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Aerospace and Electronic Systems, IEEE Transactions on

Issue 3 • Date July 2003

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Displaying Results 1 - 25 of 35
  • From the editors

    Page(s): 737
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    Freely Available from IEEE
  • Cyclic code shift keying: a low probability of intercept communication technique

    Page(s): 786 - 798
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1039 KB) |  | HTML iconHTML  

    A low probability of intercept (LPI), or low probability of detection (LPD) communication technique known as cyclic code shift keying (CCSK) is described. We discuss the basic concepts of CCSK and describe a system based on the use of random or pseudorandom codes for biphase modulation. We use simulation to show that the bit error rate (BER) for CCSK can be closely estimated by using existing equations that apply to M-ary orthogonal signaling (MOS). Also, we show that significantly fewer computations are required for CCSK than for MOS when the number of bits per symbol is the same. We show that using biphase modulation results in waveforms that have a large time-bandwidth product and very low input signal-to-noise ratio (SNR) and thus inherently have an LPI by a radiometer. We evaluate detection by a radiometer and show that LPI can be achieved by using codes of lengths greater than about 2/sup 12/ (i.e., by transmitting more than about 12 bits per symbol). Results illustrate the effect that the CCSK symbol length and error probability, and the radiometer integration time and probability of false alarm (PFA), have on detection by a radiometer. We describe a variation of CCSK called truncated CCSK (TCCSK). In this system, the code of length 2/sup k/ is cyclically shifted, then truncated and transmitted. Although shortened, the truncated code still represents k bits of information, thus leading to an increased data rate. We evaluate radiometer detection of TCCSK and it is shown that the probability of detection is increased compared with the detection of CCSK. View full abstract»

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  • 2002 Pioneer award

    Page(s): 1115 - 1119
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    Freely Available from IEEE
  • ACSS for paralleled multi-inverter systems with DSP-based robust controls

    Page(s): 1002 - 1015
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2483 KB) |  | HTML iconHTML  

    An averaged current-sharing strategy (ACSS) for paralleled multi-inverter systems with digital signal processor (DSP)-based robust controls is presented. With an ACSS, the inverters are in parallel operation and each inverter has a voltage robust controller to achieve system stability and robustness, and a current robust controller to track the averaged inductor current of the inverters to achieve equal current distribution. In the proposed system, the current-sharing control loop is independent of the voltage control loop. Therefore, equal current distribution among the inverters, fast response, and tight regulation can be achieved. Additionally, the ACSS in each inverter can be readily implemented with two operational amplifiers. Simulation results and hardware measurements or a single-inverter system and a two-inverter system, and simulation results of a three-inverter system with linear and nonlinear loads have demonstrated the feasibility of the proposed control scheme in equal current distribution and fast regulation. View full abstract»

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  • Bomb damage assessment using a dispensed sensor projectile

    Page(s): 813 - 823
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1050 KB) |  | HTML iconHTML  

    The problem of obtaining images of a target site after munition impact is approached by releasing a small projectile equipped with a camera from a dropped munition. A ballute is deployed from the sensor projectile shortly after release from the munition. This type of system is capable of viewing munition impact and subsequent target effects over a wide variety of conditions and offers the possibility of real-time battle damage assessment (BDA). However, fundamental limits exist on the duration that the camera is able to view the target after impact for a particular required separation distance between the sensor projectile and the target at impact and the field of regard (FOR) of the camera. Munition release altitude and velocity significantly affect these fundamental limits. Optimal performance is attained under high altitude and low speed munition drop conditions. Basic characteristics of the camera projectile also significantly influence system performance. Maximum target view time is attained with a low weight high drag configuration., To reduce the maximum acceleration experienced by the sensor projectile, a small delay time between the release of the small sensor projectile from the munition and inflation of ballute is required. View full abstract»

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  • Dual-frequency distortion predictions for the Cutler VLF array

    Page(s): 1016 - 1034
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    The VLF transmitting system in Cutler, ME currently broadcasts at one frequency through a two-element antenna system. This study investigates simultaneous operation at 24.0 and 17.8 kHz. Detailed nonlinear PSPICE models were generated for the system including the amplifier triodes, saturable dynamic-tuning reactors, and the closely-coupled antenna elements. The predicted behavior is in close agreement with available observations. Upper limits are placed on harmonic content, <-59.8 dBc, and intermodulation distortion, <-78 dBc. View full abstract»

