Showing papers on "Impulse noise published in 2003"

Selective removal of impulse noise based on homogeneity level information

Abstract: We propose a decision-based, signal-adaptive median filtering algorithm for removal of impulse noise. Our algorithm achieves accurate noise detection and high SNR measures without smearing the fine details and edges in the image. The notion of homogeneity level is defined for pixel values based on their global and local statistical properties. The cooccurrence matrix technique is used to represent the correlations between a pixel and its neighbors, and to derive the upper and lower bound of the homogeneity level. Noise detection is performed at two stages: noise candidates are first selected using the homogeneity level, and then a refining process follows to eliminate false detections. The noise detection scheme does not use a quantitative decision measure, but uses qualitative structural information, and it is not subject to burdensome computations for optimization of the threshold values. Empirical results indicate that our scheme performs significantly better than other median filters, in terms of noise suppression and detail preservation.

Impulsive noise suppression in OFDM-based communication systems

Abstract: Orthogonal frequency division multiplexing (OFDM) is a technique used for terrestrial digital video broadcasting (DVB-T) and many other modern applications. The longer OFDM symbol duration provides an advantage in a presence of weak impulsive noise, because impulsive noise energy is spread among simultaneously transmitted OFDM sub-carriers. However, it has been recently recognized that this advantage turns into a disadvantage if the impulsive noise energy exceeds certain threshold. In this paper the algorithm for impulsive noise suppression in OFDM receivers is proposed and investigated. Whereas traditional methods for impulsive noise suppression are implemented in a time domain before OFDM demodulation, proposed algorithm compensates impulsive noise in a frequency domain after OFDM demodulation and channel equalization. The method is applied to DVB-T and its performance is studied by means of simulation.

Advanced signal processing for power line communications

Abstract: In this article, signal processing techniques to combat the adverse communications environment on power lines are addressed, so as to enable reliable high speed data communications over low-voltage power distribution networks for Internet access and in-home/office networking. It is seen that multicarrier code-division multiple access, multiuser detection, and turbo decoding, having demonstrated their limit-approaching capacity in DSL and wireless communication systems, are readily applied to power line communications. In particular, it is argued that these methods can successfully mitigate the influence of the principal impairments in PLC channels: time-varying channel attenuation, multipath frequency-selective fading, multiple access interference, and background noise. Strategies to deal with the most unfavorable noise source, the impulse noise, are also discussed.

Robust L-estimation based forms of signal transforms and time-frequency representations

Abstract: The L-estimation based signal transforms and time-frequency (TF) representations are introduced by considering the corresponding minimization problems in the Huber (1981, 1998) estimation theory. The standard signal transforms follow as the maximum likelihood solutions for the Gaussian additive noise environment. For signals corrupted by an impulse noise, the median-based transforms produce robust estimates of the non-noisy signal transforms. When the input noise is a mixture of Gaussian and impulse noise, the L-estimation-based signal transforms can outperform other estimates. In quadratic and higher order TF analysis, the resulting noise is inherently a mixture of the Gaussian input noise and an impulse noise component. In this case, the L-estimation-based signal representations can produce the best results. These transforms and TF representations give the standard and the median-based forms as special cases. A procedure for parameter selection in the L-estimation is proposed. The theory is illustrated and checked numerically.

Impulse noise and risk criteria.

Abstract: Impulse noise causes evidently more severe hearing loss than steady state noise. The additional effect of occupational impulse noise on hearing has been shown to be from 5 to 12 dB at 4 kHz audiometric frequency. Reported cases for compensated for hearing loss are prevalent in occupations where noise is impulsive. For impulse noise two measurement methods have been proposed: the peak level method and energy evaluation method. The applicability of the peak level method is difficult as even the recurrent impulses have different time and frequency characteristics. Various national risk criteria differ from international risk criteria. In France the maximum A-weighted peak level is 135 dB, and in the United Kingdom the C-weighted peak sound pressure is limited to 200 Pa (140 dB). This criterion of unweighted 200 Pa (140 dB) is used in European Union (EU) directive 86/188 and ISO 1999-1990 regardless of the number of impulses. The American Conference of Governmental Industrial Hygienists (ACGIH) has recommended that no exposure in excess of a C-weighted peak sound pressure level of 140 dB should be permitted. At work places these norms do not cause any practical consequences since the impulses seldom exceed 140 dB peak level. In several occupations the impulses are so rapid that they contribute only a minimal amount to the energy content of noise. These impulses can damage the inner ear even though they cause reduced awareness of the hazard of noise. Based to the present knowledge it is evident that there is the inadequacy of the equal energy principle in modelling the risk for hearing loss. The hearing protectors attenuate industrial impulse noise effectively due to the high frequency contents of impulses. Directive regarding the exposure of workers to the risks arising from noise requires that in risk assessment attention should be paid also to impulsive noise. So far there is no valid method to combine steady state and impulse noise. A statistical method for the measurements of industrial impulse noise is needed to get a preferably single number for risk assessment. There is an urgent task to develop risk assessment method and risk criteria for impulsive noise to meet the requirements of the upcoming European Union noise directive.

