Fast decoder for reed-solomon codes which can also be used as an encoder, and recording/playback apparatus comprising such an encoder/decoder

摘要

A decoding device for code words which are protected against the occurrence of several symbol errors per code word by means of a Reed-Solomon code is provided with a word buffer which comprises a space for the storage of an erasure indication per symbol received. For correction of the code word, first the syndrome symbols are formed by multiplication by the parity check matrix. The sum of twice the number of error symbols and once the number of erasure symbols may not be larger than the number of syndrome symbols. First the syndrome symbols are modified so that the syndrome symbols which could possibly relate to error symbols (non-erasure symbols) are no longer influenced by the erasure symbols. The key equation and error locator equation for the non-influenced syndrome symbols can then be separately solved, so that the locations of error symbols can be found. The latter syndrome symbols are then modified, when necessary, for calculated error locations, while the error values or erasure values are determined from a set of mutually independent syndrome symbols whose number equals the sum of error symbols and erasure symbols. There is provided an arithmetic unit for the Galois-field which, for the sake of simplicity, performs the calculations on the exponents of the symbols which are written as powers of the basic symbol of the Galois-field.