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  • Analysis, design, and practical considerations for 500 W power factor correctors

    Page(s): 961 - 975
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1371 KB) |  | HTML iconHTML  

    This paper presents analysis, design, and practical considerations for 500 W boost power factor correctors (PFCs). The boost PFCs with three active soft-switching cells, which are boost, forward and flyback, and a passive soft-switching cell are first discussed. The operating principle and performance characteristics of the PFCs are then presented in detail, from which the boost with a flyback soft-switching cell and that with a passive soft-switching cell are designed and implemented. Performance comparison among these PFCs is also presented. Hardware measurements are used to verify the theoretical discussion. The presented information can provide designers a good application reference. View full abstract»

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  • Design and testing of spacecraft power systems using VTB

    Page(s): 976 - 989
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1984 KB) |  | HTML iconHTML  

    A study is presented on the design and testing of spacecraft power systems using the virtual test bed (VTB). The interdisciplinary components such as solar array and battery systems were first modeled in native VTB format and validated by experiment data. The shunt regulator and battery charge controller were designed in Simulink according to the system requirements and imported to VTB. Two spacecraft power systems were then designed and tested together with the control systems. View full abstract»

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  • Evaluation and reduction of multipath-induced bias on GPS time-of-arrival

    Page(s): 911 - 920
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (673 KB) |  | HTML iconHTML  

    New expressions are presented for the multipath-induced pseudorange error (i.e. bias) and variance introduced by multipath onto the time-of-arrival estimate obtained using a noncoherent early-late gate discriminator. The results include the effect of front-end bandwidth and early-late gate spacing. We also investigate a blind method for cancelling the multipath, in order to improve the time-of-arrival estimate. Our approach uses early-late gate processing on an objective function derived from an adaptive finite impulse response (FIR) filter that attempts to match the crosscorrelation of the received signal with a multipath-free replica of the desired crosscorrelation. This method performs reasonably well, and decreases the multipath-induced pseudorange error by approximately a factor of 2, even in very stressing multipath environments. View full abstract»

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  • Tracking evasive move-stop-move targets with a GMTI radar using a VS-IMM estimator

    Page(s): 1098 - 1103
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    We present the design of a variable structure interacting multiple model (VS-IMM) estimator for tracking evasive ground targets using ground moving target indicator (GMTI) reports obtained from an airborne sensor. In order to avoid detection by the GMTI sensor, the targets use a "move-stop-move" strategy, where a target deliberately stops or moves at a very low speed for some time before accelerating again. In this case, when the target's radial velocity (along the line of sight from the sensor) falls below a certain minimum detectable velocity, the target is not detected by the sensor. Under these conditions, the use of an estimator, which does not take care of this move-stop-move motion explicitly, will result in broken tracks. The tracker proposed here handles the evasive move-stop-move motion via the VS-IMM estimator, where the tracker mode set is augmented with a "stopped-target" model when the estimated speed of the target falls below a certain threshold. Using this additional stopped-target model, the target track is kept "alive" even in the absence of a measurement. A simulated scenario is used to illustrate the selection of design parameters and the operation of the tracker. Performance measures are presented to contrast the benefits of the VS-IMM estimator, which uses the stopped-target model, over a standard IMM estimator. View full abstract»

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  • Propagation velocity uncertainty on GPR SAR processing

    Page(s): 849 - 861
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    To detect buried landmines, Planning Systems Incorporated (PSI) has developed a ground-penetrating synthetic aperture radar (GPSAR) system. Since the electromagnetic wave propagation velocity in the soil depends on many factors, velocity uncertainty is inevitable. However, we have observed that, unlike conventional airborne/spaceborne synthetic aperture radar (SAR) systems, the PSI GPSAR system is very robust against the velocity uncertainty under mild conditions. Theoretical analysis is provided to explain this observation. Although our discussion is based on the PSI GPSAR system, it applies to other GPR-based (ground-penetrating radar) landmine detection systems as well. View full abstract»

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  • Statistical characterization of clutter scenes based on a Markov random field model

    Page(s): 1035 - 1050
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4215 KB) |  | HTML iconHTML  

    The problem of clutter region identification based on Markov random field (MRF) models is addressed. Observations inside each clutter region are assumed homogenous, i.e., observations follow a single probability distribution. Our goal is to partition clutter scenes into homogenous regions and to determine this underlying probability distribution. Metropolis-Hasting and reversible jump Markov chain (RJMC) algorithms are used to search for solutions based on the maximum a posteriori (MAP) criterion. Several examples illustrate the performance of our algorithm. View full abstract»

