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    Reliability Ratio-Based Serial Algorithm of LDPC Decoder for Turbo Equalization Schemes
    (2022-02-01)
    Khittiwitchayakul, Sirawit
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pornchai
    Serial decoding algorithms of low-density parity-check (LDPC) code converge efficiently with low errors. Previously, a serial decoding algorithm, named a shuffled belief-propagation (SBP), was applied in turbo equalization of bit-patterned magnetic recording (BPMR) systems. With the SBP algorithm, an LDPC decoder converged twice as fast as one using conventional BP algorithms. We further improved the convergence speed of SBP by updating the messages in an adaptive order, which played a flexible role throughout decoding. We proposed two adaptive-serial algorithms for LDPC codes in turbo equalization. One updated the messages using the extrinsic loglikelihood ratio (LLR) and the result of the parity-check equation checking. The second contained an additional rule that tracked the LLR sign changes in each iteration. Both algorithms converged faster and with lower bit error rates (BERs) than the SBP and previous adaptive-serial algorithms in a BPMR system with media noise.
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    Sliding-Window Turbo Equalization and Its Reduced-Complexity Decoding Techniques
    (2022-01-01)
    Khittiwitchayakul, Sirawit
    ;
    Phakphisut, Watid
    Turbo equalization is a cooperative error-correcting approach to achieve a target bit-error rate over inter-symbol interference channels. In this paper, we proposed a new turbo equalization, called sliding-window turbo equalization (SW-TE), consisting of the Bahl-Cocke-Jelinek-Raviv detector and a spatially coupled, low-density, parity-check decoder. Moreover, the Protograph-based Extrinsic Information Transfer (P-EXIT) chart was modified to investigate the asymptotic behavior of SW-TE. Our analyses showed that SW-TE outperformed conventional turbo equalization in terms of decoding threshold. Based on the P-EXIT chart analysis, we further proposed a guideline of the reduced-complexity decoding techniques for SW-TE, eliminating unnecessary branch metric updates during turbo iterative decoding. Our simulations corroborated the analytical results, showing that SW-TE outperformed conventional turbo equalization while maintaining an acceptable level of complexity.
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    Sliding-window processing of turbo equalization for partial response channels
    (2019-04-01)
    Khittiwitchayakul, Sirawit
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pornchai
    Spatially coupled low-density parity-check (SC-LDPC) codes are the attractive candidates for the application requiring a practical constraint on the latency and complexity. In previous works, the turbo equalization consisting the SC-LDPC window decoder and Bahl-Cocke-Jelinek-Raviv (BCJR) detector is used to tackle the inter-symbol interferences (ISIs) in the magnetic recording systems. However, the prior works consider only the SC-LDPC codes which replace the conventional LDPC block codes. In this work, we propose the modification of turbo equalization processing whereby both the SC-LDPC decoder and BCJR detector operate using the sliding window. The results show that the proposed turbo equalization schemes used in the partial response (PR) channel can provide better bit error rate (BER) performances than the conventional turbo equalization.
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    Reduced Complexity Window Decoding of Spatially Coupled LDPC Codes for Magnetic Recording Systems
    (2018-11-01)
    Khittiwitchayakul, Sirawit
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pornchai
    Spatially coupled low-density parity-check (SC-LDPC) codes have emerged to possess capacity-approaching performance. The SC-LDPC codes can be decoded by a sliding window, therefore, the decoding latency and complexity of SC-LDPC codes are lower than those of underlying LDPC codes when the codeword length is very large. In this paper, the SC-LDPC decoder with the sliding window is employed in turbo equalization of magnetic recording systems. We examine the bit error rates (BERs) of the output of the sliding window during the iterative decoding, and then observe that the consecutive code blocks have approximately the same BERs. Herein, to reduce decoding complexity of SC-LDPC codes, the consecutive code blocks can be considered as the output of SC-LDPC codes. In addition, the non-uniform schedule update is adopted in the window decoding to avoid unnecessary updates within a window. The simulation results show that the proposed decoding algorithms applied in bit-patterned media magnetic recording systems can achieve a significant reduction in complexity compared to the traditional decoding without any loss in BER performance.