CAPITAL CURRENTS: Cell phone E911 location update

Mon, 12/31/2007 - 7:05pm
Jeffrey Krauss, President of Telecommunications and Technology Policy

The FCC has just released a decision that requires cell phone companies to meet the location accuracy requirements over much smaller geographical areas than is the current practice, and you can hear their screams for miles. Even though the FCC allowed five years for full implementation, the screams seem justified.

Jeffrey Krauss

The operational
burden is evident

There are two kinds of cell phone location technologies, and the FCC has different accuracy requirements for them. For “network-based” technologies, accuracy must be within 100 meters for 67 percent of calls, 300 meters for 95 percent of calls; for “handset-based” technologies, within 50 meters for 67 percent of calls, 150 meters for 95 percent of calls. The remaining 5 percent of calls are handled on a “best efforts” basis.

“Network-based” generally means Time Difference of Arrival (TDOA) – a carrier has receivers located at cell towers and determines a cell phone location by processing the signals received from that cell phone, which arrive at slightly different times at the different receiver locations. “Handset-based” generally means a cell phone has a built-in Global Positioning System (GPS) receiver – it calculates its own location by receiving transmissions from at least three GPS satellites.

They both work well in some areas but not so well in other areas. Network-based systems work well in urban areas where there are many receiver locations, but not so well in rural areas. Handset-based systems work well in rural areas where there is a clear line-of-sight path to the satellites, but not so well in urban areas and indoors where the satellite signals are blocked by buildings.

Cell phone companies claim that they meet the FCC accuracy requirements. But the national operators (AT&T, Sprint, Verizon and T-Mobile) have been meeting the requirements on a national average basis. Now the FCC has decided that they must meet the accuracy requirement within the geographical coverage area of every Public Safety Answering Point (PSAP). According to Consumer Reports magazine, accurate location information is not delivered at the PSAP level in nearly half of the country. According to a list maintained by the FCC, there are around 6,000 to 7,000 PSAPs in the U.S. Verizon says it has deployed E911 wireless location capability in areas served by more than 2,800 PSAPs. But it has run into cases where cities and counties conflict with one another, each claiming PSAP jurisdiction over the same area. And PSAP service areas vary in size and shape. But the FCC said, “We recognize that geographical variations in service areas can present challenges to the provision of E911 service, but in the interest of public safety, we cannot permit those challenges to justify diminished location accuracy.”

The FCC accuracy rules are statistical in nature, and hundreds of test calls are required to determine the 95 percent confidence level. That would translate into millions of test calls if accuracy had to be confirmed for each PSAP separately. So the operational burden is evident. But the FCC was unsympathetic, saying, “While we acknowledge that meeting the deadline and benchmarks may require the investment of significant resources by certain carriers, we believe that such expenditures are more than justified by the accompanying public safety benefits.”

But more importantly, there is widespread agreement among everyone but the FCC that achieving the accuracy requirements within every PSAP area with today’s technologies is infeasible. For example, using GPS in urban areas with tall buildings or indoors, it may be impossible to achieve any location fix at all in more than 5 percent of locations, so the 95 percent requirement could never be satisfied.

Several companies proposed a hybrid approach, using both GPS and TDOA. The carriers that have deployed GPS handsets would have to add cell tower receivers for TDOA. The carriers that have deployed cell tower receivers for TDOA would have to include GPS in new cell phones. But while the hybrid approach would improve location accuracy, and might satisfy FCC requirements in the majority of PSAPs, even proponents agree that improvement might not be sufficient to satisfy the accuracy requirements in every PSAP. While the accuracy standard applies to 95 percent of calls, it applies to 100 percent of PSAPs.

This new requirement is potentially a big deal for cable operators, if the FCC decides to apply it to VoIP phone service. Cable MSO VoIP service is intended to be used only at the subscriber location, which is known precisely. But what about “over-the-top” voice services like Vonage and Skype? Suppose the FCC creates a VoIP location accuracy requirement, and then imposes it on the underlying ISP rather than the “over-the-top” vendor.

This new FCC requirement will certainly be appealed in court. Courts have not been too sympathetic to the cell phone industry, affirming earlier FCC decisions that required aggressive deployment of existing location technologies. But this is different, because the FCC has no evidence that it is technically feasible to meet the accuracy limits within every PSAP area. The last time I can recall that a court had to review an FCC decision that was technically infeasible, it dealt with noise figure limits for UHF TV tuners, and the FCC was reversed. It could happen again.


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