Showing papers on "Impulse noise published in 1988"

Median filters with adaptive length

Abstract: Two algorithms using adaptive-length median filters are proposed for improving impulse-noise-removal performance for image processing. The algorithms can achieve significantly better image quality than regular (fixed-length) median filters when the images are corrupted by impulse noise. One of the algorithms, when realized in hardware, requires rather simple additional circuitry. Both algorithms can easily be integrated into efficient hardware realizations for median filters. The performance of the proposed filters is compared with regular median filters, generalized mean filters, and nonlinear mean filters. The hardware complexities of the filters are also compared. >

Noise annoyance with regard to neurophysiological sensitivity, subjective noise sensitivity and personality variables.

Abstract: To evaluate the relation between annoyance to environmental noise, general neurophysiological sensitivity, subjective noise sensitivity and other individual characteristics, experiments were undertaken in which 93 subjects assessed their subjective annoyance after exposure to noise under laboratory conditions. Evaluations were made of the discomfort threshold for pulsating sound, the light discomfort, and heat and cold discomfort. The heart rate and discomfort after exposure to a series of impulse noises was also determined. Subjective noise sensitivity, attitudes to noise, mood and personality characteristics of the subjects were evaluated using questionnaires. The results show that the annoyance after exposure to noise was not closely related to the general neurophysiological sensitivity, measured as discomfort threshold for noise, heat, cold and light; or to the heart rate reaction or discomfort after exposure to impulse noise. The annoyance was highly correlated with subjectively reported noise sensitivity and with the attitude to noise. There was also a relationship with neuroticism, measured with the EPI scale. It is suggested that the subjective noise sensitivity, attitude and neuroticism for the definition of noise sensitivity be defined in future studies of long term effects of noise exposure.

A VLSI median filter for impulse noise elimination in composite or component TV signals

Abstract: A VLSI median filter with novel masking modes and adaptive threshold control is described. The 16 masking modes select 1, 3, 5 or 9 pixels of a 5*3 pixel field for filtering. This feature makes it possible to median-filter NTSC composite video (baseband) or component R, G, and B signals. The input threshold value and the SWAP signal (indicating substitution of the median value) can be used together to adapt transmission path conditions. The circuit removes impulsive noise caused by FM-carrier-to-noise degradation, common in cable and satellite TV systems. The filter is applicable to other impulse noise sources created by auto engines and household appliances, and is also generally useful in image and signal processing tasks. >

Fourier-Bessel error performance analysis and evaluation of M-ary QAM schemes in an impulsive noise environment

Abstract: The authors derive closed-form expressions for the BER (bit error rate) performance of coherent M-ary quadrature amplitude modulated (QAM) system in the presence of an additive combination of Gaussian and highly impulsive noise by using a Fourier-Bessel series expansion method. The model used for the impulse noise, which closely models atmospheric and/or ignition noise, consists of a stream of Poisson impulses with areas distributed according to a bilateral Rayleigh probability distribution function. Although the methodology is general enough to accommodate any M-ary QAM scheme, they present analytical as well as some computer simulated results for 16-, 64-, and 256-QAM systems. An almost insignificant increase of the truncation error with the increase of the modulation levels verifies that the proposed method of analysis can be a useful tool in evaluating the performance of very large-alphabet M-ary QAM systems, e.g. M>or=256. >

Forward error correction of data transmitted via television signals

Abstract: An encoding technique for data that enables the data to be reliably transmitted via television signals, even when impulse noise may be present, uses a two-fold approach for forward error correction. As a first step, the data is assembled into blocks of suitable length and each block is encoded with an error correcting code to enable individual bit errors to be identified and corrected at the receiving end. In addition, the blocks of data are interleaved over several different lines of information. Each line of information is transmitted during the vertical blanking interval in a respective field of a video signal. At the receiving end, the individual lines of data are reassembled into the blocks of information. If impulse noise or other disruptions cause one of the lines to be lost, the result at the receiving end would only be the loss of one bit of data in each block. The error correcting code with which each block is encoded enables this individual bit error to be identified and corrected.

Impulse noise and hand-arm vibration in relation to sensory neural hearing loss.

