A Comparison of Two Coding Schemes for Generating DC-Free Runlength-Limited Sequences

Abstract

We report on the performance assessment of two methods for generating DC-free runlength-limited sequences. Redundant bits used to optimize the low-frequency properties are multiplexed with user data or encoded data. In the first method, the redundant bits are multiplexed with the channel bits generated by a (d,k) encoder. In the second method, on the other hand, the redundant bits are multiplexed with the user data. i.e. prior to application of the (d,k) encoder. The second method can only be used if the (d,k) encoder satisfies the parity preserving condition, i.e., data words and code words of that code must have the same parity. In the article we describe in detail an example of a parity preserving (1, 8) code.

<title>Performance evaluation of asymmetrical run-length-limited code for optical disks</title>

“…A new d = 1 runlength-limited (RLL) code has been proposed for optical recording systems, for the purpose of increasing the capacity of recording media [1] [2]. To increase the capacity, it is necessary to use technology for high-density recording, such as a high-aperture lens, blue-violet laser, partial response maximum likelihood (PRML) detection and highperformance modulation code, and it is also necessary to consider the affinities of these technologies.…”

On Parity-Preserving Variable-Length Constrained Coding

“…One commonly used strategy to achieve DC control is allowing input blocks to be mapped to more than one codeword, and the encoder then selects the codeword that yields a better DC suppression [10, p. 29]. In the Blu-ray standard, this strategy is applied through the use of parity-preserving encoders: such encoders map each input block to a codeword that has the same parity (of the number of 1s), and DC control is achieved by reserving one bit in the input block to be set to a value that minimizes the DC contents [8, §11.4.3], [9], [11], [12], [13], [16].…”

On Parity-Preserving Constrained Coding

“…One implementation of this strategy uses parity-preserving encoders, whereby the parity (i.e., the modulo-2 sum) of the input sequence within nonoverlapping windows (each consisting of one or more pblocks) is preserved at the output. DC control can be achieved by reserving one input bit in that window and selecting its value so as to minimize the DC contents [9, §11.4.3], [10], [14], [15], [16], [18]. Parity-preserving RLL codes are used in the Blu-ray standard.…”