Showing papers on "Signal-to-noise ratio published in 1990"
Journal Article•
TL;DR: In this paper, the authors consider an asynchronous code-division multiple access (CDMA) environment where the receiver has knowledge of the signature waveforms of all the users and compare detectors by their worst case bit error rate in a low background noise near-far environment.
Abstract: We consider an asynchronous code-division multiple-access environment in which the receiver has knowledge of the signature waveforms of all the users. Under the assumption of white Gaussian background noise, we compare detectors by their worst case bit error rate in a low background noise near-far environment where the received energies of the users are unknown to the receiver and are not necessarily similar.
1,008 citations
TL;DR: A model of catecholamine effects in a network of neural-like elements is presented, which shows that changes in the responsivity of individual elements do not affect their ability to detect a signal and ignore noise but the same changes in cell responsivity do improve the signal detection performance of the network as a whole.
Abstract: At the level of individual neurons, catecholamine release increases the responsivity of cells to excitatory and inhibitory inputs. A model of catecholamine effects in a network of neural-like elements is presented, which shows that (i) changes in the responsivity of individual elements do not affect their ability to detect a signal and ignore noise but (ii) the same changes in cell responsivity in a network of such elements do improve the signal detection performance of the network as a whole. The second result is used in a computer simulation based on principles of parallel distributed processing to account for the effect of central nervous system stimulants on the signal detection performance of human subjects.
760 citations
TL;DR: It is shown that the POF appears to provide a good compromise between noise tolerance and peak sharpness, with the help of a new family of filters called fractional power filters (FPFs).
Abstract: Several performance criteria are described to enable a fair comparison among the various correlation filter designs: signal-to-noise ratio, peak sharpness, peak location, light efficiency, discriminability, and distortion invariance. The trade-offs resulting between some of these criteria are illustrated with the help of a new family of filters called fractional power filters (FPFs). The classical matched filter, phase-only filter (POF), and inverse filter are special cases of FPFs. Using examples, we show that the POF appears to provide a good compromise between noise tolerance and peak sharpness.
572 citations
03 Apr 1990
TL;DR: Initial efforts to make Sphinx, a continuous-speech speaker-independent recognition system, robust to changes in the environment are reported, and two novel methods based on additive corrections in the cepstral domain are proposed.
Abstract: Initial efforts to make Sphinx, a continuous-speech speaker-independent recognition system, robust to changes in the environment are reported. To deal with differences in noise level and spectral tilt between close-talking and desk-top microphones, two novel methods based on additive corrections in the cepstral domain are proposed. In the first algorithm, the additive correction depends on the instantaneous SNR of the signal. In the second technique, expectation-maximization techniques are used to best match the cepstral vectors of the input utterances to the ensemble of codebook entries representing a standard acoustical ambience. Use of the algorithms dramatically improves recognition accuracy when the system is tested on a microphone other than the one on which it was trained. >
461 citations
TL;DR: A novel approach to the general problem of signal parameter estimation is described, and although discussed in the context of direction-of-arrival estimation, ESPRIT can be applied to a wide variety of problems.
Abstract: High-resolution signal parameter estimation is a problem of significance in many signal processing applications. Such applications indude direction-of-arrival estimation, system identification, and time series analysis. A novel approach to the general problem of signal parameter estimation is described. Although discussed in the context of directionof-
arrival estimation, ESPRIT can be applied to a wide variety of problems. It exploits an underlying rotational invariance among signal subspaces
induced by an array of sensors with a translational invariance structure. The technique, when applicable, manifests significant performance and computational advantages over previous algorithms such as Burg's maximum entropy method, Capon's maximum likelihood method, and Schmidt's multiple signal classification.
461 citations
TL;DR: Several closely related estimators are proposed whose main characteristics are simplicity, accuracy, and ease of online or offline implementation for moderately high signal-to-noise ratios they are unbiased and attain the Cramer-Rao bound.
