Patent ID: 6670896
Filing Date: 2003-12-30
Classification: G11B,H03M

Abstract:
A modulation method comprising the steps of:modulating â€œpâ€ -bit input data words into â€œqâ€ -bit output code words by referring to a set of main encoding tables, a set of first substitution encoding tables, and a set of second substitution encoding tables, wherein â€œpâ€  denotes a first predetermined natural number and â€œqâ€  denotes a second predetermined natural number greater than the number â€œpâ€ ; wherein the main encoding tables contain output code words assigned to input data words, and contain state information accompanying each output code word, wherein the state information designates an encoding table among the main encoding tables and the first and second substitution encoding tables which is used next to generate an output code word immediately following the output code word accompanied with the state information in a manner such that a resultant succession of the output code words follows prescribed run length limiting rules, and wherein NRZI conversion results of output code words in first specified one of the main encoding tables which are assigned to prescribed input data words are opposite in polarity to NRZI conversion results of output code words in second specified one of the main encoding tables which are assigned to the prescribed input data words; wherein the first substitution encoding tables contain output code words assigned to input data words, and contain state information accompanying each output code word, wherein the state information designates an encoding table among the main encoding tables and the first and second substitution encoding tables which is used next to generate an output code word immediately following â€œrâ€  connection bits connected to the output code word accompanied with the state information in a manner such that a resultant succession of the output code words with the connection bits follows the prescribed run length limiting rules, and wherein â€œrâ€  denotes a third predetermined natural number; wherein the second substitution encoding tables contain output code words assigned to input data words, and contain state information accompanying each output code word, wherein the state information designates an encoding table among the main encoding tables and the first and second substitution encoding tables which is used next to generate an output code word immediately following â€œrâ€  connection bits connected to the output code word accompanied with the state information in a manner such that a resultant succession of the output code words with the connection bits follows the prescribed run length limiting rules; wherein NRZI conversion results of output code words in the first substitution encoding tables which are assigned to input data words are opposite in polarity to NRZI conversion results of output code words in the second substitution encoding tables which are assigned to said input data words, and wherein the first substitution encoding tables are equal to the second substitution encoding tables in assignment of state information to input data words; periodically selecting the main encoding tables instead of the first and second substitution encoding tables, and using the selected main encoding tables in modulating â€œpâ€ -bit input data words into â€œqâ€ -bit output code words; periodically selecting the first and second substitution encoding tables instead of the main encoding tables, and using the selected first and second substitution encoding tables in modulating â€œpâ€ -bit input data words into â€œqâ€ -bit output code words; generating a final â€œqâ€ -bit output code word in response to a current input data word different from the prescribed input data words by referring to one of the main encoding tables when the main encoding tables are selected; generating a first candidate output code word in response to a current input data word equal to one of the prescribed input data words by referring to the first specified one of the main encoding tables when the main encoding tables are selected; generating a second candidate output code word in response to the current input data word equal to said one of the prescribed input data words by referring to the second specified one of the main encoding tables when the main encoding tables are selected; calculating a first DSV from a succession of output code words including the first candidate output code word; calculating a second DSV from a succession of output code words including the second candidate output code word; determining which of an absolute value of the first DSV and an absolute value of the second DSV is smaller; selecting one from the first and second candidate output code words which corresponds to the smaller DSV absolute value as a final â€œqâ€ -bit output code word; generating a third candidate output code word in response to a current input data word by referring to one of the first substitution encoding tables when the first and second substitution encoding tables are selected; adding â€œrâ€  connection bits to the third candidate output code word to get a fourth candidate output code word; generating a fifth candidate output code word in response to the current input data word by referring to one of the second substitution encoding tables when the first and second substitution encoding tables are selected; adding â€œrâ€  connection bits to the fifth candidate output code word to get a sixth candidate output code word; calculating a third DSV from a succession of output code words including the fourth candidate output code word; calculating a fourth DSV from a succession of output code words including the sixth candidate output code word; determining which of an absolute value of the third DSV and an absolute value of the fourth DSV is smaller; selecting one from the fourth and sixth candidate output code words which corresponds to the smaller DSV absolute value as a final â€œq+râ€ -bit output code word; and connecting final â€œrâ€ -bit output code words and final â€œq+râ€ -bit output code words into an output-code-word sequence which follows the prescribed run length limiting rules.