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Aerospace and Electronic Systems, IEEE Transactions on

Issue 3 • Date July 1993

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Displaying Results 1 - 25 of 47
  • The hit array: a synthesis tool for multiple access frequency hop signals

    Page(s): 624 - 635
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (895 KB)  

    The hit array formalism was developed for the analysis of general frequency hop waveforms, in the context of coherent active radar and sonar echolocation systems, or multiple access spread spectrum communications. This formalism is shown to be useful for synthesis as well. Necessary and sufficient conditions are derived for a given hit array to be realizable, i.e., to correspond to a valid frequency hopping pattern. A general backtracking-type algorithm is presented to reconstruct the pattern(s) associated with this hit array. This makes it possible to synthesize a set of frequency hop waveforms directly from any given (realizable) hit array, and thus, because of the correspondence between hit array and ambiguity function, from any physically meaningful ambiguity function. In particular, for limited a priori range and Doppler shifts, this is the first efficient algorithm for direct synthesis from ideal ambiguity function specifications. Several reconstruction examples are shown for illustration purposes.<> View full abstract»

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  • Comments on "Comments on Mismatched filter design for periodical binary phased signals" by V.P. Ipatov

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (106 KB)  

    In a comment on a paper by H. Rohling and W. Plagge (ibid., vol.25, no.6, p.890-896, Nov. 1989), V.P. Ipatov (ibid., vol.27, no. 6, p.906-908, Nov. 1991) pointed out that he had already suggested and investigated sequences with zero sidelobes in their cross-correlation function as early as in 1977. G. Sarafin et al., the present commenters, draw attention to their own work (ibid., vol.AES-23, no.5, p.708-710, Sept. 1987), in which they investigated a closely related topic and also suggested a method of synthesizing sequences with zero sidelobes in their cross-correlation function.<> View full abstract»

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  • Performance prediction of the interacting multiple model algorithm

    Page(s): 755 - 771
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1136 KB)  

    The interacting multiple model (IMM) algorithm has been shown to be one of the most cost-effective estimation schemes for hybrid systems. Its performance, however, could only be evaluated via expensive Monte Carlo simulations. An effective hybrid approach to the performance evaluation without recourse to simulations is presented. This approach is based on a scenario-conditional performance measure of hybrid nature in the sense that it is a continuous-valued matrix function of a discrete-valued random sequence-the system mode sequence. This system mode sequence is an essential description of the scenario of the problem of interest on which the performance of the algorithm is to be predicted. The performance measure is calculated efficiently in an offline recursion. The ability of this approach to predict accurately the average performance of the algorithm is illustrated via two important examples: a generic air traffic control tracking problem and a nonstationary noise identification problem View full abstract»

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  • A simple fixed-lag algorithm for tracking frequency rate-of-change

    Page(s): 677 - 684
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    A family of simple fixed-lag frequency smoothing algorithms which provide good estimates of both frequency and frequency rate-of-change is reported. The smoothers were developed from a fixed-gain αβ tracker by replacing the recursive derivative estimator with a finite-impulse-response (FIR) differentiator. Simulation results are presented which show that the smoothing algorithms provide frequency estimates with a similar variance to those produced by the αβ filter but with greatly improved frequency-rate estimates. The smoothing algorithms and the αβ filter are also compared on the basis of the bias and delay introduced in the frequency-rate estimates. Although the results presented are for frequency estimation, the smoothing algorithms can be used in any single-input tracking application where some lag in the estimates is allowable View full abstract»

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  • A new approach to robust fault detection and identification

    Page(s): 685 - 695
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    A methodology for instrument fault detection and identification (FDI) in linear dynamical systems subject to plant parameter variations or uncertainties is presented. At the heart of this approach is a robust estimator for which the necessary and sufficient conditions to its existence are outlined. The robust estimator can simultaneously estimate the unmeasurable state variables of the system for the purpose of control and provide necessary information for FDI purposes. A novel feature of this approach is that it can actually identify the shape and magnitude of the failures. The scheme allows for fast and accurate FDI, and can account for structural uncertainties and variations in the parameters of the dynamical model of the system. The overall fault tolerant control system strategy proposed is verified through simulation studies performed on the control of a vertical takeoff and landing (VTOL) aircraft in the vertical plane View full abstract»

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  • Global communication using a constellation of low Earth meridian orbits