Abstract: The problem of the parameter estimation of chirp signals is addressed. Several closely related estimators are proposed whose main characteristics are simplicity, accuracy, and ease of online or offline implementation. For moderately high signal-to-noise ratios they are unbiased and attain the Cramer-Rao bound. Monte Carlo simulations verify the expected performance of the estimators. It should be easy to extend this approach to signals having polynomials of any degree in the exponent. All the derivations will be done under the assumption that the signal-to-noise ratio is sufficiently high. >
395 citations
01 Apr 1990
TL;DR: The class of spectral self-coherence restoral (SCORE) objective functions is introduced, and algorithms for adapting antenna arrays to optimize these objective functions are developed to maximize the signal-to-interference-and-noise ratio at the output of the narrowband antenna array.
Abstract: A new approach to blind adaptive signal extraction using narrowband antenna arrays is presented. The approach has the capability to extract communication signals from cochannel interference environments using only known spectral correlation properties of those signals, i.e. without using knowledge of the content or direction of arrival of the transmitted signal, or the array manifold or background noise covariance of the receiver, to train the antenna array. The class of spectral self-coherence restoral (SCORE) objective functions is introduced, and algorithms for adapting antenna arrays to optimize these objective functions are developed. Using the theory of spectral correlation, it is shown by analysis and simulation that these algorithms maximize the signal-to-interference-and-noise ratio at the output of the narrowband antenna array when a single communication signal with spectral self-coherence at a known value of frequency separation, along with an arbitrary number of interferers without spectral self-coherence at that frequency separation, are impinging on the array. >
328 citations
TL;DR: While implementing the full MLSD is clearly out of the question for high densities with severe intersymbol interference (ISI), there exists an efficient detection scheme which achieves an excellent compromise between hardware complexity and detection performance.
Abstract: Various detection schemes suitable for magnetic recording are compared in terms of their effective signal-to-noise ratios. It is shown that at high densities the performance of conventional detectors such as a peak detector, a threshold detector with partial response equalization, a decision feedback equalizer, and a Viterbi algorithm detector tuned to a linearly truncated channel fall far below the optimum performance that can be achieved by the maximum-likelihood sequence detector (MLSD). It is shown that while implementing the full MLSD is clearly out of the question for high densities with severe intersymbol interference (ISI), there exists an efficient detection scheme which achieves an excellent compromise between hardware complexity and detection performance. This scheme, which is called the fixed-delay tree search with decision feedback, combines a fast and efficient tree-search algorithm with a decision feedback equalizer to cancel out a portion of ISI without noise enhancement. It is well suited for run-length-limited systems and attains performance close to that of MLSD while maintaining reasonable implementation cost and processing requirements. >
217 citations
TL;DR: It is demonstrated that the resolution threshold is proportional to the dimension of the noise subspace; therefore, the threshold can be reduced substantially by utilizing an appropriate beamformer to reduce thedimension of thenoise subspace.
Abstract: An analysis of a beamspace version of the MUSIC algorithm applicable to two closely spaced emitters in diverse scenarios is presented. Specifically, the analysis is applicable to uncorrelated far-field emitters of any relative power level, confined to a known plane, and observed by an arbitrary array of omnidirectional sensors. An expression for the threshold array signal-to-noise ratio at which beamspace MUSIC is able to resolve the emitters is obtained. The preprocessor that minimizes the resolution threshold is identified. It is demonstrated that the resolution threshold is proportional to the dimension of the noise subspace; therefore, the threshold can be reduced substantially by utilizing an appropriate beamformer to reduce the dimension of the noise subspace. It is also demonstrated that MUSIC in conjunction with a suitable preprocessor can provide a resolution threshold lower than conventional (sensor-space) MinNorm. >
214 citations
TL;DR: The dynamic range of phase‐ reconstructed magnetic resonance images is compared to that of magnitude‐reconstructed images, verifying that the noise in the two receiver channels is uncorrelated and an artifact‐free technique is presented for correcting phase spillover, which further extends the phase angle dynamic range.
