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Aerospace and Electronic Systems, IEEE Transactions on

Issue 1 • Date Jan. 1995

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Displaying Results 1 - 25 of 51
  • Resolution of a 2/spl pi/ ambiguity problem in multiple frequency spectral estimation

    Page(s): 2 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB)  

    An algorithm is proposed to resolve a fundamental 2/spl pi/ ambiguity problem occurring in multiple frequency spectral estimation. Given M frequencies f/sub m/, and I separate frequency estimators with unambiguous bandwidths F/sub i/, the ambiguity problem can be stated as solving for the fm, given the estimator outputs, /spl alphasub mi/, (1/spl les/m/spl les/M;1/spl les/i/spl les/I) where f/sub m/=/spl alphasub mi/+K/sub mi/F/sub i/ and K/sub mi/ is some integer. The proposed algorithm exhaustively resolves all possible /spl alphasub mi/ groupings into single frequency values using a noise insensitive technique that exchanges system bandwidth for noise protection. The correct multiple frequencies are then defined as the single frequencies that repeat a specified number of times. A complete analysis is included.<> View full abstract»

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  • A unified approach to the design of decentralized detection systems

    Page(s): 9 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1177 KB)  

    A unified approach to the design of decentralized detection networks with arbitrary topologies is proposed and analyzed. In this approach, a decentralized detection system of arbitrary topology is represented by a communication matrix that specifies the interconnection structure of the detection network. This matrix is used to derive the general decision rule using the person-by-person-optimal (PBPO) solution methodology. It is shown that the PBPO decision rule is a likelihood ratio test for statistically independent observations. The threshold of the test is shown to be a function of the decision input vector of the detector under consideration. This unified approach is used to obtain the PBPO decision rules of decentralized detection systems with various topologies. Various results in the literature are verified. In addition, the PBPO decision rules for a decentralized detection system with peer communication are presented. Numerical examples are presented for illustration.<> View full abstract»

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  • Dignet: an unsupervised-learning clustering algorithm for clustering and data fusion

    Page(s): 21 - 38
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4782 KB)  

    Dignet is a self-organizing artificial neural network (ANN) that exhibits deterministically reliable behavior-to-noise interference, when the noise does not exceed a prespecified level of tolerance. The complexity of the proposed ANN, in terms of neuron requirements versus stored patterns, increases linearly with the number of stored patterns and their dimensionality. The self-organization of Dignet is based on the idea of competitive generation and elimination of attraction well in the pattern space. Dignet is used for detection and distributed decision fusion. Analytical and numerical results are included.<> View full abstract»

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  • Calculating the performance of linear and square-law detectors

    Page(s): 39 - 51
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1304 KB)  

    A method is presented for calculating the performance of linear and square-law detectors in detection schemes that employ noncoherent integration. The method consists of transforming the coherent characteristic function, which is usually easy to obtain to a noncoherent moment generating function describing the test statistic of a linear or square-law detector. The method provides a single mathematical framework for many signal models (both classical and new) and can be implemented using standard numerical routines. Although the method is not always optimum in terms of computing speed for specific classical models, its common approach for all signal models makes it very efficient in term of learning and implementation times. Classical results as well as results for an extended set of target models consisting of an arbitrary number of constant amplitude random phase returns are presented to demonstrate the technique. It is shown for the signal parameters considered that the performance difference between the linear and square-law detectors is relatively insignificant.<> View full abstract»

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  • Second-order acceleration models for an MMAE target tracker

    Page(s): 151 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (7545 KB)  

    The performance of a multiple model adaptive estimator (MMAE) for an enhanced correlator/forward-looking-infrared tracker for airborne targets is analyzed in order to improve its performance. Performance evaluation is based on elemental filter selection and MMAE estimation error sizes and trends. The elemental filters are based on either first or second-order acceleration models. Improved filter selection is achieved by using acceleration models that separate the frequency content of acceleration power spectral densities into non-overlapping regions with second-order models versus the more traditional overlapping regions with first-order models. A revised tuning method is presented. The maximum a posteriori (MAP) versus the Bayesian MMAE is investigated. The calculation of the hypothesis probability calculation is altered to see how performance is affected. The impact of the ad hoc selection of a lower bound on the elemental filter probability calculation to prevent filter lockout is evaluated. Parameter space discretization is investigated.<> View full abstract»

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  • Optimal CFAR detection in Weibull clutter

    Page(s): 52 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1764 KB)  

