# Channel Capacity

Definitions :: Symmetric Channels :: Closer Look :: Typical Sequences :: Theorem

## Symmetric channels

We now consider a specific class of channels for which the entropy is fairly easy to compute, the symmetric channels.

A channel can be characterized by a
**
transmission matrix
**
such as

The indexing is

*x*for rows,

*y*for columns:

*P*

_{ x , y }=

*p*(

*y*|x).

To see this, let
denote a row of the transition matrix. Then

Equality holds if the output distribution is uniform.