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Aerospace and Electronic Systems, IEEE Transactions on

Issue 2 • Date April 1997

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Displaying Results 1 - 17 of 17
  • Power switched-capacitor DC-DC converter: analysis and design

    Page(s): 386 - 395
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1924 KB)  

    This paper shows that a switched-capacitor DC-DC converter (SCDDC) can be designed to process up to several tens of watts of output power at an efficiency exceeding 80%. Converter operation is analyzed by "modified state-space-averaging", (MSSA) which is generally suitable for analysis of converters with nonlinear ripple. A design procedure is presented along with experimental verification. View full abstract»

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  • Decentralized CFAR detection with binary integration in Weibull clutter

    Page(s): 396 - 407
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2487 KB)  

    The analysis of a distributed multiradar system with decentralized decisions, operating in the presence of nonstationary Weibull clutter is presented. Each sensor employs a constant false-alarm rate (CFAR) algorithm and binary integration and transmits its local decisions to the fusion center, which takes the final decision. Optimal local double thresholds and decision fusion rule are determined according to the Neyman-Pearson (N-P) criterion and the global performance is evaluated by a novel approach to optimize distributed binary integration systems. View full abstract»

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  • Neural network-based radar detection for an ocean environment

    Page(s): 408 - 420
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9750 KB)  

    Novel detection schemes are developed using a coherent X-band radar for the detection of small pieces of icebergs. The methods use Wigner-Ville (WV) distribution to perform detection in a joint time-frequency space. Two separate methodologies are presented. The first method extracts classification features from the ambiguity function of the received signal and a neural network is used to perform detection based on these features. The second method uses the method of Principal Components Analysis (PCA) to extract essential information from the time-frequency space for classification. Using real radar data, results are presented and the developed methods are also compared to a conventional Doppler constant false-alarm rate (CFAR) processor. View full abstract»

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  • Cramer-Rao lower bounds on estimating the parameters of a filtered burst of sinusoid

    Page(s): 421 - 431
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3273 KB)  

    Using Cramer-Rao lower bounds (CRLBs) for estimating time of arrival and frequency of a burst of sinusoid, we investigate the effect of the location and extent of the observation interval, relative to the support of the received signal pulse, and the effect of not knowing the time duration of the pulse. The effect of filtering the received waveform using a known bandpass filter is also studied and is found to be small. The tail portion of the filter response after the signal pulse ends provides almost no information about the signal parameters. The initial transient build-up portion of the signal pulse response provides specially important information about time of arrival. For observation intervals which include the whole pulse duration, there are significant potential performance differences between the cases of known and unknown pulse duration. View full abstract»

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  • Clutter-map CFAR detection for range-spread targets in non-Gaussian clutter. I. System design

    Page(s): 432 - 443
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2625 KB)  

    The problem of constant false-alarm rate (CFAR) detection of possibly range-spread targets in clutter-dominated environment, whether Weibull or lognormal is presented. The proposed scheme is a member of the clutter-map CFAR family, which relies on a combination of space and time processing as well as on the relevant properties of the location-scale distributions; it ensures CFAR against noise with biparametric variations without incurring masking effects from slow, extended targets or multiple interferers. We also give guidelines for designing the system parameters, along with approximate formulas for setting the appropriate threshold multipliers to achieve a given false-alarm rate (FAR) under Weibull and lognormal clutter. View full abstract»

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  • Clutter-map CFAR detection for range-spread targets in non-Gaussian clutter. II. Performance assessment

    Page(s): 444 - 455
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3674 KB)  

    The performance assessment of the clutter-map constant false-alarm rate (CFAR) procedure presented in Part I [1] is introduced. At first, the performance in the presence of point targets is investigated, subject to both Weibull and lognormal clutter, so as to elicit the influence of the system parameters. The study essentially relies on Monte-Carlo simulations, but approximations for the detection rate are also developed. Admittedly, a global figure of performance, the Average Threshold Deviation (ATD), is introduced and its worth as a design tool is validated. Next, the effect of extended as well as multiple targets is considered, showing that the system can be designed so as to avoid self-masking from either range-spread targets persisting on the same map cell, or spurious targets in close spatial proximity to the cell under test. Finally, the system robustness is demonstrated through a sensitivity study, aimed at investigating the effect of a possible mismatch between the design and the actual clutter distribution, that of the clutter correlation and of a thermal noise component in the overall disturbance. View full abstract»

