Impulse noise

About: Impulse noise is a research topic. Over the lifetime, 4816 publications have been published within this topic receiving 63970 citations.

Quaternion-based color image filtering for impulsive noise suppression

Abstract: It is difficult to precisely detect all impulsive noise in color images due to the nonstationarity caused by edges and fine details. For many pixels, we can not absolutely classify them as noisy or noise-free, but can only describe them using the likelihood that they are corrupted by impulsive noise. Based on this consideration, we present a new filtering solution to removing impulsive noise from color images. The proposed method first utilizes the unit transforms of quaternions to represent the chromaticity difference of two color pixels, and then divides the image into noise-free and possible noisy pixels. Finally it performs adaptive weighted vector median filtering operations on only the possible noisy pixels to suppress noise. The new weighting mechanism is based on a joint spatial/quaternion-chromaticity criterion, which ensures that pixels with different contamination likelihoods have different contributions to the filter's output. The extensive simulation results indicate that the proposed method significantly outperforms some other well-known multichannel filtering techniques.

Limitations of Using Dosimeters in Impulse Noise Environments

Abstract: The National Institute for Occupational Safety and Health (NIOSH) investigated the capabilities of noise dosimeters to measure personal exposure to impulse noise. The two leading types of commercially available dosimeters were evaluated in terms of their ability to measure and integrate impulses generated from gunfire during live-fire exercises at a law enforcement indoor firing range. Sound measurements were conducted throughout the firing range using dosimeters, sound level meters, and a measurement configuration that consisted of a quarter-inch microphone and a digital audiotape recorder to capture the impulse waveforms. Personal dosimetry was conducted on eight shooters, an observer, and the range master. Peak levels from gunfire reached 163 decibels (dB), exceeding the nominal input limit of the dosimeters. The dosimeters "clipped" the impulses by acting as if the gunfire had a maximum level of 146 dB. In other cases, however, peak levels (e.g., 108 dB) were below the dosimeter input limits, but the dosimeters still showed a peak level of 146 dB. Although NIOSH recommends that sound levels from 80 to 140 dB (A-weighted) be integrated in the calculation of dose and the time-weighted average, our present data suggest this criterion may be inadequate. These results showed that some instruments are incapable of providing accurate measures of impulse sounds because of their electroacoustic limitations.

Performance Analysis of Distributed Space–Time Block Coding Schemes in Middleton Class-A Noise

Abstract: A performance analysis of distributed space-time block coding (STBC) schemes involving multiple decode-and-forward relays is carried out in the case of Middleton class-A impulsive noise, which is one of the major sources of performance degradation in many wireless systems. The considered cooperative communication framework, according to which the signal transmitted by each relay is the product of an STBC matrix and a proper vector of length L, encompasses both centralized and decentralized protocols. Since an insightful theoretical analysis of the maximum-likelihood (ML) detector is very challenging in non-Gaussian environments, an ideal version of the ML detector, which is referred to as ideal ML (IML), is considered, along with the suboptimal minimum-distance (MD) detector. It is analytically proven that, with respect to Gaussian noise, the presence of impulsive noise does not affect the performance of both the IML and MD detectors in terms of asymptotic (i.e., when the transmit power is infinitely large) diversity order Rmax, which is equal to the minimum between L and the maximum number of cooperating nodes (relays plus source); in the case of the IML detector, the coding gain is also unaffected. Closed-form formulas involving the main parameters of noise and STBC highlight that the major effect of impulse noise on the performance of the IML and MD detectors concerns the finite signal-to-noise ratio (SNR) diversity order, which does not monotonously increase as the SNR rises; in the case of the MD detector, the coding gain is also affected by the impulsiveness of noise. In particular, it is shown that, in the case of complex orthogonal STBC, the adverse effect of impulse noise on the performance of the IML detector tends to completely disappear for sufficiently large values of Rmax, whereas increasing values of Rmax emphasize the weakness of the MD detector against non-Gaussian noise. Finally, simulation results are provided for the ML, IML, and MD detectors to corroborate and supplement the results theoretically derived.

Noise exposure assessment and abatement strategies at an indoor firing range.

Abstract: Exposure to hazardous impulse noise is common during the firing of weapons at indoor firing ranges. The aims of this study were to characterize the impulse noise environment at a law enforcement firing range; document the insufficiencies found at the range from a health and safety standpoint; and provide noise abatement recommendations to reduce the overall health hazard to the auditory system. Ten shooters conducted a typical live-fire exercise using three different weapons--the Beretta.40 caliber pistol, the Remington.308 caliber shotgun, and the M4.223 caliber assault rifle. Measurements were obtained at 12 different positions throughout the firing range and adjacent areas using dosimeters and sound level meters. Personal and area measurements were recorded to a digital audio tape (DAT) recorder for further spectral analysis. Peak pressure levels inside the firing range reached 163 decibels (dB) in peak pressure. Equivalent sound levels (Leq) ranged from 78 decibels, A-weighted (dBA), in office area adjacent to the range to 122 dBA inside the range. Noise reductions from wall structures ranged from 29-44 dB. Noise abatement strategies ranged from simple noise control measures (such as sealing construction joints and leaks) to elaborate design modifications to eliminate structural-borne sounds using acoustical treatments. Further studies are needed to better characterize the effects of firing weapons in enclosed spaces on hearing and health in general.

Performance of asymmetric digital subscriber lines in an impulse noise environment

Abstract: The paper presents a numerical study of the impact of impulse noise on asymmetric digital subscriber lines (ADSL). Methods for simulating the effect of impulse disturbances on a discrete multitone system are first presented, and actual measured noise bursts are then used for the simulations as if they were deterministic signals, in order to characterize their effects on ADSL systems. It is shown that, while a combination of coding, interleaving, and 6-dB margin is adequate in protecting ADSL systems from isolated impulses, an impulse train with long duration can cause a significant number of error bits in the system. In this case, a tradeoff among the number of error seconds, the maximum reach, and the coding delay must be made.