    Optimal, in the maximum likelihood sense, constant false-alarm rate (CFAR) detection for Weibull clutter statistics, is investigated. The proposed OW (optimal Weibull) estimator is proved to be an asymptotically efficient estimator of the mean power of the Weibull clutter. Theoretical analysis of the OW-CFAR detector is provided, while detection performance analysis is carried out using the Monte Carlo simulation method. The operation of the median and morphological (MEMO)-CFAR detector in Weibull clutter statistics is also explained. It performs almost optimally in uniform clutter and, simultaneously, it is robust in multitarget situations. The performance of the proposed OW-CFAR detector in uniformal Weibull clutter is used as a yardstick in the analysis of the MEMO cell-averager (CA) and ordered statistic (OS) CFAR detectors. Nonfluctuating and fluctuating (Swerling II) targets are considered in detection analysis. The performance of the detectors is also examined at clutter edges.<> View full abstract»

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  • Limitations of radiometer performance in spherically invariant noise

    Page(s): 65 - 68
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    The radiometer is a common method for detection of unknown signals in noise. Most analyses of radiometer performance are based on assumptions of stationary Gaussian noise with known marginal statistics. In this note, we use a spherically invariant noise model to derive simple expressions for radiometer performance degradation in noise variance uncertainty. Numerical examples are provided to show that channel uncertainty imposes a substantial penalty in detection performance.<> View full abstract»

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  • Radar target identification using the bispectrum: a comparative study

    Page(s): 69 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2869 KB)  

    Radar target identification is performed using time-domain bispectral features. The classification performance is compared with the performance of other classifiers that use either the impulse response or frequency domain response of the unknown target. The classification algorithms developed here are based on the spectral or the bispectral energy of the received backscatter signal. Classification results are obtained using simulated radar returns derived from measured scattering data from real radar targets. The performance of classifiers in the presence of additive Gaussian (colored or white), exponential noise, and Weibull noise are considered, along with cases where the azimuth position of the target is unknown. Finally, the effect on classification performance of responses horn extraneous point scatterers is investigated.<> View full abstract»

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  • Controlled-root formulation for digital phase-locked loops

    Page(s): 78 - 95
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9029 KB)  

    In a new formulation for digital phase-locked loops, loop-filter constants are determined from loop roots that can each be selectively placed in the s-plane on the basis of a new set of parameters, each with single and direct physical meaning in terms of loop noise band, width root-specific decay rate, or root-specific damping. Loops of first to fourth order are treated in the continuous-update approximation (B LT→0) and in a discrete-update formulation with arbitrary B LT. Deficiencies of the continuous-update approximation in large-B LT applications are avoided in the new discrete-update formulation. A new method for direct, transient-free acquisition with third- and fourth-order loops can improve the versatility and reliability of acquisition with such loops.<> View full abstract»

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  • The team ROC curve in a binary hypothesis testing environment

    Page(s): 96 - 105
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1816 KB)  

    We consider the distributed detection problem, in which a set of decision makers (DMs) receive observations of the environment and transmit finite-valued messages to other DMs according to prespecified communication protocols. A designated primary DM makes the find decision on one out of two alternative hypotheses. All DMs make decisions, in order to maximize a measure of organizational performance. We discuss three different types of decision rules (deterministic, independent randomization, and dependent randomization), and their implications on the organizational performance. Each DM is described by its individual receiver operating characteristic (ROC) curve, which is concave. We determine that concavity is not guaranteed for the case of the ROC curve of a team of DMs, even if the decision rules are perfectly continuous and if the individual ROC curves are strictly concave and smooth unless dependent randomization is allowed.<> View full abstract»

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  • Computer generation of correlated non-Gaussian radar clutter

    Page(s): 106 - 116
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1887 KB)  

    We develop computer simulation procedures which enable us to generate any correlated non-Gaussian radar clutter that can be modeled as a spherically invariant random process (SIRP). In most cases, when the clutter is a correlated non-Gaussian random process, performance of the optimal radar signal processor cannot be evaluated analytically. Therefore, in order to evaluate such processors, there is a need for efficient computer simulation of the clutter. We present two canonical simulation procedures for the generation of correlated non-Gaussian clutter. A new approach for the goodness-of-fit test is proposed in order to assess the performance of the simulation procedure.<> View full abstract»

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  • Real-time decision aiding: aircraft guidance for wind shear avoidance

    Page(s): 117 - 124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3396 KB)  

    Modern estimation theory and artificial intelligence technology are applied to the Wind Shear Safety Advisor, a conceptual airborne advisory system to help flight crews avoid or survive encounter with hazardous low-altitude wind shear. Numerical and symbolic processes of the system fuse diverse, time-varying data from ground-based and airborne measurements. Simulated wind-shear-encounter scenarios illustrate the need to consider a variety of factors for optimal decision reliability. The wind-shear-encounter simulations show the potential of the Wind Shear Safety Advisor for effectively integrating the available information, highlighting the benefits of the computational techniques employed.<> View full abstract»

