Noise Equalization Research Articles

Power Comparison Between High-Speed Electrical and Optical Interconnects for Interchip Communication

An I/O bandwidth commensurate with a dramatically increasing on-chip computational capability is highly desirable. Achieving this goal using board-level copper interconnects in the future will become increasingly challenging owing to severe increase in high-frequency, skin-effect and dielectric loss, noise due to crosstalk, impedance mismatch, and package reflections. The solutions designed to overcome these deleterious effects require complex signal processing at the interconnect endpoints, which results in a larger power and area requirement. Optical interconnects offer a powerful alternative, potentially at a lower power. Prior work in comparing the two technologies has entailed overly simplified assumptions pertaining to either the optical or the electrical system. In this paper, we draw a more realistic power comparison with respect to the relevant parameters such as bandwidth, interconnect length and bit error rate (BER) by capturing the essential complexity in both types of interconnect systems. At the same time, we preserve the simplicity by using mostly analytical models, verified by SPICE simulations where possible. We also identify critical device and system parameters, which have a large effect on power dissipation in each type of interconnect, while quantifying the severity of their impact. For optical interconnect, these parameters are detector and modulator capacitance, responsivity, coupling efficiency and modulator type; whereas, in the case of electrical system, the critical parameters include receiver sensitivity/offset and impedance mismatch. Toward this end, we first present an optimization scheme to minimize optical interconnect power and quantify its performance as a function of future technology nodes. Next, on the electrical interconnect side, we examine the power dissipation of a state-of-the-art electrical interconnect, which uses simultaneous bidirectional signaling with transmitter equalization and on-chip noise cancellation. Finally, we draw extensive comparisons between optical and electrical interconnects. As an example, for bandwidth of 6 Gb/s at 100 nm technology node, lengths greater than the critical length of about 43 cm yields lower power in optical interconnects. This length becomes lower (making optics more favorable) with higher data rates and lower bit error rate requirement.

Theoretical investigation of 8 10-gb/s wdmsignal transmission performance based on gain-equalized soas using backward raman pumping at dcf

We have theoretically investigated 8 × 10-Gb/s wavelength-division multiplexing (WDM) signal transmission characteristics based on semiconductor optical amplifiers (SOAs) with equalized gain using discrete Raman amplification (DRA). Gain equalization and low noise figures have been obtained by adjusting the backward Raman pumping power and wavelength at a dispersion compensating fiber (DCF) for each span. Bit-error-rate characteristics were calculated for 8 × 10-Gb/s WDM signal transmission over 6 × 40-km single-mode fiber (SMF) + DCF links with gain-equalized SOAs using DRAs at DCF. Approximately a 2.5-dB improvement of the receiver sensitivity was achieved by using SOAs and DRAs with optimized Raman pumping. One can easily upgrade the transmission length of a link based on SOAs with an appropriate backward pump laser at each DCF.

Examination of the relevance of cochlear dead regions to hearing aid fittings

Vickers et al. [J. Acoust. Soc. Am. 110, 1164–1175 (2001)] suggested that identification of Cochlear Dead Regions (CoDR) may provide information relative to hearing aid fittings. The relationship between CoDR and hearing aid fittings was explored in the current study two ways: (1) by reviewing the hearing loss characteristics of Vickers et al. (2001) subjects with CoDR using the Articulation Index, and (2) examining the frequency of CoDR in a clinical population. Using amplified, low-pass filtered nonsense syllables Vickers et al. (2001) found a relationship between the edge of the identified high-frequency CoDR and the filter setting that provided optimal syllable recognition. Because of the severity of the high-frequency hearing loss for the CoDR group the Articulation Index results from the present study suggested that these listeners may have not benefited from high-frequency amplification because of inaudibility. The frequency of CoDR was determined in a clinical population using the Threshold Equalization Noise (TEN) test described in Moore et al. [Br. J. Audiol. 34, 205–224 (2000)]. Results suggested that CoDR are not encountered as frequently as implied in the literature. These findings have important implications on how CoDR testing relates to hearing aid fittings.

Lung: feasibility of a method for changing tube current during low-dose helical CT.

A method for changing the tube current during helical scanning was applied to low-dose computed tomography (CT) in the lung. The changing method resulted in significant equalization of image noise in various lung sections compared with that at scanning with constant tube current. Detectability of nodules was equivalent between 60 mA and the changing method, whereas degradation occurred at 20 mA. This method seems feasible for the low-dose CT of lung cancer screening.