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  • Cyclostationarity-exploiting direction finding algorithms

    Page(s): 1051 - 1056
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB) |  | HTML iconHTML  

    Many modulated communication signals exhibit a cyclostationarity (or periodic correlation) property, corresponding to the underlying periodicity arising from carrier frequencies or baud rates. By exploiting cyclostationarity, the signal direction of arrival (DOA) estimation can be significantly improved. We propose two new direction finding beamformer algorithms that exploit cyclostationarity. These algorithms show very attractive estimation performance over conventional beamforming methods, as depicted by simulation results. View full abstract»

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  • Spectral analysis of periodically gapped data

    Page(s): 1089 - 1097
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1169 KB) |  | HTML iconHTML  

    We devise novel, interpolation-free, and computationally tractable extensions of the spectral analysis methods Capon and APES (amplitude and phase estimation) to periodically gapped data. Our methods are based on the observation that periodically gapped data usually have a structure that supports estimation of a relatively large number of covariance lags. The large signal-to-noise-ratio (SNR) behavior of the new algorithms is discussed, and numerical examples are provided to illustrate their performance. View full abstract»

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  • Maximum likelihood registration for multiple dissimilar sensors

    Page(s): 1074 - 1083
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (386 KB) |  | HTML iconHTML  

    A study of the maximum likelihood registration (MLR) algorithm for spatial alignment of multiple, possibly dissimilar (active or passive) sensors is presented. The MLR algorithm is a batch algorithm which outputs estimates of the registration parameters, registered sensor measurements and registered target location estimates, expressed in a common coordinate system. The Cramer-Rao type bound for registration of multiple dissimilar sensors is discussed and some numerical examples for sensor registration are presented in support of the theory. View full abstract»

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  • Analysis of an adaptive algorithm for unbiased multipath time delay estimation

    Page(s): 777 - 785
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    The multipath equalization time delay estimator (METDE) provides an adaptive approach for estimating the difference in arrival times of a signal received at spatially separated sensors as well as the multipath channel characteristics. However, the parameter estimates of the METDE are biased in the presence of noise. The METDE algorithm is improved for unbiased parameter estimation via minimizing a modified cost function. Convergence behaviors and variances of the system variables of the amended method are derived. Computer simulations are included to corroborate the theoretical analysis and to evaluate the adaptive multipath delay estimation performance of the proposed algorithm. View full abstract»

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  • Design of optimal midcourse guidance sliding-mode control for missiles with TVC

    Page(s): 824 - 837
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (759 KB) |  | HTML iconHTML  

    This work discusses a nonlinear midcourse missile controller with thrust vector control (TVC) inputs for the interception of a theater ballistic missile, including autopilot system and guidance system. First, a three degree-of-freedom (DOF) optimal midcourse guidance law is designed to minimize the control effort and the distance between the missile and the target. Then, converting the acceleration command from guidance law into attitude command, a quaternion-based sliding-mode attitude controller is proposed to track the attitude command and to cope with the effects from variations of missile's inertia, aerodynamic force, and wind gusts. The exponential stability of the overall system is thoroughly analyzed via Lyapunov stability theory. Extensive simulations are conducted to validate the effectiveness of the proposed guidance law and the associated TVC. View full abstract»

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  • Output stabilization of flexible spacecraft with active vibration suppression

    Page(s): 747 - 759
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (617 KB) |  | HTML iconHTML  

    Addressed here is the problem of designing a dynamic controller capable of performing rest-to-rest maneuvers for flexible spacecraft, by using attitude measures. This controller does not need the knowledge of modal variables and spacecraft angular velocity. The absence of measurements of these variables is compensated by appropriate dynamics of the controller, which supplies their estimates. The Lyapunov technique is applied in the design of this dynamic controller. Possible source of instability of the controlled system in real cases are the influence of the flexibility on the rigid motion, the presence of disturbances acting on the structure, and parameter variations. In order to attenuate their effects and to damp out undesirable vibrations affecting the spacecraft attitude, distributed piezoelectric actuators are used. In fact, in presence of disturbances and/or parameter variation the proposed controller ensures an approximate solution of the control problem. View full abstract»

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  • Expanded Swerling target models

