METHOD OF CONVERTING A STREAM OF DATABITS OF A BINARY INFORMATION SIGNAL INTO A STREAM OF DATABITS OF A CONSTRAINED BINARY CHANNEL SIGNAL, A DEVICE FOR ENCODING, SIGNAL COMPRISING A STREAM OF DATABITS OF A CONSTRAINED BINARY CHANNEL SIGNAL, RECORD CARRIER, METHOD FOR DECODING, DEVICE FOR DECODING

摘要

1. A method of converting a stream of databits of a binary information signal into a stream of databits of a constrained binary channel signal, wherein the stream of databits of the binary information signal is divided into n-bit information words (1), said information words being converted into m1-bit channel words (2) in accordance with a channel code C1, or m2-bit channel words (3) in accordance with a channel code C2, where m1, m2 and n are integers for which it holds that m2m1n, wherein the m2-bit channel word is chosen from at least two m2-bit channel words at least two of which have opposite parities, the concatenated m1-bit channel words and the m2-bit channel words complying with a run length constraint of the binary channel signal, the method comprising the repetitive and/or alternate steps of: selecting the m1-bit channel word from a set out of a plurality of sets of m1-bit channel words, each set comprising only m1-bit channel words having a beginning part out of a subset of beginning parts of the m1-bit channel words, each set being associated with a coding state of channel code C1, the coding state being established in dependence upon an end part of the preceding channel word, or: selecting the m2-bit channel word from a set out of a plurality of sets of m2-bit channel words, each set comprising only m2-bit channel words having a beginning part out of a subset of beginning parts of the m2-bit channel words belonging to said set, each set being associated with a coding state of channel code C2, the coding state being established in dependence upon an end part of the preceding channel word, the end parts of the m1-bit channel words in a coding state of channel code C1 and the beginning parts of the m2-bit channel words in a set of channel code C2 being arranged to comply with said run length constraint, wherein the method further comprises the step of substituting, in dependence upon a value of a predetermined property of the binary channel signal, a channel word for a substitute channel word so as to influence the value of the predetermined property of the binary channel signal, wherein the substituted channel word and the substitute channel word establish the same state. 2. A method as claimed in claim 1, wherein the step of substituting a channel word for a substitute channel word comprises different types of substitutions. 3. A method as claimed in claim 2, wherein maximally one type of substitution occurs for each information word. 4. A method as claimed in claim 1, 2 or 3, wherein the substitute channel word does not belong to the sets of channel words of channel codes C1 or C2. 5. A method as claimed in claim 1, 2, 3 or 4, wherein the substitute channel word is omitted from the sets of channel words of channel codes C1 or C2 in view of a constraint on the number of successive xT run lengths in the binary channel signal. 6. A method as claimed in claim 5, wherein x=3. 7. A method as claimed in claim 5, wherein the number of successive xT run lengths is 6. 8. A method as claimed in claim 1, 2, 3, 4, 5, 6 or 7, wherein the substitute channel word is chosen from one set out of a plurality of sets of channel words, the set being associated with a coding state different from the coding state the substituted channel word was in. 9. A device for encoding (100) a stream of databits of a binary information signal (101) into a stream of databits of a constrained binary channel signal (103), for performing one of the methods as claimed in any one of the preceding claims, the device comprising an n-to-m1-bit converter (102) for converting the n-bit information words into m1-bit channel words, an n-to-m2-bit converter (102) for converting the n-bit information words into m2-bit channel words, state-establishing means (104) for establishing a coding state of the m1-bit channel words and of the m2-bit channel words, said n-to-m1 bit converter being further arranged to select the m1-bit channel word depending on the end part of the preceding channel word, said n-to-m2 bit converter being further arranged to select the m2-bit channel word depending on the end part of the preceding channel word, wherein the n-to-m1-bit converter and/or the n-to-m2-bit converter comprise substitution means for substituting a limited number of channel words for substitute channel words so as to influence predetermined properties of the binary channel signal, the substituted channel word and the substitute channel word establishing the same state. 10. A device for encoding as claimed in claim 9, wherein the device further comprises writing means (143, 144) for writing an information pattern on a record carrier. 11. A signal comprising a stream of databits of a constrained binary channel signal, obtained after carrying out one of the methods as claimed in any one of claims 1 to 8. 12. A record carrier (110) on which the signal as claimed in claim 11 is recorded in a track (111), in which information patterns represent the signal portions, which information patterns comprise first (113) and second (114) parts, alternating in the direction of the track, the first parts presenting detectable properties and the second parts presenting detectable properties distinguishable from the first properties, the parts having the first properties representing bit cells (116) having the first logic value and the parts having the second properties representing the bit cells (117) having the second logic value. 13. A method of decoding a stream of databits of a constrained binary channel signal into a stream of databits of a binary information signal, the method comprising the step of converting the signal as claimed in claim 11 into a bit string of bits having a first or a second value, the signal comprising the m1-bit channel words and the m2-bit channel words, the bit string comprising the n-bit information words, wherein one n-bit information word is assigned to one channel word or to one substitute channel word. 14. A device for decoding (132) a stream of databits of a constrained binary channel signal (131) into a stream of databits of a binary information signal (134), the device comprising converting means for converting the signal into a bit string of bits having a first or a second value, the signal comprising the m1-bit channel words and the m2-bit channel words, the bit string comprising the n-bit information words, wherein one n-bit information word is assigned to one channel word or to one substitute channel word. 15. A device for decoding as claimed in claim 14, wherein the device further comprises reading means (152) for reading out an information pattern from a record carrier.