Public-safety agencies are benefiting from the growth of global positioning service technology as the cost of GPS receivers falls and commercial carriers make enough of a buzz to get the attention of first responders.

“We're definitely seeing things pick up,” said Gary Hoff with Pyramid Communications, a manufacturer of a GPS-based automatic vehicle location (AVL) system.

“GPS receiver costs have come down, which has definitely helped. And we've seen two-way radio dealers become a little bit more confident since Nextel has set a price point.”

Indeed, Nextel Communications' big marketing push surrounding GPS applications for public safety is improving prospects for everyone peddling a GPS solution.

Initially developed by the U.S. Department of Defense for military navigation, GPS is most commonly used as part of AVL systems connected with a computer-aided dispatch (CAD) system. However, these systems thus far have been expensive to install and maintain. Consequently, GPS-enabled mobile phones, primarily Nextel's, have become a relatively inexpensive way to receive the benefits of a positioning-and-tracking system, said Bill Pessemier, executive communications systems adviser for the International Association of Fire Chiefs (IAFC) and author of the association's interoperability handbook.

“I think probably the most exciting things about Nextel and public safety is the GPS capability or general tracking capability,” said Greg Meacham, Nextel's vice president of federal programs and homeland security. “There is so much that can be done with that.”

For instance, GeoSpatial Technologies earlier this year installed its GST Tracker at the Anaheim Fire Department in California, providing technology to track Nextel handsets in real time and allowing the department to know the current locations of all its personnel holding handsets. The same tracking system can also track vehicles installed with GST's GPS devices at the same time, and the GST Mapper displays multiple map layers provided by the city of Anaheim.

GPS programs, such as TeleNav, also can provide driving directions for responding units and personnel. Routes are automatically calculated and recalculated if the responding unit misses directions. Other providers such as ActSoft have developed applications that track the amount of time units spend on tasks and the location of those resources while completing tasks.

Despite the fact that GPS-enabled mobile phones have become a relatively inexpensive way to receive the benefits of a positioning-and-tracking system, cost still remains a barrier for many agencies that are scrambling just to keep schools funded and police cars fueled. In addition, rural agencies often are stymied by the lack of commercial service coverage in their jurisdictions.

“Commercial services are expensive because agencies have to purchase units as well as pay a monthly fee to the carrier,” said Bert Wollen, vice president with Pryme Radio Products.

Pryme is beta testing the PTG GPS speaker microphone that integrates a GPS receiver and an RF modem with a remote speaker microphone. The solution brings location capability to hand-held radios, both trunked and conventional, without adding modems and GPS receivers to the radio.

“Most first responders have their own channels and spectrum,” Wollen said. “By adding a GPS signal, they are not increasing the cost. Backhaul is free because they are using their own network. We think that is a critical piece.”

The GPS microphone includes a man-down button that gives the exact location of a first responder, while users can watch the data in real time and create data files over the air.

But the battle is heating up between AVL and handset-based solutions. For Pyramid, the hype surrounding handset-based solutions has jump-started the AVL business for the company, Hoff said.

“Handsets are a nice gimmick, but you are tracking a phone, and people turn phones off or lose them,” he said.

Wollen argues that location needs to be applied to the individual so that persons can be traced whether they are in a car, on a bike or on foot. “It's surprising to me how many places [there are] in government where they have mobile radios and want this,” he said.

Companies like RLA Geosystems are marrying Nextel phones with their vehicle reporting and tracking system software to create a lower-cost AVL system. Pyramid also works with existing two-way radios to create a larger footprint or to enable users to move between multiple states and track a vehicle nationwide.

The Arkansas Game & Fish Commission (AGFC) uses Pyramid's AVL system via the commission's statewide VHF conventional radio system to provide a safety mechanism for the commission's armed officers, who pursue poachers in rural areas. Using the Merlin AVL unit, a GPS receiver and an interface to the two-way radio, Pyramid's AVL system allows the AGFC to continually transmit location information back to a computer in slow mode or a faster mode, known as Code Three. Code Three mode is automatically used when AGFC officers are in pursuit.

“We are seeing a lot of state agencies that want to track vehicles with the state 800 system,” said Bill Carlin of Pyramid.

Still, the use of GPS technology in general has one major drawback — the inability to accurately provide location information inside buildings. Commercial systems have the advantage of using assisted-GPS, a combination of GPS capability and triangulation, which pinpoints location by determining where the signal intersects with a carrier's cell sites. The handset registers the last known position on the network before the GPS signal is blocked and then relies on triangulation to continue verifying where the user is on an ongoing basis before line-of-site with the GPS satellite is established again.

Pessemier says public safety must experiment with various ways to track units where GPS is unavailable. “There is some value in trying to experiment with GPS-type information and using that to track units assigned to different staging areas,” Pessemier said. “That sort of stuff needs to be encouraged to experiment and see how it works. It's worth the effort.”

What is GPS?

  • GPS uses 21 NAVSTAR operational satellites and three as a redundant backup that orbit the earth at an altitude of about 12,500 miles.

  • Each GPS satellite has an orbital period of 11 hours and 58 minutes. This means that each GPS satellite orbits the Earth twice each day.

  • These 24 satellites orbit in six orbital planes, or paths. This means that four GPS satellites operate in each orbital plane.

  • Each of these six orbital planes is spaced 60∞ apart. All of these orbital planes are inclined 55° from the equator.