Abstract: The dynamic range of phase-reconstructed magnetic resonance images is compared to that of magnitude-reconstructed images. From analysis of propagation of errors, the phase angle noise is phase-independent and given in radians by σ (|I|)/|I|, the noise-to-signal ratio of the corresponding magnitude-reconstructed image. As the phase can range from minus π to π the phase angle dynamic range is 2π times that of the signal magnitude. These results agree with experiment, verifying that the noise in the two receiver channels is uncorrelated. An artifact-free technique is presented for correcting phase spillover, which further extends the phase angle dynamic range. The reconstruction-based reference phase is adjusted on a local basis so that the boundary of phase wraparound is reconstructed near the center of the [ − π, π] interval. For a particular flow study, the phase signal-to-noise was extended over twofold by spillover correction, to a value 15 times that of the magnitude signal-to-noise. © 1990 Academic Press, Inc.
202 citations
TL;DR: A simplified model is used to provide an intuitive understanding of the interaction of noise correlation and phase shift phenomena in composite images with uniform noise or with uniform sensitivity.
Abstract: Multiple images acquired simultaneously from an array of surface coils can be combined to give a composite image with an improved signal-to-noise ratio (SNR) and a large field of view. The composite images' SNR can be optimized by taking advantage of noise correlations between coils and phase shifts induced by surface coil reception. Methods are derived for making optimal composite images with uniform noise or with uniform sensitivity. A simplified model is used to provide an intuitive understanding of the interaction of noise correlation and phase shift phenomena. © 1990 Academic Press, Inc.
TL;DR: In this article, a limiter is inserted in the main electrical pathway between the microphone and the receiver to provide stability in the presence of sudden sound bursts, and a noise signal is injected continuously into the electrical circuit and is used to adapt the characteristics of the filter to accommodate changes in the acoustic coupling.
Abstract: A hearing aid includes a filter in an electrical feedback path, the characteristics of which filter are calculated to model acoustic coupling between the receiver and microphone of the aid. A limiter is inserted in the main electrical pathway between the microphone and the receiver to provide stability in the presence of sudden sound bursts. A noise signal is injected continuously into the electrical circuit and is used to adapt the characteristics of the filter to accommodate changes in the acoustic coupling. The level of the noise signal can be varied to match changes in residual signal level to maintain signal to noise ratio and to optimize rate of adaption commensurate with satisfactory hearing function while the noise itself is unobtrusive to the user.
TL;DR: It is shown that efficiency is always improved when imaging with the lowest possible resolution (largest voxel dimensions) consistent with viewing the desired anatomical detail and that spatial averaging is an inefficient method of noise reduction in MRI.
Abstract: The dependence of signal-to-noise ratio (SNR) on the analog filter, the sampling rate and the number and dimensions of voxels is derived for magnetic resonance imaging (MRI). It is shown that the object signal-to-noise ratio scales directly with the voxel volume and the square root of the number of voxels. Defining an efficiency figure of merit as the SNR divided by the square root of the imaging time, it is shown that efficiency is always improved when imaging with the lowest possible resolution (largest voxel dimensions) consistent with viewing the desired anatomical detail. The results directly imply the relative efficiency of 3-D (volume), 2-D (plane), 1-D (line) and 0-D (point) imaging techniques. It is shown that spatial averaging is an inefficient method of noise reduction in MRI. As long as voxel size is maintained constant, one can image as many pixels in the readout direction as desired with no loss in SNR; that is, the number of pixels in the readout direction has no effect on the image SNR. Further, multiple sampling of each phase encoding value (to improve SNR) has no advantage over increasing the number of pixels in the phase encoding direction while leaving the voxel size constant. Some experimental observations are given.
23 May 1990
TL;DR: A data association technique that utilizes the strength of target returns to improve tracking in a cluttered environment and improved tracking performance is demonstrated for targets with several signal to noise ratio values.
