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112-423: In telecommunications and computer networking , multiplexing (sometimes contracted to muxing ) is a method by which multiple analog or digital signals are combined into one signal over a shared medium . The aim is to share a scarce resource – a physical transmission medium . For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in

224-412: A thermionic tube or thermionic valve uses thermionic emission of electrons from a heated cathode for a number of fundamental electronic functions such as signal amplification and current rectification . The simplest vacuum tube, the diode invented in 1904 by John Ambrose Fleming , contains only a heated electron-emitting cathode and an anode. Electrons can only flow in one direction through

336-437: A line of sight component) dominates, a Rician distribution provides a more accurate model, and this is known as Rician fading . Where two components dominate, the behavior is best modeled with the two-wave with diffuse power (TWDP) distribution. All of these descriptions are commonly used and accepted and lead to results. However, they are generic and abstract/hide/approximate the underlying physics. Multipath interference

448-425: A multiple-input multiple-output communications (MIMO) scheme. In wired communication, space-division multiplexing , also known as space-division multiple access (SDMA) is the use of separate point-to-point electrical conductors for each transmitted channel. Examples include an analog stereo audio cable, with one pair of wires for the left channel and another for the right channel, and a multi-pair telephone cable ,

560-411: A radio broadcasting station , the 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, where it

672-408: A time-multiplexing system of multiple Hughes machines in the 1870s. In 1874, the quadruplex telegraph developed by Thomas Edison transmitted two messages in each direction simultaneously, for a total of four messages transiting the same wire at the same time. Several researchers were investigating acoustic telegraphy , a frequency-division multiplexing technique, which led to the invention of

784-411: 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. On the macroeconomic scale, Lars-Hendrik Röller and Leonard Waverman suggested a causal link between good telecommunication infrastructure and economic growth. Few dispute the existence of a correlation although some argue it is wrong to view

896-438: A caveat for it in 1876. Gray abandoned his caveat and because he did not contest Bell's priority, the examiner approved Bell's patent on March 3, 1876. Gray had filed his caveat for the variable resistance telephone, but Bell was the first to document the idea and test it in a telephone.[88] Antonio Meucci invented a device that allowed the electrical transmission of voice over a line nearly 30 years before in 1849, but his device

1008-441: A connection between two or more users. For both types of networks, 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. Another advantage of digital systems over analogue is that their output is easier to store in memory, i.e., two voltage states (high and low) are easier to store than

1120-495: A continuous range of states. Telecommunication has a significant social, cultural and economic impact on modern society. In 2008, estimates placed the telecommunication industry 's revenue at US$ 4.7 trillion or just under three per cent of the gross world product (official exchange rate). Several following sections discuss the impact of telecommunication on society. On the microeconomic scale, companies have used telecommunications to help build global business empires. This

1232-411: A customer's residential area, but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the appropriate frequency (channel) to access the desired signal. A variant technology, called wavelength-division multiplexing (WDM) is used in optical communications . Time-division multiplexing (TDM)

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1344-406: 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 being amplitude 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

1456-450: A key advantage of digital signals over analogue signals. However, digital systems fail catastrophically when noise exceeds the system's ability to autocorrect. On the other hand, analogue systems fail gracefully: as noise increases, the signal becomes progressively more degraded but still usable. Also, digital transmission of continuous data unavoidably adds quantization noise to the output. This can be reduced, but not eliminated, only at

1568-838: A new international frequency list and used in conformity with the Radio Regulation". According to the ITU's Radio Regulations adopted in Atlantic City, all frequencies referenced in the International Frequency Registration Board , examined by the board and registered on the International Frequency List "shall have the right to international protection from harmful interference". From a global perspective, there have been political debates and legislation regarding

1680-486: A peak bit rate of 54 Mbit/s, thus increasing the total peak bit rate by the factor k . Different antennas would give different multi-path propagation (echo) signatures, making it possible for digital signal processing techniques to separate different signals from each other. These techniques may also be utilized for space diversity (improved robustness to fading) or beamforming (improved selectivity) rather than multiplexing. Frequency-division multiplexing (FDM)

