June 4, 2007 4:00 AM PDT
Homing in on a plan for cellular 911
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The FCC supports a proposal from the Association of Public Safety Communications Officials International (APCO) that specifies accuracy should be tested at the public safety answering point, or PSAP, level instead of on a statewide or regional basis. In a recent report, APCO reported that if accuracy were measured from the PSAP level, about 71 percent of tests made in seven sample regions would have failed to meet the FCC's standard for accuracy.
The cell phone industry opposes these new requirements. In a letter filed with the FCC, Verizon Wireless, T-Mobile USA, Dobson Communications and the Rural Cellular Association (RCA) said that changing the requirement would be "unwise" and "unlawful." They also fear that establishing stricter requirements would be too expensive, especially for carriers operating in rural areas.
"Rural carriers are doing everything they can to improve accuracy of E911," said Clay Dover, executive director for the RCA. "But in some of these areas you only have one cell tower, and you can't mandate companies build out a network for E911 compliance if it's cost-prohibitive."
Indeed, location accuracy can be especially problematic for carriers using GSM (Global System for Mobile Communications) technology. These carriers, which include AT&T and T-mobile, use a network-based technology that uses signals from multiple cell phone towers to determine a caller's location. But in some sparsely populated regions where there is only one cell phone tower, it's impossible to triangulate signals to get an accurate location. And putting up additional towers is too expensive.
Carriers that use CDMA (Code Division Multiple Access) technology have their own challenges. These carriers, which include Verizon Wireless and Sprint Nextel, have embedded GPS receiver chips in handsets to track devices by satellite. This solution works well in a rural or suburban area where there is a direct line of sight between the satellite and the device, but it isn't as effective in cities where tall buildings can block satellite signals.
Both the network-based technology and the handset solutions can have trouble locating people inside large buildings, because some signals can't penetrate walls.
Due to these technology limitations, the FCC has applied two different sets of standards for accuracy compliance. Carriers using GPS-enabled handsets must be able to locate callers within 150 meters 95 percent of the time and within 50 meters about 67 percent of the time. Mobile operators using a network-based solution only need to locate individuals within 300 meters 95 percent of the time and within 150 meters 67 percent of time.
In an effort to address these issues, the FCC also has proposed looking at new technologies to improve accuracy. For example, it is currently seeking public comments on whether it should mandate the use of hybrid solutions that would combine network-based triangulation technology with handset-based satellite technology.
Verizon Wireless said it is already using a hybrid solution to help improve E911 accuracy as well as to provide location and navigation services to its subscribers. The way it works is that the system first uses a GPS receiver to get the location of the handset. If the signal isn't strong enough, the system then uses data from cell sites combined with satellite information to get a location. And if that doesn't work, it can use cell site data, which is similar to triangulation used on GSM networks, said Debra Lewis, a spokeswoman for Verizon.
Regardless of which rules, if any, the commission eventually adopts, Wanda McCarley, president of APCO, said it is important that the cell phone industry and public safety groups move forward to improve location accuracy, because it's what the public expects.
"Carriers have limitations in terms of the technology that is available to them," she said. "We understand that. But I think it's clear that in some areas of the country people are not getting the services they expect. We need to deal with that and fix it."
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