were. After months of debate, the focus group issued recommendations to answer the geographical question about wireless E911 accuracy testing. The recommendations emerged from the focus group with a 48 to 1 vote.
“Right now the recommendations say state-wide accuracy testing,” says Hixson,
who served as NENA’s representative in the NRIC focus group.
According to NRIC’s recommendations, systems accuracy testing would be done twice. The first tests would run when 50 percent of a state’s PSAPs have been equipped to receive location information. The second leg of testing would take place when deployment reaches 90 percent — to confirm that accuracy ranges are still being met.
