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Title: Error-correction using low-density parity-check codes
Author: Davey, M. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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Gallager's low-density parity-check codes are defined by sparse parity-check matrices, usually with a random contruction. Such codes have near Shannon limit performance when decoded using an iterative probabilistic decoding algorithm. We report two advances that improve the error-correction performance of these codes. First, defining the codes over non-binary fields we can obtain a 0.6 dB improvement in signal to noise ratio for a given bit error rate. Second, using irregular parity-check matrices with non-uniform row and column weights we obtain gains of up to 0.5 dB. The empirical error-correction performance of irregular low-density parity-check codes is unbeaten for the additive white Gaussian noise channel. Low-density parity-check codes are also shown to be useful for communicating over channels which make insertions and deletions as well as additive (substitution) errors. Error-correction for such channels has not been widely studied, but is of importance whenever synchronisation of sender and receiver is imperfect. We introduce concatenated codes using novel non-linear inner codes which we call 'watermark' codes, and low-density parity-check codes over non-binary fields as outer codes. The inner code allows resynchronisation using a probabilistic decoder, providing soft outputs for the outer low-density parity-check decoder. Error-correction performance using watermark codes is several orders of magnitude better than any comparable results in the literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available