A controlled phantom study of a noise equalization algorithm for detecting microcalcifications in digital mammograms.

We report on some extensions and further developments of a well-known microcalcification detection algorithm based on adaptive noise equalization. Tissue equivalent phantom images with and without labeled microcalcifications were subjected to this algorithm, and analyses of results revealed some shortcomings in the approach. Particularly, it was observed that the method of estimating the width of distributions in the feature space was based on assumptions which resulted in the loss of similarity preservation characteristics. A modification involving a change of estimator statistic was made, and the modified approach was tested on the same phantom images. Other modifications for improving detectability such as downsampling and use of alternate local contrast filters were also tested. The results indicate that these modifications yield improvements in detectability, while extending the generality of the approach. Extensions to real mammograms and further directions of research are discussed.

An improved broadband active noise compressor

As the extension of active noise equalization (ANE), an active noise compressor (ANCP) has been proposed recently in the literature to nonlinearly compress the noise power to a certain desired range instead of shifting it linearly. The algorithm uses a variable gain factor to control the dynamic range of the residual noise power. However, the controllability provided by that gain factor is inadequate. In this paper, we propose a new way to represent the gain factor. The new method takes into account the desire to accurately maintain the noise power when it is tolerable and suppress it while exceeding the unbearable level. Simulation and implementation results show that the new method outperforms ANCP in controllability and additionally in computational efficiency [J. W. Feng and W. S. Gan, IEEE Signal Process. Lett. 5, 11–14 (1998)].

Normalization of local contrast in mammograms.

Equalizing image noise has been shown to be an important step in automatic detection of microcalcifications in digital mammograms. In this study, an accurate adaptive approach for noise equalization is presented and investigated. No additional information obtained from phantom recordings is involved in the method, which makes the approach robust and independent of film type and film development characteristics. Furthermore, it is possible to apply the method on direct digital mammograms as well. In this study, the adaptive approach is optimized by investigating a number of alternative approaches to estimate the image noise. The estimation of high-frequency noise as a function of the grayscale is improved by a new technique for dividing the grayscale in sample intervals and by using a model for additive high-frequency noise. It is shown that the adaptive noise equalization gives substantially better detection results than does a fixed noise equalization. A large database of 245 digitized mammograms with 341 clusters was used for evaluation of the method.

Active noise compression systems

This paper presents a new concept of narrowband and broadband active noise compression (ANCom) systems which improves the conventional active noise equalization (ANE) technique to meet some practical requirements. By using a variable equalization coefficient, the narrowband ANCom system can automatically switch among the four different operating modes of narrowband ANE, according to the primary noise power. As a result, it can “compress” the narrowband noise into a desired power range when the primary noise power varies drastically. Compared to a conventional broadband ANE system, the novel broadband ANCom system not only has the ability to shape the residual noise power spectrum, but can also compress the residual noise power into a predetermined dynamic range as the narrowband AN-Com does. Theoretical analyses are conducted for both the narrowband ANCom and broadband ANCom systems. Simulation results show that the proposed algorithms work well in both static and dynamic situations.

Patterned media recording: Noise and channel equalization

We analyze a patterned recording system in which bits are recorded on magnetic islands. Merger or disappearance of the islands due to edge jaggedness cause bit errors. This edge imperfection also manifests itself as noise causing read errors in the channel. Error probabilities from these degradation mechanisms are computed assuming a partial response read channel. The island size-to-pitch ratio giving minimum error rate is found to be independent of the jaggedness.

Broadband active noise compressor

A broadband active noise compressor (ANCP) is presented to adapt the active noise equalization (ANE) technique suitable for practical usage. Compared to the existing broadband ANE system, the novel ANCP not only has the ability to shape the residual noise spectrum, but can also automatically adjust the residual noise power. This algorithm is analyzed in steady state and verified by computer simulations.

Correction to "Frequency-domain Periodic Active Noise Control And Equalization"

Correction to "Frequency-domain Periodic Active Noise Control And Equalization"

Frequency-domain periodic active noise control and equalization

This paper analyzes a frequency-domain periodic active noise control (ANC) system. The adaptive filter employs the frequency domain complex least mean square (LMS) algorithm driven by a unit value at each frequency bin. The synchronously sampled frequency-domain adaptive structure acts as a comb filter to cancel narrowband noises with harmonically related frequencies. A frequency-domain periodic active noise equalization (ANE) system, which reshapes the residual noise by controlling the output of the adaptive comb filter at each frequency bin, is also developed and analyzed in this paper. Computer simulations and real-time experiments conducted attest to the practical usefulness of the proposed ANC and ANE systems.

