Extending GPS Capabilities

Over the next five years, wireless carriers will spend more than $2 billion on location technology. The FCC mandate is driving this demand: By Oct. 1, 2001, carriers must provide the location of wireless 911 calls to emergency service dispatchers with an accuracy better than 125 meters 67% of the time.

But 125 meters (longer than a football field, including both end zones) is not always acceptable, especially if you are in a high-rise office building, a mall, or a parking garage and need immediate assistance. That is a lot of area for police or paramedics to search when seconds are critical. Many public-safety officials are not satisfied with 125-meter accuracy, and the FCC is considering stricter requirements.

In addition, many carriers will use location technology for value-added services such as roadside assistance, mobile yellow pages, location-sensitive billing, direction services, asset tracking and fleet management. Customers won't pay for driving directions when the answer is: "Take one of the next three streets on the right." Improper billing because of inaccurate location information will be the quickest way to alienate customers.

A carrier providing only 125-meter accuracy will not be able to compete with a carrier offering 5-meter precision. At the same time, an overly expensive system will be doomed, no matter how accurate it is. In the end, the most effective location solution will be the most accurate and the least expensive.

CHOICESThere are two basic technologies that solve the wireless location problem: network-based solutions, which use radio-signal-processing methods similar to those used during World War II (see "Another Option"), and handset-based solutions, which use the U.S. military's GPS satellites. The GPS navigational system is the tool that allowed allied aircraft and missiles to produce a precise and devastating effect during the Gulf War.

As with any new technology, there are controversies over what is the best solution. Both network-based and GPS-based have advantages and disadvantages. For example, skeptics criticize GPS-based solutions because they will not work with the 68 million wireless handsets already on the market. However, vendors argue that the pace of handset purchases is accelerating as existing wireless subscribers convert from analog to digital networks and as PCS networks are deployed, generating new subscribers. A recent Peter D. Hart Research survey revealed that 33% of wireless consumers upgraded their phones in the past year,a trend expected to continue for some time. Because safety is the No. 1 reason people buy wireless phones, accurate emergency-location service could become a primary factor influencing wireless buying decisions.

So why not use a satellite navigation system that by nature provides global signal coverage? U.S. taxpayers already have paid $12 billion for the existing system, and millions of dollars are spent each year on maintenance and improvements.

GPS-based solutions also are criticized because they can't locate callers inside buildings, in cars, under dense foliage or any other place without direct line-of-sight to GPS satellites. Not many people will pay for value-added services if they can't use the service everywhere, or if they have to pull to the side of the interstate and stand outside their cars to access them. Therefore, conventional GPS is not always a practical solution to wireless location.

But technologies are advancing, and performance enhancements are emerging. As a result, your choices aren't limited to network-based vs. GPS-based. You also have to choose within the GPS category. Specifically, enhanced GPS (EGPS) is providing another viable option for location determination. The technology is 100 times more sensitive than conventional GPS and provides location fix indoors.

EGPS is primarily a software solution that runs on the handset's digital signal processor (DSP). It requires little additional hardware in the handset. Whereas conventional GPS receivers operate continuously and process data serially, consuming battery power and processing time, EGPS uses only a snapshot of the GPS signal, greatly reducing battery consumption. Although traditional GPS receivers may take several minutes to acquire and track satellites, an EGPS system can provide a first fix within a few seconds.

The performance enhancement of EGPS comes, in part, from the fact that the system uses a client-server architecture, drawing upon the processing power of a carrier's centralized network server. In this setup, a fixed network of GPS reference receivers updates the server with signal data from all GPS satellites constantly. When a user requests a location-based service, the handset queries the server and receives a short message containing information about the GPS satellites that are in view of the handset. The handset processes a snapshot of GPS data and transmits location information to the server. The server calculates longitude, latitude, and altitude and performs a series of sophisticated error corrections to improve accuracy.

Several handset and chip manufacturers, including Texas Instruments, researched this solution and determined that because parts will be limited, initial EGPS integration will cost $5 to $8 per handset. As silicon-chip density improves and integration levels increase, the cost will drop to less than $1. Because the circuitry needed for EGPS already exists in today's handsets, any increase in the size or weight of handsets will be minimal. To locate EGPS handsets, you have to install Windows NT- or UNIX-class software on a centrally located server in the existing network.

