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Browse Prior Art Database

DC Balanced Run Length Limited Code

IP.com Disclosure Number: IPCOM000048270D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Franaszek, PA: AUTHOR [+2]

Abstract

A method and a scheme for limiting error propagation in the decoding of synchronous channel codes are described. According to this method, decoding is state independent in that an error, which prevents the possibility of tracking the channel state, does not result in an indefinite number of decoding errors.

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DC Balanced Run Length Limited Code

A method and a scheme for limiting error propagation in the decoding of synchronous channel codes are described. According to this method, decoding is state independent in that an error, which prevents the possibility of tracking the channel state, does not result in an indefinite number of decoding errors.

A synchronous code is a mapping between the source data and a constrained channel sequence such that (a) the output of the coder consists of a sequence of basic words of fixed length (for example, in a rate (4/5) code the basic word length would be a fixed multiple of 5), and (b) the coding rate is constant: each basic word may be regarded as representing a fixed number of source bits.

The channel coders discussed here produce binary output sequences (+1,-1) such that (a) the number of consecutive-like symbols is limited to K + 1 and (b) the sequence digital sum (see article) is limited to L levels, where a(i) is the sequence of (+1).

The novel features of the coder/decoder design according to this disclosed method are as follows: (1) Decoding may be time varying. For example, if the basic word length is five, it may be noted that the digital sum is even after an even number of basic words and odd after an odd number. This means that a channel word may receive different assignments depending on whether the sum is odd or even without eliminating the possibility of state-independent decoding.
(2) Certain special basic words in the code provide information on how the next word is to be decoded.

The table on the next page illustrates a specific code incorporating these novel features to yield K=4, L=6, and bounds error propagation on decoding. According to this illustration, a single error in detection results in, at most, five errors after decoding. More particularly, the table shows the coding/decoding as...