GPS Phones

Imagine driving to a job interview and realizing that you're
lost. Your first impulse would probably be to call the
business that's interviewing you and ask for directions. But
if you're not sure where you are, getting directions can be
tricky.

But suppose you use your phone for another purpose -- to
figure out exactly where you are and to get turn-by-turn
directions to where you're going. New phones that include
global positioning system (GPS) receivers can do exactly that.
With the right software or service package, they can pinpoint
your location, give directions to your destination and
provide information about nearby businesses.

In this article, we'll review the basics of how cell phones
and GPS receivers work. Then, we'll explore how phones
combine these technologies.

Cell Phone Basics

A cell phone is basically a sophisticated two-way radio.
Towers and base stations, arranged into a network of cells,
send and receive radio signals. Cell phones contain low-power
transmitters that let them communicate with the nearest tower.

As you travel, you move from one cell to another, and the
base stations monitor the strength of your phone's signal. As
you move toward the edge of one cell, your signal strength
diminishes. At the same time, the base station in the cell
you are approaching notices the strength of your signal
increasing. As you move from cell to cell, the towers transfer
your signal from one to the next.

In remote locations, towers may be so far apart that they
can't provide a consistent signal. Even when towers are
plentiful, mountains and tall buildings can interrupt their
signals. Sometimes people have a hard time getting clear
signals inside buildings, especially in elevators.

Even without a GPS receiver, your cell phone can provide
information about your location. A computer can determine
your location based on measurements of your signal, such as:

* Its angle of approach to the cell towers
* How long it takes the signal to travel to multiple
towers
* The strength of your signal when it reaches the towers

Since obstacles like trees and buildings can affect how long
it takes your signal to travel to a tower, this method is
often less accurate than a GPS measurement.

GPS Receiver Basics

Like a cell phone, a GPS receiver relies on radio waves. But
instead of using towers on the ground, it communicates with
satellites that orbit the Earth. There are currently 27 GPS
satellites in orbit -- 24 are in active use and 3 act as
a backup in case another satellite fails.

In order to determine your location, a GPS receiver has to
determine:

* The locations of at least three satellites above you
* Where you are in relation to those satellites

The receiver then uses trilateration to determine your exact
location. Basically, it draws a sphere around each of three
satellites it can locate. These three spheres intersect in
two points -- one is in space, and one is on the ground. The
point on the ground at which the three spheres intersect is
your location.

A GPS receiver has to have a clear line of sight to the
satellite to operate, so dense tree cover and buildings can
keep it from getting a fix on your location.

GPS receivers and cell phones have a lot in common, and both
are very popular.

Nearly all new cell phones sold in America have some GPS
receiving capability built in. Those that don't can connect
to a server that uses techniques discussed in the last
section to analyze their signals and determine their location.
This allows the phones to transmit a person's location to
a Public Safety Answering Point (PSAP) after dialing 911. But
that's all a lot of phones can do with their GPS.

However, some phones have a complete GPS receiver located in
the phone or can connect to one with wires or through
a Bluetooth connection. These GPS-enabled phones can
understand programming languages like Java and can provide
turn-by-turn directions or information about nearby
businesses and attractions. Others can work like a tracking
device. To use any of these features, you must have:

* A GPS-enabled phone or a compatible GPS receiver
* A calling plan that supports transmission of maps and
GPS data
* A service plan or software that provides the actual
maps and directions or provides information about the phone's
location

Common uses for GPS phones include:

* Location Tracking: Some employers use GPS-enabled
phones to track their employees' locations, and some business
offer location tracking services for GPS-enabled phones. The
Wherifone locator phone provides GPS coordinates and can dial
emergency phone numbers. Parents and caregivers can track the
phone's location by phone or online and can receive
notification if it leaves a designated "safe area." Wearable
Environmental Information Networks of Japan has also
introduced the Dog @ Watch, a GPS watch phone for children.

* Turn-by-Turn Directions: GPS-enabled phones with view
screens can often display turn-by-turn directions as well as
announce them through the phone's speaker. In general,
companies that offer these services charge a monthly fee and
use a database of maps to provide the directions. The
services are only as good as their database -- outdated maps
can provide inaccurate directions. Some turn-by-turn
direction services include:

o TeleNav
o ViaMoto
o MapQuest Find Me
o smart2Go, which requires a separate Bluetooth GPS
receiver and a memory card
o Destinator SP, which is a software package for
smartphones

* Outdoor Location Services: Trimble Outdoors offers maps
and location-based services for hiking, mountain biking,
geocaching and other outdoor activities.

* Other Location-Based Services: Some companies hope to
deliver news, coupons, advertisements and other information
to cell phone users based on their location.

Some other GPS-enabled phones include:

* Mio A701 Smart Phone
* Several Motorola phones offered through Sprint/Nextel