Showing papers on "Impulse noise published in 2002"

Analysis and modeling of impulsive noise in broad-band powerline communications

Abstract: Contrary to many other communication channels, the powerline channel does not represent an additive white Gaussian noise environment. In the frequency range from several hundred kilohertz up to 20 MHz, it is mostly dominated by narrow-band interference and impulsive noise. In particular, the impulsive noise introduces significant time variance into the powerline channel. Spectral analysis and time-domain analysis of impulsive noise give some figures of the power spectral density as well as distributions of amplitude, impulse width, and "interarrival" times in typical powerline scenarios. Furthermore, the impulse rate and the disturbance ratio of the scenarios are examined. Finally, a statistical model of the time behavior of random impulsive noise based on a partitioned Markov chain is developed, which is suitable for implementation in computer-based communication system simulations.

A new impulse detector for switching median filters

Abstract: A new impulse noise detection technique for switching median filters is presented, which is based on the minimum absolute value of four convolutions obtained using one-dimensional Laplacian operators. Extensive simulations show that the proposed filter provides better performance than many of the existing switching median filters with comparable computational complexity. In particular, the proposed filter is directed toward improved line preservation.

Classification and characterization of impulsive noise on indoor powerline used for data communications

Abstract: The performance of a link using the indoor power line network as a medium for communication strongly depends on the noise characteristics. Besides the background noise and the narrow band noise mainly due to broadcast transmitters, impulsive noise adversely affects the quality of service. This paper focuses on impulsive noise measurements, their statistical properties being the basis of a noise model for optimizing a transmission scheme.

Performance bounds for optimum and suboptimum reception under Class-A impulsive noise

Abstract: The transmission over the memoryless additive white Class-A noise (AWCN) channel is considered. For uncoded transmission, an exact expression for the symbol error rate is derived. For coded transmission, the Chernoff bound on the pairwise error probability is calculated and the performance achieved on the real and the complex AWCN channels is compared. Moreover, a low-complexity, suboptimum decoding metric is derived and analyzed employing the cutoff rate as a performance criterion.

Robust weighted averaging [of biomedical signals]

Abstract: Signal averaging is often used to extract a useful signal embedded in noise. This method is especially useful for biomedical signals, where the spectra of the signal and noise significantly overlap. In this case, traditional filtering techniques introduce unacceptable signal distortion. In averaging methods, constancy of the noise power is usually assumed, but in reality noise features a variable power. In this case, it is more appropriate to use a weighted averaging. The main problem in this method is the estimation of the noise power in order to obtain the weight values. Additionally, biomedical signals often contain outliers. This requires robust averaging methods. This paper shows that signal averaging can be formulated as a problem of minimization of a criterion function. Based on this formulation new weighted averaging methods are introduced, including weighted averaging based on criterion function minimization (WACFM) and robust /spl epsi/-insensitive WACFM. Performances of these new methods are experimentally compared with the traditional averaging and other weighted averaging methods using electrocardiographic signal with the muscle noise, impulsive noise, and time-misalignment of cycles. Finally, an application to the late potentials extraction is shown.

Impulse generation with appropriate amplitude, length, inter-arrival, and spectral characteristics

Abstract: This paper proposes a suitable method for simulating impulses with appropriate amplitude, spectral, and inter-arrival characteristics. The statistics used to develop the parameters of this model are based on statistics derived from observations of impulse noise on the telephone networks of British Telecom (BT) and Deutsche Telekom (DT). This paper initially reviews the former DT approach to impulse noise generation for testing digital subscriber line systems, so called xDSL systems. Some problems are highlighted and an alternative technique is suggested that is capable of generating impulses with both appropriate amplitude an spectral characteristics.

Multiuser detection in flat fading non-Gaussian channels

Abstract: This paper deals with the problem of multiuser detection in direct-sequence code-division multiple-access (CDMA) fading channels with impulsive noise. This issue arises in practical situations because in many realistic wireless channels, the ambient channel noise is impulsive, resulting from various natural and man-made impulsive sources. An M-estimator-based structure for noncoherent demodulation of differentially phase-shift keyed (DPSK) signals transmitted simultaneously via a CDMA flat-fading channel and embedded in impulsive noise, is proposed and analyzed. Analytical and numerical results show that, in highly impulsive noise, the performance gain afforded by the proposed multiuser detector can be substantial when compared to the linear decorrelating detector for DPSK, with little attendant increase in algorithmic complexity.