1792-437: 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 to courtship . 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

1904-491: A radio as the channel "96 FM"). In addition, modulation has the advantage that it may use frequency division multiplexing (FDM). A telecommunications network is a collection of transmitters, receivers, and communications 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 analogue communications network consists of one or more switches that establish

2016-475: A service that operated for a year until the gap in the telegraph link was closed. 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

2128-539: A switched star network such as a telephone access network, a switched Ethernet network, and a mesh network . In wireless communication, space-division multiplexing is achieved with multiple antenna elements forming a phased array antenna . Examples are multiple-input and multiple-output (MIMO), single-input and multiple-output (SIMO) and multiple-input and single-output (MISO) multiplexing. An IEEE 802.11g wireless router with k antennas makes it in principle possible to communicate with k multiplexed channels, each with

2240-411: A telephone network, the caller is connected to the person to whom they wish to talk by switches at various telephone exchanges . The switches form an electrical connection between the two users and the setting of these switches is determined electronically when the caller dials the number. Once the connection is made, the caller's voice is transformed to an electrical signal using a small microphone in

2352-481: A transport stream and/or container is commonly called a multiplexer or muxer . A demuxer is software that extracts or otherwise makes available for separate processing the components of such a stream or container. In digital television systems, several variable bit-rate data streams are multiplexed together to a fixed bit-rate transport stream by means of statistical multiplexing . This makes it possible to transfer several video and audio channels simultaneously over

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2464-412: A version of the electrical telegraph that he unsuccessfully demonstrated on September 2, 1837. His code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was successfully completed on July 27, 1866, allowing transatlantic telecommunication for the first time. The conventional telephone was patented by Alexander Bell in 1876. Elisha Gray also filed

2576-412: Is a class of techniques where several channels simultaneously share the same frequency spectrum , and this spectral bandwidth is much higher than the bit rate or symbol rate . One form is frequency hopping, another is direct sequence spread spectrum. In the latter case, each channel transmits its bits as a coded channel-specific sequence of pulses called chips. Number of chips per bit, or chips per symbol,

2688-405: Is a digital (or in rare cases, analog) technology that uses time, instead of space or frequency, to separate the different data streams. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently quickly, the receiving devices will not detect that some of

2800-512: Is a form of time-division multiplexing. Digital bit streams can be transferred over an analog channel by means of code-division multiplexing techniques such as frequency-hopping spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS). In wireless communications , multiplexing can also be accomplished through alternating polarization ( horizontal / vertical or clockwise / counterclockwise ) on each adjacent channel and satellite, or through phased multi-antenna array combined with

2912-436: Is a novel method for polarized antenna transmission utilizing a differential technique. Orbital angular momentum multiplexing is a relatively new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path. It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems. As of 2012 it

3024-413: Is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and the two (or more) components of the wave interfere constructively or destructively. Multipath interference is a common cause of " ghosting " in analog television broadcasts and of fading of radio waves . The condition necessary is that the components of the wave remain coherent throughout

3136-811: Is a technique in which each channel transmits its bits as a coded channel-specific sequence of pulses. This coded transmission is typically accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber and asynchronously demultiplexed. Other widely used multiple access techniques are time-division multiple access (TDMA) and frequency-division multiple access (FDMA). Code-division multiplex techniques are used as an access technology, namely code-division multiple access (CDMA), in Universal Mobile Telecommunications System (UMTS) standard for

3248-581: Is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié . 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 communication), 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". At

3360-671: Is called point-to-point communication because it occurs between a transmitter and a receiver. Telecommunication through radio broadcasts is called broadcast communication because it occurs between a powerful transmitter and numerous low-power but sensitive radio receivers. Telecommunications in which multiple transmitters and multiple receivers have been designed to cooperate and share the same physical channel are called multiplex systems . The sharing of physical channels using multiplexing often results in significant cost reduction. Multiplexed systems are laid out in telecommunication networks and multiplexed signals are switched at nodes through to

