VITERBI DECODER

PURPOSE:To improve the decoding processing speed by using a node number and the content of a path memory corresponding to the node number and repeating the acquisition of the node selected as an alive number so as to trace the maximum likelihood path, thereby using the most significant digit in binary number of the node number reached at last as the decoded output. CONSTITUTION:ACS circuits 2(0)-2(n) calculate the pathmetic value as to two paths selected based on a brauchmetric value corresponding to each node from a distributer to select a left alive path and to output path selection signals PS(0)-PS(n). A memory 3 stores the path selection signal over a prescribed number of stages corresponding to each node. A path trace control section 4 repeates the calculation of the node number of a node selected as a left alive path at the pre-stage based on the node number of an optional node and the path selection signal of a path memory 3 corresponding to the said node number over the prescribed number of stages. The node number traced in the path trace control section 4 is stored in the trace memory 5 over the prescribed number of stages and the most significant digit in binary number of the node number of a prescribed stage number of the memory 5 is used as the decoded output.