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  • Soft-switched square-wave half-bridge DC-DC converter

    Page(s): 456 - 463
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5310 KB)  

    A constant-frequency zero-voltage-switched square-wave DC-DC converter is introduced, and results from experimental half-bridge implementations are presented. A nonlinear magnetic element produces the advantageous square waveforms, and provides isolated terminals from which the output voltage may be controlled. Semiconductor stresses and losses are minimized both by the square waveforms and by low switching losses. The active switches and the output rectifiers both exhibit zero-voltage switching. The active switches (metal-oxide-semiconductor field-effect transistors (MOSFETs)) are operated at a fixed frequency with 50% duty cycle, which allows the use of a simple open-loop gate drive. Experimental implementations verify predicted operation. View full abstract»

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  • A tracking algorithm for infrared images based on reduced sufficient statistics

    Page(s): 464 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1824 KB)  

    The problem of tracking a target using a sequence of infrared (IR) images is addressed. A Bayes-closed estimation algorithm developed by Kulhavy is shown to be well suited to the IR tracking problem. Due to the form of the model for the radiation intensity pattern on the IR focal plane array, closed-form expressions are found for the reduced sufficient statistics (RSS) which are used to approximate the true posterior density in the Kulhavy algorithm. An estimate of the target state is then derived via a reconstruction formula from the RSS. For comparison, both a previously developed IR tracking algorithm based on an extended Kalman filter (EKF) and the new RSS-based method are used to track a target through a sequence of IR images. It is shown that the RSS algorithm can maintain track in high velocity scenarios where the EKF diverges. View full abstract»

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  • Stiffening control of a class of nonlinear affine systems

    Page(s): 473 - 484
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3612 KB)  

    A control procedure is proposed for dealing with the active stiffening motion of a class of flexible structures characterized by nonlinear affine dynamics. Based on recent developments in the area of differential geometry, the procedure allows for determining the critical area for placing a sensor on a given flexible structure beyond which a centralized controller located on the rigid part becomes ineffective. This is used subsequently for locating instrumentation devices and hardware components on the elastic parts of the system. Numerical simulations are carried out to assess the validity of the theoretical framework. Several meaningful results are obtained, and propositions for further findings are outlined. View full abstract»

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  • Rocket plume image sequence enhancement using 3D operators

    Page(s): 485 - 498
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (8479 KB)  

    Reported here are the results of tests of five 3D image operators in eleven configurations to determine which is best for the enhancement of image sequences of rocket plumes. The operators enhance images both for visual inspection and for radiometric characterization. The tests used real and synthetic imagery to evaluate the operators under a variety of conditions. The results suggest the best choice of operator depends on the grayscale distribution of the noise in the image sequence. In terms of signal-to-noise ratio (SNR), long duration median filters with moderate spatial support appear to work best overall. The results show that successful enhancement for visual inspection requires the original image data to be remapped prior to filtering. This need not destroy the radiometric information in the imagery. Some attributes of rocket plume image time sequences and the noise in them are described. The remapping procedure is detailed and the operators tested are described. The methodology is explained and the results of the numerous tests on synthetic imagery are presented. The application of the procedures to two real rocket plume image sequences is described. View full abstract»

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  • DC-to-DC converter with no magnetic elements and enhanced regulation

    Page(s): 499 - 506
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3113 KB)  

    A switched-capacitor-based (SC) step-up DC converter is proposed. It contains no inductors and transformers, thus it can be realized in small size, exhibiting low weight and high power density. Two switched-capacitor circuits, operating in antiphase in each half-cycle, are used to control the energy flow from an unregulated voltage source to a regulated output. The capacitors are charged and discharged according to a designed sequence. To enhance the line and load regulation capability, in each half-cycle, each charging interval is split into two subintervals, which are followed by noncharging subintervals whose duration is dictated by the pulsewidth modulation (PWM) feedback circuit. The new converter is advantageous for applications in which significant line drops are likely to occur. View full abstract»

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  • Parallel simulation of a large-scale aerospace system in a multicomputer environment

    Page(s): 507 - 522
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9636 KB)  