3472-451: 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 analogue signals at higher frequencies. This is helpful because low-frequency analogue signals cannot be effectively transmitted over free space. Hence the information from a low-frequency analogue signal must be impressed into

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3584-468: Is called multipath fading. In analog facsimile and television transmission , multipath causes jitter and ghosting, seen as a faded duplicate image to the right of the main image. Ghosts occur when transmissions bounce off a mountain or other large object, while also arriving at the antenna by a shorter, direct route, with the receiver picking up two signals separated by a delay. In radar processing, multipath causes ghost targets to appear, deceiving

3696-434: Is commonly called "keying" —a term derived from the older use of Morse Code in telecommunications—and several keying techniques exist (these include phase-shift keying , frequency-shift keying , and amplitude-shift keying ). The " Bluetooth " system, for example, uses phase-shift keying to exchange information between various devices. In addition, there are combinations of phase-shift keying and amplitude-shift keying which

3808-794: Is converted from electricity to sound. Telecommunication systems are occasionally "duplex" (two-way systems) with a single box of electronics working as both the transmitter and a receiver, or a transceiver (e.g., a mobile phone ). The transmission electronics and the receiver electronics within a transceiver are quite independent of one another. This can be explained by the fact that radio transmitters contain power amplifiers that operate with electrical powers measured in watts or kilowatts, but radio receivers deal with radio powers measured in microwatts 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 to avoid interference. Telecommunication over fixed lines

3920-481: Is degraded by undesirable noise . Commonly, the noise in a communication system can be expressed as adding or subtracting from the desirable signal via a random process . This form of noise is called additive noise , with the understanding that the noise can be negative or positive at different instances. Unless the additive noise disturbance exceeds a certain threshold, the information contained in digital signals will remain intact. Their resistance to noise represents

4032-405: Is inherently an analog technology. FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium. In FDM the signals are electrical signals. One of the most common applications for FDM is traditional radio and television broadcasting from terrestrial, mobile or satellite stations, or cable television. Only one cable reaches

4144-522: Is likewise also true for digital subscriber lines (DSL). Fiber in the loop (FITL) is a common method of multiplexing, which uses optical fiber as the backbone . It not only connects POTS phone lines with the rest of the PSTN , but also replaces DSL by connecting directly to Ethernet wired into the home . Asynchronous Transfer Mode is often the communications protocol used. Cable TV has long carried multiplexed television channels , and late in

4256-460: Is not practical (such as where there are different sources using a single transponder ), single channel per carrier mode is used. In FM broadcasting and other analog radio media, multiplexing is a term commonly given to the process of adding subcarriers to the audio signal before it enters the transmitter , where modulation occurs. (In fact, the stereo multiplex signal can be generated using time-division multiplexing, by switching between

4368-441: Is one in which members share a number of ties stemming from more than one social context, such as workmates, neighbors, or relatives. Telecommunications Telecommunication , often used in its plural form or abbreviated as telecom , is the transmission of information with an immediacy comparable to face-to-face communication. As such, slow communications technologies like postal mail and pneumatic tubes are excluded from

4480-728: Is possible (just as in statistical multiplexing ), that the wide bandwidth allows poor signal-to-noise ratio according to Shannon–Hartley theorem , and that multi-path propagation in wireless communication can be combated by rake receivers . A significant application of CDMA is the Global Positioning System (GPS). A multiplexing technique may be further extended into a multiple access method or channel access method , for example, TDM into time-division multiple access (TDMA) and statistical multiplexing into carrier-sense multiple access (CSMA). A multiple-access method makes it possible for several transmitters connected to

4592-609: 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. 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. In Bangladesh 's Narsingdi District , isolated villagers use cellular phones to speak directly to wholesalers and arrange

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4704-448: 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 to frequencies , and each channel is assigned a separate frequency bandwidth in which to broadcast radio waves. This system of dividing

4816-418: Is still in its early research phase, with small-scale laboratory demonstrations of bandwidths of up to 2.5 Tbit/s over a single light path. This is a controversial subject in the academic community, with many claiming it is not a new method of multiplexing, but rather a special case of space-division multiplexing. Code-division multiplexing (CDM), code-division multiple access (CDMA) or spread spectrum

