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Put a Location in Wireless E-911

Cellular 911 calls are on the rise, and wireless systems are need to help dispatchers quickly pinpoint a caller's location.

We've all heard or read how a cellular phone has helped save a life or locate an individual in trouble. At last count, there were close to 60,000 wireless 911 calls made per day, coming from 50 million wireless telephone users in the United States. It is projected that by 2001 wireless call volume will exceed the number of calls initiated with wireline networks.


Wireless calls pose a challenge to 911 emergency personnel. It is difficult to track down the exact location of the emergency from a 911 wireless call. Wireline 911 calls provide information to emergency personnel, such as a callback number or the caller's location. But wireless 911 calls don't provide that information, and often the person making the call can't give a detailed description of the emergency's location.

Responding to the increase in both cellular phone usage and cellular 911 calls, the FCC issued a Report and Order (Docket 94-102) to address the lack of information from a 911 wireless call. The FCC suggested reporting a callback number and originating cell site to 911 operators when an emergency call is made. Eventually, the FCC's solution should provide the caller's location as well.

Currently, when a wireless 911 call comes into a Public Service Answering Point (PSAP), only about half the callers can tell the dispatcher where they are. Wireless 911 calls therefore usually take longer and multiple calls are often received for a single event. Multiple dispatches of emergency personnel waste equipment and staff time.

New Jersey Pilot

New Jersey was the first state to implement a wireless E-911 solution. The state's Office of Emergency Telecommunications Services (OETS) wanted to solve the 911 location problem. The test began in January 1997 and lasted 100 days. Its main objective was to determine whether the existing commercial technology meets the new FCC criteria.

OETS used an existing Comcast Cellular Communications system that covers a 50-mile corridor of the New Jersey Turnpike and I-295 through four counties. TruePosition provided the wireless location system technology; SCC Communications provided the E-911 routing and mapping capability; MapInfo provided the mapping programs; Rockwell provided the terminals and KML Technology provided the PSAP component.

TruePosition's wireless location system was a key technology. It is based on Time Difference of Arrival (TDOA), a triangulating technology based on precision timing -- to the nanosecond level of a mobile unit's signal -- as the transmission is received at various cell sites. For example, the closest cell site may receive the transmission a few nanoseconds before a slightly more distant cell site. A third site will also receive the signal after a slightly longer delay. Three to eight different cell site receivers are required to time a call and triangulate precise x and y map coordinates.

With the new system, dispatchers were able to pinpoint 911 Comcast cellular callers on an electronic map. They also received automatic caller ID information and located 67 percent of those calls within 125 meters of origin.



TDOA is at least a year ahead of other locator technologies. Although TruePostion is the first to be implemented in real-world conditions, it is expected that Raytheon, E-Systems, AccuCom Wireless and Lockheed-Sanders will also launch E-911 locator systems.

TruePosition's TDOA is a passive overlay network system similar to global positioning systems (GPS) and radar-signal positioning. "Our system is composed of receivers that listen to the signals that the cellular phone gives out," said TruePosition's President and CEO Kent Sander. "It measures that signal between cell sites and places a timestamp on the signal."

Selective routing platforms pass cellular calls through Bell Atlantic's switched network and to the closest PSAP, which maps the location for the dispatcher.

Every cell site and sector in the system is assigned an ANI (Automatic Number Identification) 10-digit identification number. When the 911 call is routed to the tandem switch, the 10-digit number is transmitted. Within five seconds, the call is recorded in a 911 location database. The database is queried for the location and the information is routed to the responsible PSAP closest to the caller. Location information is displayed, along with the caller's mobile number, on a map.

"The findings from the New Jersey trial represent significant progress in our efforts to locate emergencies after a wireless 911 call is made," said New Jersey Attorney General Peter Verniero. "With the technology in place, dispatchers will spend less time with the caller determining their location and will be able to dispatch the right emergency equipment to the right location at the right time."

"When this or comparable technology is fully in place, wireless callers will receive the same 911 benefits as those who call from wired phones," said Robert Miller, OETS director.

The Wireless Weave

Cooperation is key for effective wireless 911 location systems. "Because wireless service markets cut across towns, counties and states, all must be ready to deploy such a system," Sander said. Elected and public safety leaders have to develop a consistent approach to wireless 911 so there is interstate cooperation," he added.

Redundant antenna siting is the only way this type of technology will work. There must be proper triangulation between a number of cellular antennas. Additionally, PSAPs must have updated equipment to handle the explosion of wireless 911 calls.

Financing for the New Jersey pilot came from general revenues, government bonds and surcharges on telephone bills, including wireless accounts. Governors, state legislators, PSAPs and carriers must come together to determine cost-recovery plans for wireless location technology.

"[Other communities] can look at the technology we tested, together with other technologies which could be used for the same purpose, and make whatever refinements are necessary for full-scale implementation of the FCC's requirements," Miller said. "We've shown it can be done, now it's up to the industry to follow through."




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