Wireless 9-1-1: Phase 2
Wireless 9-1-1 Location:
A Positive Move for PSAPs
by Mark Licht
| Mark Licht is President, SigmaOne Communications Corporation, a leading provider of analog and digital wireless location tracking systems for the cellular, PCS and ESMR markets. The company uses a proprietary Correlative Angle of Arrival (AOA) technology. |
| Sidebar: Why We Need Cellular ALI |
| Related Articles: Wireless 9-1-1: Phase 1 |
| Photographs: (select thumbnail to view detail image) |
 Wireless calls are not simply for citizens. Responders are also finding them valuable for field use. The same kind of technology used to locate wireless 9-1-1 callers can aid dispatchers in managing field resources who use wireless phones. Ken Kerr |
 Cellular antennas, such as this 5-dipole DF pentagon array antenna from SigmaOne, are the focus of much wireless 9-1-1 location technology. Processes to triangulate a caller's position from two or three antennas may be the answer to the FCC's Phase II mandate to locate wireless 9-1-1 callers by October, 2001. SigmaOne |
 Arlington (TX) dispatcher Maria Dimas processes a 9-1-1 call. Wireless calls do not currently come with ANI/ALI information that 9-1-1 centers have come to expect from landline calls. Accuracy of wireless E9-1-1 location systems is critical to dispatchers being able to realistically pinpoint a caller's location. courtesy Alisa Simmons/Tarrant County 9-1-1 District |
 Some wireless E9-1-1 location technologies rely on a GPS receiver inside the cellular phone, such as this FonFinder from Tendler Cellular. The phone broadcasts the lat/long of the caller via a voice chip when the caller connects to 9-1-1. Tendler Cellular |
This article can be found on
page 64 of the May/June 1998
issue of 9-1-1 Magazine.
To declare that wireless 9-1-1 calls constitute an operational nightmare for public safety agencies is an understatement. Statistics point out that 25 percent of all 9-1-1 callers do not know where they are, making it difficult to respond to emergency needs. Add to this equation the fact that wireless carriers do not have the technology installed to determine wireless caller position location, and the real picture unfolds of how difficult it is for Public Safety Answering Points (PSAPs) to be responsive to emergency situations involving wireless calls. This scenario can be overwhelming and aggravating to those charged with amassing data and sending help.
If the trend of one-third of the 9-1-1 calls being from wireless phones continues, The Strategis Group predicts public safety telecommunicators will be answering 50 million wireless calls by the year 2000. That translates to 140,000 wireless 9-1-1 calls per day.
The FCC's requirement for wireless carriersincluding cellular, enhanced specialized mobile radio (ESMR) and personal communications services (PCS)to provide position location is a welcome ruling for public safety officials.
With the April FCC deadline for Phase 1 emergency 9-1-1 compliance having
passed, attention is turning toward Phase 2 of the FCC-mandated plan to
have wireless location accuracy of 410 feet - or one sigma - 67 percent
of the time by October 2001.
Protecting Public Safety Via Location
Today, there is no one network that all public safety emergency personnel can utilize to track and actually "know" what is happening when various emergency personnel respond to a disaster. For instance, information on the response location of police officers, where the nearest ambulance is, and where firefighters are discharged, would be beneficial in an interagency coordination effort. Such position location of various agencies would be tracked on an area map, similar to a war room strategy.
In the future with the deployment of wireless E 9-1-1 systems and the availability of inexpensive cellular and PCS phones, location technology can benefit public safety agencies with the location of emergency personnelmaking managing a disaster easier and responding to emergency needs more efficient. More importantly, these E 9-1-1 systems can be used to protect the lives of public safety personnel who have been injured or are in danger.
Wireless E 9-1-1 solutions are important to public safety officials,
but sorting out the technologies can prove to be a monumental task. PSAPs
are being inundated with the attributes of various position technologies,
but what do these mean to 9-1-1?
Sorting Through Solutions
An overview of the potential technologies available may prove beneficial to 9-1-1 officials. The technical solutions for wireless 9-1-1 tracking include the Global Positioning System (GPS), ray tracing, angle of arrival (AOA) and time difference of arrival (TDOA).
GPS is used today for tracking large fleets and courier services. The technology relies on the GPS constellation of 24 satellites to track location.
Another technology is ray tracing or multipath fingerprinting. This location technology matches the wireless signal patterns with those in a large database, then fingerprints the appropriate signal pattern. This technology requires continual database management and comprehensive updating. It still remains in the proof-of-concept stage.
