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==References==
==References==
<ref>[http://www.netspotapp.com Netspot Site Survey, free wireless site survey software for Mac OS X ]</ref>
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{{Reflist|2}}


Revision as of 22:13, 12 October 2011

For other uses, see Wireless (disambiguation).
File:Handheld Maritime VHF 217x289.png
Handheld wireless radios such as this Maritime VHF radio transceiver use electromagnetic waves to implement a form of wireless communications technology.

Wireless telecommunications, is the transfer of information between two or more points that are physically not connected. Distances can be short, as a few meters as in television remote control; or long ranging from thousands to millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, Garage door openers or garage doors, wireless computer mice, keyboards and Headset (telephone/computer), headphones, radio receivers, satellite television, broadcast television and cordless telephones.

Introduction

Wireless operations permits services, such as long range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc.) which use some form of energy (e.g. radio frequency (RF),acoustic energy, etc.) to transfer information without the use of wires.[1] Information is transferred in this manner over both short and long distances.

Wireless services

Common examples of wireless equipment include:

Wireless networks

Wireless networking (i.e. the various types of unlicensed 2.4 GHz WiFi devices) is used to meet many needs. Perhaps the most common use is to connect laptop users who travel from location to location. Another common use is for mobile networks that connect via satellite. A wireless transmission method is a logical choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless technology:

  • To span a distance beyond the capabilities of typical cabling,
  • To provide a backup communications link in case of normal network failure,
  • To link portable or temporary workstations,
  • To overcome situations where normal cabling is difficult or financially impractical, or
  • To remotely connect mobile users or networks.

Modes

Wireless communications can be via:

Applications may involve point-to-point communication, point-to-multipoint communication, broadcasting, cellular networks and other wireless networks.

Cordless

The term "wireless" should not be confused with the term "cordless", which is generally used to refer to powered electrical or electronic devices that are able to operate from a portable power source (e.g. a battery pack) without any cable or cord to limit the mobility of the cordless device through a connection to the mains power supply.

Some cordless devices, such as cordless telephones, are also wireless in the sense that information is transferred from the cordless telephone to the telephone's base unit via some type of wireless communications link. This has caused some disparity in the usage of the term "cordless", for example in Digital Enhanced Cordless Telecommunications.

History

Photophone

Main article: Photophone

The world's first wireless telephone conversation occurred in 1880, when Alexander Graham Bell and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted audio conversations wirelessly over modulated light beams (which are narrow projections of electromagnetic waves). In that distant era when utilities did not yet exist to provide electricity, and lasers had not even been conceived of in science fiction, there were no practical applications for their invention, which was highly limited by the availability of both sunlight and good weather. Similar to free space optical communication, the photophone also required a clear line of sight between its transmitter and its receiver. It would be several decades before the photophone's principles found their first practical applications in military communications and later in fiber-optic communications.

Early wireless work

Main article: Wireless telegraphy

David E. Hughes, eight years before Hertz's experiments, transmitted radio signals over a few hundred yards by means of a clockwork keyed transmitter. As this was before Maxwell's work was understood, Hughes' contemporaries dismissed his achievement as mere "Induction". In 1885, T. A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deployed a system of signaling on the Lehigh Valley Railroad. In 1891, Edison obtained the wireless patent for this method using inductance (U.S. patent 465,971).

In the history of wireless technology, the demonstration of the theory of electromagnetic waves by Heinrich Hertz in 1888 was important.[2][3] The theory of electromagnetic waves was predicted from the research of James Clerk Maxwell and Michael Faraday. Hertz demonstrated that electromagnetic waves could be transmitted and caused to travel through space at straight lines and that they were able to be received by an experimental apparatus.[2][3] The experiments were not followed up by Hertz. Jagadish Chandra Bose around this time developed an early wireless detection device and helped increase the knowledge of millimeter length electromagnetic waves.[4] Practical applications of wireless radio communication and radio remote control technology were implemented by later inventors, such as Nikola Tesla.

Further information: Invention of radio

Radio

Main article: History of radio

The term "wireless" came into public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter device), establishing its usage in the field of wireless telegraphy early on; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet. It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as "wireless remote control" or "wireless energy transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic) used. Guglielmo Marconi and Karl Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to wireless telegraphy.

Electromagnetic spectrum

See also: Spectrum management

Light, colors, AM and FM radio, and electronic devices make use of the electromagnetic spectrum. The frequencies of the radio spectrum that are available for use for communication are treated as a public resource and are regulated by national organizations such as the Federal Communications Commission in the USA, or Ofcom in the United Kingdom. This determines which frequency ranges can be used for what purpose and by whom. In the absence of such control or alternative arrangements such as a privatized electromagnetic spectrum, chaos might result if, for example, airlines didn't have specific frequencies to work under and an amateur radio operator were interfering with the pilot's ability to land an aircraft. Wireless communication spans the spectrum from 9 kHz to 300 GHz.

