- Cellular telephone, sometimes called mobile telephone, is a type of short-wave analog or digital telecommunication in which a subscriber has a wireless connection from a mobile telephone to a relatively nearby transmitter. The transmitter's span of coverage is called a cell. Generally, cellular telephone service is available in urban areas and along major highways. As the cellular telephone user moves from one cell or area of coverage to another, the telephone is effectively passed on to the local cell transmitter.
A cellular telephone is not to be confused with a cordless telephone (which is simply a phone with a very short wireless connection to a local phone outlet).
The first cellular telephone for commercial use was approved by the Federal Communications Commission (FCC) in 1983. The phone, a Motorola DynaTAC 8000X, weighed 2 pounds, offered just a half-hour of talk time for every recharging and sold for $3,995
Tuesday, July 28, 2009
GPS (Global Positioning System)
- The GPS (Global Positioning System) is a "constellation" of 24 well-spaced satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. The location accuracy is anywhere from 100 to 10 meters for most equipment. Accuracy can be pinpointed to within one (1) meter with special military-approved equipment. GPS equipment is widely used in science and has now become sufficiently low-cost so that almost anyone can own a GPS receiver.
The GPS is owned and operated by the U.S. Department of Defense but is available for general use around the world. Briefly, here's how it works:
21 GPS satellites and three spare satellites are in orbit at 10,600 miles above the Earth. The satellites are spaced so that from any point on Earth, four satellites will be above the horizon.
Each satellite contains a computer, an atomic clock, and a radio. With an understanding of its own orbit and the clock, it continually broadcasts its changing position and time. (Once a day, each satellite checks its own sense of time and position with a ground station and makes any minor correction.)
On the ground, any GPS receiver contains a computer that "triangulates" its own position by getting bearings from three of the four satellites. The result is provided in the form of a geographic position - longitude and latitude - to, for most receivers, within 100 meters.
If the receiver is also equipped with a display screen that shows a map, the position can be shown on the map.
If a fourth satellite can be received, the receiver/computer can figure out the altitude as well as the geographic position.
If you are moving, your receiver may also be able to calculate your speed and direction of travel and give you estimated times of arrival to specified destinations.
The GPS is being used in science to provide data that has never been available before in the quantity and degree of accuracy that the GPS makes possible. Scientists are using the GPS to measure the movement of the arctic ice sheets, the Earth's tectonic plates, and volcanic activity.
GPS receivers are becoming consumer products. In addition to their outdoor use (hiking, cross-country skiing, ballooning, flying, and sailing), receivers can be used in cars to relate the driver's location with traffic and weather information. Here are some Web locations that describe GPS receiver products
The GPS is owned and operated by the U.S. Department of Defense but is available for general use around the world. Briefly, here's how it works:
21 GPS satellites and three spare satellites are in orbit at 10,600 miles above the Earth. The satellites are spaced so that from any point on Earth, four satellites will be above the horizon.
Each satellite contains a computer, an atomic clock, and a radio. With an understanding of its own orbit and the clock, it continually broadcasts its changing position and time. (Once a day, each satellite checks its own sense of time and position with a ground station and makes any minor correction.)
On the ground, any GPS receiver contains a computer that "triangulates" its own position by getting bearings from three of the four satellites. The result is provided in the form of a geographic position - longitude and latitude - to, for most receivers, within 100 meters.
If the receiver is also equipped with a display screen that shows a map, the position can be shown on the map.
If a fourth satellite can be received, the receiver/computer can figure out the altitude as well as the geographic position.
If you are moving, your receiver may also be able to calculate your speed and direction of travel and give you estimated times of arrival to specified destinations.
The GPS is being used in science to provide data that has never been available before in the quantity and degree of accuracy that the GPS makes possible. Scientists are using the GPS to measure the movement of the arctic ice sheets, the Earth's tectonic plates, and volcanic activity.
GPS receivers are becoming consumer products. In addition to their outdoor use (hiking, cross-country skiing, ballooning, flying, and sailing), receivers can be used in cars to relate the driver's location with traffic and weather information. Here are some Web locations that describe GPS receiver products
What is i-Mode
- i-Mode is the packet-based service for mobile phones offered by Japan's leader in wireless technology, NTT DoCoMo. Unlike most of the key players in the wireless arena, i-Mode eschews the Wireless Application Protocol (WAP) and uses a simplified version of HTML, Compact Wireless Markup Language (CWML) instead of WAP's Wireless Markup Language (WML). NTT DoCoMo has said that eventually it will support WAP and WML, but the company has not said exactly when this will happen.
First introduced in 1999, i-Mode was the world's first smart phone for Web browsing. The i-Mode wireless data service offers color and video over many phones. Its mobile computing service enables users to do telephone banking, make airline reservations, conduct stock transactions, send and receive e-mail, and have access to the Internet. As of early 2000, i-Mode had an estimated 5.6 million users
First introduced in 1999, i-Mode was the world's first smart phone for Web browsing. The i-Mode wireless data service offers color and video over many phones. Its mobile computing service enables users to do telephone banking, make airline reservations, conduct stock transactions, send and receive e-mail, and have access to the Internet. As of early 2000, i-Mode had an estimated 5.6 million users
What is WAP
- WAP (Wireless Application Protocol) is a specification for a set of communication protocols to standardize the way that wireless devices, such as cellular telephones and radio transceivers, can be used for Internet access, including e-mail, the World Wide Web, newsgroups, and instant messaging. While Internet access has been possible in the past, different manufacturers have used different technologies. In the future, devices and service systems that use WAP will be able to interoperate.
The WAP layers are:
Wireless Application Environment (WAE)
Wireless Session Layer (WSL)
Wireless Transport Layer Security (WTLS)
Wireless Transport Layer (WTP)
The WAP was conceived by four companies: Ericsson, Motorola, Nokia, and Unwired Planet (now Phone.com). The Wireless Markup Language (WML) is used to create pages that can be delivered using WAP
The WAP layers are:
Wireless Application Environment (WAE)
Wireless Session Layer (WSL)
Wireless Transport Layer Security (WTLS)
Wireless Transport Layer (WTP)
The WAP was conceived by four companies: Ericsson, Motorola, Nokia, and Unwired Planet (now Phone.com). The Wireless Markup Language (WML) is used to create pages that can be delivered using WAP
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