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Multipath Propagation
In wireless telecommunications , MULTIPATH is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting , ionospheric reflection and refraction , and reflection from water bodies and terrestrial objects such as mountains and buildings. Multipath causes multipath interference including constructive and destructive interference , and phase shifting of the signal. Destructive interference causes fading . Where the magnitudes of the signals arriving by the various paths have a distribution known as the Rayleigh distribution
Rayleigh distribution
, this is known as Rayleigh fading . Where one component (often, but not necessarily, a line of sight component) dominates, a Rician distribution provides a more accurate model, and this is known as Rician fading
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Jitter
In electronics and telecommunications , JITTER is the deviation from true periodicity of a presumably periodic signal , often in relation to a reference clock signal . In clock recovery applications it is called TIMING JITTER. Jitter
Jitter
is a significant, and usually undesired, factor in the design of almost all communications links. Jitter
Jitter
can be quantified in the same terms as all time-varying signals, e.g., root mean square (RMS), or peak-to-peak displacement. Also like other time-varying signals, jitter can be expressed in terms of spectral density . JITTER PERIOD is the interval between two times of maximum effect (or minimum effect) of a signal characteristic that varies regularly with time. JITTER FREQUENCY, the more commonly quoted figure, is its inverse. ITU-T G.810 classifies jitter frequencies below 10 Hz as WANDER and frequencies at or above 10 Hz as jitter
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Impulse Response
In signal processing , the IMPULSE RESPONSE, or IMPULSE RESPONSE FUNCTION (IRF), of a dynamic system is its output when presented with a brief input signal, called an impulse . More generally, an impulse response is the reaction of any dynamic system in response to some external change. In both cases, the impulse response describes the reaction of the system as a function of time (or possibly as a function of some other independent variable that parameterizes the dynamic behavior of the system). In all these cases, the dynamic system and its impulse response may be actual physical objects, or may be mathematical systems of equations describing such objects. Since the impulse function contains all frequencies, the impulse response defines the response of a linear time-invariant system for all frequencies
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Receiver (radio)
In radio communications , a RADIO RECEIVER (RADIO) is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna . The antenna intercepts radio waves (electromagnetic waves ) and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The receiver uses electronic filters to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier to increase the power of the signal for further processing, and finally recovers the desired information through demodulation . The information produced by the receiver may be in the form of sound, images, or data
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Transmission (telecommunications)
In telecommunications , TRANSMISSION (abbreviation: TX) is the process of sending and propagating an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium , either wired, optical fiber or wireless. One example of transmission is the sending of a signal with limited duration, for example a block or packet of data, a phone call, or an email. Transmission technologies and schemes typically refer to physical layer protocol duties such as modulation , demodulation , line coding , equalization , error control , bit synchronization and multiplexing , but the term may also involve higher-layer protocol duties, for example, digitizing an analog message signal, and source coding (compression). Transmission of a digital message, or of a digitized analog signal, is known as digital communication
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Television
TELEVISION or TV is a telecommunication medium used for transmitting moving images in monochrome (black-and-white ), or in color, and in two or three dimensions and sound. The term can refer to a television set , a television program ("TV show"), or the medium of television transmission . Television
Television
is a mass medium for entertainment, education , news , politics, gossip, and advertising. Television
Television
became available in crude experimental forms in the late 1920s, but it would still be several years before the new technology was marketed to consumers. After World War II
World War II
, an improved form of black-and-white TV broadcasting became popular in the United States and Britain, and television sets became commonplace in homes, businesses, and institutions. During the 1950s, television was the primary medium for influencing public opinion
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Linear System
A LINEAR SYSTEM is a mathematical model of a system based on the use of a linear operator . Linear systems typically exhibit features and properties that are much simpler than the nonlinear case. As a mathematical abstraction or idealization, linear systems find important applications in automatic control theory, signal processing , and telecommunications . For example, the propagation medium for wireless communication systems can often be modeled by linear systems. CONTENTS * 1 Definition * 2 Time-varying impulse response * 3 The convolution integral * 4 Discrete time systems * 5 See also DEFINITIONA general deterministic system can be described by an operator, H {displaystyle H} , that maps an input, x ( t ) {displaystyle x(t)} , as a function of t {displaystyle t} to an output, y ( t ) {displaystyle y(t)} , a type of black box description. Linear systems satisfy the property of superposition
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Fax
FAX (short for FACSIMILE ), sometimes called TELECOPYING or TELEFAX (the latter short for TELEFACSIMILE), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer or other output device. The original document is scanned with a FAX MACHINE (or a TELECOPIER), which processes the contents (text or images) as a single fixed graphic image, converting it into a bitmap , and then transmitting it through the telephone system in the form of audio-frequency tones. The receiving fax machine interprets the tones and reconstructs the image, printing a paper copy. Early systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines modulate the transmitted audio frequencies using a digital representation of the page which is compressed to quickly transmit areas which are all-white or all-black
