Telecommunication
Earth station at the satellite communication facility in Raisting, Bavaria, Germany
Telecommunication is the transmission of signs, signals, messages, words, writings, images and sounds or information of any nature by wire, radio, optical or otherelectromagnetic systems.[1][2]Telecommunication occurs when the exchange of information betweencommunication participants includes the use of technology. It is transmitted either electrically over physical media, such ascables, or via electromagnetic radiation.[3][4][5][6][7][8] Such transmission paths are often divided into communication channels which afford the advantages ofmultiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term,telecommunications, is often used in its plural form because it involves many different technologies.[9]
Early means of communicating over a distance included visual signals, such asbeacons, smoke signals, semaphore telegraphs, signal flags, and opticalheliographs.[10] Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. 20th and 21st century technologies for long-distance communication usually involve electrical and electromagnetic technologies, such astelegraph, telephone, and teleprinter,networks, radio, microwave transmission,fiber optics, and communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909. Other notable pioneering inventors and developers in the field of electrical and electronic telecommunications include Charles Wheatstone and Samuel Morse (inventors of the telegraph), Alexander Graham Bell(inventor of the telephone), Edwin Armstrongand Lee de Forest (inventors of radio), as well as Vladimir K. Zworykin, John Logie Baird andPhilo Farnsworth (some of the inventors oftelevision).
Etymology
The word telecommunication is a compound of the Greek prefix tele (τηλε), meaningdistant, far off, or afar,[11] and the Latincommunicare, meaning to share. Its modern use is adapted from the French,[7] because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié.[12][13] Communication was first used as an English word in the late 14th century. It comes from Old French comunicacion (14c., Modern French communication), from Latin communicationem (nominative communicatio), noun of action from past participle stem of communicare "to share, divide out; communicate, impart, inform; join, unite, participate in," literally "to make common," from communis".[14]
History
Beacons and pigeons
Homing pigeons have occasionally been used throughout history by different cultures.Pigeon post had Persian roots, and was later used by the Romans to aid their military.Frontinus said that Julius Caesar used pigeons as messengers in his conquest ofGaul.[15] The Greeks also conveyed the names of the victors at the Olympic Games to various cities using homing pigeons.[16] In the early 19th century, the Dutch government used the system in Java and Sumatra. And in 1849,Paul Julius Reuter started a pigeon service to fly stock prices between Aachen andBrussels, a service that operated for a year until the gap in the telegraph link was closed.[17]
In the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London.[18]
In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system (or semaphore line) between Lille and Paris.[19] However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres (six to nineteen miles). As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880.[20]
Telegraph and telephone
Sir Charles Wheatstone and Sir William Fothergill Cooke invented the electric telegraph in 1837.[21] On July 25, 1837 the first commercial electrical telegraph was demonstrated by William Fothergill Cooke, an English inventor, and Charles Wheastone, an English scientist.[22] Both inventors viewed their device as "an improvement to the [existing] electromagnetic telegraph" not as a new device.[23]
Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837. His code was an important advance over Wheatstone's signaling method. The firsttransatlantic telegraph cable was successfully completed on 27 July 1866, allowing transatlantic telecommunication for the first time.[24]
The conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876.[25] Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849. However Meucci's device was of little practical value because it relied upon theelectrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said.[26] The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London.[27][28]
Radio and television
Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the then newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean.[29] This was the start of wireless telegraphy by radio. Voice and music were demonstrated in 1900 and 1906, but had little success. World War Iaccelerated the development of radio formilitary communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar.[30] Development of stereo FM broadcasting of radio took place from the 1930s on-wards in the United States and displaced AM as the dominant commercial standard by the 1960s, and by the 1970s in the United Kingdom.[31]
On 25 March 1925, John Logie Baird was able to demonstrate the transmission of moving pictures at the London department storeSelfridges. Baird's device relied upon theNipkow disk and thus became known as themechanical television. It formed the basis of experimental broadcasts done by the British Broadcasting Corporation beginning 30 September 1929.[32] However, for most of the twentieth century televisions depended upon the cathode ray tube invented by Karl Braun. The first version of such a television to show promise was produced by Philo Farnsworthand demonstrated to his family on 7 September 1927.[33] After World War II, the experiments in television that had been interrupted were resumed, and it also became an important home entertainment broadcast medium.
