Showing papers on "Impulse noise published in 1990"

Errors-and-erasures coding to combat impulse noise on digital subscriber loops

Abstract: The issue addressed is how closely ideal performance can be approached using a practical erasure declaration mechanism. A description is given of a specific practical erasure declaration mechanism, and the resulting coded system performance is investigated on the digital subscriber loop. Results indicate that, by appropriate choice of system parameters, it is possible to closely approach the ideal performance. >

Nonauditory injury threshold for repeated intense freefield impulse noise.

Abstract: Exposure to impulse noise is an important occupational health concern. The risk of injury to auditory structures is well recognized and provides the cornerstone for present safety standards. For freefield impulse noise, nonauditory injury is dependent on peak pressure, positive phase duration (or impulse), and number of exposures. Trivial laryngeal petechiae are shown to precede nonauditory injury to more critical organs (ie, pulmonary and gastrointestinal systems). This study identifies the critical impulse noise thresholds causing trivial laryngeal petechial changes resulting from exposure to 5, 25, and 100 repetitions of specific levels of impulse noise. Because of anatomical differences, sheep should be slightly more susceptible to impulse noise laryngeal petechial changes than man; therefore, it seems reasonable to set the absolute limits for human occupational exposure levels below those causing laryngeal petechiae in sheep for persons wearing adequate hearing protection. This study does not address human auditory injury that may occur above or below these exposure limits even with proper hearing protection.

Recursive algorithms for identification of impulse noise channels

Abstract: The Class A Middleton model is a widely accepted statistical-physical parameteric model for impulsive interference superimposed on a Gaussian background. In the present work, a recursive decision-directed estimator for online identification of the parameters of the Class A model is proposed. This estimator is based on an adaptive Bayesian classification of each of a sequence of Class A envelope samples as an impulsive sample or as a background sample. As each sample is so classified, recursive updates of the estimates of the second moment of the background component of the interference envelope density, the second moment of the impulsive component of the interference envelope density, and the probability with which the impulsive component occurs, are readily obtained. From these estimates, estimates of the parameters of the Class A model follow straightforwardly, since closed-form expressions for the parameters exist in terms of these quantities. The performance characteristics of this algorithm are investigated and an appropriately modified version is found to yield a recursive algorithm with excellent global performance. >

Impulse noise in the loop plant

Abstract: In ISDN field trials for basic access, at 144 kb/s, such impulse noise has proved to be one of the major limiting factors in the transceiver's achievable performance. It is expected to be an even more severe impairment for transceivers operating at data rates substantially larger than ISDN's basic rate. The author summarizes some of the properties of impulse noise observed in various surveys, such as frequency of occurrence, amplitude probability distribution, and time and frequency characteristics, and discusses in some detail a class of possible impulse events generated in digital subscriber loops by crosstalk coupling with switched voice circuits. A brief discussion of transceiver design issues in an impulse-noise-dominated environment is also provided. >

Digital Image Processing for Ophthalmology

Abstract: This chapter describes what happens when images are digitized, how the images are stored and retrieved, how the images can be improved in appearance, how certain aspects of the image can be emphasized, how noise and unwanted features can be minimized, and how images may be analyzed. Other issues are the capabilities the user would want in a system they are wishing to purchase.

