Channel (information theory)
A channel (also information channel , transmission channel , transmission or Shannon 'sches channel model )'s information theory to model a concept to the information loss caused by disturbances in the transmission. The channel is not limited to the medium via which the transmission takes place, but describes the entire transmission path from the transmitter to the receiver. The transmitter output stage and the receiver input stage as well as any devices connected in between can also cause interference. The channel concept is a central component of the transmitter-receiver model .
In practice, a channel is typically a copper or fiber optic cable or, in mobile communications, the relatively complex interplay between the transmitter and receiver unit and all other interference during radio transmission, e.g. B. multipath, dispersion or Doppler effect.
A storage medium (e.g. a hard drive or DVD) is also a channel in this sense, since data is sent to it (here: written) and can later be received from it (here: read).
In general, data is transmitted over a channel so that it bridges a spatial or temporal distance. A spatial transmission would be e.g. A network connection (downloading a website), a temporal transmission e.g. B. a video recording on a DVD.
The theory of channel coding deals with how information can be transmitted correctly despite interference from the channel.
Types of channels
A distinction is made between different types of channels. A channel is called
- if there are no errors due to disruption of the transmission.
- if the output value only depends on the current input value, but not previous (or even future) ones.
- if the channel is both lossless and deterministic.
- if all possibilities for falsifying data due to disturbances occur equally frequently.
- if no information is lost during the transfer. This is also known as equivocation .
Interference-free channels practically do not exist. However, by means of suitable channel coding methods, the interference can be minimized, with a corresponding effort up to practically freedom from interference.
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