On symbol permutation invariant balanced codes

A symbol permutation invariant balanced (SPI-balanced) code over the alphabet ZZ_m = {0, 1,....,m - 1} is a block code over ZZ _m such that each alphabet symbol occurs as many times as any other symbol in every codeword. For this reason every permutation among the symbols of the alphabet changes a SPI-balanced code into a SPI-balanced code. This means that SPI-balanced words are "the most balanced" among all possible m-ary balanced word types, and this property makes them very attractive from the application perspective. In particular, they can be used to achieve m-ary DC-free communication, to detect/correct asymmetric/unidirectional errors on the m-ary asymmetric/unidirectional channel, to achieve delay-insensitive communication, to maintain data integrity in digital optical disks, and so on. The paper gives some efficient methods to convert (encode) m-ary information sequences into m-ary SPI-balanced codes whose redundancy is equal to roughly double the minimum possible redundancy r_min sime [(m - 1)/2] log_m n - (1/2)[1 $(1/log_2pi m)] m - (1/log_2pim) for SPI-balanced code with k information digits and length n = k + r. For example, the first method given in the paper encodes k information digits into a SPI-balanced code of length n = k + r, with r = (m - 1) log_m k + O(m log_m k). A second method is a recursive method, which uses the first as base code, and encodes k digits into a SPI-balanced code of length n = k + r, with r sime (m - 1) log_m n $log_m[(m - 1)!]