Abstract: In this paper we present a data association technique that utilizes the strength of target returns to improve tracking in a cluttered environment. The approach generalizes the Probabilistic Data Association Filter (PDAF) to include the target amplitude, a feature which is available from the detection system that provides measurements for tracking. The probabilistic modelling of target and clutter intensities is based upon collected real data. The corresponding generalized probabilistic data association is derived and improved tracking performance is demonstrated for targets with several signal to noise ratio values.
02 Dec 1990
TL;DR: The author proposes a suboptimal trellis search algorithm that strives to achieve the optimal performance with only a linear complexity.
Abstract: Proposes a novel method for blind sequence estimation of data that are transmitted over unknown linear distortive channels. For every possible sequence that can be transmitted, the procedure finds the best possible channel fit corresponding to the noisy channel output sequence (typically using the least squares procedure). The data and the channel are estimated to be those with the overall best fit. This simple but exhaustive search procedure for blind channel equalization is noninstrumentable because of the exponential growth in its complexity with the length of the data sequence. The author proposes a suboptimal trellis search algorithm that strives to achieve the optimal performance with only a linear complexity. Fast convergence of the algorithm in estimating the channel is demonstrated for binary pulse amplitude modulation (2-PAM) and a variety of channels. Convergence at high signal-to-noise ratios (30 dB) typically occurs within 50 symbols for the channels considered. At a low SNR (10 dB), convergence occurs within 100 symbols. The number of states in the decoder trellis, which is a measure of the decoding complexity, is M/sup L/, where M is the number of modulation levels and L is the channel memory. >
TL;DR: The result implies that the bispectrum-based test may detect a weak signal of unknown form which evades detection by other methods.
Abstract: A method for detecting a transient waveform of unknown shape in additive stationary noise is presented. The method uses a statistic computed from the sample bispectrum of a sampled record of the signal-plus-noise of length T=N tau , where 1/ tau is the sampling rate. The key result underlying the method is that the bispectrum of the noise is zero in a triangle that is a proper subset of the principal domain triangle. It is shown that the probability of detecting the signal is high if (3/16)/sup 1/2/N/sup 5/6/ is larger than rho /sup -1/, where rho is the energy signal-to-noise ratio. The result implies that the bispectrum-based test may detect a weak signal of unknown form which evades detection by other methods. >
TL;DR: It is shown that the highest ratio is achieved in the limit of a distributed amplifier, but that, alternatively, periodic amplification at intervals of alpha(-1) entails a penalty of less than 2 dB compared with the (ideal) distributed case.
Abstract: The detected signal-to-noise power ratio is evaluated for fiber links with periodic amplification. It is shown that the highest ratio is achieved in the limit of a distributed amplifier (g = α), but that, alternatively, periodic amplification at intervals of α^-1 entails a penalty of less than 2 dB compared with the (ideal) distributed case.
NEC1
TL;DR: Computer simulation results show that average segmental SNR by the feedback approach is improved by as much as 4.8 dB over the conventional fixed-block-size ATC, while the feedforward approach is successful in pre-echo suppression to a satisfactory level.
Abstract: A coding technique is presented for high-quality audio signals based on adaptive transform coding (ATC). Adaptive block size selection by the proposed algorithm ensures an appropriate block size resulting in improved SNR (signal-to-noise ratio) for a wide variety of source signals. A feedback approach, based on SNR, and a feedforward approach, based on interblock differences in input time-domain samples, to adaptive block size assignment are proposed and evaluated. Computer simulation results show that average segmental SNR by the feedback approach is improved by as much as 4.8 dB over the conventional fixed-block-size ATC. The feedforward approach is realized with much-simplified hardware; nevertheless, its SNR degradation from that by the feedback approach is 1.6 dB, even in the worst case. Both approaches are successful in pre-echo suppression to a satisfactory level. Time-domain aliasing cancellation has the potential to increase the superiority of the new algorithm. >
TL;DR: In this paper, a simple delay-equalized near-field array of directional microphones is analyzed and found to be effective for increasing the signal-to-noise density ratio (SNR) and reducing the reverberant distortion of the speech, without introducing any further distortion.