4928-418: Is the spreading factor . This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber or radio channel or other medium, and asynchronously demultiplexed. Advantages over conventional techniques are that variable bandwidth

5040-449: Is the informational equivalent of two newspaper pages per person per day in 1986, and six entire newspapers per person per day by 2007. Given this growth, telecommunications play an increasingly important role in the world economy and the global telecommunications industry was about a $ 4.7 trillion sector in 2012. The service revenue of the global telecommunications industry was estimated to be $ 1.5 trillion in 2010, corresponding to 2.4% of

5152-425: Is time varying, and as such we have Very often, just one parameter is used to denote the severity of multipath conditions: it is called the multipath time , T M {\displaystyle T_{M}} , and it is defined as the time delay existing between the first and the last received impulses In practical conditions and measurement, the multipath time is computed by considering as last impulse

5264-457: The Fourier transform principle. In computer programming , it may refer to using a single in-memory resource (such as a file handle) to handle multiple external resources (such as on-disk files). Some electrical multiplexing techniques do not require a physical " multiplexer " device, they refer to a " keyboard matrix " or " Charlieplexing " design style: In high-throughput DNA sequencing ,

5376-773: The Nipkow disk by Paul Nipkow and thus became known as the mechanical television . It formed the basis of experimental broadcasts done by the British Broadcasting Corporation beginning on 30 September 1929. However, for most of the 20th century, televisions depended on the cathode ray tube invented by Karl Ferdinand Braun . The first version of such a television to show promise was produced by Philo Farnsworth and demonstrated to his family on 7 September 1927. After World War II, interrupted experiments resumed and television became an important home entertainment broadcast medium. The type of device known as

5488-422: The complex amplitude (i.e., magnitude and phase) of the generic received pulse. As a consequence, y ( t ) {\displaystyle y(t)} also represents the impulse response function h ( t ) {\displaystyle h(t)} of the equivalent multipath model. More in general, in presence of time variation of the geometrical reflection conditions, this impulse response

5600-622: The intersymbol interference that multipath propagation would cause. The ITU-T G.hn standard provides a way to create a high-speed (up to 1 gigabit per second) local area network using existing home wiring ( power lines , phone lines, and coaxial cables ). G.hn uses OFDM with a cyclic prefix to avoid ISI. Because multipath propagation behaves differently in each kind of wire, G.hn uses different OFDM parameters (OFDM symbol duration, guard interval duration) for each media. DSL modems also use orthogonal frequency-division multiplexing to communicate with their DSLAM despite multipath. In this case

5712-440: The spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, leading to the creation of electronics . In the 1940s, the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, cheaper, and more efficient, reliable, and durable than thermionic tubes. Starting in

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5824-467: The 1870s, and is now widely applied in communications. In telephony , George Owen Squier is credited with the development of telephone carrier multiplexing in 1910. The multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts

5936-705: The 1932 Plenipotentiary Telegraph Conference and the International Radiotelegraph Conference in Madrid, the two organizations merged to form the International Telecommunication Union (ITU). They defined telecommunication as "any telegraphic or telephonic communication of signs, signals, writing, facsimiles and sounds of any kind, by wire, wireless or other systems or processes of electric signaling or visual signaling (semaphores)." The definition

6048-497: The 1970s. In the 1960s, Paul Baran and, independently, Donald Davies 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 . ARPANET eventually merged with other networks to form

6160-504: The 20th century began offering the same services as telephone companies . IPTV also depends on multiplexing. In video editing and processing systems, multiplexing refers to the process of interleaving audio and video into one coherent data stream. In digital video , such a transport stream is normally a feature of a container format which may include metadata and other information, such as subtitles . The audio and video streams may have variable bit rate. Software that produces such

6272-466: The ITU was able to compile an index that measures the overall ability of citizens to access and use information and communication technologies. Using this measure, Sweden, Denmark and Iceland received the highest ranking while the African countries Niger , Burkina Faso and Mali received the lowest. Telecommunication has played a significant role in social relationships. Nevertheless, devices like

