CONVOLUTIONAL DECODER

A decoder for correcting and decoding convolutional data. Decoding of each digit of sequentially received data is postponed until a plurality of subsequent digits have been received. A message digit is then decoded by comparing the received sequence of data with a limited number of possible messages. The possible message which correlates best with the sequence of convolutional data that was received is temporarily assumed to be the correct sequence for purposes of decoding only the first message digit or perhaps the first few message digits of the data sequence currently being considered. The limited number of possible messages to be compared with the received data are selected at each branch interval by choosing one sequence terminating in each data state. During decoding, the possible messages are represented as sequences of branch transitions among a predetermined number of data states. The transitions among states are traced step by step through the possible message sequences to ascertain the data state of a survivor sequence at the decoding depth. The data state of the highest correlated survivor path is then interpreted into a decoded message bit.