Improving service through a quick, inexpensive server software upgrade can be an attractive option. Semiconductor manufacturing improvements are leading to more powerful handset DSPs, in turn allowing enhanced location services. As the integration of GPS technology into the wireless platform evolves, each technology will benefit the other.

STRAIGHT TO THE POINTGenerally, multipath is the largest contribution to error in location systems. Signal interference that reaches the receiver by two or more paths causes multipath errors. Multipath results when multiple copies of the same satellite signal are combined at the receiver antenna, and the receiver must figure out which signal to use. It also occurs when a single error-reflected copy reaches the receiver. Multipath is a common problem in cities where signals reflect off buildings, trees and other obstacles. Using these reflected signals to locate a caller is crucial in dense urban environments, where the handset only receives reflected signals.

The combination of GPS accuracy and complex error correction from the server allows EGPS to pinpoint callers quickly despite multipath error or high signal attenuation. A CDMA test group, including AirTouch Communications, Ameritech Cellular, BellSouth Mobility, GTE Wireless, PrimeCo Personal Communications, Sprint PCS and US West Wireless, conducted extensive testing, which showed that EGPS consistently located callers within an acceptable accuracy range of five to 50 meters. When used outside, in cars, houses, and 2- and 3-story buildings, EGPS pinpointed callers to within three to 20 meters consistently. Inside skyscrapers, shopping malls and in deep urban canyons where extreme signal blockage and severe multipath present serious problems for many location technologies, EGPS located callers to within 30 to 80 meters, substantially better than the FCC's 125-meter standard. Most stand-alone GPS solutions cannot even function in these environments today. Currently, a group of GSM carriers is performing these same tests on GSM networks.

But Robert Tendler, Tendler Cellular chairman & founder, said carriers should not dismiss conventional GPS technology. There is a petition to the Office of Science and Technology Advisory Council at the White House to turn off selective availability (a limitation implemented for GPS' original military use). According to Tendler, President Clinton has indicated he will do this by 2000, before the FCC deadline. When selective availability is no longer an issue, conventional GPS systems will be able to reach 10-meter accuracy. However, areas with multipath issues still may downgrade accuracy.

Just as network-based solutions and conventional GPS solutions have advantages and disadvantages, the same is true for EGPS. For example, Tendler said because EGPS solutions require an infrastructure/network enhancement that conventional GPS systems don't need, you will face additional costs. Also, there will be compatibility and interoperability issues that will require a standard for seamless operation between carriers.

YOUR CHOICENTT DoCoMo, the world's largest wireless carrier, already has signed on to use GPS for its location-based service offerings. The carrier chose EGPS because of the accuracy and sensitivity level it offers. In the crowded streets of Tokyo, 125-meter accuracy is next to useless, as is a system that cannot handle multipath.

Because each carrier has different needs, you should evaluate the many options carefully. Just make sure selection does not limit the quality of service you can offer today and the types of services you will be able to offer in the future.

The FCC has made the first move with its mandate. Now, you must decide how you will answer the call for wireless location. The option you choose should allow you to offer a low-cost and accurate service with the flexibility to continue to enhance performance cost-effectively.

>SBAnother Option

Some industry experts claim GPS-based solutions will not serve as an effective location alternative. According to "E-911: Mandate or Opportunity?" (Wireless Review, Nov. 15), many carriers have told vendors privately they prefer network-based solutions because they are more flexible and provide long-term control. Carriers would rather upgrade dozens of base stations than hundreds of thousands of handsets, which they subsidize. However, Texas Instruments projects that widespread availability will nullify this concern.

"In two years, every digital cellular phone sold will have GPS," said Tom Engibous, Texas Instruments chairman, president & CEO.

In addition, GPS proponents argue that network-based solutions have their own disadvantages. For example, cell sites used in a network-based system are situated for voice communications, not geometrically positioned to optimize radio location. In many areas, cell sites are in rows along a highway, making triangulation impossible. In more sparsely populated regions, there just are not enough cells available. Therefore, comprehensive coverage is problematic.

The notion that a network-based system will provide every wireless customer with E-911 location capability immediately is not necessarily true either. It will take time for carriers to conduct a wholesale network conversion. Because carriers will have to upgrade each cell site, most carriers will have to implement network-based solutions in stages. You will have to decide what areas to convert first, which initially may exclude a significant portion of the United States and leave some rural areas unimproved altogether.