Bounds for the capacity error function for unidirectional channels with noiseless feedback

In digital systems such as fiber optical communications, the ratio between probability of errors type 1 ? 0 and can be large. Practically, one assume that only error occur. These are called asymmetric. Unidirectional differ from asymmetric errors; here both possible, but in any submitted codeword all same type. This generalized for q -ary case. We consider unidirectional channels with feedback where have magnitude give bounds capacity function. It turns out depend on parity alphabet size . Furthermore, we show feedback, function binary channel is different symmetric channel. contrast to behavior without feedback.