A.V. Trushkin

State Diagram Approach to Feedback Encoders for Tailbiting Codes

An algorithm for finding the starting state of a feedback tailbiting encoder is proposed, based solely on the properties of the encoder state diagram. With this approach, conditions for the existence of a tailbiting code generated by such an encoder are naturally tested in the process of preparing a certain permutation table for the starting state determination algorithm. A tailbiting failure for a given information sequence length $L$ is detected when this table fails to be a permutation, which occurs if L is divisible by a length of any zero-branch cycle through nonzero states of the state diagram.