Abstract: The properties of noise fields in automobile interiors are discussed with a view toward speech enhancement for voice-activated mobile telephony. The limitations on performance of adaptive noise cancellation are explained in the context of the spatial correlation properties of the noise field. A simple delay-equalized near-field array of directional microphones is analyzed and found to be effective for increasing the signal-to-noise density ratio (SNR) and reducing the reverberant distortion of the speech, without introducing any further distortion. An array of N microphones, each with a delay and weight chosen according to its distance from the speech source, is a viable solution. Such an array gives gains on the order of N over the speech band, reduces reverberation, and does not introduce waveform distortion. Experimental results confirming the predicted performance are presented. >
01 Nov 1990
TL;DR: This paper examines the problem of instantaneous frequency estimation for Frequency Modulated (FM) signals imbedded in white Gaussian noise, and reviews currently available techniques and proposes some new ones based on a modelling of the signal phase as a polynomial.
Abstract: This paper examines the problem of instantaneous frequency (IF) estimation for Frequency Modulated (FM) signals imbedded in white Gaussian noise. It reviews currently available techniques and in addition proposes some new ones based on a modelling of the signal phase as a polynomial. Both linear least-squares techniques and Maximum Likelihood (ML) techniques are investigated for estimating the polynomial coefficients. It is seen that the linear least squares approach is efficient (i. e. unbiased and meets the Cramer-Rao bounds) for high SNR while the ML scheme is efficient for a much larger range of SNR. Theoretical lower variance bounds are given for estimating the polynomial coefficients and are compared with the results of simulations. Guidelines are given as to which estimation method should be used for a given signal class and Signal to Noise Ratio (SNR) level.
TL;DR: A frequency-hopped spread-spectrum signal is modeled as a sinusoid that has one of N random frequencies and coherent and noncoherent interception receiver structures based on Neyman-Pearson detection theory are determined.
Abstract: A frequency-hopped spread-spectrum signal is modeled as a sinusoid that has one of N random frequencies. Coherent and noncoherent interception receiver structures based on Neyman-Pearson detection theory are determined. Under the assumption that there is a single hop per detection period, the optimum receiver structure is shown to consist of a bank of matched filters called the average likelihood (AL) receiver. A suboptimum structure called the maximum likelihood (ML) receiver is also analyzed. It is shown that AL and ML receivers have essentially the same performance. Simple formulas that relate the probability of detection, P/sub D/, to the probability of false alarm, P/sub F/, and the signal-to-noise ratio (SNR) for large N are derived. Receiver structures are also derived and analyzed for the case where the signal hops a number of times in one detection interval. This may correspond to the detection of a multihop signal in one symbol interval or to detection based on integration over a number of symbol intervals. The relationships of P/sub D/ to P/sub F/, for both coherent and noncoherent multiple-hop receivers, are examined. >
TL;DR: It is shown that decision feedback is more effective for GMSK with narrow bandwidth and a 2-b DPD with decision feedback outperforms all other analyzed schemes when the signal-to-noise ratio is low.
Abstract: A formula is derived for the error probability of partial-response continuous-phase modulation (which contains Gaussian minimum shift keying (GMSK) as a special case) with N-b (N=1, 2) differential phase detection (DPD) for the satellite mobile channel, which contains as special cases the Gaussian and Rayleigh channels In the satellite mobile channel, the input signal is the sum of a direct component, a diffuse component, and white Gaussian noise The receiver is either with or without decision feedback, and the decision region is optimized for 2-b DPD to minimize the error probability The error probability for GMSK is computed as a function of signal-to-noise ratio and other system or channel parameters (Doppler frequency, Gaussian filter bandwidth, ratio of powers in the direct and diffuse signal components, etc) It is shown that decision feedback is more effective for GMSK with narrow bandwidth The 2-b DPD is superior to the 1-b DPD for low Doppler frequencies and signal-to-noise ratios For practical vehicle velocities and bit rates, a 2-b DPD with decision feedback outperforms all other analyzed schemes when the signal-to-noise ratio is low >
03 Apr 1990
TL;DR: The results, although preliminary, provide evidence that harmonic zero-phase sine-wave analysis/synthesis, combined with effective estimation of sin-wave amplitudes and probability of voicing, offers a promising approach to noise reduction.