Computers and the Internet
On 11 September 1940, George Stibitztransmitted problems for his Complex Number Calculator in New York using ateletype, and received the computed results back at Dartmouth College in New Hampshire.[34] This configuration of a centralized computer (mainframe) with remote dumb terminals remained popular well into the 1970s. However, already in the 1960s, researchers started to investigate packet switching, a technology that sends a message in portions to its destination asynchronously without passing it through a centralized mainframe. A four-node network emerged on 5 December 1969, constituting the beginnings of the ARPANET, which by 1981 had grown to 213 nodes.[35] ARPANET eventually merged with other networks to form the Internet. While Internet development was a focus of the Internet Engineering Task Force (IETF) who published a series of Request for Comment documents, other networking advancement occurred in industrial laboratories, such as the local area network(LAN) developments of Ethernet (1983) and the token ring protocol (1984).
Key concepts
Modern telecommunication is founded on a series of key concepts that experienced progressive development and refinement in a period of well over a century.
Basic elements
Telecommunication technologies may primarily be divided into wired and wireless methods. Overall though, a basictelecommunication system consists of three main parts that are always present in some form or another:
- A transmitter that takes information and converts it to a signal.
- A transmission medium, also called thephysical channel that carries the signal. An example of this is the "free space channel".
- A receiver that takes the signal from the channel and converts it back into usable information for the recipient.
For example, in a radio broadcasting stationthe station's large power amplifier is the transmitter; and the broadcasting antenna is the interface between the power amplifier and the "free space channel". The free space channel is the transmission medium; and the receiver's antenna is the interface between the free space channel and the receiver. Next, the radio receiver is the destination of the radio signal, and this is where it is converted from electricity to sound for people to listen to.
Sometimes, telecommunication systems are"duplex" (two-way systems) with a single box of electronics working as both the transmitter and a receiver, or a transceiver. For example, acellular telephone is a transceiver.[36] The transmission electronics and the receiver electronics within a transceiver are actually quite independent of each other. This can be readily explained by the fact that radio transmitters contain power amplifiers that operate with electrical powers measured inwatts or kilowatts, but radio receivers deal with radio powers that are measured in themicrowatts or nanowatts. Hence, transceivers have to be carefully designed and built to isolate their high-power circuitry and their low-power circuitry from each other, as to not cause interference.
Telecommunication over fixed lines is calledpoint-to-point communication because it is between one transmitter and one receiver. Telecommunication through radio broadcasts is called broadcast communication because it is between one powerful transmitter and numerous low-power but sensitive radio receivers.[36]
Telecommunications in which multiple transmitters and multiple receivers have been designed to cooperate and to share the same physical channel are called multiplex systems. The sharing of physical channels using multiplexing often gives very large reductions in costs. Multiplexed systems are laid out in telecommunication networks, and the multiplexed signals are switched at nodes through to the correct destination terminal receiver.
Analog versus digital communications
Communications signals can be sent either byanalog signals or digital signals. There areanalog communication systems and digital communication systems. For an analog signal, the signal is varied continuously with respect to the information. In a digital signal, the information is encoded as a set of discrete values (for example, a set of ones and zeros). During the propagation and reception, the information contained in analog signals will inevitably be degraded byundesirable physical noise. (The output of a transmitter is noise-free for all practical purposes.) Commonly, the noise in a communication system can be expressed as adding or subtracting from the desirable signal in a completely random way. This form of noise is called additive noise, with the understanding that the noise can be negative or positive at different instants of time. Noise that is not additive noise is a much more difficult situation to describe or analyze, and these other kinds of noise will be omitted here.
