Bounds on the capacity of the unidirectional channels

In the usual binary symmetric channel, both 1→0 and 0→1 types of errors can occur. In the binary asymmetric channel, only 1→0 type of errors can occur, whereas, in the unidirectional channel, both 1→0 and 0→1 types of errors can occur, but, unlike the binary symmetric channel, for any particular transmitted word of length n, all the errors are of the same type. In general, a symmetric/ unidirectional channel is a channel, which shows the behavior of both the symmetric and unidirectional channel. Many practical systems, such as semiconductor memories and circuits, can be modeled as a unidirectional and/or symmetric/unidirectional channels. This paper gives the formal definition of these last two channels and shows some interesting simple bounds on their information capacities.