A PRACTICAL METHOD FOR APPROACHING THE CHANNEL CAPACITY OF CONSTRAINED CHANNELS

A new coding technique is proposed that translates user information in to a constrained sequence using very long codewords, Huge error propag ation resulting from the use of long codewords is avoided by reversing the conventional hierarchy of the error control code and the constrai ned code, The new technique is exemplified by focusing on (d, k)-const rained codes, A storage-effective enumerative encoding scheme is propo sed for translating user data into long dh sequences and vice versa. F or dk runlength-limited codes, estimates are given of the relationship between coding efficiency versus encoder and decoder complexity. We w ill show that for most common d, k values, a code rate of less than 0. 5% below channel capacity can be obtained by using hardware mainly con sisting of a ROM lookup table of size 1 kbyte. For selected values of d and k, the size of the lookup table is much smaller, The paper is co ncluded by an illustrative numerical example of a rate 256/466, (d = 2 , k = 15) code, which provides a serviceable 10% increase in rate with respect to its traditional rate 1/2, (2,7) counterpart.