1. In a transmission system for transmitting information in frames, each frame having a plurality of parameters, an error correction encoding/decoding method comprising the steps of: (a) at a transmitter side of said transmission system, (i) placing a correlation parameter indicative of a correlation between frames in a fixed part of each frame, (ii) performing a convolutional encoding of the frames, and (iii) transmitting the encoded frames as error correction code; (b) at a receiver side of said transmission system, performing Viterbi decoding, including (i) performing calculation of a metric indicating a transitional probability of each branch of a trellis diagram using a first redundancy derived from convolutional encoding for received parameters not having the correlation between frames, (ii) performing calculation of the metric using the first redundancy derived from the convolutional encoding and a second redundancy derived from correlation between frames for received parameters having the correlation between frames.