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  • A fixed frequency LCL-Type series resonant converter

    Page(s): 125 - 137
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5907 KB)  

    A fixed frequency LCL-type series resonant converter (SRC) which uses an inductive output filter is proposed. Steady-state analysis of the converter is presented using complex ac circuit analysis. Based on the analysis, a simple design procedure is given. Detailed space integrated control experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load and supply voltage conditions. Also, detailed experimental results obtained from a metal-oxide-semiconductor field-effect transistor (MOSFET) based 500 W converter are presented to verify the analysis and SPICE simulation results. The results obtained from the analysis, SPICE simulation and the experimental converter are compared. The proposed converter requires a narrow variation in pulsewidth while maintaining lagging power factor mode of operation for a very wide variation in the load as well as supply voltage.<> View full abstract»

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  • Renewal models for maneuvering targets

    Page(s): 138 - 150
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1382 KB)  

    Most model-based tracking algorithms represent the temporal dynamics of a maneuver acceleration with a Markov process. The sample paths so generated may not be plausible. A renewal process model is shown to be more realistic, but a tracker based upon it is seen to be more complicated to implement. The response of the renewal-model tracker is compared with a simpler estimator based upon a Markov model both for the case in which the tracker utilizes an imager, and the case where it does not. It is shown in the latter case that performance improvement is not commensurate with algorithmic complexity. For an image-enhanced tracker, a sophisticated model of target dynamics promises significant performance improvement.<> View full abstract»

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  • Nonredundant error correction DQPSK for the aeronautical-satellite channel

    Page(s): 168 - 181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2595 KB)  

    The performance of differentially encoded quadrature phase-shift keying (DQPSK) system employing nonredundant error correction (NEC) receivers with single- and double-error correction capability is analyzed and evaluated for the aeronautical satellite channel. The NEC is an attractive coding technique which employs differential detectors with more than one symbol delay elements and which does not introduce any redundancy as other coding schemes do. As typical for aeronautical satellite communications, a Rician fading channel with Gaussian power spectrum has been considered. Unlike the additive, uncorrelated from symbol to symbol interference such as additive white Gaussian noise (AWGN) or static cochannel interference (CCI) which has been investigated in the past, analysis of the performance in a fading channel is much more difficult. The difficulty arises from the multiplicative and correlative nature of the fading interference. Bit error rate (BER) performance evaluation results have been obtained by means of computer simulation for various channel conditions, including different values of the K-factor and the fading B DT. These results have indicated that considerable performance gains as compared with conventional differentially detected systems are achieved for high values of K and for very fast fading. Both of these conditions are encountered in typical aeronautical communication systems. Wherever possible, heuristic explanations of the trend of the obtained BER performance evaluation results are also given.<> View full abstract»

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  • Weight effects on the periodic ambiguity function

    Page(s): 182 - 193
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3769 KB)  

    CW radar signals and processors are discussed. The use of the periodic ambiguity function (PAF) to analyze the delay-Doppler performance of CW signals and their corresponding correlation receivers, is extended to include weight function effects. This work provides tools which can predict the delay-Doppler response of almost any phase-coded CW radar. Examples demonstrate that a combination of CW signals having perfect periodic autocorrelation, a matched reference signal with a large number of modulation periods and a smooth weight function, can create a delay-Doppler response with extremely low sidelobes, strongly resembling the response of a coherent pulse train.<> View full abstract»

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  • Model-based multifrequency array signal processing for low-angle tracking

    Page(s): 194 - 210
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6281 KB)  

    Tracking low-altitude targets over the sea is problematic because of interference between the direct and reflected signal. Standard monopulse trackers can experience large errors because of multipath maximum likelihood estimation (MLE) has been used to more accurately estimate the target height in the presence of multipath MLE is a model-fitting technique where the model parameters are chosen to maximize the likelihood function. It is shown that the type of observation model has a large effect on performance. Tracking performance is compared using three different observation models employing varying amounts of a priori information. Results are presented for different array sizes: eight and 32-element arrays and two-element subarrays typical of phase monopulse. Performance is compared with that of standard techniques such as Fourier beamforming and phase monopulse.<> View full abstract»

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  • Dynamic imaging and RCS measurements of aircraft

    Page(s): 211 - 226
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (8239 KB)  