Measurement of the impulsive noise environment for satellite-mobile radio systems at 1.5 GHz

Abstract: Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented.

Fuzzy filters for image filtering

Abstract: In this paper, four fuzzy filters for filtering images contaminated with random, impulse, and sum of random and impulse noises are introduced In each of these four fuzzy filters, the output pixel of a filtered image at the center of a moving window area is defined as a normalized sum of weighted input pixels within the window Simulation results indicate that some of these fuzzy filters show improvement over the standard median and moving average filters in reducing these three noises

Detection of impulse noise using unused codes in CDMA systems

Abstract: An impulse detector which can detect both low and high levels of impulse noise in a CDMA system is comprised of circuitry to calculate the background noise level in unused codes. Another circuit calculates the average noise power in the unused codes of each spreading interval to output the noise power per spreading interval. This average is continuously averaged over spreading intervals by another circuit which outputs the average background noise power. A comparator compares the noise power in the current spreading interval with the background noise power plus a programmable threshold and generates an erasure indication if the background noise power plus a discrimination threshold is exceeded.

Robust detection in DS-CDMA

Abstract: Robust single-user detection is employed in a direct sequence code-division multiple-access (DS-CDMA) system in which the noise process contains impulsive components. The breakdown point is computed for a mixture noise model. The bit error probability expressions are derived under a Gaussian mixture. The performance is also evaluated in the presence of power imbalance and asynchronous reception. Noise, rather than interference, is shown to be the primary obstacle in achieving good performance for certain practical signal power and user load levels. It is concluded that DS-CDMA employing a robust correlator receiver performs better than the conventional matched filter in an impulsive noise environment.

Adaptive two-pass median filter to remove impulsive noise

Abstract: In this paper, we present an adaptive two-pass median filter to remove impulsive noise. In two-pass median filtering, an image contaminated by impulsive noise is processed by a median filter twice. Median filtering is a non-reversible process, i.e., useful information discarded by the filter cannot be recovered. This behavior becomes more apparent in two-pass median filtering. To correct this problem, between the two filtering processes we introduce an adaptive process to selectively replace some pixels by their original values based on the spatial distribution of estimated impulsive noise. Compared with standard median filtering and two-pass median filtering, better results are obtained in terms of visual appreciation and mean squared error. We use examples to demonstrate the performance of the method.

Measurements of radio impulsive noise from various sources in an indoor environment at 900 MHz and 1800 MHz

Abstract: This paper presents the results of the cumulative effect of impulsive radio noise measurements conducted in an indoor environment at 900 MHz and 1800 MHz. The studies are conducted on the three floors of a multi-storey office-cum-institute building. Several sets of measurements are taken on working days, when the electric devices are in ON state and also on holidays when electric devices are in OFF state. Cumulative radio noise level due to operation of electric devices including fluorescent tubes, are found significant at different frequencies. The channel noise factor, which is the average ambient noise above the thermal noise at the antenna input has been found to vary between 12.6 to 21.5.

Median M-type K-nearest neighbour (MM-KNN) filter to remove impulse noise from corrupted images

Abstract: The median M-type K-nearest neighbour (MM-KNN) filter to remove impulse noise from corrupted images is presented. This filter uses R and M estimators combined with different influence functions. Simulation results have shown that the restoration performance is better than that of other known filters.

An accurate noise detector for image restoration

Abstract: This paper proposes a new noise-detection method for restoration of images corrupted by impulsive noise. The proposed method consists of two stages. In the first stage, the pixels classified according to a new flag image are processed by different noise detectors. They are realized by using two median filters with different sizes of windows. In the second stage, each pixel once detected as an impulse in the first stage is verified by using a new system. According to the above stages, the proposed method can accurately detect the location of the impulsive noise and be effectively used as a preprocessor for noise reduction filtering. Experiments show that the proposed method can effectively detect impulsive noises in noisy images even when they are very highly corrupted.

