| 摘要 |
Recording and reproduction are performed on an information recording medium at high density. Marks having front and rear edges deviated in M levels in accordance with multilevel data are recorded at predetermined mark intervals. In information reproduction, adjoining front and rear edges are read at the same time to generate read data in succession when a spot area of a reading light beam falls on mark reference positions and space reference positions. Approximate analysis such as Viterbi decoding is performed to compare the read data with predetermined expected value data. Based on the result, the deviations of the front and rear edges of each mark are determined to decode the multilevel data. Here, a row of reference marks having front and rear edges corresponding to combinations of M levels of deviation is recorded as if the foregoing marks are. The row of reference marks is read as if the foregoing marks are, so that the expected value data for the approximate analysis is obtained. Since adjoining front and rear edges of the marks are read at the same time, the mark intervals can be reduced to achieve high density recording and reproduction. It is also possible to achieve information reproduction of high quality even if the read data is effected by nonlinear characteristics of the reproduction optical system.
|
