Synchronization method in Viterbi decoder

Claim 1

A synchronization method for performing a fast synchronization in a Viterbi decoder for decoding transmitted convolutional codes which are QPSK modulated and punctured according to a predetermined code rate among code rates having a first group of low code rates and a second group of high code rates, comprising the steps of: a) depuncturing and Viterbi decoding the convolutional code with a predetermined median code rate among the code rates comprising the first and second groups; b) calculating a channel bit error rate using the Viterbi decoded data obtained from said step a); c) comparing the channel bit error rate obtained from said step b) with a high/low threshold value and selecting the first group or the second group to which a code rate of a currently received channel belongs, according to the comparison result; d) changing a code rate into one of the code rates from the first group or the second group selected in step c), changing a phase and puncturing pattern according to the changed code rate, and depuncturing and Viterbi decoding the convolutional code with respect to the changed phase and puncturing pattern; e) calculating the channel bit error rate using the Viterbi decoded data obtained from said step d), comparing this calculated channel bit error rate to a synchronization threshold value corresponding to the changed code rate in said step d), and determining whether the synchronization is achieved according the comparison result; and f) repeating said step d) and step e) with respect to the different code rates, phases, and puncturing patterns, if the synchronization is not achieved in said step e).