Communication channel

A channel is used for information transfer of, for example, a digital bit stream, from one or several senders to one or several receivers.

A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.

A sequence of random numbers might also be added to simulate external interference or electronic noise in the receiver.

For example, in wireless communications the channel is often modeled 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.

If the attenuation term is complex it also describes the relative time a signal takes to get through the channel.

The mathematical model consists of a transition probability that specifies an output distribution for each possible sequence of channel inputs.