Broadband adaptive noise equalizer

This paper presents a broadband adaptive noise equalizer (ANE) with noise shaping capability. The residual noise spectrum can be completely controlled by inserting a shaping filter in both the canceling and balancing branches. This algorithm is analyzed in steady state and verified by computer simulations.

Development and analysis of an adaptive noise equalizer

The paper presents the development and analysis of a narrowband adaptive noise equalizer (ANE), which can either amplify or attenuate narrowband noise. The output of the ANE system contains residual narrowband components, the amplitudes of which can be linearly and arbitrarily controlled by adjusting the gain parameter of the equalizer, thus providing the desired noise shaping capability. The characteristics of the ANE system are analyzed and applied to active noise control. >

A PSK transmission system employing transmitting and receiving butterworth filters with optimized noise performance

AbstractA band‐limited phase‐shift keyed (PSK) transmission system satisfying Nyquist's first criterion by an equalizer using Butterworth filters for transmitting and receiving filters is discussed. Minimum noise equalization that minimizes the receiver equivalent noise band width is proposed and the characteristics of such a system are calculated. In addition, minimum noise equalization is compared with reference equalization and roll‐off equalization and it is clarified that minimum noise equalization is better than these equalization method in frequency and power efficiency. It is shown also that the frequency efficiency and the efficiency of transmitting power have a trade‐off relationship in a bandwidth‐limiting and then power‐amplifying scheme and the frequency efficiency is increased without decreasing the transmission power by decreasing the heat loss of a high‐order transmitting filter in a power‐amplifying and then band‐width‐limiting scheme.

Principle and application of adaptive noise equalizer

This paper presents the principle and application of an adaptive noise equalizer (ANE) with adjustable gain or attenuation capabilities. The residual error of the ANE system contains the narrow-band noise components whose amplitude can be linearly and arbitrarily controlled by adjusting the gain parameter of the equalizer. Each ANE consists of a sinusoidal reference input and two adaptive weights. A pseudo error minimum method is developed to effectively utilize the well-understood least-mean-square algorithm. By partially separating the system output from the cost function to be minimized, the ANE can perform either a harmonic noise attenuator or amplifier by a predetermined amount. The application to active noise control is presented, and computer simulation results demonstrate the desired noise shaping capability. >

Noise equalization within EIT images

The authors first describe experiments designed to measure the spatial distribution of noise within an electrical impedance tomographic (EIT) image of a saline-filled tank. These experiments show that the noise increases by a factor of up to 30 from the periphery towards the centre of the image. The authors then propose a method of noise equalization that depends upon spending longer collecting the smaller potentials than the larger potentials. The method is tested and shown to give an improvement in noise uniformity of about 16 dB.

Development and Experiment of Narrowband Active Noise Equalizer

Development and Experiment of Narrowband Active Noise Equalizer

Equalization and mode partition noise in all-plastic optical fiber data links

High-speed, short-distance data transmission over all-plastic step-index fiber (plastic optical fiber, or POF) is normally considered to be limited by intermodal dispersion. Theoretical calculations in this letter show that the baseband frequency response can be significantly improved using simple linear equalization. However, as the fiber length is increased, the sharp absorption attenuation peaks of PMMA fiber can potentially introduce mode partition noise. The bounds on practical laser characteristics and fiber lengths are explored; these results indicate that 530-Mb/s transmission over 100 m of 1-mm-diameter POF is feasible, thus potentially satisfying a significant segment of future computer interconnect applications. >

Random Noise Interference and Possible Solutions to its Effects on Image Resolution and Gray Scale

In this paper we report the effect of random noise interference in various portions of the video band spectrum' and attempt to model the human visual mechanism for resolving image in the presence of noise. Broad, narrow and mixed bands of white noise distribution effects throughout the video band are investigated. Good agreement results between the experimental data and predicted performance from computer simulation models. The analysis indicates that noise equalization, by pre-emphasizing and deemphasizing a certain portion of the video, results in a considerable improvement in resolution and gray scale of the image.