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