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.
Interceptor missiles process IR images captured by a focal plane array for locating and guiding the interceptor toward an intended target. A typical interceptor signalprocessing chain comprises two parts. Front-end v...
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ISBN:
(纸本)0819454974
Interceptor missiles process IR images captured by a focal plane array for locating and guiding the interceptor toward an intended target. A typical interceptor signalprocessing chain comprises two parts. Front-end video processing operates on all pixels of the image and performs such operations as non-uniformity correction (NUC), image stabilization, frame integration and detection. Back-end target processing, which tracks and classifies targets detected in the image, performs such algorithms as Kalman tracking, spectral feature extraction and target discrimination. signalprocessing requirements increased as sensor bandwidth increases and interceptors operate against more sophisticated targets. In the past, video processing was implemented using ASICs or FPGAs because computation requirements exceeded the throughput of general-purpose processors. Target processing was performed using hybrid architectures that included ASICs. DSPs and general-purpose processors. The resulting systems tended to be very function-specific, and required custom software development. These systems were developed using non-integrated toolsets, and test equipment had to be developed along with the processor platform. The lifespan of the interceptor platform on which the signal processors operate often spans decades, while the specialized nature of processsor hardware and software makes it difficult and costly to upgrade. As a result., the signalprocessing systems often run on outdated components, signalprocessingalgorithms are difficult to update. and system effectiveness is impaired by the inability to rapidly, respond to new threats. A new design approach to interceptor signalprocessing is made possible by three developments: Moore's Law - driven improvement in computational throughput;a newly introduced vector computing capability in general-purpose processors and a modern set of open interface software standards. Today's multiprocessor commercial-off-the-shelf (COTS) platforms hav
Fine-grain pipelined adaptive decision-feedback equalizer (ADFE) architectures are developed using the relaxed look-ahead technique. This technique, which is an approximation to the conventional look-ahead computation...
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ISBN:
(纸本)0819412767
Fine-grain pipelined adaptive decision-feedback equalizer (ADFE) architectures are developed using the relaxed look-ahead technique. This technique, which is an approximation to the conventional look-ahead computation, maintains functionality of the algorithm rather than the input-output behavior. Thus, it results in substantial hardware savings as compared to either parallel processing or look-ahead techniques. The delay relaxation, delay transfer relaxation, and sum relaxation are introduced for purposes of pipelining. Both the conventional and the predictor form of ADFE have been pipelined. The performance of the pipelined algorithms for the equalization of a magnetic recording channel is studied. It is demonstrated via simulations that, for a byte error rate of 10-7 or less, speed-ups of up to 8 can be easily achieved with the conventional ADFE. The predictor form of ADFE allows much higher speed-ups (up to 32) for less than 1 dB of SNR degradation.
We address the question of the importance of satisfying the marginal conditions in a time-frequency distribution and discuss in detail the fundamental and practical issues involved. We also examine the marginals of th...
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ISBN:
(纸本)0819450782
We address the question of the importance of satisfying the marginal conditions in a time-frequency distribution and discuss in detail the fundamental and practical issues involved. We also examine the marginals of the spectrogram. The spectrogram often gives reasonable results even though both marginals can never be satisfied exactly, but sometimes it can give very unreasonable results. We show by examples that the spectrogram gives the clearest characterization of the time-frequency properties of a signal when the combined error in both of its marginals is as small as possible. In contrast, when the error in either one of the marginals of the spectrogram is large, the time-frequency characterization degrades. Some different error measures are described. We discuss the issues involved both theoretically and by way of numerical simulations. We also address the issue of marginals for the random case.
In time-frequency analysis, we extend functions of one variable to functions of two variables. The functions of two variables provide information about the signal that is not easily discernible from the functions of o...
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ISBN:
(纸本)0819425842
In time-frequency analysis, we extend functions of one variable to functions of two variables. The functions of two variables provide information about the signal that is not easily discernible from the functions of one variable. In this paper, we investigate a method for creating quartic functions of three variables and also a quartic function of all four variables. These quartic functions provide a meaningful representation of the signal that goes beyond the well known quadratic functions. The quartic functions are applied to the design of signal-adaptive kernels for Cohen's class and shown to provide improvements over previous methods.
In this paper, the coherent signal-subspace method (CSM) is extended for estimation of bearing, elevation and range of multiple, near-field, broad-band sources. Analytical results are also derived to justify the effec...
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ISBN:
(纸本)0819412767
In this paper, the coherent signal-subspace method (CSM) is extended for estimation of bearing, elevation and range of multiple, near-field, broad-band sources. Analytical results are also derived to justify the effectiveness of the near-field CSM. It is shown that the coherently averaged sample covariance matrix in the near-field CSM has complex Wishart distribution with number of degrees-of-freedom equaling the time-bandwidth product, provided that (1) the frequency components of the array output are statistically independent and Gaussian distributed, and (2) the errors between all the actual source locations and the preliminary estimate of the source cluster center are upperly bounded by a small constant. Some simulation results are provided to show the effectiveness of the near-field CSM.
A simple formulation is given for generating convolution theorems in any representation. Using this method we obtain the convolution theorem for the scale representation. We generalize the concept of invariance to any...
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ISBN:
(纸本)081940943X
A simple formulation is given for generating convolution theorems in any representation. Using this method we obtain the convolution theorem for the scale representation. We generalize the concept of invariance to any basis set and devise a method for handling linear invariant systems for arbitrary quantities. The Wiener-Khinchin theorem is generalized to arbitrary power energy densities. Also, we show how standard probability theory can be formulated in terms of signals.
Cohen's class of time-frequency distributions has been recognized to have significant potential for the analysis of complicated signals. The spectrogram, though it offers comparatively lower time-frequency resolut...
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ISBN:
(纸本)081940943X
Cohen's class of time-frequency distributions has been recognized to have significant potential for the analysis of complicated signals. The spectrogram, though it offers comparatively lower time-frequency resolution than other, more recently investigated members of Cohen's class, is still the most broadly used TFD today. Packages are available which perform SP evaluation and offer signal synthesis from the closely related short-time Fourier transform. These packages allow the SP to be the widely accessible signalprocessing tool that it is. In this paper, we introduce two decompositions of TFDs, the SP decomposition and the weighted reversal correlator decomposition. The decompositions are useful for TFD interpretation, fast implementations using SP building blocks and related high-resolution, linear signal synthesis method using STFT signal synthesis building blocks. It is hoped that these decompositions will facilitate the development of TFD signal analysis/synthesis packages (using existing SP analysis/synthesis packages), and that these packages will make TFDs other than the SP accessible to a broad audience.
A new method for numerically integrating partial differential equations (PDEs) has been under study for the last few years. This method is based on principles of multidimensional (MD) Kirchhoff circuits and multidimen...
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ISBN:
(纸本)0819412767
A new method for numerically integrating partial differential equations (PDEs) has been under study for the last few years. This method is based on principles of multidimensional (MD) Kirchhoff circuits and multidimensional wave digital filters (MD WDFs), which explains why it has probably not been discovered earlier. It makes wide use of methods and results that have been developed by extensive research in the areas of circuit theory and digital signalprocessing, but that are rather unknown outside of the small circle of experts on MD WDFs. Instead of talking about MD WDFs we prefer using, within the context of numerical integration, the designation `discrete multidimensionally passive (MD-passive) dynamical systems.'
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