What are GPS phones?

Imagine driving to a job interview and realizing thatGPS receivers and cell phones have a lot in common,
you're lost. Your first impulse would probably be to calland both are very popular. In the next section, we'll look
the business that's interviewing you and ask forat some of the features of GPS-enabled cell phones.
directions. But if you're not sure where you are, gettingWireless-Assisted GPS
directions can be tricky.Some GPS phones use wireless-assisted GPS to
But suppose you use your phone for another purposedetermine the user's location. In wireless-assisted
-- to figure out exactly where you are and to getsystems, the phone uses the orbiting GPS satellites in
turn-by-turn directions to where you're going. Newconjunction with information about the cell phone's
phones that include global positioning system (GPS)signal. Sometimes called enhanced GPS,
receivers can do exactly that. With the right softwarewireless-assisted GPS can often get a fix on the
or service package, they can pinpoint your location,user's location faster than a GPS-only receiver. Some
give directions to your destination and providewireless-assisted systems can work inside buildings,
information about nearby businesses.under dense foliage and in city areas where traditional
In this article, we'll review the basics of how cell phonesreceivers cannot receive signals. You can learn more
and GPS receivers work. Then, we'll explore howabout wireless-assisted GPS through Lucent
phones combine these technologies.Technologies.
Cell Phone BasicsGPS Phones
A cell phone is basically a sophisticated two-way radio.Nearly all new cell phones sold in America have some
Towers and base stations, arranged into a network ofGPS receiving capability built in. Those that don't can
cells, send and receive radio signals. Cell phonesconnect to a server that uses techniques discussed in
contain low-power transmitters that let themthe last section to analyze their signals and determine
communicate with the nearest tower.their location. This allows the phones to transmit a
As you travel, you move from one cell to another, andperson's location to a Public Safety Answering Point
the base stations monitor the strength of your phone's(PSAP) after dialing 911. But that's all a lot of phones
signal. As you move toward the edge of one cell, yourcan do with their GPS.
signal strength diminishes. At the same time, the baseHowever, some phones have a complete GPS
station in the cell you are approaching notices thereceiver located in the phone or can connect to one
strength of your signal increasing. As you move fromwith wires or through a Bluetooth connection. These
cell to cell, the towers transfer your signal from one toGPS-enabled phones can understand programming
the next.languages like Java and can provide turn-by-turn
In remote locations, towers may be so far apart thatdirections or information about nearby businesses and
they can't provide a consistent signal. Even whenattractions. Others can work like a tracking device. To
towers are plentiful, mountains and tall buildings canuse any of these features, you must have:
interrupt their signals. Sometimes people have a hardA GPS-enabled phone or a compatible GPS receiver
time getting clear signals inside buildings, especially inA calling plan that supports transmission of maps and
elevators.GPS data
Even without a GPS receiver, your cell phone canA service plan or software that provides the actual
provide information about your location. A computermaps and directions or provides information about the
can determine your location based on measurementsphone's location
of your signal, such as:Common uses for GPS phones include:
Its angle of approach to the cell towersLocation Tracking: Some employers use GPS-enabled
How long it takes the signal to travel to multiple towersphones to track their employees' locations, and some
The strength of your signal when it reaches thebusiness offer location tracking services for
towersGPS-enabled phones. The Wherifone locator phone
Since obstacles like trees and buildings can affect howprovides GPS coordinates and can dial emergency
long it takes your signal to travel to a tower, thisphone numbers. Parents and caregivers can track the
method is often less accurate than a GPSphone's location by phone or online and can receive
measurement.notification if it leaves a designated "safe area."
GPS Receiver BasicsWearable Environmental Information Networks of
Like a cell phone, a GPS receiver relies on radioJapan has also introduced the Dog @ Watch, a GPS
waves. But instead of using towers on the ground, itwatch phone for children.
communicates with satellites that orbit the Earth. ThereTurn-by-Turn Directions: GPS-enabled phones with
are currently 27 GPS satellites in orbit -- 24 are inview screens can often display turn-by-turn directions
active use and 3 act as a backup in case anotheras well as announce them through the phone's
satellite fails.speaker. In general, companies that offer these
In order to determine your location, a GPS receiverservices charge a monthly fee and use a database of
has to determine:maps to provide the directions. The services are only
The locations of at least three satellites above youas good as their database -- outdated maps can
Where you are in relation to those satellitesprovide inaccurate directions. Some turn-by-turn
The receiver then uses trilateration to determine yourdirection services include:
exact location. Basically, it draws a sphere aroundTeleNav
each of three satellites it can locate. These threeViaMoto
spheres intersect in two points -- one is in space, andMapQuest Find Me
one is on the ground. The point on the ground at whichsmart2Go, which requires a separate Bluetooth GPS
the three spheres intersect is your location.receiver and a memory card
A GPS receiver has to have a clear line of sight to theDestinator SP, which is a software package for
satellite to operate, so dense tree cover and buildingssmartphones
can keep it from getting a fix on your location.