Wireless communication or just wireless , when the context allows is the electromagnetic transfer of information between two or more points that are not connected by an electrical conductor. The most common wireless technologies use radio waves. With radio waves, intended distances can be short, such as a few meters for Bluetooth or as far as millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios , cellular telephones , personal digital assistants PDAs , and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers , wireless computer mouse , keyboards and headsets , headphones , radio receivers , satellite television , broadcast television and cordless telephones. Somewhat less common methods of achieving wireless communications include the use of other electromagnetic wireless technologies, such as light, magnetic, or electric fields or the use of sound. The term wireless has been used twice in communications history, with slightly different meaning. It was initially used from about for the first radio transmitting and receiving technology, as in wireless telegraphy , until the new word radio replaced it around Radios in the UK that were not portable continued to be referred to as wireless sets into the s. The term was revived in the s and s 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 s, due to the advent of technologies such as mobile broadband , Wi-Fi and Bluetooth. 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 the telecommunications industry to refer to telecommunications systems e. The first wireless telephone conversation occurred in , when Alexander Graham Bell and Charles Sumner Tainter invented the photophone , a telephone that sent audio over a beam of light. The photophone required sunlight to operate, and a clear line of sight between transmitter and receiver. These factors greatly decreased the viability of the photophone in any practical use. It would be several decades before the photophone's principles found their first practical applications in military communications and later in fiber-optic communications. A number of wireless electrical signaling schemes including sending electric currents through water and the ground using electrostatic and electromagnetic induction were investigated for telegraphy in the late 19th century before practical radio systems became available. These included a patented induction system by Thomas Edison allowing a telegraph on a running train to connect with telegraph wires running parallel to the tracks, a William 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 the Great Blizzard of and earth conductive systems found limited use between trenches during World War I but these systems were never successful economically. In , Guglielmo Marconi began developing a wireless telegraph system using radio waves , which had been known about since proof of their existence in by Heinrich Hertz , but discounted as a communication format since they seemed, at the time, to be a short range phenomenon. Marconi and Karl Ferdinand Braun were awarded the Nobel Prize for Physics for their contribution to this form of wireless telegraphy. The wireless revolution began in the s,    with the advent of digital wireless networks leading to a social revolution, and a paradigm shift from wired to wireless technology,  including the proliferation of commercial wireless technologies such as cell phones , mobile telephony , pagers , wireless computer networks ,  cellular networks , the wireless Internet , and laptop and handheld computers with wireless connections. RF CMOS integrated circuits enabled sophisticated, low-cost and portable end-user terminals, and gave rise to small, low-cost, low-power and portable units for a wide range of wireless communication systems. This enabled "anytime, anywhere" communication and helped bring about the wireless revolution, leading to the rapid growth of the wireless industry. In recent years, an important contribution to the growth of wireless communication networks has been interference alignment, which was discovered by Syed Ali Jafar at the University of California, Irvine. Radio and microwave communication carry information by modulating properties of electromagnetic waves transmitted through space. Free-space optical communication FSO is an optical communication technology that uses light propagating in free space to transmit wirelessly data for telecommunications or computer networking. This contrasts with other communication technologies that use light beams traveling through transmission lines such as optical 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 which 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 is consumer IR devices such as remote controls and IrDA Infrared Data Association networking, which is used as an alternative to WiFi networking to allow laptops, PDAs, printers, and digital cameras to exchange data. Sonic, especially ultrasonic 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-range RFID tags. Common examples of wireless equipment include: . AM and FM radios and other electronic devices make use of the electromagnetic spectrum. 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 an amateur radio operator was interfering with a pilot's ability to land an aircraft.
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