Adaptive Nonlinear Filters

Abstract: The nonlinear filters described in the previous chapters are usually optimized for a specific type of noise and sometimes for a specific type of signal. However, this is not usually the case in many applications of nonlinear filtering, especially in image processing. Images can be modeled as two-dimensional stochastic processes, whose statistics vary in the various image regions. Images are nonstationary processes. Furthermore the noise statistics, e.g., the noise standard deviation and even the noise probability density function, vary from application to application, as was described in chapter 3. Sometimes, the noise characteristics vary in the same application from one image to the next. Such cases are the channel noise in image transmission and the atmospheric noise (e.g., the cloud noise) in satellite images. In these environments non-adaptive filters cannot perform well because their characteristics depend on the noise and signal characteristics, which are unknown. Therefore, adaptive filters are the natural choice in such cases. Their performance depends on the accuracy of the estimation of certain signal and noise statistics, namely the signal mean and standard deviation and the noise standard deviation. The estimation is usually local, i.e., relatively small windows are used to obtain the signal and noise characteristics. An important property of these estimators is their robustness to impulse noise, which is present in many image processing applications. Another reason for using adaptive filters is the fact that edge information is very important for the human eye and must be preserved. Certain filters, e.g., the moving average, perform well in homogeneous image regions but fail close to edges. The opposite is true for other filters, e.g., for the median. A combined filter which performs differently in the image edges than in the image plateaus can be used in such a case. These filters are also called decision directed filters because they employ an edge detector to decide if an edge is present or not. Decision directed filtering can also be used in the cases of mixed additive white noise and impulsive noise. Impulses can be detected and removed before the additive noise filtering is performed. Another approach related to decision directed filtering is the two-component model filtering. An image is assumed to consist of two components, the low-pass and the high-pass component. The first one is mainly related to homogeneous image regions, whereas the second one is related to edge information. These two components can be processed in different ways. The output of the two corresponding filters can be recombined to give the final filtered image. The two-component image processing model has been used both for noise removal and image enhancement applications.

The effects of impulse noise on hearing.

Abstract: Impulse noise is a peculiar type of noise that retains its separate status, both as a physical phenomenon and as an adverse influence exerted upon human recipients. The ongoing research and numerous experiments with animals and industrial populations have not yet fully explained its nature. There are no clear-cut standards of measurement procedures, an impulse evaluation, and no admissible intensity levels. A comprehensive review of both Polish and foreign literature on this subject shows that the following features have the most traumatizing effect on the hearing organs: peak value, impulse duration rate, spectrum composition, repetition frequency, equivalent energy level, and a total number of impulses.

Compatible analog coding of television signals for correction of transmission burst errors: a computer evaluation

Abstract: Methods for encoding a TV signal in analog or digital formats in such a manner that bursts of impulse errors can be corrected are described. The procedure is insensitive to ghosts and other horizontal processing, and can be applied to composite signals prior to operations such as ghost removal, separation of chrominance and luminance, motion estimation, and scan conversion; thereby, these latter algorithms and the image viewing quality are enhanced by burst error correction. Redundant lines, transmitted during vertical retrace, are added to each field in a TV signal. As few as two lines need be added, amounting to 0.76% redundancy, and they can be computed by the addition and subtraction of field lines, a special case of vertical (comb) filtering. The predicted performance in the presence of background and impulse noise is good, and is verified by computations on NTSC fields. >

Noise levels and hearing protection devices: effect on student welding performance

Abstract: Recent researchers have shown that high levels of background noise have a detrimental effect on students’ abilities to perform learning tasks. Daniels (1985), Jewell (1977, 1978), and HambrickDixon found that high noise levels produced a detrimental effect on students’ abilities to perform cognitive or psychomotor skills. Jewel1 (1977, 1978) also discovered that students exposed to higher levels of sound required more time to complete assigned tasks. Another area of concern is the effect of impact or impulse noise. Research has shown that sudden impact noise (such as welding metal dropped on a concrete floor) or impulse noise (a grinding wheel intermittently coming in contact with steel) can cause actual damage to parts of the inner ear (Bohne, 1976; Luz & Hodge, 1971). Depending on the decibel level, impact or impulse noise levels can cause temporary loss of hearing activity or even result in damage that is permanent. The use of hearing protective devices (HPD’s) has been established as a sound practice to reduce the negative effect of loud noise on students’ performance levels (Feldman and Grimes, 1985; Hartley, 1974; Miller, 1986). Experimental research (Miller, 1986) has shown that HPD’s areeffective in maintaining higher levels of student performance when completing learning activities under noisy conditions. Standard maximum levels of noise exposure have been established by the Occupational Safety and Health Administration (OSHA, 1981). The maximum exposure levels and time periods during a working day without hearing protection are shown in Table 1. More recent federal regulations (OSHA, 1981) are imposing a maximum eight hour exposure limit of 85 decibels as the point where employers are required to monitor noise levels, notify employees, and recommend use of HPD’s. At noise levels of 90 decibels and above, employees are required to use HPD’s. Table 1 Permissible Exposure Time by Intensitv of Sound Pressure Level in Decibels (dBA)

Detail-preserving impulse noise removal of images using modified dynamic programming

