Communications channel

A channel (including information channel, transmission channel, transmission or SHANNON channel model ) is a concept in information theory to the loss of information due to disturbances in the transmission to model. The channel does not restrict itself only to the medium through which the transfer is made, but describes the entire transmission path from transmitter to receiver. The transmitter output stage and the receiver input stage, and possibly intermediary devices can cause interference. The channel concept is a central part of the sender-receiver model.

In practice, a channel is typically a copper or fiber cable or mobile communications, the relatively complex interplay of transmitting and receiving unit, and all other disturbances during radio transmission, such as multipath propagation, dispersion or Doppler effect.

Also a storage medium ( such as a hard disk or DVD ) is in this sense a channel because data is sent to it (in this case written ) and later received it (in this case read) can be.

General data to be transmitted over a channel, so that they bridge a spatial or temporal distance. A spatial transfer would be, for example, a network connection ( downloading a web page ), a temporal transfer such as a video recording on a DVD.

The theory of channel coding is concerned with how information, despite interference from the channel can be transmitted correctly.

The ratio of useful signal to interference signal is referred to as signal-to- noise ratio. The channel has a certain capacity, for determining the maximum data rate.

Types of channels

We distinguish between different types of channels. A channel is called

• Deterministic, if added no error by interfering with the transmission.
• Memoryless if the output value depends only on the current input value, but not the previous ( or even future).
• Trouble-free, if the channel is both lossless and deterministic.
• Symmetric, if all possibilities for corruption of data equally often caused by interference.
• Lossless if no information is lost during transmission. This is also referred to as equivocation.

Trouble-free channels practically non-existent. However, by appropriate channel coding method, the disturbance can be minimized with appropriate effort to practical freedom from interference.