6384-744: The Internet. While Internet development was a focus of the Internet Engineering Task Force (IETF) who published a series of Request for Comments documents, other networking advancements occurred in industrial laboratories , such as the local area network (LAN) developments of Ethernet (1983), Token Ring (1984) and Star network topology. The effective capacity to exchange information worldwide through two-way telecommunication networks grew from 281 petabytes (PB) of optimally compressed information in 1986 to 471 PB in 1993 to 2.2 exabytes (EB) in 2000 to 65 EB in 2007. This

6496-506: The United Kingdom had used the service to coordinate social arrangements and 42% to flirt. 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

6608-797: The United States was spent on media that depend upon telecommunication. Many countries have enacted legislation which conforms to the International Telecommunication Regulations established by the International Telecommunication Union (ITU), which is the "leading UN agency for information and communication technology issues". In 1947, at the Atlantic City Conference, the ITU decided to "afford international protection to all frequencies registered in

6720-460: The airport ticket desk back to the airline data center are also installed. Some web proxy servers (e.g. polipo ) use TDM in HTTP pipelining of multiple HTTP transactions onto the same TCP/IP connection . Carrier-sense multiple access and multidrop communication methods are similar to time-division multiplexing in that multiple data streams are separated by time on the same medium, but because

6832-493: The caller's handset . This electrical signal is then sent through the network to the user at the other end where it is transformed back into sound by a small speaker in that person's handset. Multi-path propagation Where the magnitudes of the signals arriving by the various paths have a distribution known as the Rayleigh distribution , this is known as Rayleigh fading . Where one component (often, but not necessarily,

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6944-444: The capacity to carry several HDTV channels in one multiplex. In digital radio , a multiplex (also known as an ensemble) is a number of radio stations that are grouped together. A multiplex is a stream of digital information that includes audio and other data. On communications satellites which carry broadcast television networks and radio networks , this is known as multiple channel per carrier or MCPC . Where multiplexing

7056-457: The case of CCITT7 signaling systems and 30 voice channels for customer-connected Q931, DASS2, DPNSS, V5 and CASS signaling systems. Polarization-division multiplexing uses the polarization of electromagnetic radiation to separate orthogonal channels. It is in practical use in both radio and optical communications, particularly in 100 Gbit/s per channel fiber-optic transmission systems . Differential Cross-Polarized Wireless Communications

7168-425: The circuit time was used to serve another logical communication path. Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 baud , so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from

7280-437: The correct destination terminal receiver. Communications can be encoded as analogue or digital signals , which may in turn be carried by analogue or digital communication systems. Analogue signals vary continuously with respect to the information, while digital signals encode information as a set of discrete values (e.g., a set of ones and zeroes). During propagation and reception, information contained in analogue signals

7392-500: The definition. Many transmission media have been used for telecommunications throughout history, from smoke signals , beacons , semaphore telegraphs , signal flags , and optical heliographs to wires and empty space made to carry electromagnetic signals. These paths of transmission may be divided into communication channels for multiplexing , allowing for a single medium to transmit several concurrent communication sessions . Several methods of long-distance communication before

7504-519: The development of optical fibre. The Internet , a technology independent of any given medium, has provided global access to services for individual users and further reduced location and time limitations on communications. Telecommunication is a compound noun of the Greek prefix tele- (τῆλε), meaning distant , far off , or afar , and the Latin verb communicare , meaning to share . Its modern use

7616-537: The device—from the cathode to the anode. Adding one or more control grids within the tube enables the current between the cathode and anode to be controlled by the voltage on the grid or grids. These devices became a key component of electronic circuits for the first half of the 20th century and were crucial to the development of radio, television, radar, sound recording and reproduction , long-distance telephone networks, and analogue and early digital computers . While some applications had used earlier technologies such as

7728-591: The distance (in Hz) between two consecutive valleys (or two consecutive peaks), is roughly inversely proportional to the multipath time. The so-called coherence bandwidth is thus defined as For example, with a multipath time of 3 μs (corresponding to a 1 km of added on-air travel for the last received impulse), there is a coherence bandwidth of about 330 kHz. [REDACTED]  This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from