    This work describes the application of newly developed parallel processing techniques that exploit the irregularly-structured functional parallelism present within a test-bed aerospace system (i.e., a Space Shuttle main rocket engine simulation) utilizing a reduced complexity multicomputing architecture with an arbitrary topology. The methodologies are applicable to real time parallel simulation of large-scale dynamic systems and include deterministic model optimization and decomposition techniques, automated translation mechanisms, and a newly developed task allocation heuristic. The effectiveness of these techniques are illustrated with performance being measured empirically for a wide range of topological configurations using a partially reconfigurable network of Transputers. View full abstract»

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  • A generalized S-D assignment algorithm for multisensor-multitarget state estimation

    Page(s): 523 - 538
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3883 KB)  

    We develop a new algorithm to associate measurements from multiple sensors to identify the real targets in a surveillance region, and to estimate their states at any given time. The central problem in a multisensor-multitarget state estimation problem is that of data association-the problem of determining from which target, if any, a particular measurement originated. The data association problem is formulated as a generalized S-dimensional (S-D) assignment problem, which is NP-hard for S≥3 sensor scans (i.e., measurement lists). We present an efficient and recursive generalized S-D assignment algorithm (S≥3) employing a successive Lagrangian relaxation technique, with application to the localization of an unknown number of emitters using multiple high frequency direction finder sensors (S=3, 5, and 7). View full abstract»

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  • Subspace selection for partially adaptive sensor array processing

    Page(s): 539 - 544
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1728 KB)  

    This paper introduces a cross-spectral metric for subspace selection and rank reduction in partially adaptive minimum variance array processing. The counter-intuitive result that it is suboptimal to perform rank reduction via the selection of the subspace formed by the principal eigenvectors of the array covariance matrix is demonstrated. A cross-spectral metric is shown to be the optimal criterion for reduced-rank Wiener filtering. View full abstract»

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  • Accuracy requirements in off-line array calibration

    Page(s): 545 - 556
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3099 KB)  

    Practical sensor arrays are characterized by certain physical parameters, related to the array shape and its electrical properties. Accurate direction finding requires calibration of these parameters to a relatively high accuracy. Depending on the application, calibration may be performed either off-line or on-line. Off-line calibration is performed by transmitting signals from known locations and measuring the array response. The array parameters can then be estimated by maximum likelihood, least-squares, or some other algorithm. This work relates the parameter estimation accuracy achieved in off-line calibration to the direction-of-arrival (DOA) errors during on-line operation. It then proposes a criterion for choosing the off-line calibration points (number and location) so as to meet on-line accuracy requirements. View full abstract»

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  • A unified approach to proportional navigation

    Page(s): 557 - 567
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1932 KB)  

    In this paper, the two major classes of proportional navigation (PN), namely, true proportional navigation (TPN) and pure proportional navigation (PPN) are analyzed and solved by a unified approach. The analytical tools used in the line-of-sight (LOS) referenced systems such as TPN, realistic true proportional navigation (RTPN), generalized true proportional navigation (GTPN) and ideal proportional navigation (IPN), are extended here to handle the interceptor velocity referenced systems such as PPN and its variants. It is found that the above two branches of guidance systems belong to a more general PN scheme which defines the acceleration of the interceptor as being proportional to the LOS rate with direction normal to an arbitrarily assigned vector L&oarr;. For example, L&oarr; of TPN is LOS, and L&oarr; of PPN is the interceptor's velocity. Every PN scheme associates with a specific form of L&oarr;. The optimal PN (OPN) problem which concerns the determination of the optimal direction L&oarr; is also addressed. Under the proposed general PN scheme, its six special cases, i.e., TPN, RTPN, GTPN, IPN, PPN, and OPN are solved in a unified way from which many new relations among them can be revealed, and their performances can be compared on a common basis. View full abstract»

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  • Demonstration of a jitter rejection technique for free-space laser communication

    Page(s): 568 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3297 KB)  

    An active jitter compensation scheme intended for free space intersatellite laser communication, utilizing self-tuning feedforward compensation, is developed. It is implemented via computer-controlled analog circuitry. The theory, design, and implementation of the laboratory prototype are discussed. A performance evaluation, comparing the feedforward compensator with the existing closed-loop control, is presented with the feedforward technique demonstrating significant jitter reduction. View full abstract»

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IEEE Transactions on Aerospace and Electronic Systems focuses on the equipment, procedures, and techniques applicable to the organization, installation, and operation of functional systems designed to meet the high performance requirements of earth and space systems.

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Editor-in-Chief
Lance Kaplan
Army Research Laboratory