Higher-order Wigner distributions are not unique: definitions differ in the lag separations between the terms used in the time-domain product, as well as in how many of the terms are conjugated. We study a class of th...
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ISBN:
(纸本)081940943X
Higher-order Wigner distributions are not unique: definitions differ in the lag separations between the terms used in the time-domain product, as well as in how many of the terms are conjugated. We study a class of third-order WDs (TWD), parameterized by a single parameter (alpha) , and show that there is a duality between the choices of (alpha) equals -1/3 (Gerr's definition) and (alpha) equals -1. Interesting signal attributes, such as the instantaneous frequency, the derivative of the log-magnitude, and the group delay can be recovered from the TWD. Important issues such as aliasing problems and sampling requirements, and whether or not the analytic form of a real signal should be used, are addressed. It is shown theoretically that the TWD with (alpha) equals -1 is particularly useful for the detection of transients in the presence of colored Gaussian noise.
In a very recent past, new techniques, referred to as time-scale methods and making use of the so-called wavelet transform, have been proposed for the analysis of nonstationary or time-varying signals. They are basica...
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ISBN:
(纸本)0819404098
In a very recent past, new techniques, referred to as time-scale methods and making use of the so-called wavelet transform, have been proposed for the analysis of nonstationary or time-varying signals. They are basically devoted to the description of signal time evolutions at different observation scales; this is achieved by using shifted and dilated versions of some elementary analyzing waveform along the time axis. The purpose of this paper is twofold: it is intended (1) to provide a brief overview of linear wavelet techniques (continuous and discrete transforms) and bilinear time-scale methods (time-scale energy distributions), and (2) to put them in some common perspective with existing signalprocessing tools (Gabor decompositions, constant-Q analysis, quadrature mirror filters, wideband ambiguity functions, time-frequency energy distributions). Existing or potentially relevant applications are also pointed out.
A new high-performance systolic architecture for calculating the discrete Fourier transform (DFT) is described which is based on two levels of transform factorization. One level uses an index remapping that converts t...
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A new high-performance systolic architecture for calculating the discrete Fourier transform (DFT) is described which is based on two levels of transform factorization. One level uses an index remapping that converts the direct transform into structured sets of arithmetically simple four-point transforms. Another level adds a row/column decomposition of the DFT. The architecture supports transform lengths that are not powers of two or based on products of coprime numbers. Compared to previous systolic implementations, the architecture is computationally more efficient and uses less hardware. It provides low latency as well as high throughput, and can do both one- and two-dimensional DFTs. An automated computer-aided design tool was used to find latency and throughput optimal designs that matched the target field programmable gate array structure and functionality.
The primary basis for adaptive radar algorithm design is that (1) a Binary Hypothesis formulation with unknown parameters is an adequate test and (2) that radar interference is composed of combinations of thermal nois...
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ISBN:
(纸本)0819425842
The primary basis for adaptive radar algorithm design is that (1) a Binary Hypothesis formulation with unknown parameters is an adequate test and (2) that radar interference is composed of combinations of thermal noise, self induced clutter, and extraneous noise. This is the typical generalized likelihood formulation that yield the CFAR characteristic for the assumed conditions. implementations have shown that such formulations yield inadequate performance in complex clutter environments. As compensation measure, a secondary CFAR process then addresses the potential violation of this assumption by large ''target-like'' interference such as large Clutter discretes or a large number of targets interfering with each other. In order to detect small targets, an approach based on the Likelihood Statistic provides a technique for optimally suppressing the neighboring large signals. Performance is characterized as a function of a generalized distance and relative signal power ratios in the Joint Space-Time domain.
We argue that the standard definition of signal to noise ratio may be misleading when the signal or noise are nonstationary. We introduce a new measure that we call local signal to noise ratio (LSNR) which is well sui...
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ISBN:
(纸本)0819463922
We argue that the standard definition of signal to noise ratio may be misleading when the signal or noise are nonstationary. We introduce a new measure that we call local signal to noise ratio (LSNR) which is well suited to take into account nonstationary situations. The advantage of our measure is that it is a local property unlike the standard SNR which is a single number representing the total duration of the signal. We simulated a number of cases to show that our measure is more indicative of the noise and signal level for nonstationary situations.
We present a general procedure for obtaining equations of motion for the Wigner distribution of functions that are governed by ordinary and partial differential equations. For the case of fields we show that in genera...
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ISBN:
(纸本)0819437611
We present a general procedure for obtaining equations of motion for the Wigner distribution of functions that are governed by ordinary and partial differential equations. For the case of fields we show that in general one must consider Wigner distributions of the four variables, position, momentum, time and frequency. We also show that in general one cannot write an equation of motion for position and momentum however it can be done in some cases, the Schrodinger equation being one such case. Our method leads to an equation of motion for the Schrodinger equation with time dependent potentials in contrast to the result obtained by Wigner and Moyal which was for time independent potentials.
A comprehensive theory for time-frequency based signal detection has been developed during the past decade. The time-frequency detectors proposed in literature are linear structures operating on the time-frequency rep...
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ISBN:
(纸本)0819450782
A comprehensive theory for time-frequency based signal detection has been developed during the past decade. The time-frequency detectors proposed in literature are linear structures operating on the time-frequency representation of the signals and are equivalent to quadratic receivers that are defined in the,time domain. In this paper, an information theoretic approach for signal detection on the time-frequency plane is introduced. In recent years, Renyi entropy has been proposed as an effective measure for quantifying signal complexity on the time-frequency plane and some important properties of this measure have been proven. In this paper, a new approach that uses the entropy functional as the test statistic for signal detection is developed. The minimum error detection algorithm is derived and the performance of this new signal detection method is demonstrated through examples.
We present a number of methods that use image and signed processing techniques for removal of noise from a signal. The basic idea is to first construct a time-frequency density of the noisy signal. The time-frequency ...
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ISBN:
(纸本)0819432938
We present a number of methods that use image and signed processing techniques for removal of noise from a signal. The basic idea is to first construct a time-frequency density of the noisy signal. The time-frequency density, which is a function of two variables, can then be treated as an "image", thereby enabling use of image processing methods to remove noise and enhance the image. Having obtained an enhanced time-frequency density, one then reconstructs the signal. Various time frequency-densities are used and also a number of image processing methods are investigated. Examples of human speech and whale sounds are given. In addition, new methods are presented for estimation of signal parameters from the time-frequency density.
This paper considers a class of blind beamforming problems in which the amount of prior information is very limited. The array sensors are placed in unknown locations within a geographical region, and have unknown fre...
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ISBN:
(纸本)0819422347
This paper considers a class of blind beamforming problems in which the amount of prior information is very limited. The array sensors are placed in unknown locations within a geographical region, and have unknown frequency/spatial response. The sensors communicate synchronously with a main processor unit. The array is illuminated by a source, which may be narrow- or broadband, in near or far field. Additional disturbances may be present, in the form of interferers, possibly correlated or coherent with the main signal, and additive noise. The goal is required to steer beam toward the desired signal. Four schemes are presented, each based on the type of prior available information.
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