Zheng Wu

University of California, San Diego, San Diego, California, United States

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Publications (4)6.56 Total impact

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    ABSTRACT: In high density perpendicular magnetic recording channels, nonlinear transition shift (NLTS) is one of the distortions that can degrade the system performance. Write precompensation is a standard method used to combat the negative effect of NLTS. In this paper, we present an analysis of the bit-error-rate (BER) for perpendicular recording systems with NLTS and write precompensation. Media jitter noise and additive white Gaussian noise are also considered in the model. A BER lower bound is derived, as well as a more easily computed estimate of the bound. The write precompensation values that numerically minimize the estimate of the BER lower bound prove to be very close to those found using Monte-Carlo channel simulation. We then apply these methods to the design of multilevel precompensation schemes, for which the optimization of precompensation values by Monte-Carlo channel simulation is computationally infeasible. The results show that for higher recording densities subject to increased ISI and noise, the use of more complex precompensation schemes does not significantly improve the system performance.
    IEEE Journal on Selected Areas in Communications 03/2010; 28(2-28):158 - 166. DOI:10.1109/JSAC.2010.100204 · 4.14 Impact Factor
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    ABSTRACT: In high-density perpendicular magnetic recording channels, nonlinear transition shift (NLTS) is one of the distortions that can degrade the system performance. Write precompensation is a standard method used to combat the negative effect of NLTS. In this paper, we propose a modified pattern-dependent noise predictive (PDNP) detection algorithm for use on channels with electronics noise, transition jitter noise, and NLTS. We show that this detector can offer significant improvement in bit-error-rate (BER) compared to conventional Viterbi and PDNP detectors. Moreover, the system performance can be further improved by combining the new detector with a simple write precompensation scheme.
    IEEE Transactions on Magnetics 12/2008; DOI:10.1109/TMAG.2008.2002423 · 1.21 Impact Factor
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    ABSTRACT: The read-write process in perpendicular magnetic recording channels includes a number of nonlinear effects. Nonlinear transition shift (NLTS) arising from previously written transitions is one of these. The signal distortion induced by NLTS is reduced by use of write precompensation during data recording. In this paper, we numerically evaluate the effect of NLTS on the read-back signal by using the model proposed by Bertram and Nakamoto. By means of computer simulation, we examine the effectiveness of two write precompensation schemes in combating NLTS effects in a channel characterized by both transition jitter noise and additive white Gaussian electronics noise. We numerically optimize the precompensation schemes according to channel bit-error-rate, as well as more computationally tractable criteria. Our results suggest that a write-precompensation technique with as few as two adjustable parameters can be very effective against NLTS effects.
    Communications, 2008. ICC '08. IEEE International Conference on; 06/2008
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    ABSTRACT: To optimize a high-density magnetic recording system, one needs to know the tradeoffs between various components of the system including the read/write transducers, the magnetic medium, and the read channel. In this paper, we consider a channel model characterized by three parameters: the replay pulse width T<sub>50</sub>, the transition jitter noise standard deviation sigma<sub>J</sub>, and the signal-to-electronic-noise ratio SNR<sub>WG</sub>. We utilize information-theoretic tools to determine the acceptable region for the channel parameters T<sub>50</sub> and sigma<sub>J</sub> when optimal detection and linear coding techniques are used. This paper is an extension of a similar analysis for a system that utilized a minimum mean-squared error (MMSE) equalizer, a Viterbi detector, and a Reed-Solomon (RS) code. Our main conclusion is that there is a considerable potential gain to be achieved by using improved detection and coding schemes as compared with the present system
    IEEE Transactions on Magnetics 03/2007; DOI:10.1109/TMAG.2006.888369 · 1.21 Impact Factor

Publication Stats

9 Citations
6.56 Total Impact Points

Institutions

  • 2008–2010
    • University of California, San Diego
      • Department of Electrical and Computer Engineering
      San Diego, California, United States
  • 2007
    • CSU Mentor
      • Department of Electrical & Computer Engineering
      Long Beach, California, United States