A new design of EFM constrained codes

A rate 8/15(2,10) constrained code with 5 encoding states is designed in this paper. This code is of particular interest in recording systems, achieving more than 98% coding efficiency. Its encoding FSTD has five states. Its state-independent decoder has a decoding window of 2, requiring current codeword and one look-ahead codeword to decode current codeword. The power spectra of the RLL (3,11) sequence with maxentropy and the sequence dictated by the rate 8/15(2,10) constraint code are evaluated respectively, exhibiting a DC component. The number of states in the designed encoder is shown to be minimum for rate 8/15(2,10) constrained codes by use of Marcus-Roth's bound on the number of encoding states for constrained codes. This newly designed code has a benefit of higher coding rate compared with the EFM mapping approach and is optimal in the sense that the number of encoding states is minimum.