Carrier phase synchronous type maximum likelihood decoder

A carrier phase synchronous type maximum likelihood decoder for estimating a maximum likelihood sequence of data, said data being transmitted from a transmit side, by following a transition and synthesizing partial series, states i (i=1, . . . , m) in times k (k=1, . . . , n) providing a basis for indicating a partial series of said sequence of data;

• a transition being from a certain state in time k to another state in time (k+1);
• said carrier phase synchronous type maximum likelihood decoder comprising for each state i (i=1, . . . , m):
• a memory means for memorizing a path metric and carrier phase shift amount in time k,
• a carrier phase adjust means for shifting a carrier phase of a signal input in time (k+1) by said carrier phase shift amount memorized in said memory means,
• a branch metric calculate means for calculating a branch metric by evaluating a difference between an output signal of said carrier phase adjust means and a reference signal,
• a carrier phase error calculate means for calculating a carrier phase error which is an angle difference between said output signal of said carrier phase adjust means and said reference signal,
• a carrier phase shift amount calculate means for calculating a carrier phase shift amount candidate for a successor state in time (k+1) on the basis of said carrier phase error and said carrier phase shift amount memorized in said memory means,
• a path metric candidate calculate means for calculating a path metric candidate for a successor state in time (k+1) on the basis of said path metric memorized in said memory means and said branch metric from said branch metric calculate means;
• said carrier phase synchronous type maximum likelihood decoder further comprising:
• a path metric selecting means for selecting a path metric for a successor state in time (k+1) by comparing two said path metric candidates calculated by said path metric candidate calculate means, one of which corresponds to a transition from state i in time k to a successor state in time (k+1) and the other of which corresponds to a transition from a state other than i in time k to the successor state in time (k+1), and
• a carrier phase shift amount select means for selecting a first carrier phase shift amount from two carrier phase shift amounts, said first carrier phase shift amount corresponding to a selected transition which said path metric select means selects.