    Page(s): 1059 - 1069
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    Radar target fluctuation models were first introduced by Swerling in the 1950s and they proved to be very useful. Swerling soon realized, however, that his original four models were inadequate and generalized them through use of the gamma distribution. These generalized results still had serious limitations in modeling fluctuating targets. For some targets the Swerling I correlated model produced an overly pessimistic value for PD at large signal-to-noise ratios (SNRs) while the Swerling III correlated model produced an overly optimistic one. As a result, other fluctuation models, such as the log-normal and Weibull, remain useful in spite of their own limitations. Two new models that expand on the generalized Swerling model are presented here. They are physically motivated and can produce the desired PD levels at high SNR values. They are described in detail and both the moment generating functions (MGFs) and PD expressions are determined. They provide a significant advance in our modeling capabilities through their flexibility for modeling many different types of target radar cross section (RCS) responses. These new models apply to both the case where the pulse-to-pulse target responses are correlated as well as the case where they are uncorrelated, thereby overcoming the limitations of the log-normal and Weibull models. View full abstract»

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  • Medium PRF radar PRF selection using evolutionary algorithms

    Page(s): 990 - 1001
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1137 KB) |  | HTML iconHTML  

    Evolutionary algorithms are applied to the optimization of pulse repetition frequency (PRF), for both eight-and nine PRFs, in medium PRF radar while considering the detailed effects of sidelobe clutter and many other technical factors. The algorithm presented also ensures that all the solutions produced are fully decodable and have no blind velocities. The evolutionary algorithm was able to identify near-optimum PRF sets for a realistic radar system with only a modest computational effort. View full abstract»

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  • Multivehicle reconnaissance route and sensor planning

    Page(s): 799 - 812
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4513 KB) |  | HTML iconHTML  

    A novel approach is described for the real-time coordination of multivehicle teams to perform reconnaissance and surveillance missions. Our approach incorporates a powerful algorithmic framework, which we have used to develop dynamic route and sensor planning algorithms for multivehicle team coordination. Furthermore, this framework allows the development of a class of algorithms to match the extent of communication and coordination permissible for the particular mission. We have implemented a prototype of this framework and presented results for the case when full coordination between the teammates is allowed. View full abstract»

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  • Superiority of canards in homing missiles

    Page(s): 740 - 746
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (447 KB) |  | HTML iconHTML  

    We suggest a first-order model to distinguish between nose control (canards) and tail control. We present optimal guidance strategies and demonstrate the superiority of nose control. This simple model enables us to develop simple and robust guidance strategies based on three approaches: unconstrained optimal control, constrained optimal control, and constrained differential games. It turns out that nose control requires low gain and is capable of forcing small miss distance in the presence of a maneuvering target. View full abstract»

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  • Median cascaded canceller for robust adaptive array processing

    Page(s): 883 - 900
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (804 KB) |  | HTML iconHTML  

    A median cascaded canceller (MCC) is introduced as a robust multichannel adaptive array processor. Compared with sample matrix inversion (SMI) methods, it is shown to significantly reduce the deleterious effects of impulsive noise spikes (outliers) on convergence performance of metrics; such as (normalized) output residue power and signal to interference-plus-noise ratio (SINR). For the case of no outliers, the MCC convergence performance remains commensurate with SMI methods for several practical interference scenarios. It is shown that the MCC offers natural protection against desired signal (target) cancellation when weight training data contains strong target components. In addition, results are shown for a high-fidelity, simulated, barrage jamming and nonhomogenous clutter environment. Here the MCC is used in a space-time adaptive processing (STAP) configuration for airborne radar interference mitigation. Results indicate the MCC produces a marked SINR performance improvement over SMI methods. View full abstract»

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  • Attitude and antenna pointing design of bistatic radar formations

    Page(s): 949 - 960
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (860 KB) |  | HTML iconHTML  

    Spaceborne bistatic radar observations allow original scientific applications to be carried out. Furthermore, assuming transmitting and receiving antennas operating on separated platforms, key design issues relevant to formation flying must be solved. Mathematical models are presented for computation of attitude and pointing angles. Main design constraint is the capability of maintaining swath overlap, but selected strategy also depends on the cost of spacecraft attitude maneuvering or antenna beam electronic steering. The model has been applied considering a large transmitting/receiving primary mission and a receiving-only small satellite. In this case antenna steering was preferred. Finally, if the passive antenna is smaller than the active one, overlap maintenance is simplified, obviating the need for yaw rotations. 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