David: We all pretty much know that GPS can help us understand our location. But how does it work?

Rob: The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations.

The satellites are used to send radio signals to receivers on the ground. They use a method called "triangulation" to determine the location. Triangulation measures the distance using the travel time of the radio signals its sends to the ground.

GPS requires an unobstructed view of the sky, so it often does not perform well inside of buildings or in areas where there are a lot of tall structures or natural barriers, such as forests.

David: How did GPS get started? What's the history of the technology?

Rob: GPS was designed and built, and is operated and maintained by the U.S. Department of Defense. It used to be known as the Navstar Global Positioning System, which was conceptually devised by the Pentagon in 1973 in an effort to create an error-proof satellite system. In 1978, the first operational GPS satellite was launched. By the mid-1990s, the system was fully operational with 24 satellites.

More information about the general history of GPS can be found in a number of sources online.

David: GPS is a convenience, certainly. But in this age of Homeland Security, isn't GPS also a danger?

Rob: This question may be better answered by Homeland Security or Defense Department officials.

David: Hmmm...guess we'll come back to this question with other experts in a future issue. Let's move on. Since we're interviewing you about GPS, you obviously have something to do with GPS. But isn't Nextel a phone provider? Where does the GPS come in?

Rob: In most of today's cell phones, GPS location technology is standard equipment due largely in part to the fact that the FCC has mandated cell phone providers be able to determine a user's location if they are using their cell phone in an emergency situation.

Nextel was the first carrier to introduce a Java-enabled GPS phone in late 2002. At the same time, Nextel launched an open programming interface that would allow the iDEN (Integrated Digital Enhanced Network) software development community to build applications that leveraged location-based information on the handset, and the first applications were introduced in early 2003.

All of Nextel's current wireless phone models, including the BlackBerry 7520, come equipped with GPS receivers built into the handsets. In fact, Nextel is the first and only wireless provider to offer a BlackBerry with GPS functionality. This allows Nextel to combine its voice and data communications services (cellular, Direct Connect instant walkie-talkie and short message service to name a few) with GPS location-based services on a single device.

This eliminates the need to carry a separate cell phone, pager and GPS receiver. It also enhances the power of the mobile phone by leveraging its physical location to not only bring users personalized content and information but more valuable services such as helping them identify the top five restaurants in their vicinity, along with providing their menus and pricing.