An adaptive channel estimation algorithm using time-frequency polynomial model for OFDM with fading multipath channels

Abstract: Orthogonal frequency division multiplexing (OFDM) is an effective technique for the future 3G communications because of its great immunity to impulse noise and intersymbol interference. The channel estimation is a crucial aspect in the design of OFDM systems. In this work, we propose a channel estimation algorithm based on a time-frequency polynomial model of the fading multipath channels. The algorithm exploits the correlation of the channel responses in both time and frequency domains and hence reduce more noise than the methods using only time or frequency polynomial model. The estimator is also more robust compared to the existing methods based on Fourier transform. The simulation shows that it has more than 5 dB improvement in terms of mean-squared estimation error under some practical channel conditions. The algorithm needs little prior knowledge about the delay and fading properties of the channel. The algorithm can be implemented recursively and can adjust itself to follow the variation of the channel statistics.

Performance evaluation of OFDM transmission over impulsive noisy channels

Abstract: Our aim is to investigate the effect of impulsive noise on the performance of an OFDM system The employed model of impulsive noise consists of Bernoulli distributed impulse arrivals and Gaussian distributed impulse amplitudes The bit error rate performance results are provided by means of simulation The effect of changing the number of carriers of the OFDM system, the impulsivity of the noise, different relative powers of the impulsive noise as well as different impulse-shaping filters are investigated and are compared with the additive white Gaussian noise (AWGN) case Results show that for large signal-to-noise ratios (SNR), and, particularly, very impulsive noise, the OFDM system with a large number of carriers can cope with the impulsivity of the noise, and can improve the performance

Detection of clicks in audio signals using warped linear prediction

Abstract: Warped linear prediction (WLP) is applied to a model-based method to detect impulsive disturbances in audio signals. According to simulations performed on artificially corrupted audio signals, the adoption of negative values for the warping factor favors the click detection scheme. As a consequence, for equal levels of missing (false) detection, the WLP-based scheme yields a consistently lower percentage of false (missing) detection than the conventional method.

Rank-ordered mean filter for removal of impulse noise from images

Abstract: This paper presents a new algorithm for detection of fixed-valued and random-valued impulses from images based on locally obtained statistics. By incorporating the rank-conditioned median (RCM) and center-weighted median (CWM) filters into an impulse noise detection framework, an adaptive mechanism is formed for effectively reducing impulse noise while preserving image details. The rank-conditioned mechanism checks whether the central pixel is well-within the ordered data set, while the center-weighted mechanism is to select more appropriate local thresholds. Simulations show that the proposed scheme works well in suppressing both types of impulses at different noise ratios.

A posteriori control of complex Reed Solomon decoding with application to impulse noise cancellation in HIPERLAN/2

Abstract: In OFDM systems, pilot tones are emitted for synchronization or channel estimation purposes. These pilot tones are generally scattered among the information ones. Our approach is to use these pilot tones as syndromes, in order to correct impulse noise. We previously proposed (see Abdelkefi, F. et al., ISSPA, 2001) a decoding algorithm in three steps: (1) estimate the amount of impulse noise; (2) seek the location; (3) correct the errors. A protection subsystem was introduced after the decoding operation in order to detect malfunction. Indeed, we added a control step which is able to estimate carefully whether the decoding procedure has worked correctly. We now explain this a posteriori control which is based on the hypothesis test. This approach is new in impulse noise cancellation in multicarrier transmission. The efficiency of this technique is also corroborated with simulations in the practical context of HIPERLAN/2.

Adaptive Rank-Ordered Mean Filter for Removal of Impulse Noise from Images.

Abstract: This paper presents a new algorithm for detection of fixed-valued and random-valued impulses from images based on locally obtained statistics. By incorporating the rank-conditioned median (RCM) and center-weighted median (CWM) filters into an impulse noise detection framework, an adaptive mechanism is formed for effectively reducing impulse noise while preserving image details. The rank-conditioned mechanism checks whether the central pixel is well-within the ordered data set, while the center-weighted mechanism is to select more appropriate local thresholds. Simulations show that the proposed scheme works well in suppressing both types of impulses at different noise ratios.