Abstract: An algorithm that removes impulse noise in images using a modified dynamic programming method is outlined. The restoration process combines two operations. In the first operation, the pixels corrupted by impulse noise are detected by a dynamic programming based searching strategy. In the second operation, the original gray levels of the noisy pixels are estimated by a linear interpolation or extrapolation approach. A separable process is used to detect the noisy pixels of the images. In order to preserve the details of the images and reduce the computational complexity of conventional dynamic programming, two modifications have been developed. One is called neighborhood searching with an adaptive figure of merit and the other is called overlapping block processing. The actual performance of the proposed technique is compared with that of the commonly used median filter by filtering noise-corrupted images. Some computational considerations are also discussed. >

Pulse noise removing circuit

Abstract: PURPOSE: To interpolate an impulse noise part and to remove impulse noise by providing a switching circuit to select a demodulated input signal side when a pulse noise detection circuit does not detect pulse noise and to select a luminance component before or after one horizontal period to be outputted from a low-pass filter when the pulse noise is detected. CONSTITUTION: When a switching signal is not supplied from a noise detection circuit 1, a switching circuit 4 connects a terminal 4a and a common terminal 4c, selects an NTSC signal to be outputted from a demodulator and supplies this signal as the NTSC signal to a next-step circuit. When the switching signal is supplied from the noise detection circuit 1, the switching circuit 4 connects a terminal 4b and the common terminal 4c, selects a luminance signal to be outputted from a filter 3, namely, selects a luminance component included in the NTSC signal before one horizontal period and supplies this as the NTSC signal to the next-step circuit. Thus, the signal of an impulse noise part P is interpolated by the luminance component extracted from the NTSC signal before one horizontal period. COPYRIGHT: (C)1992,JPO&Japio

Instantaneous CFAR algorithm (spread spectrum receivers)

Abstract: For practical realizations of spread-spectrum receivers, automatic threshold level control (ATLC) in synchronization schemes is crucial. A novel ATLC system is described and analyzed. The system uses a fixed threshold which provides a constant false alarm rate (CFAR) independent of signal to noise ratio variations that may be generated due to impulse noise. The in sync./out of sync. decision variable is formed by using the ratio of the correlation functions of the input signal and two mutually delayed pseudo-noise sequences. Numerical results of the system performance analysis are presented and discussed. >

Measuring apparatus of urban noise

Abstract: PURPOSE:To enable measurement of the frequency of generation of impulse noise and the time distribution thereof by measuring the number of times of generation of the impulse noise within each observation time period by a counter. CONSTITUTION:The amplitude of a received noise signal received through an antenna 1 for detecting a noise field is sampled by a sampling circuit 14 and the maximum value of a sample value output from the circuit 14 is held in a maximum hold circuit 15. Besides, the received noise signal is supplied from an amplifier circuit 23 to a counting circuit 25 of a counter circuit 26 and the arrival impulse of the received noise signal is counted by the circuit 25. The maximum sample value held in the circuit 15 and a count value in the circuit 26 are read in a statistical computation processing circuit 16 at each prescribed time by an observation time clock source 19, the contents of the circuit 15 and the circuit 25 are set by the clock source 19, and a time-to-noise field intensity, the number of times of time-to-noise pulse generation, a time rate-to-noise field intensity and the number of times of time rate-to-noise pulse generation are culculated from the maximum sample value and the count value read by the processing circuit 16.

Basic Image Filtering Operations

Abstract: This chapter discusses the basic image filtering operations. The idea is to locate those pixels in the image that have extreme and, therefore, highly improbable intensities and to ignore their actual intensities, replacing them with more suitable values. This is akin to drawing a graph through a set of plots and ignoring those plots that are evidently a long way from the best fit curve. To develop this technique, it is necessary to examine the local intensity distribution within a particular neighborhood. Points at the extremes of the distribution are quite likely to have arisen from impulse noise. Not only is it sensible to eliminate these points, as in the limit filter, but it is also reasonable to try taking the process further, removing equal areas at either end of the distribution and ending with the median. Having considered the mean and the median of the local intensity distribution as candidate intensity values for noise smoothing filters, it also seems relevant to consider the mode of the distribution.

