Kanal atawa saluran (Basa Inggris: channel, Basa Walanda: kanaal), dina télékomunikasi (nu kalan-kalan disebut kanal komunikasi), nujul kana medium nu digunakeun pikeun ngirimkeun informasi ti hiji pangirim (atawa pamancar) ka panarima.
Aya rupa-rupa bentuk kanal. Conto kanal komunikasi di antarana:
|Artikel ieu keur dikeureuyeuh, ditarjamahkeun tina basa Inggris.
Bantosanna diantos kanggo narjamahkeun.
- A connection between initiating and terminating nodes of a circuit.
- A buffer from which messages can be put and gotten. See Actor model and process calculi for discussion on the use of channels.
- A single path provided by a transmission medium via either
- A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths.
- The portion of a storage medium, such as a track or a band, that is accessible to a given réading or writing station or héad.
- In a communications system, the part that connects a data source to a data sink.
- A specific radio frequency, pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement.
- Marine VHF radio uses some 88 channels in the VHF band for two-way FM voice communication. Channel 16, for example, is 156.800 MHz. Seven additional channels, WX1 - WX7, are allocated for wéather broadcasts.
- Television channels such as North American TV Channel 2 = 55.25 MHz, Channel 13 = 211.25 MHz. éach channel is 6 MHz wide. Besides these "physical channels", television also has "virtual channels".
- Wi-Fi consists of unlicensed channels 1-13 from 2412 MHz to 2484 MHz in 5 MHz steps.
- A room in the Internet Relay Chat (IRC) network, in which participants can communicate with éach other.
All of these communications channels share the property that they transfer information. The information is carried through the channel by a signal.
A channel can be modélled physically by trying to calculate the physical processes which modify the transmitted signal. For example in wireless communications the channel can be modélled 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 modélled as a triple consisting of an input alphabet, an output alphabet, and for éach 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 modélling can be combined. For example in wireless communications the channel is often modélled 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 modél 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. The statistics of the random attenuation are decided by previous méasurements or physical simulations.
Channel modéls may be continuous channel modéls 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 réal world communication system in which the analog->digital and digital->analog blocks are out of the control of the designer. The mathematical modél consists of a transition probability that specifies an output distribution for éach 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.
Types of communications channelsÉdit
- C. E. Shannon, A mathematical theory of communication, Bell System Technical Journal, vol. 27, pp. 379–423 and 623–656, (July and October, 1948)
- Amin Shokrollahi, LDPC Codes: An Introduction
- Hsu, Hwei P., Schaum's Outline of Théory and Problems of Analog and Digital Communications, McGraw Hill, 1993