Coding and decoding method of suppressing dc component in codestream

Abstract

A code modulation and demodulation method includes removing a DC component of a code stream to be modulated when source data is recorded on an optical information storage medium and controlling a suppression of the DC component contained in the code stream when the source data is converted into a codeword to be recorded on an optical information storage medium. The method includes determining a control timing to suppress the DC component of the code stream to which the source data are converted, performing a code conversion at each control time for the DC component so that the code stream branches into a pair of branch code streams one of which extends in a direction where a running digital sum (RDS) of the code stream increases, and another one of which extends in the direction where the RDS of the code stream decreases, and selecting the path of the code stream that has a most bounded path around RDS '0' from the paths of the branch code streams each control time. By performing a regular DC suppression control when the source data is converted, and by selecting one of the branch code streams when the DC suppression control is performed, more DC components in the code stream can be effectively removed.