    Page(s): 696 - 705
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    The concept of meridian orbits is briefly reviewed. It is shown that, if a satellite in the meridian orbit makes an odd number (>1) of revolutions per day, then the satellite passes over the same set of meridians twice a day. Satellites in such orbits pass over the same portion of the sky twice a day and every day. This enables a user to adopt a programmed mode of tracking, thereby avoiding a computational facility for orbit prediction, look angle generation, and auto tracking. A constellation of 38 or more satellites placed in a 1200-km altitude circular orbit is favorable for global communications due to various factors. It is shown that appropriate phasing in right ascension of the ascending node and mean anomaly results in a constellation wherein each satellite appears over the user's horizon one satellite after another. Visibility and coverage plots are provided to verify the continuous coverage View full abstract»

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  • Tracking with debiased consistent converted measurements versus EKF

    Page(s): 1015 - 1022
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    In tracking applications target motion is usually best modeled in a simple fashion using Cartesian coordinates. Unfortunately, in most systems the target position measurements are provided in terms of range and azimuth (bearing) with respect to the sensor location. This situation requires either converting the measurements to a Cartesian frame of reference and working directly on converted measurements or using an extended Kalman filter (EKF) in mixed coordinates. An accurate means of tracking with debiased consistent converted measurements which accounts for the sensor inaccuracies over all practical geometries and accuracies is presented. This method is compared with the mixed coordinates EKF approach as well as a previous converted measurement approach which is an acceptable approximation only for moderate cross-range errors. The new approach is shown to be more accurate in terms of position and velocity errors and provides consistent estimates (i.e., compatible with the filter calculated covariances) for all practical situations. The combination of parameters (range, range accuracy, and azimuth accuracy) for which debiasing is needed is presented in explicit form View full abstract»

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  • Multiple hypothesis track confirmation for infrared surveillance systems

    Page(s): 810 - 824
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB)  

    An overall methodology is described for the application of a multiple hypothesis tracking (MHT) algorithm to the infrared (IR) surveillance system problem of establishing tracks on dim targets in a heavy clutter or false alarm background. The authors discuss the manner in which the detection and tracking systems are jointly designed to optimize performance. They present approximate methods that can conveniently be used for preliminary system design and performance prediction. They discuss the use of a detailed Monte Carlo simulation for final system evaluation and present results illustrating the proposed methods and comparing predicted and simulation performance View full abstract»

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  • Quantitative heat transfer measurements in hypersonic wind tunnels by means of infrared thermography

    Page(s): 878 - 893
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1256 KB)  

    A description of infrared (IR) thermography, as it is employed in a hypersonic blowdown wind tunnel for the acquisition of high quality two-dimensional heat transfer data over aerodynamic surfaces, is given. It is shown that the availability of an IR scanning radiometer and a standard digital image processing (DIP) system in the laboratory provides the means for highly efficient (in terms of time and cost) heat transfer measurement, with accuracy levels comparable to those achieved by classical discrete point gauges, such as thin-film surface resistance thermometers and thermocouples. The advantages of IR thermal mapping over the classical techniques, not only in measuring heat transfer distributions over complex three-dimensional configurations and in locating and quantifying highly localized hot spots, but also in interpreting puzzling results observed on simple configurations, are illustrated using a series of examples. A discussion of the limitations of the technique indicates that most of such limitations are common to classical `zero-dimensional' instrumentation as well View full abstract»

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  • Dim target detection using high order correlation method

    Page(s): 841 - 856
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1180 KB)  

    This work presents a method for clutter rejection and dim target track detection from infrared (IR) satellite data using neural networks. A high-order correlation method which recursively computes the spatio-temporal cross-correlations between data of several consecutive scans is developed. The implementation of this scheme using a connectionist network is presented. Several important properties of the high-order correlation method which indicate that the resultant filtered images capture all the target information are established. The simulation results obtained with this approach show at least 93% clutter rejection. Further improvement in the clutter rejection rate is achieved by modifying the high-order correlation method to incorporate the target motion dynamics. The implementation of this modified high-order correlation using a high-order neural network architecture is demonstrated. The simulation results indicate at least 97% clutter rejection rate for this method. A comparison is also made between the methods developed here and the conventional frequency domain three-dimensional (3-D) filtering scheme, and the simulation results are provided View full abstract»

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  • Angle and polarization estimation in a coherent signal environment