Efficient Removal of Impulse Noise from Highly Corrupted Digital Images by a Simple Neuro-Fuzzy Operator

Abstract: A new neuro-fuzzy operator for removing impulse noise from highly corrupted digital images is presented. The proposed operator is very simple and comprises two identical neuro-fuzzy filters combined with a postprocessor. The internal parameters of the filters are adaptively adjusted by training. Training of the filters is easily accomplished by using a simple computer generated artificial image. The fundamental advantage of the proposed operator over other operators is that it offers superior noise removal performance while at the same time efficiently preserving details and texture in the noisy input image. Experiments prove that the proposed operator may be used for efficient removal of impulse noise from highly corrupted images without distorting the useful information in the image.

Method and system for receiving a multi-carrier signal

Abstract: Method and system for tolerating impulsive burst noise in pilot based OFDM systems, especially using DVB-T standard. The method contains following steps: 1) recognition of the impulse position and possibly length in the time domain symbol, 2) blanking of those samples of the symbol where significant amount of impulse noise is present, 3) calculating the first estimate of the received signal from the blanked symbol, 4) using a prior information (guard band carriers, pilot carriers) an estimate of the blanked symbol is calculated using inverse FFT on the differences of the observed carrier values from the known values in the frequency domain, 5) correction values for the frequency domain carriers are derived taking the FFT of the restored time domain samples, 6) finally the corrected estimate of the received symbol is derived by summing the correction values of step 5 to the first estimate of carriers derived in step 3. The method allows correction of relatively long bursts of impulse noise with minor degradation. The method provides considerably reliable data reception in broadcast systems.

Fuzzy Filters for Noise Reduction in Images

Abstract: In this chapter, seven fuzzy filters for noise reduction in images are introduced. These seven fuzzy filters include the Gaussian fuzzy filter with median center (GMED), the symmetrical triangular fuzzy filter with median center (TMED), the asymmetrical triangular fuzzy filter with median center (ATMED), the Gaussian fuzzy filter with moving average center (GMAV), the symmetrical triangular fuzzy filter with moving average center (TMAV), the asymmetrical triangular fuzzy filter with moving average center (ATMAV), and the decreasing weight fuzzy filter with moving average center (DWMAV). Each of these fuzzy filters, applies a weighted membership function to an image within a window to determine the center pixel, is easy and fast to implement. Simulation results on the filtering performance of these seven fuzzy filters and the standard median filter (MED) and moving average filter (MAV) on images contaminated with low, medium, high impulse and random noises are presented. Results indicate that these seven fuzzy filters achieve varying successes in noise reduction in images as compared to the standard MED and MAV filters.

Real-time Image Noise Cancellation Based on Fuzzy Similarity

Abstract: We propose a new filter structure for the reduction of mixed noise in images. It is based on the evaluation of fuzzy similarities between pixels in a local processing window and is suitable for high-speed hardware implementation. The filter involves two tunable parameters and is fairly robust against changes in noise distribution. Furthermore, we outline a modular hardware architecture for general high-speed image processing tasks.

Iterative median filtering for restoration of images with impulsive noise

Abstract: Iterative median filtering for restoration of images corrupted by impulsive noise is considered. A modified version of median filtering that can be also applied iteratively is also proposed. The methods are compared with an iterative method suggested by Marvasti for images with high pixel loss. The results show that applying the median filter iteratively results in well sighted resulting images. Moreover, despite the implementation simplicity, the proposed modified median filtering scheme provides a considerably higher convergence speed which intends a lower numerical complexity.

Excess noise generation during spectral broadening in a microstructured fiber

Abstract: We observe that nanojoule femtosecond pulses that are spectrally broadened in a microstructured fiber acquire excess noise. The excess noise is manifested as an increase in the noise floor of the rf spectrum of the photocurrent from a photodetector illuminated by the pulse train from the laser oscillator. Measurements are made of the intensity dependence of the excess noise for both 100 fs and sub-10 fs pulses. The excess noise is very strong for 100 fs pulses, but barely measurable for sub-10 fs pulses. A rigorous quantum treatment of the nonlinear propagation of ultrashort pulses predicts that, for a fixed generated bandwidth, the amount of excess noise decreases with pulse duration, in agreement with the experimental results.

