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