TDOA utilizes "trilateration" requiring three cell sites for location determination. It calculates the difference in time it takes a signal to reach various cell sites to calculate a point that represents the caller's location. Location data comes from the control channel, which is used when a wireless subscriber signs on to a system prior to beginning a voice conversation. When a wireless user changes locations, position location tracking becomes difficult because TDOA has difficulty in locating on the voice channel.
Traditional AOA only requires two cell sites to determine location. AOA uses a special array antenna to actually determine the location of an incoming signal. A cross-vector from a second cell site pinpoints the caller's location.
AOA ranks as a reliable and highly accurate technology. It has been proven
in a harsh and difficult environmentthe military. With AOA, location is
possible on both the control and voice channels, which eases the tracking
of moving vehicles and people and allows for flexibility of use and improved
accuracy.
Some Technologies May Not Be Effective for 9-1-1
Although GPS is quite accurate in open areas with good line-of-sight to the satellites, the signal can be lost in urban areas and in areas with heavy foliage.
Some industry officials deem GPS as not effective for 9-1-1 due to the heavy costs associated with retrofitting the 100 million subscriber phones that are expected to be in the market by 2001. In addition, all wireless handset manufacturers would need to adopt GPS and incorporate the chips in their phones in order for this technology to satisfy 9-1-1 location needs.
For example, if some manufacturers did not construct their phones with
GPS due to cost restraints, the wireless subscribers who purchase these
phones would be unable to be located when they sign on to a wireless network.
In addition, price-sensitive consumers may not want to pay for more expensive
wireless phones that are retrofitted with GPS chips in order to incorporate
position location features. Of the technological solutions available to
solve the wireless location, some are only able to pinpoint a caller's location
at the onset of a call and cannot track the caller if mobile.
Buying Into Location
Although cost-recovery mechanisms are in place for state agencies to collect a surcharge from the public for wireless E 9-1-1 deployment and implementation, PSAPs remain concerned about costs. For example, what percentage of these funds will be allocated to pay for public safety agencies to modernize their computers and systems to be effective to handle wireless E 9-1-1 position information? And, what percentage of these public funds will go toward the carriers' costs of building the wireless infrastructure to handle position location? This is a gray area.
"Look at it from the PSAP side," says industry analyst Clem Driscoll. "With the potential for nine cellular, PCS and ESMR carriers, local PSAPs might have to reimburse nine systems. You can bet cost will be a major discussion point."
The big disagreement remains with where the funds should go. "Regardless of the cost-recovery mechanisms used, the implementation of location technologies across wireless networks is likely to cost more than $2 billion and is likely to occupy wireless carrier and public safety resources well beyond the five years specified in the FCC Rulemaking," according to The Strategis Group.
"Cost is a major concern for public safety. The FCC order allows the wireless companies to recover their costs but it also requires a PSAP to order the service," said Bill Munn, president of the National Emergency Number Association and executive director of Tarrant County 9-1-1 in Fort Worth/Arlington, TX. Munn emphasizes: "Public safety's primary concerns over location technology are accuracy and cost."
The role PSAPs play in the E 9-1-1 deployment will be to actively evaluate systems and work jointly with the carriers to find equitable solutions to E 9-1-1 implementation.
Location can be a value-added service to both PSAPs and wireless carriers.
Cooperative agreements with PSAPs and carriers in both Phase 1 and Phase
2 deployment will be essential in meeting position needs for all concerned.
Evaluating E 9-1-1 Systems
Important factors to consider when evaluating wireless E 9-1-1 systems include:
Accuracy - What is the real accuracy of the system in different environments - urban, suburban and rural?
Availability - 67% is mandated by the FCC, but this is not optimal. What percentage of calls will not display location?
Interstate Highways and Rural Areas - TDOA systems, for example, have difficulty providing location along highways where only two sites are visible.
Capacity - If these E 9-1-1 systems are to be used by public safety on a daily basis, as well as during disasters, their capacity will be important.
Proven Technology - The technology chosen must have a long track record of deployment. For example, AOA and TDOA systems have been developed and fielded over the past 30 years. There is too much at stake - and too little time - to experiment.
9-1-1 Location Must Be Available to all Wireless users - Location solutions that require modification of all wireless handsets with GPS receivers will have difficulty in meeting this goal.
Quality of Location Information - Location systems will need to provide both an initial location and location updates as required by the PSAP call taker.
Company Stability - Companies providing location systems will need to
have the financial and manpower resources to support the manufacturing,
deployment and operational requirements of wireless E 9-1-1 location.
Conclusion
Location systems not only will provide needed position services but will parlay into diverse applications that law enforcement personnel can utilize to enhance their own operations. For the E 9-1-1 mandate and resulting location technology deployment to be successful for both the public and law enforcement, carriers and public safety officials need to cooperate on technology review and deployment strategies.
