C.M. Melas

Bio: C.M. Melas is an academic researcher from IBM. The author has contributed to research in topics: Equalization (audio) & Adaptive filter. The author has an hindex of 3, co-authored 4 publications receiving 256 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. >

Path Rearranging in a Data Switching Network

Abstract: Path rearranging results in a 60 percent savings of hardware in a nonblocking 2048-line switch. The blocked connection is freed up by exchanging paths between two middle matrices. Selection criteria for the middle matrices include the incidence of duplicate connections through these matrices. A path rearranging algorithm is derived from the Paull method and implemented in software by the network control microprocessor. Two buses are required for data switching to prevent any interruption in the data stream during rearranging.

An adaptive dfe for storage channels suffering nonlinear is1

Abstract: Interest has been growing in the use of sophisticated detection methods to increase the density of bits that can be stored on a disk. Decision Feedback Equalization (DFE) is a strong candidate among these methods, especially when implemented as an adaptive filter[l]. An adaptive DFE can be used to compensate for radial channel variation and can also substantially reduce manufacturing and servicing costs for the disk drive by broadening the range of acceptable components. To date, DFE studies have assumed the existence of a linear cliannel[2]. However, in the rapidly growing area of thin-film disks, the storage channel can exhibit significant nonlinearity at high densities. This effect tends to reduce the performance of the DFE. In this paper, we present a simple modification of the DFE to accommodate the disk-channel.

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.

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.

Modulation and coding for information storage

Abstract: Many of the types of modulation codes designed for use in storage devices using magnetic recording are discussed. The codes are intended to minimize the negative effects of intersymbol interference. The channel model is first presented. The peak detection systems used in most commercial disk drives are described, as are the run length-limited (d,k) codes they use. Recently introduced recording channel technology based on sampling detection-partial-response (or PRML) is then considered. Several examples are given to illustrate that the introduction of partial response equalization, sampling detection, and digital signal processing has set the stage for the invention and application of advanced modulation and coding techniques in future storage products. >

Equalization in high-speed communication systems

Abstract: The article first discusses the major non-ideal issues of low-cost transmission media for over Gbps data transmissions - the frequency dispersion loss and channel noise. The former causes ISI in received signal, which presents difficulty for clock and data recovery at high frequencies and results higher BER. The latter further degrades the received signal quality and further limits the data transmission rate and transmission distance. Then, two equalization approaches - transmitter pre-emphasis and receiver equalization, are reviewed, in addition to various adaptation criteria and algorithms.