Low disparity binary codes

Claim 3

A method according to claim 1, in which m is even and mCm/2 is less than 2n, including the step of recoding mCm/2 of the 2n possible different groups of n digits into different m-digit groups of zero disparity and recoding the remaining different groups of n digits as different m-digit groups having alternative positive and negative disparities.

Claim 4

A method according to claim 2, in which m equals n + 1, including the step of deriving each of the m digit groups having zero disparity from a respective one of the mCm/2 of the groups of n digits having unit disparity by adding at a predetermined position in that group one extra digit of the appropriate type to produce zero disparity.

Claim 5

A method according to claim 3, including the step of recoding each of the remaining groups of n digits into a selected one of two m-digit groups, of which one group is complementary to the other, and the selection is made in dependence upon the disparity required.

Claim 6

A method according to claim 2 in which n 5 and m 6.

Claim 7

A method of transforming a sequence of binary digits from a form having lower disparity and produced by a method according to claim 3, including the steps of selecting successive groups of m digits, ascertaining the disparity of each group, transforming each group of m digits of zero disparity into a group of n digits by removing the extra digit from the predetermined position, and transforming each group of m digits of nonzero disparity into a group of n digits, each group of n digits which corresponds to a group of m digits having nonzero disparity also corresponding to an alternative group of m digits having a disparity of the same magnitude but opposite sign.

Claim 8

A method of transmitting binary-coded digital data including the steps of: transforming the data into a form having lower disparity by a method according to claim 3, transmitting the lower disparity data, and transforming the lower disparity data after transmission into its original form by a method including the step of removing the extra digit from the predetermined position in each group of zero disparity.

Claim 9

Apparatus for transforming a sequence of binary digits into a form having lower disparity comprising means for selecting successive groups of n binary digits in the sequence, means for recoding each group of n binary digits as a group of m binary digits, where m is greater than n, in such a way that some but not all of the groups of m digits have minimum disparity and that each group of n digits which is recoded as a group of m digits having nonzero disparity is also recoded as an alternative group of m digits having a disparity of the same magnitude but opposite sign, and means for selecting the groups so that successive groups of m digits having nonzero disparity have disparities of opposite signs.

Claim 10

Apparatus for transforming a sequence of binary digits into a form having lower disparity comprising means for selecting successive groups of n binary digits in the sequence, means for recoding each group of n binary digits as a group of m binary digits, where m is greater than n, in such a way that some but not all of the groups of m digits have minimum disparity and that each group of n digits which is recoded as a group of m digits having nonzero disparity is also recoded as an alternative group of m digits having a disparity of the same magnitude but opposite sign, and means for selecting the groups so that successive groups of m digits having nonzero disparity have disparities of opposite signs.

Claim 11

Apparatus according to claim 8, in which m is even and mCm/2 is less than 2n in which the means for recoding the selected group of n binary digits as a group of m binary digits is such that mCm2 of the 2n possible different groups of n digits are recoded into different m digit groups of zero disparity and the remaining different groups of n digits are recoded as different m-digit groups having alternate positive and negative disparities.

Claim 12

Apparatus according to claim 9, in which m n + 1 and the means for recoding a selected group of n binary digits as a group of m digits includes storage means for the selected group of n binary digits, means for ascertaining the disparity of that group of digits, means responsive to unit disparity and for adding a generated digit to the selected group in a predetermined position, and means responsive to disparities greater than unity for enabling a translator to respond to the selected group of digits to produce a corresponding group of m digits.

Claim 13

Apparatus according to claim 10, in which the translator includes means for producing for each group of n digits having disparities greater than unity a corresponding group of m digits, and the complement of that group, and means for selecting as the output either the group of m digits or its complement in dependence upon the disparity of the last m-digit group output of the translator.

Claim 14

Apparatus according to claim 9, in which n 5 and m 6.

Claim 15

Apparatus for transforming into its original form a sequence of binary digits which has been transformed into a form having lower disparity by recoding successive groups of n binary digits in the sequence as groups of m binary digits, where m is even and equals n + 1, and both are positive integers, the apparatus including: means for ascertaining the disparity of each of successive groups of m digits and producing an indication if the group has zero disparity, means responsive to the indication to derive an n-digit group from that group of digits by extracting a digit from a predetermined position in that group, the arrangement being such as to transform into their original form mCm/2 of the 2n possible different groups of n digits recoded into different m digit groups of zero disparity by the addition at the predetermined position of one extra digit of the appropriate type to produce zero disparity, and means responsive to m-digit groups of nonzero disparity to transform into their original form the remaining different groups of n digits recoded as different m-digit groups of nonzero disparity, each group of n digits which corresponds to a group of m digits having nonzero disparity also corresponding to an alternative group of m digits having a disparity of the same magnitude but opposite sign.

Claim 16

Apparatus for transforming into its original form a sequence of binary digits which has been transformed into a form having lower disparity by recoding successive groups of n binary digits in the sequence as groups of m binary digits, where m is even and equals n + 1, and both are positive integers, the apparatus including: means for ascertaining the disparity of each of successive groups of m digits and producing an indication if the group has zero disparity, means responsive to the indication to derive an n-digit group from that group of digits by extracting a digit from a predetermined position in that group, the arrangement being such as to transform into their original form mCm/2 of the 2n possible different groups of n digits recoded into different m digit groups of zero disparity by the addition at the predetermined position of one extra digit of the appropriate type to produce zero disparity, and means responsive to m-digit groups of nonzero disparity to transform into their original form the remaining different groups of n digits recoded as different m-digit groups of nonzero disparity, each group of n digits which corresponds to a group of m digits having nonzero disparity also corresponding to an alternative group of m digits having a disparity of the same magnitude but opposite sign.