K.D. Fisher

Bio: K.D. Fisher is an academic researcher from Stanford University. The author has contributed to research in topics: Equalization (audio) & Adaptive equalizer. The author has an hindex of 9, co-authored 12 publications receiving 562 citations.

Adaptive equalization in magnetic-disk storage channels

Abstract: The use of adaptive equalization to increase storage density is discussed. Adaptive equalization is attractive since it permits a significant reduction in manufacturing costs by allowing a greater component yield due to relaxed tolerances and also permits a reduction in servicing costs because of a reduced need for fine-tuning on the customer's premises. The differences between data storage and data transmission channels are examined. The storage channel's important signal-processing characteristics are described, covering read and write processes, detection methods, and various types of distortion that can occur in storage channels. The use of signal-to-noise ratio as a performance measure is considered. Equalization methods for peak detection and for sampling detection are discussed. Gains in both linear and areal (track) density are addressed. Some of the basic performance advantages of using adaptive equalization are illustrated. The future of communication technology in storage systems is assessed. >

An adaptive RAM-DFE for storage channels

Abstract: A modification of the decision feedback equalizer (DFE), RAM-DFE, is presented and analyzed for use in channels with trailing nonlinear intersymbol interference, especially binary saturation-recording channels. In the RAM-DFE, a look-up table, which can be easily implemented with random access memory, (RAM), replaces the transversal filter feedback section of the DFE. The feedforward section of the equalizer remains linear. A general nonlinear Markov (or finite-state machine) model is used to model the nonlinear intersymbol interference (ISI) channel. With this Markov model, a method is introduced for computing the minimum-mean-squared-error settings of the feedforward filter coefficients and the feedback filter and look-up table contents for the linear DFE and the RAM-DFE, respectively. RAM-DFE with these settings can be significantly better than the linear DFE for channels with trailing nonlinear ISI. Globally convergent gradient-type algorithms for updating the feedforward section coefficients and the contents of the feedback table are introduced and analyzed. Results based on data taken from disk storage units are discussed. >

Adaptive decision feedback equalizer apparatus for processing information stored on digital storage media

Abstract: Adaptive decision feedback equilizer apparatus for processing information including a data input buffer (34), a gain acquisition circuit (42), a timing acquisition circuit (40) operative to generate timing error signals, a synchronizing circuit (44) for generating sync detect signals and polarity signals, an FIR filter (36) for generating linear filter output signals, register (39), feedforward update logic (38) for adjusting the equalizer coefficient signals, a dual ported RAM (50) for storing the equalizer coefficient signals, feedback logic (48) responsive to the linear filter output signals, feedback update logic (52) for adjusting the values of the coefficient signals, steady-state timing logic (54), and a controller (46) responsive to the polarity signals and the sync detect signals and operative to generate the train data signals.

The ITU-T's new g.vector standard proliferates 100 mb/s dsl

Abstract: This article explores the recently issued ITUT G.vector (G.993.5) that allows expanded use of 100 Mb/s DSL. A tutorial description on G.vector's crosstalk noise reduction methods leads to specific projections and measurements of expanded DSL 100 Mb/s reach. A discussion on dynamic maintenance to enhance G.vector's practical application then concludes this article.

A MMSE interpolated timing recovery scheme for the magnetic recording channel

Abstract: Advances in VLSI technology permit the use of interpolated timing recovery (ITR) as a replacement for the conventional VCO-based phase lock loop. Fully digital ITR has the advantage of lower cost and higher stability. In this paper, we present an interpolated timing recovery scheme that requires almost no oversampling, which should be suitable for high-speed storage channels.

The finite-length multi-input multi-output MMSE-DFE

Abstract: A new theoretical framework is introduced for analyzing the performance of a finite length minimum-mean-square error decision feedback equalizer (MMSE-DFE) in a multi-input multi-output (MIMO) environment. The framework includes transmit and receive diversity systems as special cases and quantifies the diversity performance improvement as a function of the number of transmit/receive antennas and equalizer taps. Fast and parallelizable algorithms for computing the finite-length MIMO MMSE-DFE are presented for three common multi-user detection scenarios.

Electrical signal processing techniques in long-haul fiber-optic systems

Abstract: The potential for electrical signal processing to mitigate the effect of intersymbol interference in long-haul fiber-optic systems is discussed. Intersymbol interference can severely degrade performance and consequently limit both the maximum distance and data rate of the system. Several techniques for reducing intersymbol interference in single-mode fiber systems with single-frequency lasers are presented, and those techniques which are appropriate at high data rates in direct coherent detection systems are identified. The performances of linear equalization (tapped delay lines), nonlinear cancellation (variable threshold detection), maximum-likelihood detection, coding, and multilevel signaling are analyzed. The results for a simulated binary 8-Gb/s system show that simple techniques can be used to reduce intersymbol interference substantially, thereby increasing the system margin by several decibels. A six-tap linear equalizer increases the dispersion-limited distance (due to chromatic or polarization dispersion) by 20% (or reduces the optical power penalty by as much as a factor of two) in direct detection systems, even when the distortion is nonlinear. A nonlinear cancellation technique (adjusting the decision threshold in the detector based on previously detected bits) can more than double the dispersion-limited distance and/or data rate. >

Lexical frequency and acoustic reduction in spoken Dutch

Abstract: This study investigates the effects of lexical frequency on the durational reduction of morphologically complex words in spoken Dutch. The hypothesis that high-frequency words are more reduced than low-frequency words was tested by comparing the durations of affixes occurring in different carrier words. Four Dutch affixes were investigated, each occurring in a large number of words with different frequencies. The materials came from a large database of face-to-face conversations. For each word containing a target affix, one token was randomly selected for acoustic analysis. Measurements were made of the duration of the affix as a whole and the durations of the individual segments in the affix. For three of the four affixes, a higher frequency of the carrier word led to shorter realizations of the affix as a whole, individual segments in the affix, or both. Other relevant factors were the sex and age of the speaker, segmental context, and speech rate. To accommodate for these findings, models of speech production should allow word frequency to affect the acoustic realizations of lower-level units, such as individual speech sounds occurring in affixes.

Expanded information capacity for existing communication transmission systems

Abstract: A system for transmitting digital programming includes a program source providing digital information, circuitry for modulating the digital information onto a visual carrier modulated with analog television programming, and a visual transmitter coupled to the modulating circuitry. Using a phase modulation method, the system phase modulates the digital information onto a visual carrier, reduces the baseband frequencies of the phase modulated visual carrier, and amplitude modulates the phase-modulated video carrier onto a video signal. The amplified and encoded video signal are combined with an amplified sound signal and transmitted. Using an additive method, the system modulates the sidebands of the video carrier with the digital information and amplitude modulates the video signal onto the video carrier. The data-modulated sidebands are phase-shifted such that they will be in quadrature with the amplitude-modulated video signal. The system combines the amplitude-modulated video carrier and the data-modulated quadrature sidebands. With a blended multiplicative/additive method, the system provides phase modulation and quadrature sideband addition to provide an optimized result.