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GSM
GSM
GSM
(GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS, originally GROUPE SPéCIAL MOBILE) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation digital cellular networks used by mobile devices and mobile telephones , first deployed in Finland
Finland
in December 1991. As of 2014 , it has become the de facto global standard for mobile communications – with over 90% market share, operating in over 219 countries and territories. 2G networks developed as a replacement for first generation (1G ) analog cellular networks, and the GSM
GSM
standard originally described as a digital, circuit-switched network optimized for full duplex voice telephony
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Ethernet Over Coax
ETHERNET OVER COAX (EOC) is a family of technologies that supports the transmission of Ethernet
Ethernet
frames over coaxial cable . CONTENTS * 1 History * 2 Standards * 2.1 IEEE
IEEE
1901 (HomePlug) * 2.2 ITU-T G.hn
G.hn
* 2.3 SLOC * 2.4 Other standards * 3 CATV compatibility * 4 See also * 5 References HISTORYThe first Ethernet
Ethernet
standard, known as 10BASE5 (ThickNet) in the family of IEEE 802.3 , specified baseband operation over 50 ohm coaxial cable, which remained the principal medium into the 1980s, when 10BASE2 (ThinNet) coax replaced it in deployments in the 1980s; both being replaced in the 1990s when thinner, cheaper twisted pair cabling came to dominate the market
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Impedance Matching
In electronics , IMPEDANCE MATCHING is the practice of designing the input impedance of an electrical load or the output impedance of its corresponding signal source to maximize the power transfer or minimize signal reflection from the load. In the case of a complex source impedance ZS and load impedance ZL, maximum power transfer is obtained when Z S = Z L {displaystyle Z_{mathrm {S} }=Z_{mathrm {L} }^{*},} where the asterisk indicates the complex conjugate of the variable. Where ZS represents the characteristic impedance of a transmission line , minimum reflection is obtained when Z S = Z L {displaystyle Z_{mathrm {S} }=Z_{mathrm {L} },} The concept of impedance matching found first applications in electrical engineering , but is relevant in other applications in which a form of energy, not necessarily electrical, is transferred between a source and a load
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Signal Reflection
SIGNAL REFLECTION occurs when a signal is transmitted along a transmission medium, such as a copper cable or an optical fiber . Some of the signal power may be reflected back to its origin rather than being carried all the way along the cable to the far end. This happens because imperfections in the cable cause impedance mismatches and non-linear changes in the cable characteristics. These abrupt changes in characteristics cause some of the transmitted signal to be reflected. In radio frequency (RF) practice this is often measured in a dimensionless ratio known as voltage standing wave ratio (VSWR) with a VSWR bridge. The ratio of energy bounced back depends on the impedance mismatch . Mathematically, it is defined using the reflection coefficient . Because the principles are the same, this concept is perhaps easiest to understand when considering an optical fiber. Imperfections in the glass create mirrors that reflect the light back along the fiber
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Power Line Communication
POWER-LINE COMMUNICATION (PLC) is a communication method that uses electrical wiring to simultaneously carry both data and electric power. It is also known as POWER-LINE CARRIER, POWER-LINE DIGITAL SUBSCRIBER LINE (PDSL), MAINS COMMUNICATION, POWER-LINE TELECOMMUNICATIONS, or POWER-LINE NETWORKING (PLN). A wide range of power-line communication technologies are needed for different applications, ranging from home automation to Internet access which is often called broadband over power lines (BPL). Most PLC technologies limit themselves to one type of wire (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations
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ITU-T
The ITU
ITU
TELECOMMUNICATION STANDARDIZATION SECTOR (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication
Telecommunication
Union (ITU); it coordinates standards for telecommunications . The standardization efforts of ITU
ITU
commenced in 1865 with the formation of the INTERNATIONAL TELEGRAPH UNION ( ITU
ITU
). ITU
ITU
became a specialized agency of the United Nations in 1947. The International Telegraph and Telephone Consultative Committee (CCITT, from French: Comité Consultatif International Téléphonique et Télégraphique) was created in 1956, and was renamed ITU-T in 1993. ITU-T has a permanent secretariat, the Telecommunication Standardization
Standardization
Bureau (TSB), based at the ITU
ITU
headquarters in Geneva, Switzerland
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G.hn
G.HN is a specification for home networking with data rates up to 1 Gbit/s and operation over three types of legacy wires: telephone wiring , coaxial cables and power lines . A single G.hn
G.hn
semiconductor device is able to network over any of the supported home wire types. Some benefits of a multi-wire standard are lower equipment development costs and lower deployment costs for service providers (by allowing customer self-install)
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Equalization (communications)
In telecommunication , EQUALIZATION is the reversal of distortion incurred by a signal transmitted through a channel . EQUALIZERS are used to render the frequency response —for instance of a telephone line—flat from end-to-end. When a channel has been equalized the frequency domain attributes of the signal at the input are faithfully reproduced at the output. Telephones, DSL
DSL
lines and television cables use equalizers to prepare data signals for transmission. Equalizers are critical to the successful operation of electronic systems such as analog broadcast television . In this application the actual waveform of the transmitted signal must be preserved, not just its frequency content. Equalizing filters must cancel out any group delay and phase delay between different frequency components
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