Decoder for a tail-biting trellis code generated by an encoder and method for decoding a tail-biting trellis code

摘要

The present invention relates to a decoder for a tail-biting trellis code. A circular maximum and posteriori (MAP) decoder for error-correcting trellis codes that employ tail biting produces soft-decision outputs provides an estimate of the probabilities of the states in the first stage of the trellis, which probabilities replace the a priori knowledge of the starting state in a conventional MAP decoder. The circular MAP decoder provides the initial state probability distribution in either of two ways. The first involves a solution to an eigenvalue problem for which the resulting eigenvector is the desired initial state probability distribution; with knowledge of the starting state, the circular MAP decoder performs the rest of the decoding according to the MAP decoding algorithm. The second is based on a recursion for which the iterations converge to a starting state distribution. After sufficient iterations, a state on the circular sequence of states is known with high probability, and the circular MAP decoder performs the rest of the decoding according to the MAP decoding algorithm.