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Weijun Tan , Haitao Xia and J. R. Cruz Communications Signal Processing Laboratory

Weijun Tan , Haitao Xia and J. R. Cruz Communications Signal Processing Laboratory The University of Oklahoma. Erasure Detection Algorithms for Magnetic Recording Channels. Outline. Media Defect Model Precoding Performance Loss BCJR Analysis of Erasure Detection Improved Algorithm

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Weijun Tan , Haitao Xia and J. R. Cruz Communications Signal Processing Laboratory

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  1. Weijun Tan, Haitao Xia and J. R. Cruz Communications Signal Processing Laboratory The University of Oklahoma Erasure Detection Algorithms for Magnetic Recording Channels

  2. Outline • Media Defect Model • Precoding Performance Loss • BCJR Analysis of Erasure Detection • Improved Algorithm • Simulation Results • Summary 9th MMM/Intermag

  3. Media Defect Model Envelope 1-η η=0.5 Partial erasure Full erasure η=1.0 t 9th MMM/Intermag

  4. Precoding Loss • LDPC coded ME2PR4 channel • AWGN • Ideally detected erasures • Several precoders • Asymptotic density evolution (DE) analysis of code (3,30) • Simulation of code (4376,3,30) 9th MMM/Intermag

  5. Numerical Results • Precoding causes a loss of 0.2~0.7 dB • 1/(1+D) is the best precoder • DE and simulation results are consistent • The ranking of the precoders does not change with erasures 9th MMM/Intermag

  6. BCJR Analysis • BCJR algorithm • Erasure section • No useful signal, zi=ni 9th MMM/Intermag

  7. Erasure Detection Non-Precoded 1/(1+D)-Precoded • γi(s',s,yi=0)>γi(s',s,yi≠0) • αi(s=●)>αi(s≠●) • βi(s=●)> βi(s≠●) • (s'→s,yi=0) selected • Non-precoded: 00…00, 11…11, 10…10, RLL(0,G|I) • 1/(1+D) precoded: 00…00, 11…11, RLL(0,k) 9th MMM/Intermag

  8. BCJR LLRs Nonprecoded, η=0.5 • Amplitude of BCJR LLRs attenuated • Long runs of zi =0 • Erasures 1/(1+D)-Precoded, η=0.5 1/(1+D)-Precoded, η=1.0 Non-Precoded, η=1.0 1/(1+D)-Precoded, η=0.5 Non-Precoded, η=0.5 • Can be used to detect (partial) erasures in combination with RLL codes 9th MMM/Intermag

  9. Improved Algorithm • Tentative BCJR decisions • Broader RLL checks • Runs of • Runs of • Runs of 9th MMM/Intermag

  10. Simulation Results • ME2PR4/(1+D),Sc=2.995 • LDPC (4608,3751),R=0.814 • L=192, k = 28 • The new algorithm is slightly better • EPR4/(1+D2),Sc=2.995 • LDPC (4608,4096),R=0.899 • L=128, k = 28 • The new algorithm is 0.5 dB better 9th MMM/Intermag

  11. Summary • 1/(1+D) is the best precoder for the ME2PR4 channel, if needed • BCJR analysis of erasure detection • RLL(0,k) for 1/(1+D)-precoded ME2PR4 • RLL(0,G|I) for non-precoded ME2PR4 • BCJR LLR amplitude thresholding • Improved algorithm • Better performance 9th MMM/Intermag

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