Method and apparatus for protecting data from mis-synchronizatio

Details Method and apparatus for protecting data from mis-synchronizatio Method and apparatus for protecting data from mis-synchronizatio

1995-02-02

1996-06-18

Baker, Stephen M.

Excavating

371 401, G11B 2018, H03M 1300

Patent

active

055286070

ABSTRACT:
An encoder in a data processing system generates, from a single m-bit coset leader constant, or symbol, a coset leader, which is a series of k m-bit symbols that resembles a random sequence of km bits. The encoder encodes the m-bit initial coset leader constant in a linear feedback shift register that is characterized by a maximum length polynomial over GF(2). The constants are produced by the register at the same times as the error correction symbols are produced by the encoder. The corresponding constants and symbols are then XOR'd together before the symbols are concatenated with the data symbols to form a code word for recording. A decoder similarly generates the coset leader from the initial constant. The decoder XOR's these constants with the error correction symbols in a retrieved code word as part of a demodulation operation. If the head was in synchronism with the stored information during a read operation, XOR'ing the k coset leader constants with the error correction symbols of the retrieved code word removes the coset leader from these symbols, and thus, reproduces the original error correction symbols. Otherwise, the XOR operation combines the coset leader with a shifted version of itself and introduces into the retrieved code word a number of errors that exceeds the error correction capability of the error correction code used to encode the data. In the preferred embodiment, the linear feedback shift register is characterized by the maximum length polynomial X.sup.9 +X.sup.8 +X.sup.7 +X.sup.3 +X.sup.2 +1 over GF(2), and the m-bit initial coset leader constant is 100001011.

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Glover, N., et al., "Practical Error Correction Design for Engineers", 2nd edition, Data Systems Technology Corp., pp. 256-269. Aug. 1988.

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