7840-422: The electrical telegraph, the last commercial line was abandoned in 1880. On July 25, 1837, the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke and English scientist Sir Charles Wheatstone . Both inventors viewed their device as "an improvement to the [existing] electromagnetic telegraph" and not as a new device. Samuel Morse independently developed

7952-403: The expense of increasing the channel bandwidth requirement. 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 fibres for some kinds of optical communications , coaxial cables for communications by way of

8064-458: The first decade of the 20th century, a revolution in wireless communication began with breakthroughs including those made in radio communications by Guglielmo Marconi , who won the 1909 Nobel Prize in Physics . Other early pioneers in electrical and electronic telecommunications include co-inventors of the telegraph Charles Wheatstone and Samuel Morse , numerous inventors and developers of

8176-413: The first one which allows receiving a determined amount of the total transmitted power (scaled by the atmospheric and propagation losses), e.g. 99%. Keeping our aim at linear, time invariant systems, we can also characterize the multipath phenomenon by the channel transfer function H ( f ) {\displaystyle H(f)} , which is defined as the continuous time Fourier transform of

8288-431: The importance of social conversations and staying connected to family and friends. 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

8400-519: The impulse response h ( t ) {\displaystyle h(t)} where the last right-hand term of the previous equation is easily obtained by remembering that the Fourier transform of a Dirac pulse is a complex exponential function, an eigenfunction of every linear system. The obtained channel transfer characteristic has a typical appearance of a sequence of peaks and valleys (also called notches ); it can be shown that, on average,

8512-600: The light takes 3 μs to cross a 1 km span). Thus, the received signal will be expressed by where N {\displaystyle N} is the number of received impulses (equivalent to the number of electromagnetic paths, and possibly very large), τ n {\displaystyle \tau _{n}} is the time delay of the generic n t h {\displaystyle n^{th}} impulse, and ρ n e j ϕ n {\displaystyle \rho _{n}e^{j\phi _{n}}} represent

8624-552: The management of telecommunication and broadcasting. The history of broadcasting discusses some debates in relation to balancing conventional communication such as printing and telecommunication such as radio broadcasting. The onset of World War II brought on the first explosion of international broadcasting propaganda. Countries, their governments, insurgents, terrorists, and militiamen have all used telecommunication and broadcasting techniques to promote propaganda. Patriotic propaganda for political movements and colonization started

8736-567: 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

8848-414: The medium into communication channels is called " time-division multiplexing " ( TDM ), and is used in optical fibre communication. Some radio communication systems use TDM within an allocated FDM channel. Hence, these systems use a hybrid of TDM and FDM. The shaping of a signal to convey information is known as modulation . Modulation can be used to represent a digital message as an analogue waveform. This

8960-742: The mid-1930s. In 1936, the BBC broadcast propaganda to the Arab World to partly counter similar broadcasts from Italy, which also had colonial interests in North Africa. Modern political debates in telecommunication include the reclassification of broadband Internet service as a telecommunications service (also called net neutrality ), regulation of phone spam , and expanding affordable broadband access. According to data collected by Gartner and Ars Technica sales of main consumer's telecommunication equipment worldwide in millions of units was: In

9072-596: The mid-1960s, thermionic tubes were replaced with the transistor . Thermionic tubes still have some applications for certain high-frequency amplifiers. On 11 September 1940, George Stibitz transmitted problems for his Complex Number Calculator in New York using a teletype and received the computed results back at Dartmouth College in New Hampshire . This configuration of a centralized computer ( mainframe ) with remote dumb terminals remained popular well into

9184-429: The modern era used sounds like coded drumbeats , the blowing of horns , and whistles . Long-distance technologies invented during the 20th and 21st centuries generally use electric power, and include the telegraph , telephone , television , and radio . Early telecommunication networks used metal wires as the medium for transmitting signals. These networks were used for telegraphy and telephony for many decades. In