Abstract: Noise reduction is performed in the context of a high-quality harmonic zero-phase sine-wave analysis/synthesis system which is characterized by sine-wave amplitudes, a voicing probability, and a fundamental frequency. Least-squared error estimation of a harmonic sine-wave representation leads to a soft decision template estimate consisting of sine-wave amplitudes and a voicing probability. The least-squares solution is modified to use template-matching with nearest neighbors. The reconstruction is improved by using the modified least-squares solution only in spectral regions with low signal-to-noise ratio. The results, although preliminary, provide evidence that harmonic zero-phase sine-wave analysis/synthesis, combined with effective estimation of sine-wave amplitudes and probability of voicing, offers a promising approach to noise reduction. >
TL;DR: It was found that the measured SNR improvement factor due to quantum noise agreed closely with that determined from the measured transmission values of a grid, as predicted from the theoretical model.
Abstract: We developed a theoretical model which describes the improvement of signal-to-noise ratio (SNR) by a grid in digital radiography. The model takes into account the effects of spatial variations in the scatter-to-primary ratio and in the large-area contrast over an image with structured background on quantum noise, and the effects of noise in the imaging system such as electronic noise and digitization noise. Based on the theoretical model, we analyzed the effects of these factors on the SNR when a grid is employed. We performed experimental measurements to evaluate the improvement in the SNR by a grid when quantum noise is the dominant noise source. It was found that the measured SNR improvement factor due to quantum noise agreed closely with that determined from the measured transmission values of a grid, as predicted from our theoretical model. In order to evaluate the relative performance of grids with various geometric design parameters for digital radiographic systems, we employed Monte Carlo calculations and determined the transmission values of a number of grids under various scatter conditions. The calculated SNR improvement factor, due to quantum noise, correlated well with the measured improvement of the SNR by the grids. Our model predicts that the SNR improvement factor depends strongly on the local contrast ratio and also on the scatter-to-primary ratio. The SNR improvement factor is higher in the underpenetrated regions than in the well-penetrated regions of an image.
TL;DR: It is shown that, under certain low signal-to-noise ratio (SNR) conditions, the HOS-based method performs much better than the conventional energy one.
Abstract: The use of higher-order spectra (HOS) is proposed for improving detection performance in non-Gaussian signals. The method comprises two stages. First, the higher-order spectra of the received signal are estimated using conventional spectral estimation techniques; then, a (maximum) likelihood ratio test (LRT) is performed in the higher-order-spectra domain. It is shown that, under certain low signal-to-noise ratio (SNR) conditions, the HOS-based method performs much better than the conventional energy one. The required processor is derived and its performance is analyzed. While the method is demonstrated using the third-order spectrum (called bispectrum), it can easily be extended to higher-order analysis (e.g. trispectrum, etc.). >
05 Dec 1990
TL;DR: It is shown that the proposed estimator is statistically efficient even in the difficult situation when the platform does not maneuver and the observability is obtained only by the use of the frequency measurements.
