Decoding device and decoding method

A decoding method of decoding digital information based on a detected signal obtained from a medium having predetermined frequency characteristics,

• the decoding method comprising:
• a first decoding step in which a difference between a detected signal that is obtained when the digital information subjected to error correction coding in accordance with a predetermined error correction encoding system and also subjected to modulation encoding in accordance with a predetermined modulation system is passed through the medium and expectation signals that are obtained when arbitrary pattern signals are passed through the medium is calculated, and which outputs a pattern signal for which the calculated difference is smallest as a first decoded signal;
• a first demodulating step in which the first decoded signal is demodulated in accordance with the modulation system to generate a first demodulated signal;
• a first error correcting step in which error correction is performed on the first demodulated signal in accordance with the error correction encoding system to generate a first digital signal;
• and
• a re-modulating step in which the first digital signal is re-modulated in accordance with the modulation system to generate a re-modulated signal;
• an interference canceling step in which, from states of 2K-number (where K is a natural number) of detected signals that are predicted in the interference canceling step to likely be within a range of K bit width where an interference between bits of the digital information occurs due to the predetermined frequency characteristics, 2M-number (where M is a natural number) of detected signals, most likely, as predicted in the interference canceling step, respectively corresponding to states of 2M-number of detected signals which exist within a range of M bit width that is included in the range of K bit width are extracted using the re-modulated signal;
• a second decoding step in which a second decoded signal is generated by calculating a difference integrated value in the K bit width range between the 2M-number of detected signals extracted in the interference canceling step and expectation signals respectively corresponding to the 2M-number of detected signals and also by selecting a transition sequence of a state of a detected signal for which the calculated difference integrated value is smallest;
• a second demodulating step in which the second decoded signal is demodulated in accordance with the modulation system to generate a second demodulated signal;
• and
• a second error correcting step in which error correction is performed on the second demodulated signal in accordance with the error correction encoding system to generate a second digital signal.