Maximum likelihood decoder

Abstract: PURPOSE:To attain a low bit error rate by detecting an impulse noise having a long amplitude by suppressing its pass likelihood at the time of receiving this impulse noise. CONSTITUTION:A likelihood correcting part 13-1 is placed between a maximum value selecting part 21-1 and a pass memory selecting part 22, and a maximum value Pj of outputs P1 to PM of results of a pass likelihood calculating part 20-1 of a state 1 is inputted to an impulse noise detecting part 11-1, which discriminates whether this maximum value has an extent due to the impulse noise or not, and a discrimination result C and the value Pj are inputted to a likelihood suppressing part 12-1 to obtain an output Pj . The impulse noise detecting part 11-1 compares the output Pj with a preliminarily given threshold value theta to output the discrimination result C. The likelihood suppressing part 12-1 suppresses the likelihood in the case of C=1 but outputs the output Pj as it is in case of C=0. Thus, the bit error rate is reduced.

A comparison of hearing losses in the workers of a shipyard and in loggers in relation to individual risk factors

Abstract: It is suggested that, within the same energy level, an impulse noise is more hazardous to hearing than a permanent noise. To justify this hypothesis, a study was performed with groups of wood-cutters and shipyard workers to investigate different characteristics of noise load (noise levels, noise impulsivity from the outside and under the ear-flaps, noise emission levels with regard to the length of work and using ear-flaps), and hearing losses (both real and forecasted on the Robinson model). To avoid individual factors, a computerized assessment of 38 pairs of workers from both teams was performed (with regard to similar noise emission levels, diastolic pressures, smoking habits, their military service backgrounds as to the service in heavy artillery units, absence of otic diseases, low consumption of salicylates). The results showed that, within the same energy level, the noise in the shipyard was three times as impulsive and more otic disorders inducing than the noise in the wood-cutters' working conditions.

Applications of Neural Networks in Video Signal Processing

Abstract: Although color TV is an established technology, there are a number of longstanding problems for which neural networks may be suited. Impulse noise is such a problem, and a modular neural network approach is presented in this paper. The training and analysis was done on conventional computers, while real-time simulations were performed on a massively parallel computer called the Princeton Engine. The network approach was compared to a conventional alternative, a median filter. Real-time simulations and quantitative analysis demonstrated the technical superiority of the neural system. Ongoing work is investigating the complexity and cost of implementing this system in hardware.

Signal processing for a spectrum efficient single channel digital radio system

Abstract: A modem design for single-channel (64-kb/s) point-to-point digital radio applications is presented and discussed. Emphasis is placed on a number of dedicated techniques and algorithms adopted to treat all the problems peculiar to single-channel spectrum-efficient transmission. A number of problems concerning Gaussian and impulse noise, both influencing a very-low-capacity radio system which adopts multilevel quadrature amplitude modulation (QAM) and coherent demodulation, are investigated. Viable solutions are found using complex baseband signal processing for modulation and demodulation. The extensive use of software-programmable digital signal processors (DSPs), already adopted on telephone channel modems, is demonstrated to be an optimum solution for radio applications also. Advantages in terms of design flexibility, compactness, and performance are obtained mainly when a very high bandwidth efficiency is required. Some preliminary experimental results are presented. >

Analysis of impulse noise immunity standards

Abstract: It is pointed out that international and national impulse immunity standards provide for different test procedures, pulse parameters, and output impedances of the simulators. Studies of pulse generation in electrical systems, and of equipment susceptibility and pulse noise simulation show that the calibration of test pulses on open circuits is more adequate to real noise in mains. The output impedance of simulators for shipboard equipment testing must be close to 10 Omega , paralleled by 10 mu H. It is noted that energy and pulse duration are important for withstand testing. >

Determination of occupational noise exposure limits for very high intensity impulses when hearing protection is used

Abstract: The U.S. Army needs validation of safe limits for exposure to impulse noise produced by heavy weapons. Current impulse noise limits are based on data from small arms. Recent studies indicate these standards may be overly conservative. In order to define new limits, a systematic study of the effects of high‐intensity impulse noise on human volunteers is underway. The number of impulses, the peak pressure level, and spectral distribution of energy are being varied systematically. Four groups of at least 60 volunteers will be given a series of exposures to one of four impulse types. The impulse spectrum is varied by changing the distance between the volunteer and an explosive detonation. The peak pressure level is varied in 3‐dB steps by changing the weight of the explosive charge. The number of impulses is 6, 12, 25, 50, or 100. Volunteers wear hearing protection for all exposures. After each exposure, TTS is determined. Each volunteer starts with an exposure of six impulses at the lowest intensity. If the ...