    Page(s): 706 - 716
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    It is shown how a uniform linear array of crossed dipoles may be used with the ESPRIT algorithm and spatial smoothing techniques to estimate the arrival directions and polarizations of incoming coherent plane waves. Some examples showing typical performance are presented. One method of smoothing can be used where it is necessary to estimate both the arrival angles and polarizations of signals. Two other methods can be used when only the arrival angles are of interest View full abstract»

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  • A fast adaptive null-steering algorithm based on output power measurements

    Page(s): 717 - 725
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Presented and investigated here is a simple and fast adaptive algorithm for linear power inversion arrays whose nulls can be accurately steered by controlling the element weights. Based on measurements of the powers of the three signals derived from the array output and the output of an auxiliary beamformer, the algorithm tracks unknown jammers in the environment by steering the nulls of the array one by one in a cyclical time-multiplexed manner. When compared with the least mean square (LMS) algorithm, the proposed algorithm has about the same implementation complexity, a better convergence behavior and the advantage that nulls are directly available View full abstract»

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  • Computation of the circular error probability (CEP) integral

    Page(s): 1023 - 1024
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    A substantial portion of the findings of J.T. Gillis (ibid., vol.27, no.6, p.906-910, Nov. 1991) were reported in the open literature nearly 45 years ago, using far simple methods. An expression for the circular error probability (CEP) which takes into account the correlation between two jointly Gaussian random variables (an aspect overlooked by Gillis) is derived and numerical results are presented. For all practical purposes, it is found that the influence of the correlation coefficient on the CEP is not particularly strong View full abstract»

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  • Parallel load-flow algorithm using a decomposition method for space-based power systems

    Page(s): 1024 - 1030
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    This work presents a method for load-flow analysis of a power system using a decomposition approach. The power system for the US Space Shuttle is used as a model for the load-flow analysis. The decomposition algorithm is well suited for parallel processing implementation and provides an increase in the execution speed View full abstract»

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  • Electrooptical navigation for aircraft

    Page(s): 825 - 833
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    Concurrently with the development of guidance laws for low-altitude rotorcraft flight operations, efforts are underway to develop automated systems for locating the terrain and the obstacles using inputs from passive electrooptical sensors such as TV cameras and infrared imagers. A passive obstacle location algorithm that uses image sequences from cameras undergoing translational and rotational motion is developed. The algorithm is in a general form and can operate in multicamera imaging environments. Performance results using an image sequence from an airborne camera are given View full abstract»

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  • A 10 kW DC-DC converter using IGBTs with active snubbers

    Page(s): 857 - 865
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    This full bridge DC-DC converter employs zero voltage switching (ZVS) on one leg and zero current switching (ZCS) on the other. This technique produces exceptionally low insulated-gate bipolar transistor (IGBT) switching losses through the use of an active snubber that recycles energy back to the source. Experimental results are presented for a 10-kW, 20-kHz converter View full abstract»

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  • Fixed-gain two-stage estimators for tracking maneuvering targets

    Page(s): 1004 - 1014
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The two-stage alpha-beta-gamma estimator is proposed as an alternative to adaptive gain versions of the alpha, beta and alpha, beta, and gamma filters for tracking maneuvering targets. The aim is to achieve fixed-gain, variable dimension filtering. The two-stage alpha-beta-gamma estimator is derived from the two-stage Kalman estimator, and the noise variance reduction matrix and steady-state error covariance matrix are given as a function of the steady-state gains. A procedure for filter parameter selection is also given along with a technique for maneuver response and a gain scheduling technique for initialization. The kinematic constraint for constant speed targets is also incorporated into the two-stage estimator to form the two-stage alpha-beta-gamma-lambda estimator. Simulation results are given to compare the performances of other estimators with that of the alpha-beta-gamma filter View full abstract»

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  • Satellite intercept targeting DSP algorithm design and evaluation

    Page(s): 726 - 740
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    A unified processing approach for the detection and localization of satellites or other exoatmospheric targets is presented. Enhanced filtering and centroid determination algorithms were developed based on real-time implementation constraints, mission conditions including accuracy requirements, and signature structure. The signature structure consisted of target returns, high-frequency random noise, low-frequency structured noise, and contamination sources resulting from debris and cosmic events. Detailed signal processing analyses were performed to verify the required subsample accuracy and the sensitivity to hardware and system constraints. The resultant system design was functionally verified in a real-time breadboard processor View full abstract»

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  • Ionospheric scintillation-induced integration losses for space-based radar

    Page(s): 636 - 650
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1288 KB)  