Abstract: The present study was carried out to determine whether impulse noise and simultaneous exposure to noise and vibration can aggravate sensory neural hearing loss (SNHL) among forest (N = 199) and shipyard (N = 171) workers. The average level of exposure to noise outside the used earmuffs and the average exposure over time were nearly equal for the two groups. The impulsiveness of the noise and the average exposure level inside the earmuffs were measured with a miniature microphone. The hearing threshold of the workers was measured at 4 kHz and then estimated according to Robinson's model to compare the observed and expected hearing loss. The impulsiveness of the noise was greater both outside and inside the earmuffs in shipyard work than in forest work. The average SNHL was higher than predicted for the shipyard workers and about the same as predicted for the forest workers. The total exposure level inside the earmuffs was influenced by the total wearing time. The low frequencies of the chain-saw noise were not attenuated sufficiently by the earmuffs to protect the workers' hearing. The present study suggests that exposure to impulse noise increases the risk of SNHL, but that simultaneous exposure to hand-arm vibration and noise does not.

Use of coding to combat impulse noise on digital subscriber loops

Abstract: The authors describe an approach to combatting impulse noise (IN) on digital subscriber loops using short-constraint length convolutional codes and Viterbi decoding operating in hard-decision-and-erasure mode. Attention is restricted to time-compression-multiplexing transmission schemes using bipolar, or alternate-mark inversion (AMI), line coding, and a rather idealized IN model, although the approach and general conclusions are more broadly applicable. They discuss the tradeoffs in choosing the channel encoding rate to yield an optimum compromise between error-control protection and the combined effects of intersymbol interference and crosstalk. Numerical results are demonstrated for selected typical line configurations. >

Suitable MAC Protocols for an OFDM Based PLC Network

Abstract: - In this paper we propose a MAC protocol for PLC networks. The model for our PLC network istypical for the “last mile”- network in Germany and consists of one transformer station with branches, whereabout 35 households are supplied. The physical layer is based on OFDM-technique. We discuss solutions aboutorganization of the MAC layer. The MAC layer consists of number of 64 kbit/s transmission channels, whichcan be allocated to one particular or more stations. For this proposal we derive an analytical model at the calllevel to see how many subscriber stations (access units) is reasonable to connect. We investigate the utilization,the blocking probability of voice, and the average rate of the data transmission depending on the load in thesystem. The analytical results take in consideration the channel outages because of erasures. 1. Introduction After the deregulation of the telecommunications market powerline communications (PLC) gained bigimportance for the last mile (or access) network providers. The great advantage of PLC is that in every home andin every room there are sockets, which can be used for telecommunications, too. We consider two differentservices – telephony and internet, which are currently the most usable services in private homes. The bigproblem, however, is that the powerline network has been designed for electricity distribution and not for datatransfer. As a result, the characteristics of the powerline make it an unreliable channel, dominated by distance,time and frequency dependent attenuation and impulse noise. The development of a suitable MAC protocolrequires an appropriate channel model (Chapter 2). There are many factors, which affect the channelcharacteristics like channel attenuation, white noise, radio frequency noise (RF noise) from nearby radiotransmitters, impulse noise from electrical machines and relays (man-made interference), etc. The noisespectrum is highly varying with frequency, location and time. We describe them as rare events. In practice theimpact of RF noise on a channel can be reduced significantly with Orthogonal Frequency-Division Multiplexing(OFDM). The investigation and implementation of an appropriate Medium Access Control (MAC) protocol isvery important for the quality of the network services and data transmission (Chapter 3).In our model we investigate two types of traffic – telephony and data transmission (Internet). For both of themwe analyse the performance following features: blocking probability, throughput, and average data ratedepending on the load in the system (Chapter 4).

Nonlinear C-filters for nonstationary signals and deconvolution in impulsive noise

Abstract: The combination filter or C-filter incorporates both temporal and rank-order information of the input sequence to produce its outputs. It can be used as an equalization filter to restore an original waveform which has been dispersed by a channel, in the presence of additive white Gaussian and impulsive noise. The filter coefficients can be designed by using the LMS (least mean squares) algorithm. This approach is examined and an example is given demonstrating the usefulness of the C-filter. The authors consider a technique which combines both rank-order statistics and FIR (finite impulse response) filtering schemes to deconvolve noisy channel characteristics, and to simultaneously reject the impulse noise. The problem of gain normalization at frequencies other than zero is also addressed; this arises during filtering of nonstationary signals in impulsive noise. It is concluded that the C-filter provides a useful alternative to the FIR filter for applications in inverse filtering and frequency-selective nonstationary signal restoration when the additive noise contains impulsive components and step nonstationarity in signal level. >

Residue series solution of impulse noise propagation into a shadow zone

Abstract: Previously published calculations of impulse noise propagation into a shadow zone have been performed using expressions that are only valid above the creeping wave layer [C. G. Don and A. J. Cramond, J. Acoust. Soc. Am. 80, 302–305 (1986)]. In this letter the results of a calculation accurate within the creeping wave layer will be described.