    Results on radar cross section (RCS) measurements and inverse synthetic aperture radar images of a Mooney 231 aircraft using a ground-to-air measurement system (GTAMS) and a KC-135 airplane using an airborne radar are presented. The Mooney 231 flew in a controlled path in both clockwise and counterclockwise orbits, and successively with the gear down, flaps in the take-off position and with the speed brakes up. The data indicates that RCS pattern measurements from both ground-based and airborne radar of flying aircraft are useful and that the inverse synthetic aperture radar (ISAR) images obtained are valuable for signature diagnostics.<> View full abstract»

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  • Efficient and high precision space-variant processing of SAR data

    Page(s): 227 - 237
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4054 KB)  

    We investigate the space-variance of the synthetic aperture radar (SAR) transfer function due to focus depth variation and Earth rotation effect. We introduce a procedure for efficient space-variance compensation which is based on the use of a nonstandard Fourier transform (FT). A number of experiments confirming theoretical results are presented.<> View full abstract»

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  • Analysis of multiframe target detection using pixel statistics

    Page(s): 238 - 247
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2350 KB)  

    Current track-before-detect (TBD) algorithms are developed and analyzed using a path statistic for each potential object trajectory. However this path statistic does not characterize overall performance gain. We propose a pixel-based statistic. This allows the TBD approach to be characterized as an image enhancement algorithm with detection gains compared with single frame detections. It is shown that for the TBD approach to have superior detection over single frame detection the target signal-to-noise ratio (SNR) must be greater than a threshold SNR in order to overcome the uncertainty in the target path. Tradeoffs are made for a class of velocity constrained target paths in terms of the detection gain with respect to the maximum target velocity and number of frames integrated.<> View full abstract»

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  • Analysis of the linear amplifier/analog-digital converter interface in a digital microwave receiver

    Page(s): 248 - 256
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3081 KB)  

    An analysis of the relationship between a linear amplifier chain and an analog-to-digital converter (ADC) in a digital microwave receiver, with respect to sensitivity and dynamic range issues, is presented. The effects of gain, third-order intermodulation products and ADC characteristics on the performance of the receiver are illustrated and design criteria for the linear amplifier chain (given a specified ADC) are developed. A computer program is included which calculates theoretical receiver performance based on gain and third-order intermodulation product selections. Experimental results are also presented and compared with theoretical values.<> View full abstract»

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  • Multimodule parallel series-loaded resonant converters

    Page(s): 257 - 266
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2481 KB)  

    The design and implementation of a multimodule parallel series-loaded resonant (SLR) converter system is presented. The SLR converter to be paralleled is operated in the n=2 discontinuous mode (DCM). Its dc analysis and dynamic modeling are made. In parallel operation, an average control technique is proposed to compensate the mismatch in current control characteristics of each parallel converter. Good dynamic and static current sharing characteristics are obtained. In addition, to obtain good output voltage regulating control performance, a design procedure is presented to find the parameters of feedback voltage controller according to the prescribed specifications.<> View full abstract»

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  • Nonlinear apodization for sidelobe control in SAR imagery

    Page(s): 267 - 279
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1983 KB)  

    Synthetic aperture radar (SAR) imagery often requires sidelobe control, or apodization, via weighting of the frequency domain aperture. This is of particular importance when imaging scenes containing objects such as ships or buildings having very large radar cross sections. Sidelobe improvement using spectral weighting is invariably at the expense of mainlobe resolution presented here is a class of nonlinear operators which significantly reduce sidelobe levels without degrading mainlobe resolution implementation is via sequential nonlinear operations applied to complex-valued (undetected) SAR imagery. SAR imaging is used to motivate the concepts developed in this work. However, these nonlinear apodization techniques have potentially broad and far-ranging applications in antenna design, sonar, digital filtering etc., i.e., whenever data can be represented as the Fourier transform of a finite-aperture signal.<> View full abstract»

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  • A study of volume versus frequency for soft switching IGBT converters

    Page(s): 280 - 287
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1469 KB)  

    Earlier references have described a new soft switched ZVS/ZCS (zero voltage switching, zero current switching) converter for IGBTs that allows operation above 20 kHz. Although frequencies above 20 kHz are now possible for IGBT converters, the optimum frequency for minimum volume may be below 20 kHz because of heat sink requirements. A comparative study considers the reactive component versus heat sink volume tradeoff for two 6 kW converters, one using ZVS/ZCS and the other using a more conventional circuit with hard switching.<> View full abstract»

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  • Functional models for space power electronic circuits

    Page(s): 288 - 296
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2948 KB)  

    Presented here is a new approach to model power electronic components so that system level issues of large space power systems can be studied. To demonstrate this approach, the models for two major power electronic components in the space station power system are described. The new models are useful not only in system level studies but also in the design/analysis of particular components.<> View full abstract»

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Aims & Scope

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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Meet Our Editors

Editor-in-Chief
Lance Kaplan
Army Research Laboratory