Patent ID: 8248902
Filing Date: 2012-08-21
Classification: G11B

Abstract:
1. A reproduction signal evaluation method for evaluating a quality of a reproduction signal reproduced from an information recording medium based on a binary signal generated from the reproduction signal using a Partial Response Maximum Likelihood (PRML) signal processing system, the reproduction signal evaluation method comprising: a pattern extraction step of extracting, from the binary signal, a specific state transition pattern which has a possibility of causing a bit error; a differential metric computing step of computing a differential metric, which is a difference of a first metric which is a square of a Euclidean distance between an ideal signal of a most likely first state transition sequence corresponding to the binary signal and the reproduction signal, and a second metric which is a square of a Euclidean distance between an ideal signal of a second most likely second state transition sequence corresponding to the binary signal and the reproduction signal, based on the binary signal of the state transition pattern extracted in the pattern extraction step; a first integration step of integrating the differential metric computed in the differential metric computing step; a first count step of counting a number of times of integration processing in the first integration step; a setting step of setting a square of a Euclidian distance between the ideal signal of the most likely first state transition sequence and the ideal signal of the second most likely second state transition sequence, as a signal processing threshold; a differential metric extraction step of comparing between the differential metric computed in the differential metric computing step, and the signal processing threshold set in the setting step, and extracting the differential metric not greater than the signal processing threshold; a second integration step of integrating the differential metric not greater than the signal processing threshold extracted in the differential metric extraction step; a second count step of counting a number of times of integration processing in the second integration step by counting a number of times that the differential metric is determined to be not greater than the signal processing threshold in the differential metric extraction step; an error rate computing step of computing an error rate predicted based on an integration value that is integrated in the first integration step, a count value that is counted in the first count step, an integration value that is integrated in the second integration step, and a count value that is counted in the second count step; a standard deviation computing step of computing a standard deviation based on the error rate that is computed in the error rate computing step; and an evaluation step of evaluating a quality of the reproduction signal using the standard deviation computed in the standard deviation computing step, wherein the error rate computing step computes a standard deviation of differential metrics not greater than a mean value of differential metric output, using a linear expression which includes the integration value that is integrated in the first integration step, the count value that is counted in the first count step, the integration value that is integrated in the second integration step, and the count value that is counted in the second count step, and computes the error rate based on the standard deviation.