Applications of wireless technology

Security systems

Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings.[5]

Mobile telephones

One of the best-known examples of wireless technology is the mobile phone, also known as a cellular phone, with more than 4.6 billion mobile cellular subscriptions worldwide as of the end of 2010.[6] These wireless phones use radio waves to enable their users to make phone calls from many locations worldwide. They can be used within range of the mobile telephone site used to house the equipment required to transmit and receive the radio signals from these instruments.

Wireless data communications

Wireless data communications are an essential component of mobile computing.[7] The various available technologies differ in local availability, coverage range and performance[8][9], and in some circumstances, users must be able to employ multiple connection types and switch between them. To simplify the experience for the user, connection manager software can be used [10][11], or a mobile VPN deployed to handle the multiple connections as a secure, single virtual network.[12] Supporting technologies include:

Wi-Fi is a wireless local area network that enables portable computing devices to connect easily to the Internet. Standardized as IEEE 802.11 a,b,g,n, Wi-Fi approaches speeds of some types of wired Ethernet. Wi-Fi has become the de facto standard for access in private homes, within offices, and at public hotspots.[13] Some businesses charge customers a monthly fee for service, while others have begun offering it for free in an effort to increase the sales of their goods.[14]
Cellular data service offers effective coverage within a range of 10-15 miles from the nearest cell site.[8] Speeds have increased as technologies have evolved, from earlier technologies such as GSM, CDMA and GPRS, to 3G networks such as W-CDMA, EDGE or CDMA2000.[15][16]
Mobile Satellite Communications may be used where other wireless connections are unavailable, such as in largely rural areas[17] or remote locations.[8] Satellite communications are especially important for transportation, aviation, maritime and military use.[18]

Wireless energy transfer

Main article: Wireless energy transfer

Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of interconnecting wires.

Computer interface devices

Answering the call of customers frustrated with cord clutter, many manufactures of computer peripherals turned to wireless technology to satisfy their consumer base. Originally these units used bulky, highly limited transceivers to mediate between a computer and a keyboard and mouse, however more recent generations have used small, high quality devices, some even incorporating Bluetooth. These systems have become so ubiquitous that some users have begun complaining about a lack of wired peripherals.[who?] Wireless devices tend to have a slightly slower response time than their wired counterparts, however the gap is decreasing. Initial concerns about the security of wireless keyboards have also been addressed with the maturation of the technology.

Categories of wireless implementations, devices and standards

See also

References

[19]

  1. ^ "ATIS Telecom Glossary 2007". atis.org. Retrieved 2008-03-16.
  2. ^ a b Story, Alfred Thomas (1904). A story of wireless telegraphy. New York, D. Appleton and Co.
  3. ^ a b "Heinrich Rudolf Hertz". chem.ch.huji.ac.il. Retrieved 2008-03-16.
  4. ^ J.C. Bose, Collected Physical Papers. New York, N.Y.: Longmans, Green and Co., 1927
  5. ^ Hard-wired VS Wireless Home Security Systems
  6. ^ Robust demand for mobile phone service will continue, UN agency predicts UN News Centre February 15, 2010
  7. ^ TCO Insights on Rugged Mobile Computers, VDC Research, 2007.
  8. ^ a b c High Speed Internet on the Road, http://www.geeksontour.com/showme/wifi/wifi00_3ways.cfm
  9. ^ Mitchell, Bradley. Wireless Internet Service: An Introduction
  10. ^ What is Connection Manager? Microsoft Technet, March 28, 2003
  11. ^ Unwired Revolution
  12. ^ http://www.gd-itronix.com/index.cfm?page=Products:MobilityXE
  13. ^ "Wi-Fi"
  14. ^ O'Brien, J. & Marakas, G.M.(2008) Management Information Systems (pp. 239). New York, NY: McGraw-Hill Irwin
  15. ^ Lachu Aravamudhan, Stefano Faccin, Risto Mononen, Basavaraj Patil, Yousuf Saifullah, Sarvesh Sharma, Srinivas Sreemanthula. "Getting to Know Wireless Networks and Technology", InformIT
  16. ^ "What really is a Third Generation (3G) Mobile Technology", ITU
  17. ^ Geier, Jim. Wireless Network Industry Report 2007, Wireless-Nets, Ltd., 2008
  18. ^ Ilcev, Stojce Dimov, Global Mobile Satellite Communications for Maritime, Land and Aeronautical Applications, Springer, 2005
  19. ^ Netspot Site Survey, free wireless site survey software for Mac OS X

Further reading

  • Geier, Jim (2001). Wireless LANs. Sams. ISBN 0672320584.
  • Goldsmith, Andrea (2005). Wireless Communications. Cambridge University Press. ISBN 0521837162.
  • Molisch, Andreas (2005). Wireless Communications. Wiley-IEEE Press. ISBN 047084888X.
  • Rappaport, Theodore (2002). Wireless Communications: Principles and Practice. Prentice Hall. ISBN 0130422320.
  • Rhoton, John (2001). The Wireless Internet Explained. Digital Press. ISBN 1555582575.
  • Tse, David; Viswanath, Pramod (2005). Fundamentals of Wireless Communication. Cambridge University Press. ISBN 0521845270.
Wikibooks has a book on the topic of: Nets, Webs and the Information Infrastructure
Look up wireless in Wiktionary, the free dictionary.


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