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Wireless communication (or justwireless, when the context allows) is the transfer of information (telecommunication) between two or more points without the use of anelectrical conductor,optical fiber or other continuous guidedmedium for the transfer. The most common wireless technologies useradio waves. With radio waves, intended distances can be short, such as a few meters forBluetooth, or as far as millions of kilometers fordeep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, includingtwo-way radios,cellular telephones, andwireless networking. Other examples of applications of radiowireless technology includeGPS units,garage door openers, wirelesscomputer mice,keyboards andheadsets,headphones,radio receivers, satellite television,broadcast television andcordless telephones. Somewhat less common methods of achieving wireless communications involve otherelectromagnetic phenomena, such as light and magnetic or electric fields, or the use of sound.
The termwireless has been used twice in communications history, with slightly different meanings. It was initially used from about 1890 for the first radio transmitting and receiving technology, as inwireless telegraphy, until the new wordradio replaced it around 1920. Radio sets in the UK and the English-speaking world that were not portable continued to be referred to aswireless sets into the 1960s.[1][2] The termwireless was revived in the 1980s and 1990s mainly to distinguish digital devices that communicate without wires, such as the examples listed in the previous paragraph, from those that require wires or cables. This became its primary usage in the 2000s, due to the advent of technologies such asmobile broadband,Wi-Fi, andBluetooth.
Wireless operations permit services, such as mobile and interplanetary communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in thetelecommunications industry to refer totelecommunications systems (e.g. radio transmitters and receivers, remote controls, etc.) that use some form of energy (e.g.radio waves and acoustic energy) to transfer information without the use of wires.[3][4][5] Information is transferred in this manner over both short and long distances[6].
The first wireless telephone conversation occurred in 1880 whenAlexander Graham Bell andCharles Sumner Tainter invented thephotophone, a telephone that sent audio over a beam of light. The photophone required sunlight to operate, and a clear line of sight between the transmitter and receiver, which greatly decreased the viability of the photophone in any practical use.[7] It would be several decades before the photophone's principles found their first practical applications inmilitary communications and later infiber-optic communications.
A number of wireless electrical signaling schemes including sending electric currents through water and the ground using electrostatic andelectromagnetic induction were investigated for telegraphy in the late 19th century before practical radio systems became available. These included a patented induction system byThomas Edison allowing a telegraph on a running train to connect with telegraph wires running parallel to the tracks, aWilliam Preece induction telegraph system for sending messages across bodies of water, and several operational and proposed telegraphy and voice earth conduction systems.
The Edison system was used by stranded trains during theGreat Blizzard of 1888 and earth conductive systems found limited use between trenches duringWorld War I but these systems were never successful economically.
In 1894,Guglielmo Marconi began developing a wireless telegraph system usingradio waves, which had been known about since proof of their existence in 1888 byHeinrich Hertz, but discounted as a communication format since they seemed, at the time, to be a short-range phenomenon.[8] Marconi soon developed a system that was transmitting signals way beyond distances anyone could have predicted (due in part to the signals bouncing off the then unknownionosphere). Marconi andKarl Ferdinand Braun were awarded the 1909Nobel Prize for Physics for their contribution to this form of wireless telegraphy.
Millimetre wave communication was first investigated byJagadish Chandra Bose during 1894–1896, when he reached anextremely high frequency of up to 60 GHz in his experiments.[9] He also introduced the use ofsemiconductor junctions to detect radio waves,[10] when he patented the radiocrystal detector in 1901.[11][12]
The wireless revolution began in the 1990s,[13][14][15] with the advent of digitalwireless networks leading to a social revolution, and a paradigm shift from wired to wireless technology,[16] including the proliferation of commercial wireless technologies such ascell phones,mobile telephony,pagers, wirelesscomputer networks,[13]cellular networks, thewireless Internet, and laptop andhandheld computers with wireless connections.[17] The wireless revolution has been driven by advances inradio frequency (RF),microelectronics, andmicrowave engineering,[13] and the transition from analog to digital RF technology,[16][17] which enabled a substantial increase in voice traffic along with the delivery ofdigital data such as text messaging,images andstreaming media.[16]
Wireless communications can be via:
Radio andmicrowave communication carry information bymodulating properties ofelectromagnetic waves transmitted through space. Specifically, the transmitter generates artificial electromagnetic waves by applying time-varyingelectric currents to itsantenna. The waves travel away from the antenna until they eventually reach the antenna of a receiver, which induces an electric current in the receiving antenna. This current can be detected anddemodulated to recreate the information sent by the transmitter.
Optical wireless communications (OWC) is a form ofoptical communication in which unguided light is used "in the air" (or inouter space), without anoptical fiber.Visible,infrared (IR), orultraviolet (UV) light is used to carry a wireless signal. It is generally used in short-range communication; extensions exist forlong-range andultra-long range.
