E-911 Unveiled

The E-911 Phase II deadline is October 2001. Here's a rundown of handset- and network-based solutions.

With nearly one-third of all 911 calls coming from wireless phones, all wireless providers have until October 2001 to implement a solution capable of locating a 911 caller within 120 meters for at least 67% of all calls. Several solutions exist, and providers must pick one by this October.

The industrywide deployment of location technology is expected to seed the market for enhanced services that will use the E-911 location technology:

• Users will be able to find nearby stores and restaurants.

• "Buddy services" will notify them when friends are nearby.

• Real-time traffic reporting services will provide up-to-the-minute status of various routes and suggest alternates when traffic jams emerge.

• Location-based billing services will be differentiated based on the user's location.

• Companies could locate and direct fleets, while parents could keep track of their kids and pets.

These services will create new revenue streams for wireless providers and help defray the cost of meeting the E-911 mandate.

Developing the Infrastructure
In order to implement the new services and meet the mandate, providers must deploy four components: a location gateway, the applications themselves, a data-communications network linked to the 911 centers and location technology.

Several vendors provide parts of the first three components. For example, Internet-service providers such as InfoSpace are creating the applications, while Xypoint and other vendors have developed data-communications networks for passing the location data to the public-safety answering points (PSAPs). It uses a technology called non-call-associated signaling (NCAS) to handle the location data outside of the LEC network. The traditional phone network can handle only 10-digit phone numbers, and the PSAP uses a database to associate them with a location. However, because wireless phones are mobile, the NCAS must carry the exact location coordinates to the 911 center.

"Since most carriers have made Phase I software technology choices, they only have to figure out how they locate the phone," said Eric McCabe, SignalSoft vice president of marketing. "Hooking that into the existing infrastructure is a fairly straightforward process."

Making GPS Viable
Although providers have several choices for location solutions, they can be divided into two types: network-based and handset-based, which uses GPS.

A chief drawback is that the satellites' signals are relatively weak and don't penetrate buildings and urban canyons. Sirf and SnapTrack have developed combinations of GPS receivers and network-based enhancements to provide highly accurate location readings within cities.

"If you are in a wireless network, you know approximately where you are," said Kanwar Chada, Sirf founder. "My receiver does not have to do a blind search of the sky, so I can narrow down the search for the weaker signals."

In addition, the network can provide the phone with frequency and time-domain information, which enable the phone to track GPS signals that are 10dB less than the minimum possible with unassisted GPS.

In SnapTrack's system, the phone forwards the satellites' information to the wireless provider's servers, which process the GPS signal far quicker and more accurately than the phone's processor could. John Cunningham, SnapTrack marketing manager, said this approach allows them to process GPS signals that are 20dB weaker than unassisted GPS can use.

"With wireless assist, you can integrate this into a cell phone with minimal impact on battery life," Cunningham said.

Another concern with handset-based solutions is the installed base: There are more than 100 million handsets now in use, and barring some sort of GPS peripheral, they won't be location-enabled. But some don't see that as an insurmountable hurdle.

"Since the consumer is buying a new phone every 1 to 3 years, the problem will go away in 3 to 4 years," Chada said.

Enabling the Network
The network-based approach uses special receivers at multiple cell sites to calculate the phone's location. Most network-based solutions fall into two categories: Angle of arrival (AOA) uses an array of smart antennas at multiple sites to receive different phases of the same signal. By comparing the phases, a computer can determine the angles from which they arrived and narrow down the general area where the signal originated. Time difference of arrival (TDOA) compares the times that an E-911 signal arrives at two or more sites. Some vendors combine AOA and TDOA to improve accuracy and limit the effects of multipath.

"The advantage of these technologies is that you don't require any modifications on the mobile handset," said Stephen Beckert, Strategis Group analyst. "The disadvantage is that you need three cell sites to determine the subscriber's location. In rural areas, the subscriber will not be in range of three cell sites, so it is harder to triangulate."

Both AOA and TDOA ca n run into problems when the signal bounces off of buildings or mountains because the receiver doesn't know which signal came straight from the source and which one was reflected. U.S. Wireless uses this multipath as an asset with its Location Pattern Matching technology, which has a database of how signals propagate in each area of a particular market. When an E-911 call is made, the computer compares that pattern to its database to locate the caller. The solution also requires fewer sites to locate each E-911 call.

Verizon Wireless recently trialed U.S. Wireless' solution but like most providers, it hasn't committed to any solution.

"We conducted our testing in Baltimore, a challenging urban radio-propagation environment, and the results are encouraging," said Ted Hoffman, Verizon vice president of technology development. "We will continue to work with U.S. Wireless and are evaluating the company's location offering."

Although most E-911 vendors plan to sell their equipment to wireless providers, both U.S. Wireless and Cell-Loc have developed business models where they'll license the service to multiple providers. The vendor will set up a single network, which allows multiple providers to share the cost rather than building their own.

"This will allow us to be price-competitive because multiple carriers have similar needs of location," said Oliver Hilsenrath, U.S. Wireless CEO.

One concern with this approach is that the location providers are going to start with the major markets, while wireless providers probably will want to use a single technology throughout all their markets. Hilsenrath said that to address this problem "we will have to commit to wherever a carrier wants to achieve uniformity. The most significant element is consistency."

Lawton (www.glawton.com) is a freelance writer and consultant based in Brisbane, CA.