Abstract: A target motion analysis for a narrowband passive sonar that yields bearing and frequency measurements in the presence of false detections (clutter) in a low signal-to-noise ratio (SNR) environment is proposed. The likelihood function used to compute the maximum likelihood estimation of the track parameters (localization and frequency) incorporates the false alarms via the probabilistic data association technique. The Cramer-Rao lower bound is calculated, and results obtained from simulations are shown to be compatible with it. A test of track acceptance is presented. It is shown that the proposed estimator is statistically efficient even in the difficult situation when the platform does not maneuver and the observability is obtained only by the use of the frequency measurements. >
TL;DR: A contrast-detail study shows that the fluoroscopic system is better at detecting large, low contrast objects than portal films and modifications to the metal plate/phosphor detector, lens, TV camera, and frame grabber should improve the performance of the system further.
Abstract: We have been developing a digital fluoroscopic imaging system to replace the portal films that are currently used to verify patient positioning during radiotherapy treatments. Our system differs from previously reported devices in the construction of the detector and in the operation of the TV camera. The signal, noise, and signal-to-noise properties of this system have been determined by measuring the modulation transfer function [MTF(f)], the noise power spectra [NPS(f)], and by calculating the detective quantum efficiency [DQE(f)] of the system. The results show: (i) that the spatial resolution of the system is determined largely by the lens of the TV camera and by frame grabber; and (ii) that the noise in the system is dominated by the secondary light quanta, due to the poor light collection efficiency of the optical chain. Despite these physical limitations, a contrast-detail study shows that the fluoroscopic system is better at detecting large, low contrast objects than portal films. Therefore the system is already a reasonable alternative to portal films and modifications to the metal plate/phosphor detector, lens, TV camera, and frame grabber should improve the performance of the system further.
TL;DR: In this article, a new technique which allows electro-optic sampling to be performed in a frequency range which is above the 1/f noise regime of the pump-probe laser, while at the same time utilizing the high sensitivity, low noise properties of an audio-frequency lock-in amplifier is presented.
Abstract: We report on a new technique which allows electro‐optic sampling to be performed in a frequency range which is above the 1/f noise regime of the pump‐probe laser, while at the same time utilizing the high‐sensitivity, low‐noise properties of an audio‐frequency lock‐in amplifier. This new approach to electro‐optic signal extraction has resulted in an unprecedented improvement of two orders of magnitude in signal‐to‐noise capability. The new technique is compared to previous, conventional approaches.
TL;DR: A method is proposed for decorrelating the correlated sources, and an analytical expression is derived to show the decorrelation effect of the proposed technique for a line array of equispaced elements.
Abstract: Expressions are derived for the SNR (signal-to-noise-ratio) at the output of two antenna array processors in the presence of correlated arrivals, and the effect on the output SNR of the magnitude and the phase of the correlation, the number of elements in the array, the direction of the level of the interference source, and the level of the uncorrelated noise is investigated. The two processes considered are the optimal element space processor (ESP) and the optimal postbeamformer interference canceller (PIC). The PIC processes the signal by forming two beams and adjusting the weights of one beam, in contrast to the ESP where the signals from all the elements are weighted and all the weights are adjusted. A method is proposed for decorrelating the correlated sources, and an analytical expression is derived to show the decorrelation effect of the proposed technique for a line array of equispaced elements. Numerical examples are included. >
TL;DR: In this article, the current usage of linear pulse-shaping filters is reviewed and it is shown that pulse amplifiers with different shaping networks are best compared for spectral resolution and count-rate capability at a shaped-pulse width measured at a specific fraction of peak height.
Abstract: The current usage of linear pulse-shaping filters is reviewed. It is shown that pulse amplifiers with different shaping networks are best compared for spectral resolution and count-rate capability at a shaped-pulse width measured at a specific fraction of peak height, preferably 50% (t/sub 1/2/). With this normalization, it is shown that the best tradeoff between noise and resolving time is obtained with the quasi-triangular waveform, the worst with the cusp. Noise, resolving time, and ballistic deficit are compared through graphs and tables for the cusp, true Gaussian, true triangle, CR-(RC)/sup n/, sine/sup n/, and quasi-triangular shapes for normalizations at t/sub p/, t/sub 1/2/, and t/sub 0.01/. Rules are given for estimating the effect of pulse shape on noise performance. >