Median cascaded canceller for robust adaptive array processing

Abstract: A median cascaded canceller (MCC) is introduced as a robust multichannel adaptive array processor. Compared with sample matrix inversion (SMI) methods, it is shown to significantly reduce the deleterious effects of impulsive noise spikes (outliers) on convergence performance of metrics; such as (normalized) output residue power and signal to interference-plus-noise ratio (SINR). For the case of no outliers, the MCC convergence performance remains commensurate with SMI methods for several practical interference scenarios. It is shown that the MCC offers natural protection against desired signal (target) cancellation when weight training data contains strong target components. In addition, results are shown for a high-fidelity, simulated, barrage jamming and nonhomogenous clutter environment. Here the MCC is used in a space-time adaptive processing (STAP) configuration for airborne radar interference mitigation. Results indicate the MCC produces a marked SINR performance improvement over SMI methods.

Fuzzy filters for noisy image filtering

Abstract: In this paper, seven fuzzy filters for noise reduction in images are introduced. Each of these fuzzy filters applies a weighted membership function to an image within a window to determine the center pixel, and is easy and fast to implement. Simulation results on the filtering performance of these seven fuzzy filters, the standard median filter (MED), and the standard moving average filter (MAV) on images contaminated with low, medium and high impulse and random noise are presented. Results indicate that these seven fuzzy filters achieve varying success in noise reduction in images as compared to the MED and MAV filters.

Impulse burst position detection and channel estimation schemes for OFDM systems

Abstract: A new method for compensating the effects of impulse noise in OFDM systems has been presented by Rinne, Henriksson and Hazmi (see Proc. 7th International OFDM Workshop, Hamburg. Germany, p.183-187, Sept. 2002). It is shown that in the AWGN case, the method can effectively cancel the impulse noise. However in the time-frequency selective channel further measures are needed. The purpose of this paper is to present an enhanced channel estimation scheme for the standard method to overcome its sensitivity to the time frequency selective channel estimates. The scheme uses the impulse free pilots to estimate the corrupted ones. Three different alternatives are discussed. Their performances in mean squared error (MSE) versus Doppler frequency are studied analytically. Bit error rate ratio (BER) simulations results are given, in the cases of SFN hilly terrain static and mobile channels. Additionally, results on simple practical impulse burst position detection method are also presented.

A new kind of impulse noise filter based on PCNN

Abstract: Median filter can inhibit the impulse noise in the image, but it always erodes or dilates the edges of images. H.S. Ranganath mentioned that impulse noise could be removed through modifying the intensity of those contaminated pixels step by step using PCNN. Obviusly, this method consumes much more time in computation. Combining the PCNN model with the median filter, this paper presents an impulse noise filter based on a simplified PCNN model which has less parameters. Not only can it remove the impulse noise effectively, but it also keeps the details of the images as much as possible. It can be verified through experiments and theoretical analysis that this kind of filter is superior to the normal median filter and the filter mentioned by H.S. Ranganath, whether in the aspect of noise removal or of keeping details.

Impulsive noise on indoor power lines: characterization and mitigation of its effect on PLC systems

Abstract: Intensive measurements of impulsive noise have been carried out on indoor power lines. From this approach, various types of transients are classified and a stochastic noise model is deduced from the statistical analysis of their main characteristics. A power line communication, based on an OFDM transmission scheme is simulated and, owing to the noise model, different channel coding schemes are tested and optimized to cope with the disturbing effect of this non stationary noise

