Johannes Wilhelmus Maria Bergmans

Two-dimensional optical storage

With storage capacities increasing much faster than data rates, fast read-out of content is becoming a bottleneck for the convenient use of optical storage devices. Two-dimensional optical storage (TwoDOS) is a new concept that solves this data-rate problem by using a multi-spot parallel readout system. In addition, the storage capacity is increased with a factor of at least 2. Using the same read-out physics as in the Blu-ray disc standard, single layered 12 cm discs with capacities up to 50 GB have been read out successfully at bit-rates as high as 560 Mbit/s. Basic pillars of TwoDOS are advanced signal processing and disc mastering techniques, and a proper design of the optical path.

Characterization of digital recording channels by means of echo cancellation techniques

A simple yet accurate method is described for characterizing digital recording channels in terms of linear and nonlinear intersymbol interference and noise. The method is based on echo cancellation techniques, enables recorder operating conditions close to actual use, and delivers a joint portrait of the disturbances rather than isolated assessments. Experimental results for a high-density digital video tape recorder are included. >

Decision feedback equalization for run-length-limited codes with d=1

This paper provides a survey of decision feedback equalization for runlength-limited modulation codes with minimum run-length parameter d=1. The survey covers existing approaches such as the zero-forcing and multi-level decision feedback equalizer, as well as a novel one which exploits two pre-cursive intersymbol interference components. Performances of these approaches are analyzed mathematically, and are pitted against those of (1,7)ML and EEPRML for a Lorentzian channel.

Analysis of a biphase-based servo format for hard-disk drives

Biphase modulation in an embedded-servo format for hard-disk drives is investigated. It is shown that for biphase, at the low linear densities typical of servo information, near-maximum-likelihood performance can be attained by a simple bit detector consisting of a full-response linear equalizer and a binary slicer. Compared to the commonly used method of dibit coding, a signal-to-noise ratio gain of some 4 dB is achieved. The same equalizer may be used as the basis for near-maximum-likelihood position error signal amplitude estimation and timing recovery. Simulations of a practical servo demodulator based on a fifth-order analog filter show that at typical linear densities, this ideal performance is closely approached. The equalizer has a band-pass character and yields excellent suppression of the effects of thermal asperities and magneto-resistive head asymmetry.

Dual-DFE read/write channel IC for hard-disk drives

The channel IC described here achieves data rates of 380 Mb/s at performance levels that improve in various directions upon the state of the art. It accomplishes these feats in a mature 1 /spl mu/m CBiCMOS technology at a readmode power consumption of only 800 mW. The paper discusses some of the underlying architectural concepts.

Structure and adjustment of a novel write-precompensation scheme

At high data rates and information densities, recorded data patterns in digital magnetic recording systems can exhibit severe nonlinearities. Key causes for these nonlinearities are bandwidth limitations of the write path and demagnetizing fields in the recording medium. The present note reviews the structure of these nonlinearities, develops a simple yet generic write-precompensation scheme that is capable of counteracting them, and derives a technique for adjusting this scheme according to information extracted within the data receiver.

Near-Minimum Bit-Error Rate Equalizer Adaptation for PRML Systems

Receivers for partial response maximum-likelihood systems typically use a linear equalizer followed by a Viterbi detector. The equalizer tries to confine the channel intersymbol interference to a short span in order to limit the implementation complexity of the Viterbi detector. Equalization is usually made adaptive in order to compensate for channel variations. Conventional adaptation techniques, e.g., LMS, are, in general, suboptimal in terms of bit-error rate (BER). In this paper, we present a new equalizer adaptation algorithm that seeks to minimize the BER at the Viterbi detector output. The algorithm extracts information from the sequenced amplitude margin (SAM) histogram and incorporates a selection mechanism that focuses adaptation on particular data and noise realizations. The selection mechanism is based on the reliability of the add compare select (ACS) operations in the Viterbi detector. From a complexity standpoint, the algorithm is essentially as simple as the conventional LMS algorithm. Moreover, we present a further simplified version of the algorithm that does not require any hardware multiplications. Simulation results, for an idealized optical storage channel, confirm a substantial performance improvement relative to existing adaptation algorithms.

Measurements of nominal channel characteristics and temporal variations in digital video tape recorders

A method based on simple interpolation and correlation techniques is described for the estimation of some of the nominal characteristics and temporal variations of a digital magnetic recording channel for video recording. These estimates include the linear and nonlinear channel responses, timing jitter, and amplitude and bandwidth variations along a track in normal and fast forward modes of operation. The same technique can also be applied to examine transient channel variations around the time of dropouts. These estimates may be useful for the design of a phase-locked loop and an adaptive equalizer for a digital video tape recorder.<<ETX>>

Partial-response decoding of rate 1/2 modulation codes for digital storage

In digital storage systems, receivers for rate 1/2 modulation codes are usually oversampled by a factor of two with respect to the data stream that they attempt to reconstruct. It is shown that oversampling can be avoided by detecting a decimated ternary signal, from which the original data can be recovered by a simple decoder. A method is described to find all such decoders for a given rate 1/2 code. Examples treated are modified frequency modulation, Miller-squared, and two-to-seven. Mean-square performances of the old and new reception schemes are compared for a Lorentzian channel. The relative merits are found to depend quite heavily on the information density. The results obtained seem to contradict the belief that high-density performance benefits from a large minimum run length.<<ETX>>

GEN04-6: Near Minimum-BER all-Adaptive Partial Response Equalization For High Density Recording Systems

In order to reduce the implementation complexity of maximum likelihood sequence detectors (MLSD), equalized maximum likelihood receivers are often used. This consists of employing an equalizer to transform the channel response to a short target response to which the Viterbi detector is matched. Existing equalizer and target adaptation schemes are often based on the minimum mean-square error (MMSE) criterion which is not always optimal in terms of detection bit-error rate at the Viterbi detector output. In this paper we consider minimum bit-error rate joint adaptation of equalizer and target response and present a practical adaptation algorithm that achieves near minimum bit-error rate performance. Our new equalizer and target adaptation scheme shows significant performance improvements in the presence of channel nonlinearities and media noise when compared to MMSE adaptation schemes. This is very promising for high density recording systems that are mainly hampered by media noise and channel nonlinearities. Moreover, from a complexity standpoint, the proposed algorithm is comparable to the MMSE-based algorithms.