9296-452: 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

9408-400: The neighbourhood of 94.5  MHz (megahertz) while another radio station can simultaneously broadcast radio waves at frequencies in the neighbourhood of 96.1 MHz. Each radio station would transmit radio waves over a frequency bandwidth of about 180  kHz (kilohertz), centred at frequencies such as the above, which are called the "carrier frequencies" . Each station in this example

9520-411: The original channels on the receiver end. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX or DMX). Inverse multiplexing (IMUX) has the opposite aim as multiplexing, namely to break one data stream into several streams, transfer them simultaneously over several communication channels, and recreate

9632-455: The original data stream. In computing , I/O multiplexing can also be used to refer to the concept of processing multiple input/output events from a single event loop , with system calls like poll and select (Unix) . Multiple variable bit rate digital bit streams may be transferred efficiently over a single fixed bandwidth channel by means of statistical multiplexing . This is an asynchronous mode time-domain multiplexing which

9744-515: 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 phrase communications 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

9856-465: The quality of communications. The errors are due to intersymbol interference (ISI). Equalizers are often used to correct the ISI. Alternatively, techniques such as orthogonal frequency division modulation and rake receivers may be used. In a Global Positioning System receiver , multipath effects can cause a stationary receiver's output to indicate as if it were randomly jumping about or creeping. When

9968-491: The radar receiver . These ghosts are particularly bothersome since they move and behave like the normal targets (which they echo), and so the receiver has difficulty in isolating the correct target echo. These problems can be minimized by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below the ground or above a certain height (altitude). In digital radio communications (such as GSM ) multipath can cause errors and affect

10080-406: The receiver, due to the presence of the multiple electromagnetic paths, more than one pulse will be received, and each one of them will arrive at different times. In fact, since the electromagnetic signals travel at the speed of light , and since every path has a geometrical length possibly different from that of the other ones, there are different air travelling times (consider that, in free space ,

10192-434: The reflections may be caused by mixed wire gauges , but those from bridge taps are usually more intense and complex. Where OFDM training is unsatisfactory, bridge taps may be removed. The mathematical model of the multipath can be presented using the method of the impulse response used for studying linear systems . Suppose you want to transmit a single, ideal Dirac pulse of electromagnetic power at time 0, i.e. At

10304-709: The relationship as causal. 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 the International 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,

10416-498: The same frequency channel, together with various services. This may involve several standard-definition television (SDTV) programs (particularly on DVB-T , DVB-S2 , ISDB and ATSC-C), or one HDTV , possibly with a single SDTV companion channel over one 6 to 8 MHz-wide TV channel. The device that accomplishes this is called a statistical multiplexer . In several of these systems, the multiplexing results in an MPEG transport stream . The newer DVB standards DVB-S2 and DVB-T2 has

10528-531: The same physical medium to share their capacity. Multiplexing is provided by the physical layer of the OSI model , while multiple access also involves a media access control protocol, which is part of the data link layer . The Transport layer in the OSI model, as well as TCP/IP model, provides statistical multiplexing of several application layer data flows to/from the same computer. Code-division multiplexing (CDM)

10640-584: The signals have separate origins instead of being combined into a single signal, are best viewed as channel access methods , rather than a form of multiplexing. TD is a legacy multiplexing technology still providing the backbone of most National fixed-line telephony networks in Europe, providing the 2 Mbit/s voice and signaling ports on narrow-band telephone exchanges such as the DMS100. Each E1 or 2 Mbit/s TDM port provides either 30 or 31 speech timeslots in

10752-516: The telephone including Antonio Meucci , Philipp Reis , Elisha Gray and Alexander Graham Bell , inventors of radio Edwin Armstrong and Lee de Forest , as well as inventors of television like Vladimir K. Zworykin , John Logie Baird and Philo Farnsworth . Since the 1960s, the proliferation of digital technologies has meant that voice communications have gradually been supplemented by data. The physical limitations of metallic media prompted

10864-405: The telephone . In telephony , a customer 's telephone line now typically ends at the remote concentrator box, where it is multiplexed along with other telephone lines for that neighborhood or other similar area. The multiplexed signal is then carried to the central switching office on significantly fewer wires and for much further distances than a customer's line can practically go. This

