Patent ID: 6751770
Filing Date: 2004-06-15
Classification: H03M

Abstract:
A decoder for decoding a data stream transmitted across a noisy channel into estimated bits, the data stream being encoded according to a cyclic code into a plurality of code words in sequence, the decoder comprising:input means for receiving input of a vector of noisy received values r(i) (where 0&lE;i&lE;nâˆ’1) of the data stream, a code length n of the code words, and a parity-check polynomial h(x) corresponding to the cyclic code, the parity-check polynomial h(x) having J-number of nonzero coefficients; a scaler for multiplying each noisy received value r(i) by a constant, and outputting each product as a log-likelihood ratio LLR(i); a Z processor for: receiving n-sets of &pgr;z(i,j) metrics (where 0&lE;j&lE;Jâˆ’1), each set including J-number of &pgr;z(i,j) metrics; and calculating n-sets of &lgr;z(i,j) metrics based on the &pgr;z(i,j) metrics, each set including J-number of &lgr;z(i,j) metrics; an X processor for: receiving n-sets of &lgr;x(i,j) metrics, each set including J-number of &lgr;x(i,j) metrics, calculating n-number of a-posteriori values q(i) based on the &lgr;x(i,j) metrics and the log-likelihood ratios LLR(i); calculating n-sets of &pgr;x(i,j) metrics based on the &lgr;x(i,j) metrics and the a-posteriori values q(i), each set including J-number of &pgr;x(i,j) metrics; and determining n-number of estimated code bits i based on the a-posteriori values q(i); and an information exchange control unit for: distributing the &pgr;x(i,j) metrics based on a cyclic shift of the parity-check polynomial h(x) to produce the &pgr;z(i,j) metrics; and distributing the &lgr;z(i,j) metrics based on a reverse order of the cyclic shift of the parity-check polynomial h(x) to produce the &lgr;x(i,j) metrics.