DC-free run-length-limited codes for magnetic recording

In this paper, a method to design high-efficiency codes with combined run-length and dc-null constraints is presented. Using the new method, two new dc-free (1,7) codes, with rates of 12/20 and 16/26 were developed. The code efficiencies are 89.31 and 91.6%, respectively. The proposed approach is more general than the technique used to design the existing dc-free d=1 code. The performances of the new codes are also compared with that of the rate 8/10 dc-free (0,4) code. The minimum distance analysis and the bit error rate simulation both show that while at low densities the proposed codes exhibit performance degradation compared to the higher rate (0,4) code, they perform better than the latter as density increases, despite the code rate disadvantage.