Analysis of the impact of impulse noise in digital subscriber line systems

Abstract: In recent years, Digital subscriber line (DSL) technology has been gaining popularity as a high speed network access technology, capable of the delivery of multimedia services. A major impairment for DSL is impulse noise in the telephone line. However, evaluating the data errors caused by this noise is not trivial due to its complex statistical nature, which until recently had not been well understood, and the complicated error mitigation and framing techniques used in DSL systems. This thesis presents a novel analysis of the impact of impulse noise and the DSL framing parameters on transmission errors, building on a recently proposed impulse noise model. It focuses on errors at higher protocol layers, such as asynchronous transfer mode (ATM), in the most widely used DSL version, namely Asymmetric DSL (ADSL). The impulse noise is characterised statistically through its amplitudes, duration, inter-arrival times, and frequency spectrum, using the British Telecom / University of Edinburgh / Deutsche Telekom (BT/UE/DT) model. This model is broadband, considers both the time and the frequency domains, and accounts for the impulse clustering. It is based on recent measurements in two different telephone networks (the UK and Germany) and therefore is the most complete model available to date and suited for DSL analysis. A new statistical analysis of impulse noise spectra from DT measurements shows that impulse spectra can be modelled with three spectral components with similar bandwidth statistical distributions. Also, a novel distribution of the impulse powers is derived from the impulse amplitude statistics. The performance of a generic ADSL modem is investigated in an impulse noise and crosstalk environment for different bit rates and framing parameters. ATM cell and ADSL frame error rates, and subjective MPEG2 video quality are used as performance metrics. A new modification of a bit loading algorithm is developed to enable stable convergence of the algorithm with trellis coding and restricted subtone constellation size. It is shown that while interleaving brings improvement if set at its maximum depth, at intermediate depths it actually worsens the performance of all considered metrics in comparison with no interleaving. No such performance degradation is caused by combining several symbols in a forward error correction (FEC) codeword, but this burst error mitigation technique is only viable at low bit rates. Performance improvement can also be achieved by increasing the strength of FEC, especially if combined with interleaving. In contrast, trellis coding is ineffective against the long impulse noise error bursts. Alien as opposed to kindred crosstalk degrades the error rates and this is an important issue in an unbundled network environment. It is also argued that error free data units is a better performance measure from a user perspective than the commonly used error free seconds. The impact of impulse noise on the errors in DSL systems has also been considered analytically. A new Bernoulli-Weibull impulse noise model at symbol level is proposed and it is shown that other models which assume Gaussian distributed impulse amplitudes or Rayleigh distributed impulse powers give overly optimistic error estimates in DSL systems. A novel bivariate extension of the Weibull impulse amplitudes is introduced to enable the analysis of orthogonal signals. Since an exact closed-form expression for the symbol error probability of multi-carrier QAM assuming Bernoulli-Weibull noise model does not exist, this problem has been solved numerically. Multi-carrier QAM is shown to perform better at high signal-to-noise ratio (SNR), but worse at low SNR than single carrier QAM, in both cases because of the spreading of noise power between subcarriers. Analytical expressions for errors up to frame level in the specific case of ADSL are then derived from the impulse noise model, with good agreement with simulation results. The Bernoulli-Weibull model is applied to study the errors in single-pair highspeed DSL (SHDSL). The performance of ADSL is found to be better when the burst error mitigation techniques are used, but SHDSL has advantages if low bit error rate and low latency are required. Declaration of originality I hereby declare that the research recorded in this thesis and the thesis itself was composed and originated entirely by myself in the School of Engineering and Electronics at The University of Edinburgh. The software used to perform the simulations was written by myself with the following exceptions: The routines in the ADSL simulation performing interleaving/deinterleaving, RS coding/decoding, and finding the root of a function are modified versions of code written by Dr. David I. Laurenson.

A byte-erasure method for improved impulse immunity in DSL systems using soft information from an inner code

Abstract: A significant portion of the end-to-end delay in high-rate DSL systems is due to the impulse noise protection scheme employed in order to shield those systems against random, non-stationary noise bursts of high energy that appear on the copper lines. Systems are protected from impulse noise using a combination of interleaving and Reed-Solomon codes. In order to lower the end-to-end delay without reducing the data rate that is available to the user, one needs to decrease the interleaver depth. This paper presents a way to achieve this reduction without compromising neither the robustness to noise bursts nor the data rate of the system. The proposed algorithm relies on the inner code used by many DSL systems and uses the metric provided by the inner code decoder at the receiver. A DMT-VDSL system is used as a particular example of the achieved reduction of the end-to-end delay.

Vector median filter for removal of impulse noise from color images

Abstract: This paper presents a vector median filter that incorporates mechanism for the detection of impulses from color images. The vector pixels in a specified window is ranked on the basis of sum of the distances to other vector pixels in the window. The center vector pixel is declared as corrupted if its rank is bigger than a predefined rank and its distance from a nearby healthy vector pixel is bigger than a pre-defined threshold. The corrupted vector pixel is replaced by the vector median. The experimental results show the better performance of the proposed method than a number of existing schemes for color images corrupted by high percentage of fixed-valued and random-valued impulse noises.

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.

Generalized adaptive vector sigma filters

Abstract: In this paper we provide a new filtering scheme for the detection and the removal of impulsive noise in digital color images. The proposed adaptive nonlinear vector filters take the advantages of the robust order-statistic theory, generalized directional distance filter and standard sigma filter concept. The principles of the design are explained in detail. Simulation studies indicate that the proposed method is computationally attractive and is able to achieve excellent balance between the image-detail preservation and the noise attenuation.

