Recording state evaluation method, recording compensation method, and information recording/playback device

A recording state evaluation method of a recording medium configured to optically perform information recording, the recording state evaluation method comprising:

• a recording step of generating a first recording signal having a length L, which is a signal sequence of two or more types of predetermined level values, and of forming a plurality of types of different first recording marks corresponding to the first recording signal on the recording medium;
• a playback step of obtaining a playback signal of the first recording marks formed on the recording medium;
• and
• a mark level estimation step of setting a recording state where the playback signal is equal to a first expected value obtained by a convolution calculation of the first recording signal and a predetermined impulse response as a second recording mark, and of calculating a first level estimation vector in which a deviation amount between a mark shape of the first recording mark and a mark shape of the second recording mark is represented by N types of arrangement patterns having a length M (the length M is smaller than the length L), which is a signal sequence of the two or more types of level values,
• wherein the mark level estimation step includes
• a level-shifting step of shifting a level of an i-th arrangement pattern (i is an integer of 1 to N) of the first level estimation vector by a predetermined amount Δ in each of a positive direction and a negative direction,
• a recording signal generation step of adding a second level estimation vector level-shifted in the positive direction to the first recording signal to generate a second recording signal having a predetermined length L, and of similarly adding a third level estimation vector level-shifted in the negative direction to the first recording signal to generate a third recording signal having the predetermined length L,
• an expected value generation step of generating a second expected value signal and a third expected value signal by convoluting the impulse response with the second recording signal and convolving the impulse response with the third recording signal,
• a square error calculation step of calculating a second square error by squaring an error between the second expected value signal and the playback signal corresponding to the second expected value signal and integrating the squared error by a length L and of calculating a third square error by squaring an error between the third expected value signal and the playback signal corresponding to the third expected value signal and integrating the squared error by the length L,
• an error sensitivity calculation step of calculating error sensitivity of an i-th arrangement pattern, and calculating error sensitivity of all patterns of an arrangement pattern of i=1 to N, by obtaining a difference between the second square error and the third square error,
• a threshold determination step of determining whether there is a pattern that exceeds a predetermined threshold in the error sensitivity of all patterns, and
• a level estimation vector update step of, when there is the pattern that exceeds the predetermined threshold in the threshold determination step, multiplying the amplitude error sensitivity of all patterns by a predetermined coefficient k such that an absolute value after the multiplication is 0.5 or less and adding a result of the multiplication to the first level estimation vector, and of returning to the level-shifting step after updating the first level estimation vector, and
• wherein in the mark level estimation step, an initial value of the first level estimation vector is set to all elements 0, and a processing is repeatedly performed until the error sensitivity of all patterns is equal to or smaller than a predetermined threshold, so that a deviation amount between a mark shape of the first recording mark recorded on the recording medium and a mark shape of the second recording mark is estimated.

A recording compensation method of an information recording/playback device configured to optically perform information recording on a recording medium, the recording compensation method comprising:

• a step of forming a recording mark on the recording medium by a predetermined recording signal;
• a step of obtaining a playback signal of the recording mark formed on the recording medium;
• a step of generating an expected value signal of the playback signal based on the recording signal;
• a step of, based on an amplitude error between the playback signal and the expected value signal, for each predetermined unit of the recording signal, calculating a deviation amount of a mark shape of a recording mark from which the playback signal is obtained with respect to a mark shape of an ideal recording mark from which a playback signal having no amplitude error can be obtained, and estimating a mark shape of the recording mark formed on the recording medium;
• and
• a step of, based on the deviation amount of the mark shape of the recording mark, calculating a correction amount for each predetermined unit of the recording signal and adjusting a level of the recording signal, wherein
• in the step of estimating the mark shape,
• a level estimation vector of a predetermined number of elements is defined as a parameter indicating a deviation amount of a mark shape of the recording mark, an amplitude error between the playback signal and the expected value signal when a level of the recording signal is shifted is obtained by using a level estimation vector level-shifted for each predetermined unit of the recording signal, and a level estimation vector indicating a deviation amount of a mark shape from the ideal recording mark is calculated based on the amplitude error, and
• in the step of adjusting the level of the recording signal,
• the correction amount is calculated and the level of the recording signal is adjusted, based on the level estimation vector indicating the deviation amount of the mark shape from the ideal recording mark.