Maximum likelihood differential detecting method and differential detector thereof

摘要

The phase of a received signal is detected by a phase detector at symbol intervals T relative to the phase of a local signal. The detected phase is input to delay circuits that are connected in series and each of which has the delay interval T. Phases &PSgr;.sub.n (where n=0, 1, . . . , N) with delays of 1 to N symbols are output to a metric calculating portion. The sum of a partial sequence {&Dgr;&phgr;.sub.i ; i=n+1-q, n+2- q, . . . , n} of a N-symbol phase difference sequence candidate {&Dgr;. phi..sub.n ; n=0, 1, . . . , N} is added to a detected phase &PSgr;.sub.n- q at a time point (n-q)T (where q=1, 2, . . . , N) so as to obtain an estimated value of the received signal phase &PSgr;.sub.n. The v-th power value of the absolute value of a difference &mgr;.sub.n (q) between the estimated value and the received signal phase is defined as a branch metric of q-symbol differential phase detection. &Sgr;| &mgr;. sub.n (q)|.sup.v =&lgr;.sub.n, which the summation of metrics from q=1 to n, is defined as a branch metric at the time point nT. A path metric &Lgr;=&Sgr;&lgr;.sub.n, which is the summation of branch metrics from a time point 1T to a time point NT, is calculated for all N- symbol phase difference candidates. A candidate sequence with a minimum value is decided as a decoded sequence.