OWC systems operating in the visible band (390–750 nm) are commonly referred to asvisible light communication (VLC). VLC systems take advantage oflight-emitting diodes (LEDs) which can be pulsed at very high speeds without a noticeable effect on the lighting output and human eye. VLC can be possibly used in a wide range of applications including wirelesslocal area networks, wirelesspersonal area networks andvehicular networks, among others.[18] On the other hand, terrestrial point-to-point OWC systems, also known as thefree space optical (FSO) systems,[19] operate at the near IR frequencies (750–1600 nm). These systems typically use laser transmitters and offer a cost-effective protocol-transparent link with highdata rates, i.e., 10 Gbit/s per wavelength, and provide a potential solution for thebackhaul bottleneck.
There has also been a growing interest in ultraviolet communication (UVC) as a result of recent progress in solid-state optical sources/detectors operating withinsolar-blind UV spectrum (200–280 nm). In this so-called deep UV band, solar radiation is negligible at the ground level and this makes possible the design of photon-counting detectors with wide field-of-view receivers that increase the received energy with little additional background noise. Such designs are particularly useful for outdoor non-line-of-sight configurations to support low-power short-range UVC such as in wireless sensors and ad-hoc networks.
Free-space optical communication (FSO) is anoptical communication technology that uses light propagating in free space to transmit wireless data for telecommunications orcomputer networking. "Free space" means the light beams travel through the open air or outer space. This contrasts with other communication technologies that use light beams traveling throughtransmission lines such asoptical fiber or dielectric "light pipes".
The technology is useful where physical connections are impractical due to high costs or other considerations. For example, free space optical links are used in cities between office buildings that are not wired for networking, where the cost of running cable through the building and under the street would be prohibitive. Another widely used example isconsumer IR devices such asremote controls and IrDA (Infrared Data Association) networking, which is used as an alternative toWiFi networking to allow laptops, PDAs, printers, and digital cameras to exchange data.
Sonic, especiallyultrasonic short-range communication involves the transmission and reception of sound.
Electromagnetic induction only allows short-range communication and power transmission. It has been used in biomedical situations such as pacemakers, as well as for short-rangeRFID tags.
Common examples of wireless equipment include:[20]
AM and FM radios and other electronic devices make use of theelectromagnetic spectrum. The frequencies of theradio spectrum that are available for use for communication are treated as a public resource and are regulated by organizations such as the AmericanFederal Communications Commission,Ofcom in the United Kingdom, the internationalITU-R or the EuropeanETSI. Their regulations determine 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 did not have specific frequencies to work under and anamateur radio operator was interfering with a pilot's ability to land an aircraft. Wireless communication spans the spectrum from 9 kHz to 300 GHz.[citation needed]
One of the best-known examples of wireless technology is the mobile phone, also known as a cellular phone, with more than 6.6 billion mobile cellular subscriptions worldwide as of the end of 2010.[22] These wireless phones use radio waves from signal-transmission towers to enable their users to make phone calls from many locations worldwide. They can be used within the range of themobile telephone site used to house the equipment required to transmit and receive the radio signals from these instruments.[23]
Wirelessdata communications allowwireless networking betweendesktop computers, laptops,tablet computers, cell phones, and other related devices. The various available technologies differ in local availability, coverage range, and performance,[24] and in some circumstances, users employ multiple connection types and switch between them using connection manager software[25][26] or amobile VPN to handle the multiple connections as a secure, singlevirtual network.[27] Supporting technologies include:
Wireless data communications are used to span a distance beyond the capabilities of typical cabling inpoint-to-point communication andpoint-to-multipoint communication, 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.
Peripheral devices in computing can also be connected wirelessly, as part of a Wi-Fi network or directly via an optical or radio-frequency (RF) peripheral interface. Originally these units used bulky, highly local transceivers to mediate between a computer and a keyboard and mouse; however, more recent generations have used smaller, higher-performance devices. Radio-frequency interfaces, such asBluetooth orWireless USB, provide greater ranges of efficient use, usually up to 10 feet, but distance, physical obstacles, competing signals, and even human bodies can all degrade the signal quality.[35] Concerns about the security of wireless keyboards arose at the end of 2007 when it was revealed that Microsoft's implementation of encryption in some of its 27 MHz models were highly insecure.[36]
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. There are two different fundamental methods for wireless energy transfer. Energy can be transferred using either far-field methods that involve beaming power/lasers, radio or microwave transmissions, or near-field using electromagnetic induction.[37] Wireless energy transfer may be combined with wireless information transmission in what is known as Wireless Powered Communication.[38] In 2015, researchers at the University of Washington demonstrated far-field energy transfer using Wi-Fi signals to power cameras.[39]
New wireless technologies, such as mobile body area networks (MBAN), have the capability to monitor blood pressure, heart rate, oxygen level, and body temperature. The MBAN works by sending low-powered wireless signals to receivers that feed into nursing stations or monitoring sites. This technology helps with the intentional and unintentional risk of infection or disconnection that arise from wired connections.[40]
In definitions given in the index, p. 162, the term "radio set" is listed as synonymous with the term "wireless set"
(p.396) In a public opinion poll in Sweden in 1942, 31.4 percent answered 'Yes' to the question "Do you usually listen to the foreign news on the wireless?'
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