REVERSE BIASED P-N JUNCTION NOISE IN GaAsP DIODES WITH AVALANCHE BREAKDOWN INDUCED MICROPLASMAS

Abstract: Random two-level or multiple-level current impulses may occur in electronic devices containing reverse biased p-n junctions in a certain operating mode. These impulses are usually rectangular, featuring constant amplitude, random pulse width and pulse origin time points. This phenomenon is generally ascribed to local avalanche breakdowns originating in p-n junction defect regions called microplasma regions. Based on experiment results, a two-state model of stochastic generation-recombination process has been elaborated for the two-level impulse noise allowing to derive some statistical characteristics of this process. It can be shown that the distribution of the probability density w(τ0) of the impulse separation τ0 and the probability density w(τ1) of the impulse width τ1 have exponential courses. The power spectral density of the noise current is of a G-R process type and depends on the particular microplasma properties. From the viewpoint of noise diagnostics, the most important features are the spectral density Su and noise current IN versus reverse current IR plots, because each local extreme of these plots corresponds to an active microplasma region. Thus obtained results may be used for p-n junction non-destructive diagnostics and quality assessment.

Multi-carrier CDMA over copper lines - comparison of performances with the ADSL system

Abstract: This paper deals with the comparison of two multi carrier modulation techniques over existing copper twisted pairs: the Discrete Multi Tone (DMT) modulation and the Multi Carrier Code Division Multiple Access (MC-CDMA) modulation The first form has been proposed for Asymmetrical Digital Subscriber Line (ADSL) However in ADSL, the wire pairs suffer from disturbances such as transients, radio-frequency noise Among them, impulse noise is considered to be one of the most damaging impairments Then, our proposal intends to limit the effects of such a noise thanks to the use of the latter form of modulation which combines multi carrier technique with spread spectrum In order to improve the performances of the system proposed still further various detection techniques are studied In this context, we show that the MC-CDMA technique presents better performances than the normalised ADSL technique under identical simulation parameters (data rate, bandwidth, transmitted power, coding, interleaver)

Turbo decoding with erasures for high-speed transmission in the presence of impulse noise

Abstract: If impulse noise is not taken into account, turbo codes are highly attractive for transmissions over asymmetric digital subscriber lines. We show that impulse noise could devastate turbo coding performance if appropriate precautions are not taken. A possible solution of using an outer Reed-Solomon code to combat impulse noise results in very large delays. We propose erasure turbo decoding to improve the turbo trellis coded modulation performance against impulse noise. We also show that when a concatenated coding structure is employed, in addition to improving the bit error rate performance, erasure turbo decoding can also significantly reduce the delay of the outer Reed-Solomon code.

Estimates of the wigner distribution in Gaussian noise environment

Abstract: Summary The influence of Gaussian noise to the Wigner distribution is considered.Due to the quadratic nature of the Wigner distribution, the resulting noise exhibits impulse nature even in the case of Gaussian input noise. Estimators of the Wigner distribution which take into account this fact are considered.They can outperform the standard and the robust Wignerdistribution.

On adaptive IIR lattice notch filter using a robust variable step-size for the detection of sinusoid

Abstract: Adaptive IIR lattice notch filter using a robust variable step-size for the detection of sinusoid in noise is presented. It is shown that the estimated frequency of the proposed algorithm for a single sinusoid is unbias, low variance and low mean square error (MSE) in both high and low signal to noise ratio (SNR) environments. Also, the proposed algorithm works well in high impulse noise environment. The computer simulations are presented to show the performances of the proposed adaptive notch filter.

Power supply noise sensor

Abstract: A power supply noise sensor includes a noise sensing section A to sense impulse noise applied to a power supply line and an output holding section B to hold a sense output from the noise sensing section A. The noise sensing section A includes a time constant circuit to gradually vary a power supply voltage including impulse noise. When a peak value of the impulse noise reduces after the peak value exceeds a predetermined value, a direction of a current flowing through the time constant circuit is inverted to hold a noise output from the output holding section B also after the impulse noise disappears. Therefore, the impulse noise in the forward direction and the impulse noise in the reverse direction superimposed onto the power supply system of the sensor can be sensed in a simple configuration.