Data Compression Strategies for RDAT/DDS Media in Hostile Environments

  • Owen Thomas

    Student thesis: Doctoral Thesis


    This thesis investigates the prevention of error propagation in magnetically recorded compressed data when severe environmental conditions result in uncorrected channel errors.

    The tape format DDS is examined and a computer simulation of its error correction procedures is described. This software implementation uses explicit parity byte equations and these are presented for all three Reed-Solomon codes. The simulation allows the calculation of the uncorrected error patterns when the recording is compromised and uncorrected byte errors are determined for given initial random and burst errors.

    Some of the more familiar data compression algorithms are visited before the little known adaptive Rice algorithm is described in detail. An analytic example is developed which demonstrates the coding mechanism.

    A synchronized piecewise compression strategy is adopted in which the synchronizing sequences are placed periodically into the compressed data stream. The synchronizing sequences are independent of the compression algorithm and may occur naturally in the compressed data stream. A cyclic count is added to the compressed data stream to number the groups of data between synchronizing sequences and prevent slippage in the data. The Rice algorithm is employed in the strategy to compress correlated physical data. A novel compressor is developed to compress mixed correlated physical data and text within the synchronization strategy. This compressor uses the Rice algorithm to compress the correlated data and a sliding window algorithm to compress the text and switches between the two algorithms as the data type varies. The sliding window compressor T.ZR is adopted when the same principles are applied to the robust compression of English text alone. TJ7R is modified to improve compression of relatively small pieces of English text.

    The synchronization strategy incorporating these algorithms has been simulated computationally. This simulation is linked to that of DDS in each test performed when the errors are both random and bursty. The decompressed data is compared to the original. The strategy is demonstrated to be effective in preventing error propagation beyond the data immediately affected by errors without significant damage to the compression ratio.
    Date of AwardSept 1996
    Original languageEnglish
    SupervisorDerek Smith (Supervisor)

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