HP Labs Technical Reports
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On Runlength-Limited Coding with DC Control
Roth, Ron M.
Keyword(s): runlength-limited coding, optical recording, magnetic
, DC control
Abstract: This work describes a lossless coding scheme that maps
unconstrained binary sequences into sequences that obey the (d,k)-RLL constraint. The input sequence is divided into nonoverlapping blocks, and a number of input blocks can be encoded into two different codewords which have different parity of 1's, thus allowing for DC control. The proposed scheme uses a compact table of codewords that serves all states, as well as a simple mechanism to locate the codeword, or codewords, that are associated with each input block. Decoding is carried out in a state-independent manner. Two examples are provided. The first example is a four-state (2,10)-RLL encoder at rate 8:16, using a table of 546 codewords. The percentage of bytes that allow for DC control is 49.7%, on the average. Decoding is carried out by recovering the input byte from the current 16-bit codeword. The second example is a (2,12)-RLL encoder at rate 8:15, using a table of 551 codewords. The percentage of bytes that allow for DC control ranges between 7.6% and 12.2%, depending on the number of states of the encoder which, in turn, can range between four and eight. Decoding is carried out by recovering the input byte from the current, and possible the next 15-bit codeword.
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