A new class of median/mean based filters

Abstract: A new class of nonlinear filters which combines the thresholding operation with a median or mean filter is introduced. A simple but robust method to generate thresholds is proposed. Based on it, the new filters are analyzed for their white noise attenuation and abilities to eliminate impulse noise and preserve edges. Results are compared to those of the median, FIR median hybrid (FMH), and mean filters, showing several advantages of the new filters. >

Impulse eliminating device for digital signal

Abstract: PURPOSE:To suppress the occurrence of impulse noise by monitoring the change of the dynamic range of an A signal and the state of a D signal and substituting erroneous demodulated data with specific data when the A signal is demodulated with the error crossing over a phase gap. CONSTITUTION:A coarsely quantized level signal (D signal) of a sample of a transmission signal and the other high-precision signal (A signal) are subjected to phase modulation. The A signal outputted from a gap eliminating circuit 29 is inputted to a subtractor 11, and the output of the subtractor 11 is inputted to a comparator 12. When a pulse P1 is outputted from the comparator 12, an exclusive NOR circuit 15 operates exclusive NOR between the output of a delay circuit 13 and the input D signal; and when both inputs have the same level, a pulse P2 is obtained from an AND circuit 13 and an impulse noise part is substituted with specific data. Thus, the occurrence of impulse noise caused by demodulating the A signal with the error crossing over the phase gap is suppressed.

Noise gate circuit

Abstract: PURPOSE:To remove impulse noise having periods longer than set time for limiting the re-trigger of a re-triggerable multivibrator by appropriately setting the set time. CONSTITUTION:This noise gate circuit is constituted of a receiving section 1 for receiving signals, target detecting section 2 for detecting a target signal, navigating section 3 which navigates an under-water navigating body by means of the target signal, and noise gate circuit 4 which remove a noise component. The circuit 4 is composed of a signal comparator 41, which controlling section 42, and switch 43, which are the constituents of a circuit for removing impulse noise having period longer than set time tau1. The switch 44 makes a turning off operation when a control signal 14 is high in level and turning on operation when the signal 14 is low in level. Therefore, the output signal of the circuit becomes a signal from which impulse noise is removed. The output signal is inputted to the target detecting section 2 and pulse signals corresponding to signals higher than a fixed level can be outputted as target detect signals 16.

Noise eliminating circuit for reproducing device

Abstract: PURPOSE:To eliminate an impulse noise mixed into a regenerative signal, and to prevent a malfunction and defective reproduction by providing a special noise eliminating circuit including a diode. CONSTITUTION:A voltage Vcc is applied between an amplifying buffer circuit 4 and a ground, and the circuit 4 is power-energized, the inputted regenerative signal is amplified and outputted, and the signal is applied to a noise eliminating circuit 6. Between an output line 14 of the regenerative signal and a means 12 to output a reference level fixed beforehand, diodes D1 and D2 having a forward directional voltage drop slightly larger than the amplitude of the regenerative signal are connected mutually in parallel and mutually in a reverse direction. Thus, the noise mixed into the regenerative signal is eliminated, and the defective reproduction and the malfunction of the reproducing operation are prevented.

Compatible analog coding of television signals for correction of

Abstract: Methods for encoding a TV signal in new and existing, analog or digital formats in such a manner that bursts of impulse errors can be corrected are described. The procedure is insensitive to ghosts and other horizontal processing and can be applied to composite signals prior to operations such as ghost removal, separation of chrominance and luminance, motion estimation, and scan conversion; thereby, these latter algorithms as well as the image viewing quality are enhanced by burst error correction. Redundant lines, transmitted during vertical retrace, are added to each field in a TV signal. As few as two lines need be added, amounting to -76% redundancy, and they can be computed by the addition and subtraction of field lines, a special case of vertical (comb) filtering. The predicted performance in the presence of background as well as impulse noise is good and is verified by computations on NTSC fields, performed on SUN workstations.