Peer region determination based impulsive noise detection

Abstract: A peer region determination (PRD) algorithm for impulsive noise detection in digital images is proposed; it removes random-valued impulsive noise while preserving very fine image details. This algorithm determines the peer region for each pixel adaptively by finding the variation of pixel values in a 5/spl times/5 filter window. If the number of member pixels in the peer region is very small, the pixel being processed is thought to be isolated from other pixels and thus considered as impulsive noise. In addition, this noise detector can be easily modified to perform feature selective filtering. Experimental results show that the proposed noise detection algorithm outperforms other existing non-linear filters and adaptive noise detection based filters in noise removal and image detail preservation. Finally, the concept of the PRD algorithm applied to other image processing applications is discussed.

A square distance-based byte-erasure method for reduced-delay protection of DSL systems from non-stationary interference

Abstract: DSL systems achieve high rate transmission through copper pairs traditionally used for voiceband communication In order to attain high rates, sophisticated system designs are employed to cope with both stationary and non-stationary disturbers In current DSL systems, protection against nonstationary interference, comprising impulse noise and radio frequency ingress (RFI), is achieved using a forward error correction (FEC) scheme consisting of a Reed-Solomon (RS) code and interleaving However, interleaving results in increased end-to-end delay The end-to-end delay can be reduced by taking advantage of the erasure decoding property of RS codes The paper presents a byte-erasure technique that allows erasure decoding to be employed The method locates the possibly erroneous bytes in each RS codeword by comparing the square distance between each received carrier symbol of the interleaved stream and the closest point of the constellation to which the symbol belongs Thus, the interleaving delay can be reduced by a factor up to 2 when impulse noise impairs transmission The method can also be applied to systems affected by both impulse noise and RFI, since it can distinguish between the two sources of non-stationary interference Finally, no change is required at the transmitter, and hence compatibility with currently deployed systems is guaranteed A DMT-VDSL system is used as a particular example of the achieved reduction of the interleaving delay

A normalized mixed-norm adaptive filtering algorithm robust under impulsive noise interference

Abstract: A normalized robust mixed-norm (NRMN) algorithm for system identification in the presence of impulsive noise is introduced. The standard robust mixed-norm (RMN) algorithm, despite its ability to cope with impulsive noise by virtue of combining the first and second error norm in the cost function it minimizes, exhibits slow convergence, requires a stationary operating environment, and employs a constant step-size which needs to be determined a-priori. To overcome these limitations, the proposed NRMN algorithm introduces a time varying learning rate which is derived based upon the dynamics of the input signal, and thus no longer requires a stationary environment, a major drawback of the RMN algorithm. The normalized step-size is bounded from above and a parameter is introduced within its upper-bound, which provides a trade-off between the convergence rate and the steady-state coefficient error. The analysis and experimental results show that the proposed NRMN exhibits increased convergence rate and substantially reduces the steady-state coefficient error, as compared to the least absolute deviation (LAD) and RMN algorithms.

A hybrid filter for the cancellation of mixed Gaussian noise and impulse noise

Abstract: A hybrid filter for mixed noise cancellation is introduced in this paper. The proposed approach combines the advantages of the improved adaptive Wiener filter and bilinear interpolation filter, which can efficiently reduce both the white Gaussian noise and impulse noise. To select the corresponding filters with respect to the noise types, a novel method for impulse noise detection is also designed. Experimental and comparison results show that the proposed approach is particularly effective in removing the mixed Gaussian and impulse noises even with the severe contamination.

An LMS adaptive equalizer using threshold in impulse noise environments

Abstract: The paper proposes a threshold algorithm for channel equalization in impulse noise environments The variance of the received signal is calculated and used as the threshold for the LMS algorithm The proposed algorithm makes filtering systems robust to impulse noise By computer simulations, it is shown that the proposed algorithm is effectively used as the adaptation scheme for a linear transversal equalizer

A simple byte-erasure method for improved impulse immunity in DSL

Abstract: The data that is transmitted in DSL system is subject to corruption by impulse noise, i.e., noise bursts of high energy that interfere with the transmitted symbols. As DSL data rates increase the crosstalk mitigation techniques become more sophisticated, impulse noise limits service in terms of rate or delay. Because of the highly non-stationary nature of impulse noise, a combination of interleaving and Reed-Solomon coding is currently used to shield systems from noise burst. This paper presents a modified impulse noise protection algorithm that takes advantage of the improved performance of Reed-Solomon codes when the location of the impaired bytes is known. Without changing the structure of the encoder or the interleaver, it is shown that the delay, or equivalently the overhead due to forward error correction coding, can be reduced without compromising the immunity of the system to impulses. A DMT-VDSL system is used as a particular example of the improvement achieved using byte-erasure.