Almost-Certainly Runlength-Limiting Codes

Standard runlength-limiting codes – nonlinear codes defined by trellises – have the disadvantage that they disconnect the outer errorcorrecting code from the bit-by-bit likelihoods that come out of the channel. I present two methods for creating transmissions that, with probability extremely close to 1, both are runlength-limited and are codewords of an outer linear error-correcting code (or are within a very small Hamming distance of a codeword). The cost of these runlength-limiting methods, in terms of loss of rate, is significantly smaller than that of standard runlength-limiting codes. The methods can be used with any linear outer code; low-density parity-check codes are discussed as an example. The cost of the method, in terms of additional redundancy, is very small: a reduction in rate of less than 1% is sufficient for a code with blocklength 4376 bits and maximum runlength 14. This paper concerns noisy binary channels that are also constrained channels, having maximum runl...

• Type: Conference
• Year: 2001
• Where: IMA
• Authors: David J. C. MacKay
• Keywords: Cryptology, IMA 2001, Linear Error-correcting Code, Outer Errorcorrecting Code, Standard Runlength-limiting Codes