On the other hand, unless the additive noise disturbance exceeds a certain threshold, the information contained in digital signals will remain intact. Their resistance to noise represents a key advantage of digital signals over analog signals.[37]
Telecommunication networks
A telecommunications network is a collection of transmitters, receivers, andcommunications channels that send messages to one another. Some digital communications networks contain one or more routers that work together to transmit information to the correct user. An analog communications network consists of one or more switches that establish a connection between two or more users. For both types of network, repeaters may be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combat attenuation that can render the signal indistinguishable from the noise.[38] Another advantage of digital systems over analog is that their output is easier to store in memory, i.e. two voltage states (high and low) are easier to store than a continuous range of states.
Communication channels
The term "channel" has two different meanings. In one meaning, a channel is the physical medium that carries a signal between the transmitter and the receiver. Examples of this include the atmosphere for sound communications, glass optical fibersfor some kinds of optical communications,coaxial cables for communications by way of the voltages and electric currents in them, andfree space for communications using visible light, infrared waves, ultraviolet light, andradio waves. Coaxial cable types are classified by RG type or "radio guide", terminology derived from World War II. The various RG designations are used to classify the specific signal transmission applications.[39] This last channel is called the "free space channel". The sending of radio waves from one place to another has nothing to do with the presence or absence of an atmosphere between the two. Radio waves travel through a perfect vacuum just as easily as they travel through air, fog, clouds, or any other kind of gas.
The other meaning of the term "channel" in telecommunications is seen in the phrasecommunications channel, which is a subdivision of a transmission medium so that it can be used to send multiple streams of information simultaneously. For example, one radio station can broadcast radio waves into free space at frequencies in the neighborhood of 94.5 MHz (megahertz) while another radio station can simultaneously broadcast radio waves at frequencies in the neighborhood of 96.1 MHz. Each radio station would transmit radio waves over a frequency bandwidth of about 180 kHz (kilohertz), centered at frequencies such as the above, which are called the "carrier frequencies". Each station in this example is separated from its adjacent stations by 200 kHz, and the difference between 200 kHz and 180 kHz (20 kHz) is an engineering allowance for the imperfections in the communication system.
In the example above, the "free space channel" has been divided into communications channels according tofrequencies, and each channel is assigned a separate frequency bandwidth in which to broadcast radio waves. This system of dividing the medium into channels according to frequency is called "frequency-division multiplexing". Another term for the same concept is "wavelength-division multiplexing", which is more commonly used in optical communications when multiple transmitters share the same physical medium.
Another way of dividing a communications medium into channels is to allocate each sender a recurring segment of time (a "time slot", for example, 20 milliseconds out of each second), and to allow each sender to send messages only within its own time slot. This method of dividing the medium into communication channels is called "time-division multiplexing" (TDM), and is used in optical fiber communication. Some radio communication systems use TDM within an allocated FDM channel. Hence, these systems use a hybrid of TDM and FDM.
Modulation
The shaping of a signal to convey information is known as modulation. Modulation can be used to represent a digital message as an analog waveform. This is commonly called"keying" – a term derived from the older use of Morse Code in telecommunications – and several keying techniques exist (these includephase-shift keying, frequency-shift keying, andamplitude-shift keying). The "Bluetooth" system, for example, uses phase-shift keying to exchange information between various devices.[40][41] In addition, there are combinations of phase-shift keying and amplitude-shift keying which is called (in the jargon of the field) "quadrature amplitude modulation" (QAM) that are used in high-capacity digital radio communication systems.
Modulation can also be used to transmit the information of low-frequency analog signals at higher frequencies. This is helpful because low-frequency analog signals cannot be effectively transmitted over free space. Hence the information from a low-frequency analog signal must be impressed into a higher-frequency signal (known as the "carrier wave") before transmission. There are several different modulation schemes available to achieve this [two of the most basic beingamplitude modulation (AM) and frequency modulation (FM)]. An example of this process is a disc jockey's voice being impressed into a 96 MHz carrier wave using frequency modulation (the voice would then be received on a radio as the channel "96 FM").[42] In addition, modulation has the advantage that it may use frequency division multiplexing (FDM).