    An estimate of the impact of very severe ionospheric conditions on the coherent and noncoherent integration process from a two-way, transionospheric, propagation path is obtained for a specific type of frequency-diverse waveform. A bound on the total integration loss that would result from using this waveform during such ionospheric conditions is obtained through the analysis of data from the wideband satellite experiment View full abstract»

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  • Universal linearization concept for extended Kalman filters

    Page(s): 946 - 962
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (996 KB)  

    The performance of a universal-linearization-concept-based extended Kalman filter (EKF) is evaluated by experimentally comparing its performance to that of a classical, linearization-based EKF, in the case of a simple nonlinear dynamical system. Instances of superior performance of the universal-linearization-based EKF are observed. In the case of nonlinear dynamics and linear measurements, the estimation advantage of the universal-linearization EKF increases when the process noise intensity decreases. Conversely, in the case of linear dynamics and nonlinear measurements, the estimation accuracy advantage increases when the process noise intensity increases. Furthermore, the universal-linearization EKF is more robust with respect to variations in the dynamics' parameters, in both linear and nonlinear dynamics cases. The advantage of the universal-linearization EKF is more pronounced in the case of small process noise intensity View full abstract»

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  • A pure-Cartesian formulation for tracking filters

    Page(s): 749 - 754
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    A pure-Cartesian formulation is presented for angle-only and angle-plus-range tracking filters. Unlike conventional angle-only filters, which use target elevation and bearing as measurements, the filter expresses the sensor measurements in Cartesian coordinates. Consequently, the filter performs equally well for any line-of-sight (LOS) geometry, even when target elevation approaches or is equal to ±90° View full abstract»

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  • Constrained bandwidth waveforms with minimal dilation sensitivity

    Page(s): 666 - 676
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    Bandpass waveforms which have envelopes which are insensitive to this velocity-induced time dilation can be efficiently processed by narrowband receivers in which envelope correlation is fixed and Doppler tested using fast Fourier transform (FFT) processing. The peak level of the waveform ambiguity function (AF) can be used to gauge the distortion of the waveform induced by dilation. The degree of AF attenuation is shown to be proportional to the dilation parameter or velocity, waveform traveling wave (TW) product, and a sensitivity parameter which depends on the envelope function utilized. Classes of symmetric, constrained bandwidth, phase modulated envelope functions which are minimally dilation sensitive (Doppler tolerant) are derived. When the resulting waveforms are used with a simple correlation receiver structure and the echo data is derived from slowly fluctuating point scattering in white Gaussian noise, the receiver becomes an uncoupled joint estimator of delay and dilation (Doppler). In the case of the bandpass waveforms, only odd symmetry of the phase modulation (PM) yields an uncoupled estimator View full abstract»

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  • Biparametric CFAR procedures for lognormal clutter

    Page(s): 798 - 809
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    The authors consider procedures for constant false alarm rate in lognormal clutter, accounting for variations of both the scale and a shape parameter of the clutter. Adaptivity to both parameters is obtained through biparametric estimation based on a sliding window surrounding the radar cell under test. Some procedures exploiting best linear unbiased estimation (BLUE) are presented and compared to a previous procedure called Log-t, which uses maximum likelihood estimation (MLE). The comparison is carried on for both a homogeneous clutter environment and for instances of inhomogeneous environment (clutter edges and spurious targets). In the latter instances, some advantages of BLUE procedures which stem from the opportunity of censoring are highlighted View full abstract»

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  • Range-time-sidelobe reduction technique for FM-derived polyphase PC codes

    Page(s): 834 - 840
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    A simple, easy to implement technique is presented that can significantly reduce the range-time-sidelobes of a class of polyphase pulse compression codes. This technique reduces the highest sidelobes to only one code element magnitude independent of effective pulse compression ratio. The codes considered are polyphase codes that are derived from the step-approximation-to-linear-frequency-modulation and linear-frequency-modulation waveforms such as the P1, P3, P4, and the Frank codes. The characteristics of these codes that make this possible are explained View full abstract»

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  • ISAR using Thomson's multiwindowed adaptive spectrum estimation method

    Page(s): 1065 - 1070
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    The authors compare two of Thomson's multiwindowed spectral estimation methods to conventional windowed discrete Fourier transform (DFT) methods for generating inverse synthetic-aperture radar (ISAR) images. The compared images are generated from synthetic data and data obtained from the IPIX research radar. The images show that Thomson's adaptive multiwindowed spectral estimation method is superior to the windowed fast Fourier transform (FFT) in generating ISAR images 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