Adaptive-length median filters for image processing

Abstract: The authors propose algorithms using adaptive-length median filters, for improving impulse-noise-removal performance for image processing. The algorithms can achieve significantly better image quality than regular (fixed-length) median filters when the images are corrupted by impulse noise. One of the advantages of the algorithms is that, when realized in hardware, the additional circuitry required is rather simple. Furthermore, the algorithms can easily be integrated into efficient hardware realizations for median filters. Performance-simulation results and implementation issues are discussed. >

Multi-level trellis codes for the Gaussian channel and for channels subject to impulsive noise

Abstract: The author designs multilevel trellis codes based on lattices and cosets that provide greater immunity to Gaussian noise and/or greater resistance to impulse noise than previous approaches. He shows how to calculate minimum-squared distance and path multiplicity in terms of the norms and multiplicities of the different cosets. The multilevel structure allows the redundancy in the coset selection procedure to be allocated efficiently among the different levels. The proposed codes admit a staged decoding procedure that requires very few trellis states and has performance/complexity advantages over maximum-likelihood decoding. >

A hybrid differential encoder and non-linear filter (DEN filter)

Abstract: A system is presented to combine two goals in image processing; compression and non-linear filtering. The compression is done using a modified differential Huffman coding technique. The non-linear filter uses a bounding technique to filter impulse noise while passing edges. Simulation results are presented in tabular form, along with several original and filtered images added for subjective viewing. Future avenues of research, possibly leading to higher compression ratios, are suggested. >

Reception demodulation circuit for modem

Abstract: PURPOSE:To prevent disturbance due to one-shot impulse noise by inserting an analog switch circuit between a reception band pass filter and an AGC circuit and using an output of a reception carrier detection circuit so as to control the analog switch. CONSTITUTION:An analog switch circuit 21 is controlled by an output of a reception carrier detection circuit 18, passes a signal when its control input set and no signal passes when its control input is reset. The circuit 18 converts an AC signal into a DC signal and has a leading time constant. Thus, the circuit 16 does not respond to the noise even when one-shot impulse noise is inputted just before the reception signal and responds to a delay time to a consecutive reception signal. Since the circuit 21 is controlled by the output of the circuit 16, the circuit 21 is not turned on before the circuit 16 is turned off and the input signal is then inputted to an AGC circuit 13 of the next stage. Thus, the circuit 16 does not respond to the circuit 18 against one-shot impulse noise and the circuit 13 is not activated.

Adaptive detection of CPFSK signals in non-Gaussian noise

Abstract: Adaptive detection of CPFSK (continuous phase frequency shift keying) signals corrupted by class-A impulse noise is presented. The EM algorithm (E for expectation, M for maximize) is used to estimate the noise characteristics. Performance of the EM algorithm and the adaptive detector are reported. The results show that the adaptive detector performs very close to optimal for reasonable sample sizes and well-separated components. Even when the sample size is reduced and the components are close together, the performance of the adaptive detector is still very acceptable despite the degradation. The EM algorithm is not restricted to class-A noise. >

Extending the impulse response in order to reduce errors due to impulse noise and signal fading

Abstract: A finite impulse response (FIR) digital smearing filter was designed to produce maximum intersymbol interference and maximum extension of the impulse response of the signal in a noiseless binary channel. A matched FIR desmearing filter at the receiver then reduced the intersymbol interference to zero. Signal fades were simulated by means of 100 percent signal blockage in the channel. Smearing and desmearing filters of length 256, 512, and 1024 were used for these simulations. Results indicate that impulse response extension by means of bit smearing appears to be a useful technique for correcting errors due to impulse noise or signal fading in a binary channel.