Society
Telecommunication has a significant social, cultural and economic impact on modern society. In 2008, estimates placed thetelecommunication industry's revenue at $4.7 trillion or just under 3 percent of the gross world product (official exchange rate).[43]Several following sections discuss the impact of telecommunication on society.
Economic impact
Microeconomics
On the microeconomic scale, companies have used telecommunications to help build global business empires. This is self-evident in the case of online retailer Amazon.com but, according to academic Edward Lenert, even the conventional retailer Walmart has benefited from better telecommunication infrastructure compared to its competitors.[44]In cities throughout the world, home owners use their telephones to order and arrange a variety of home services ranging from pizza deliveries to electricians. Even relatively poor communities have been noted to use telecommunication to their advantage. InBangladesh's Narshingdi district, isolated villagers use cellular phones to speak directly to wholesalers and arrange a better price for their goods. In Côte d'Ivoire, coffee growers share mobile phones to follow hourly variations in coffee prices and sell at the best price.[45]
Macroeconomics
On the macroeconomic scale, Lars-Hendrik Röller and Leonard Waverman suggested a causal link between good telecommunication infrastructure and economic growth.[46][47]Few dispute the existence of a correlation although some argue it is wrong to view the relationship as causal.[48]
Because of the economic benefits of good telecommunication infrastructure, there is increasing worry about the inequitable access to telecommunication services amongst various countries of the world—this is known as the digital divide. A 2003 survey by theInternational Telecommunication Union (ITU) revealed that roughly a third of countries have fewer than one mobile subscription for every 20 people and one-third of countries have fewer than one land-line telephone subscription for every 20 people. In terms of Internet access, roughly half of all countries have fewer than one out of 20 people with Internet access. From this information, as well as educational data, the ITU was able to compile an index that measures the overall ability of citizens to access and use information and communication technologies.[49] Using this measure, Sweden, Denmark and Iceland received the highest ranking while the African countries Nigeria, Burkina Faso and Mali received the lowest.[50]
Social impact
Telecommunication has played a significant role in social relationships. Nevertheless, devices like the telephone system were originally advertised with an emphasis on the practical dimensions of the device (such as the ability to conduct business or order home services) as opposed to the social dimensions. It was not until the late 1920s and 1930s that the social dimensions of the device became a prominent theme in telephone advertisements. New promotions started appealing to consumers' emotions, stressing the importance of social conversations and staying connected to family and friends.[51]
Since then the role that telecommunications has played in social relations has become increasingly important. In recent years, the popularity of social networking sites has increased dramatically. These sites allow users to communicate with each other as well as post photographs, events and profiles for others to see. The profiles can list a person's age, interests, sexual preference and relationship status. In this way, these sites can play important role in everything from organising social engagements tocourtship.[52]
Prior to social networking sites, technologies like short message service (SMS) and the telephone also had a significant impact on social interactions. In 2000, market research group Ipsos MORI reported that 81% of 15- to 24-year-old SMS users in the United Kingdom had used the service to coordinate social arrangements and 42% to flirt.[53]
Other impacts
In cultural terms, telecommunication has increased the public's ability to access music and film. With television, people can watch films they have not seen before in their own home without having to travel to the video store or cinema. With radio and the Internet, people can listen to music they have not heard before without having to travel to the music store.
Telecommunication has also transformed the way people receive their news. A 2006 survey (right table) of slightly more than 3,000 Americans by the non-profit Pew Internet and American Life Project in the United States the majority specified television or radio over newspapers.
Telecommunication has had an equally significant impact on advertising. TNS Media Intelligence reported that in 2007, 58% of advertising expenditure in the United States was spent on media that depend upon telecommunication.[55]
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