In this paper, we propose a partial erasure decoding scheme with erasure-decision threshold for Reed-Solomon (RS) codes and analyze its performance in frequency-hopped multiple-access communications. RS code is used to correct erasures and errors caused by other-user interference. Binary FSK is employed to transmit the channel symbol. The proposed decoder decides whether to erase the received RS code symbol based on the ersure decsion threshold. The approximated formula for optimal erasure decision threshold is derived in such a way that packet error probability can be minimized. Numerical results show that the employment of adaptive erasure decision threshold attains the higher normalized throughput in the areas of high channel traffic cases.

Dual FDTS/DF detector is an advanced version of FDTS/DF detector that gives significant performance improvement over FDTS/DF scheme on linear channels, and moreover, in contrast to other dual-detector schemes, it is suitable for various d-constraint coded channels. As recording density increases, channel nonlinearities such as non-linear transition shift (NLTS) and partial erasure (PE) degrade the performance of detectors. In this paper, we use nonlinear channel models to study the BER performance of dual FDTS/DF detector and compare the performances with those of other detectors through bit-by-bit simulations. Simulation results show that the dual FDTS/DF detector is superior in performance compared to FDTS/DF and MDFE detectors even on nonlinear channels, and it gives comparable BER performance with M2DFE (adv.) on nonlinear channels. Results also indicate that the detectors on the d=1 coded channels are more robust to channel nonlinearities compared to those of other detectors (such as PRML family detectors) on the d=0 coded channels.

In various digital wireless communication systems, it is known that turbo coding provides an error rate performance within a few tenths of a dB of the theoretical Shannon limit. The error correcting capability of turbo coding is attractive for a recording code in a digital magnetic recording system. The performance of a partial response maximum-likelihood (PRML) system with any recording code is degraded by many undesirable factors such as linear and nonlinear distortions. For improving the performance of the PRML system, it is useful to adopt a high-order PRML system or high rate code in general. In this paper, the two-track recording system using turbo coding which can increase the coding rate over 1 and improve the performance is proposed. Turbo-coding provides a near-ML performance by the suboptimum symbol-by-symbol maximum a posteriori probability (MAP) decoding algorithm. Our proposed turbo-coded class 4 partial response (PR4) systems use the rate 4/6, 8/10 and 16/18 turbo codes for high-density two-track digital magnetic recording. The error rate performance is obtained by computer simulation, taking account of the partial erasure which is a prominent nonlinear distortion in high-density recording. As a result, the proposed systems are hardly affected by partial erasure and maintains good performance compared with the conventional NRZ coded PR4ML system.

Recently, it is widely known that the partial response maximum-likelihood (PRML) system has attracted much attention as one of indispensable signal processing technique for achieving high density digital magnetic recording. But, the performance of PRML system is degraded by many undesirable causes in recording channel. For improving the performance, it is desirable to use any high order PRML system or high rate code. Our proposed two-track recording method increases the coding rate over 1, and contributes to decrease these degradation effects. The recording code in our system adopts a turbo code which provides a substantial near-ML performance by the suboptimum iterative decoding algorithm. In this paper, the turbo coded class four partial response (PR4) systems using the rate 4/6, 8/10 and 16/18 codes for high density two track digital magnetic recording are proposed. The error rate performance of the proposed system is obtained by computer simulation taking account of the partial erasure, which is one of nonlinear distortions at high densities. The performance of our system is compared with that of the conventional NRZ coded PR4ML system. The result shows that the proposed system is hardly affected by partial erasure and keeps good performance in high density recording. In especial, the proposed system using the rate 16/18 turbo code can achieve a bit error rate of 10-4 with SNR of approximately 12.2 dB less than the conventional NRZ coded PR4ML systems at a normalized linear density of 3.

In general, the performance of partial response maximum-likelihood (PRML) system is degraded by nonlinear distortion and high frequency noise in high-density digital magnetic recording. Conventional PRML system for single-track recording improves the performance when high order PRML systems and high rate codes are adopted. But, in general it is difficult to realize LSI circuits for high order PRML system and high rate code. In this paper, a trellis coded class four partial response maximum-likelihood (TC-PR4ML) system for high density two-track digital magnetic recording is proposed. Our two-track recording method can increase the coding rate over 1, which contributes to a decrease in both degradation effects from partial erasure, one of nonlinear distortions, and high frequency noise in high density recording. The error rate performance of the proposed system is obtained by computer simulation taking account of the partial erasure and it is compared with that of a conventional NRZ coded class four partial response maximum-likelihood (NRZ-PR4ML) system. The results show that the proposed system is hardly affected by partial erasure and keeps good performance in high density recording.

A modified frequency domain method for analyzing nonlinear waveform distortion in a magnetic recording process is presented. The measurement technique combines a 5th harmonic measurement technique, which uses a specific 30-bit pattern including dibits, and a precompensation technique for the dibits. The 5th harmonic voltage ratio given by the former technique includes the amount of NLTS (Nonlinear transition shift) and PE (Partial erasure) in dibits. The latter precompensation technique is employed to evaluate the PE as the minimum in the 5th harmonic voltage ratio. The true NLTS can be estimated from the amount of distortion and the evaluated PE. The high accuracy of the technique was confirmed by an examination using a pulse pattern generator with varied phase and amplitude. Finally, the effects of medium properties such as coercivity and squareness on the nonlinear distortions have been investigated by applying the technique to particulate flexible media. The NLTS increased with squareness from 3.5% to 7% while PE was less than 6% for any squareness at a recording density of 76 kFRPI. When coercivity became large, NLTS and PE decreased. The direction of NLTS for Ba-ferrite media agreed with that for a perpendicular Co-Cr thin-film medium.

A punctured convolutional coded PR4ML system for digital magnetic recording, which applies a punctured coding method to the convolutional code and records the punctured code sequences on two tracks, is proposed. In this study, the bit error rate performance of the proposed system is obtained by computer simulation taking account of partial erasure, which is one of the nonlinear distortions at high densities, and it is compared with those of a conventional 8/9 coded PR4ML system and an I-NRZI coded PR4ML system. The results show that the proposed system is hardly affected by partial erasure and exhibits good performance in high-density recording. A bit error rate of 10-4 can be achieved with SNR's of approximately 13.2 dB and 9.1 dB less than those of the conventional 8/9 coded and I-NRZI coded PR4ML systems, respectively, at a normalized linear density of 3.