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Encyclopedia > Channel (communications)

Channel, in communications (sometimes called communications channel), refers to the medium used to convey information from a sender (or transmitter) to a receiver. Look up medium in Wiktionary, the free dictionary. ... Information is the result of processing, manipulating and organizing data in a way that adds to the knowledge of the person receiving it. ... A source is one of the components of communication and information processing. ... The word receiver has a number of different meanings: In communications and information processing, a receiver is the recipient (observer) of a message (information), which is sent from a source (object). ...

Contents

Overview

A Channel can take many forms. Examples of communications channels include:

  1. A connection between initiating and terminating nodes of a circuit.
  2. A buffer from which messages can be put and gotten. See Actor model and process calculi for discussion on the use of channels.
  3. A single path provided by a transmission medium via either
  4. A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths.
  5. The portion of a storage medium, such as a track or a band, that is accessible to a given reading or writing station or head.
  6. In a communications system, the part that connects a data source to a data sink.
  7. A specific radio frequency or band of frequencies, usually in conjunction with a predetermined letter, number, or codeword, and allocated by international agreement.
    Examples:
    • Wi-Fi consists of unlicensed channels 1-13 from 2412MHz to 2484MHz in 5MHz steps.
    • Television channels such as North American TV Channel 2 = 55.25MHz, Channel 13 = 211.25MHz.
  8. A room in the Internet Relay Chat (IRC) network, in which participants can communicate with each other.
  9. A Nintendo Wii Channel, which is a layout of internal system features.

All of these communications channels share the property that they transfer information. The information is carried though the channel by a signal. A telecommunication circuit is defined as follows: The complete path between two terminals over which one-way or two-way communications may be provided. ... In computer science, the Actor model and process calculi are two closely related approaches to the modelling of concurrent digital computation. ... Look up path in Wiktionary, the free dictionary. ... A transmission medium is any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable, dielectric-slab waveguide, water, or air, that can be used for the propagation of signals, usually in the form of modulated radio, light, or acoustic waves, from one point to another. ... 6 or 15cm outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. ... Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal. ... Time-division multiplexing (TDM) is a type of digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i. ... Look up storage in Wiktionary, the free dictionary. ... In telecommunication, a communications system is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. ... In general, data consist of propositions that reflect reality. ... Many modern sinks are made of stainless steel such as this self-rimming example In plumbing, a sink or basin is a bowl-shaped fixture that is used for washing hands or small objects such as food, dishes, nylons, socks or underwear. ... Rough plot of Earths atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. ... Wi-Fi (also WiFi, wifi, etc. ... The lists of television channels are grouped by name, country or language: For an alphabetical list see Television station. ... IRC redirects here. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ...


Channel models

A channel can be physically modelled by trying to calculate the physical processes which modify the transmitted signal. For example in wireless communications the channel can be modelled by calculating the reflection off every object in the environment. A sequence of random numbers might also be added in to simulate external interference and/or electronic noise in the receiver.


Statistically a communication channel is usually modelled as a triple consisting of an input alphabet, an output alphabet, and for each pair (i, o) of input and output elements a transition probability p(i, o). Semantically, the transition probability is the probability that the symbol o is received given that i was transmitted over the channel.


Statistical and physical modelling can be combined. For example in wireless communications the channel is often modelled by a random attenuation (known as fading) of the transmitted signal, followed by additive noise. The attenuation term is a simplification of the underlying physical processes and captures the change in signal power over the course of the transmission. The noise in the model captures external interference and/or electronic noise in the receiver. If the attenuation term is complex it also describes the relative time a signal takes to get through the channel (technically called a phase shift). The statistics of the random attenuation are decided by previous measurements or physical simulations. Fading (or fading channels) are mathematical models for the distortion that a carrier-modulated telecommunication signal experiences over certain propagation media. ...


Channel models may be continuous channel models in that there is no limit to how precisely their values may be defined.


Communication channels are also studied in a discrete-alphabet setting. This corresponds to abstracting a real world communication system in which the analog->digital and digital->analog blocks are out of the control of the designer. The mathematical model consists of a transition probability that specifies an output distribution for each possible sequence of channel inputs. In information theory, it is common to start with memoryless channels in which the output probability distribution only depends on the current channel input. A bundle of optical fiber. ...


Types of communications channels

A simplex communication system is one where all signals flow in one direction. ... It has been suggested that this article or section be merged with duplex (telecommunications). ...

See also

// In telecommunications It has been suggested that this article or section be merged into Return channel. ... All signals are comprised of a whole range of different frequencies added up together. ... In coding theory, a binary symmetric channel (or BSC) is an idealized model of a communications channel that sends bits. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ... Claude Elwood Shannon (April 30, 1916 _ February 24, 2001) has been called the father of information theory, and was the founder of practical digital circuit design theory. ... A bundle of optical fiber. ... In information theory, the Shannon-Hartley theorem states the maximum amount of error-free digital data (that is, information) that can be transmitted over a communication link with a specified bandwidth in the presence of noise interference. ... In information theory, the Shannon–Hartley theorem is an application of the noisy channel coding theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. ...

References


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