10976-412: 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

11088-407: The term is used to indicate that some artificial sequences (often called barcodes or indexes ) have been added to link given sequence reads to a given sample, and thus allow for the sequencing of multiple samples in the same reaction. In sociolinguistics , multiplexity is used to describe the number of distinct connections between individuals who are part of a social network . A multiplex network

11200-631: The then-newly discovered phenomenon of radio waves , demonstrating, by 1901, that they could be transmitted across the Atlantic Ocean. This was the start of wireless telegraphy by radio. On 17 December 1902, a transmission from the Marconi station in Glace Bay, Nova Scotia, Canada , became the world's first radio message to cross the Atlantic from North America. In 1904, a commercial service

11312-432: The third-generation (3G) mobile communication identified by the ITU. The earliest communication technology using electrical wires, and therefore sharing an interest in the economies afforded by multiplexing, was the electric telegraph . Early experiments allowed two separate messages to travel in opposite directions simultaneously, first using an electric battery at both ends, then at only one end. Émile Baudot developed

11424-471: The two (left channel and right channel) input signals at an ultrasonic rate (the subcarrier), and then filtering out the higher harmonics.) Multiplexing in this sense is sometimes known as MPX , which in turn is also an old term for stereophonic FM, seen on stereo systems since the 1960s. In spectroscopy the term is used to indicate that the experiment is performed with a mixture of frequencies at once and their respective response unraveled afterward using

11536-419: The unit is moving the jumping or creeping may be hidden, but it still degrades the displayed accuracy of location and speed. Multipath propagation is similar in power line communication and in telephone local loops . In either case, impedance mismatch causes signal reflection . High-speed power line communication systems usually employ multi-carrier modulations (such as OFDM or wavelet OFDM) to avoid

11648-490: The voltages and electric currents in them, and free space for communications using visible light , infrared waves, ultraviolet light , and radio 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. This last channel is called the "free space channel". The sending of radio waves from one place to another has nothing to do with

11760-492: The wartime purposes of aircraft and land communication, radio navigation, and radar. Development of stereo FM broadcasting of radio began in the 1930s in the United States and the 1940s in the United Kingdom, displacing AM as the dominant commercial standard in the 1970s. On March 25, 1925, John Logie Baird demonstrated the transmission of moving pictures at the London department store Selfridges . Baird's device relied upon

11872-433: The whole extent of their travel. The interference will arise owing to the two (or more) components of the wave having, in general, travelled a different length (as measured by optical path length – geometric length and refraction (differing optical speed)), and thus arriving at the detector out of phase with each other. The signal due to indirect paths interferes with the required signal in amplitude as well as phase which

11984-418: The world's gross domestic product (GDP). Modern telecommunication is founded on a series of key concepts that experienced progressive development and refinement in a period of well over a century: Telecommunication technologies may primarily be divided into wired and wireless methods. Overall, a basic telecommunication system consists of three main parts that are always present in some form or another: In

12096-490: Was during the Spanish Armada , when a beacon chain relayed a signal from Plymouth to London . In 1792, Claude Chappe , a French engineer, built the first fixed visual telegraphy system (or semaphore line ) between Lille and Paris. 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

12208-407: Was established to transmit nightly news summaries to subscribing ships, which incorporated them into their onboard newspapers. World War I accelerated the development of radio for military 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 the development of radio for

12320-471: Was later reconfirmed, according to Article 1.3 of the ITU Radio Regulations , which defined it as "Any transmission , emission or reception of signs, signals, writings, images and sounds or intelligence of any nature by wire , radio, optical, or other electromagnetic systems". Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots and

12432-676: Was later used by the Romans to aid their military. Frontinus claimed Julius Caesar used pigeons as messengers in his conquest of Gaul . The Greeks also conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. 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 and Brussels ,

12544-486: Was of little practical value because it relied on the electrophonic effect requiring users to place the receiver in their mouths to "hear". The first commercial telephone services were set up by the Bell Telephone Company in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. In 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using

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