| Imagine driving to a job interview and
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| | dense tree cover and buildings can keep
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| realizing that you're lost. Your first
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| | it from getting a fix on your location.
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| impulse would probably be to call the
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| | GPS receivers and cell phones have a lot
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| business that's interviewing you and ask
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| | in common, and both are very popular. In
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| for directions. But if you're not sure
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| | the next section, we'll look at some of
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| where you are, getting directions can be
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| | the features of GPS-enabled cell phones.
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| tricky.
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| | Wireless-Assisted GPS
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| But suppose you use your phone for
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| | Some GPS phones use wireless-assisted GPS
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| another purpose -- to figure out exactly
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| | to determine the user's location. In
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| where you are and to get turn-by-turn
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| | wireless-assisted systems, the phone uses
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| directions to where you're going. New
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| | the orbiting GPS satellites in
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| phones that include global positioning
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| | conjunction with information about the
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| system (GPS) receivers can do exactly
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| | cell phone's signal. Sometimes called
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| that. With the right software or service
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| | enhanced GPS, wireless-assisted GPS can
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| package, they can pinpoint your location,
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| | often get a fix on the user's location
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| give directions to your destination and
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| | faster than a GPS-only receiver. Some
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| provide information about nearby
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| | wireless-assisted systems can work inside
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| businesses.
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| | buildings, under dense foliage and in
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| In this article, we'll review the basics
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| | city areas where traditional receivers
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| of how cell phones and GPS receivers
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| | cannot receive signals. You can learn
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| work. Then, we'll explore how phones
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| | more about wireless-assisted GPS through
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| combine these technologies.
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| | Lucent Technologies.
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| Cell Phone Basics
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| | GPS Phones
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| A cell phone is basically a sophisticated
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| | Nearly all new cell phones sold in
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| two-way radio. Towers and base stations,
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| | America have some GPS receiving
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| arranged into a network of cells, send
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| | capability built in. Those that don't can
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| and receive radio signals. Cell phones
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| | connect to a server that uses techniques
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| contain low-power transmitters that let
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| | discussed in the last section to analyze
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| them communicate with the nearest tower.
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| | their signals and determine their
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| As you travel, you move from one cell to
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| | location. This allows the phones to
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| another, and the base stations monitor
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| | transmit a person's location to a Public
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| the strength of your phone's signal. As
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| | Safety Answering Point (PSAP) after
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| you move toward the edge of one cell,
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| | dialing 911. But that's all a lot of
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| your signal strength diminishes. At the
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| | phones can do with their GPS.
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| same time, the base station in the cell
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| | However, some phones have a complete GPS
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| you are approaching notices the strength
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| | receiver located in the phone or can
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| of your signal increasing. As you move
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| | connect to one with wires or through a
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| from cell to cell, the towers transfer
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| | Bluetooth connection. These GPS-enabled
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| your signal from one to the next.
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| | phones can understand programming
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| In remote locations, towers may be so far
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| | languages like Java and can provide
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| apart that they can't provide a
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| | turn-by-turn directions or information
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| consistent signal. Even when towers are
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| | about nearby businesses and attractions.
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| plentiful, mountains and tall buildings
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| | Others can work like a tracking device.
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| can interrupt their signals. Sometimes
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| | To use any of these features, you must
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| people have a hard time getting clear
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| | have:
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| signals inside buildings, especially in
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| | A GPS-enabled phone or a compatible GPS
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| elevators.
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| | receiver
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| Even without a GPS receiver, your cell
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| | A calling plan that supports transmission
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| phone can provide information about your
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| | of maps and GPS data
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| location. A computer can determine your
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| | A service plan or software that provides
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| location based on measurements of your
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| | the actual maps and directions or
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| signal, such as:
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| | provides information about the phone's
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| Its angle of approach to the cell towers
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| | location
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| How long it takes the signal to travel to
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| | Common uses for GPS phones include:
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| multiple towers
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| | Location Tracking: Some employers use
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| The strength of your signal when it
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| | GPS-enabled phones to track their
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| reaches the towers
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| | employees' locations, and some business
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| Since obstacles like trees and buildings
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| | offer location tracking services for
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| can affect how long it takes your signal
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| | GPS-enabled phones. The Wherifone locator
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| to travel to a tower, this method is
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| | phone provides GPS coordinates and can
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| often less accurate than a GPS
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| | dial emergency phone numbers. Parents and
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| measurement.
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| | caregivers can track the phone's location
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| GPS Receiver Basics
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| | by phone or online and can receive
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| Like a cell phone, a GPS receiver relies
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| | notification if it leaves a designated
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| on radio waves. But instead of using
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| | "safe area." Wearable Environmental
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| towers on the ground, it communicates
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| | Information Networks of Japan has also
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| with satellites that orbit the Earth.
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| | introduced the Dog @ Watch, a GPS watch
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| There are currently 27 GPS satellites in
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| | phone for children.
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| orbit -- 24 are in active use and 3 act
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| | Turn-by-Turn Directions: GPS-enabled
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| as a backup in case another satellite
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| | phones with view screens can often
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| fails.
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| | display turn-by-turn directions as well
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| In order to determine your location, a
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| | as announce them through the phone's
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| GPS receiver has to determine:
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| | speaker. In general, companies that offer
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| The locations of at least three
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| | these services charge a monthly fee and
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| satellites above you
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| | use a database of maps to provide the
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| Where you are in relation to those
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| | directions. The services are only as good
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| satellites
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| | as their database -- outdated maps can
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| The receiver then uses trilateration to
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| | provide inaccurate directions. Some
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| determine your exact location. Basically,
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| | turn-by-turn direction services include:
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| it draws a sphere around each of three
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| | TeleNav
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| satellites it can locate. These three
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| | ViaMoto
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| spheres intersect in two points -- one is
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| | MapQuest Find Me
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| in space, and one is on the ground. The
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| | smart2Go, which requires a separate
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| point on the ground at which the three
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| | Bluetooth GPS receiver and a memory card
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| spheres intersect is your location.
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| | Destinator SP, which is a software
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| A GPS receiver has to have a clear line
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| | package for smartphones
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| of sight to the satellite to operate, so
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