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Aerospace and Electronic Systems, IEEE Transactions on

Issue 4 • Date Oct. 1994

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Displaying Results 1 - 25 of 28
  • Comments on "Effect of wet snow an the null-reference ILS system"

    Publication Year: 1994 , Page(s): 1086 - 1090
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    The subject paper (July 1993) has raised some issues regarding the probability of the Instrument Landing System (ILS) radiating out-of-tolerance vertical guidance signals. An independent study has substantiated the findings of that paper and adds further concern regarding some FAA ILS snow procedures. The principal conclusions of this paper are: 1) an analysis, based on Walton's discovery of rare snow conditions that cause the null-reference ILS antenna image to disappear, indicates that these conditions can cause out-of-tolerance guidance signals, 2) operation without a monitor of the image radiation can result in signal-in-space guidance signal errors that are significantly beyond the intended limit values, and 3) the integrity of image glide path equipment in snow environments does not satisfy the ILS integrity requirements.<> View full abstract»

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  • Comment on "Inversion of all principal submatrices of a matrix"

    Publication Year: 1994 , Page(s): 1114 - 1115
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB)  

    The paper by Koc and Chen (1994) includes new formulas for computational complexity, but the method itself is already known and has dubious numerical stability. A poorly conditioned example is shown.<> View full abstract»

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  • Patch diameter limitation due to high chirp rates in focused SAR images

    Publication Year: 1994 , Page(s): 1125 - 1129
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    Polar-format processed synthetic aperture radar (SAR) images have a limited focused patch diameter that results from unmitigated phase errors. Very high chirp rates, encountered with fine-resolution short-pulse radars, exasperate the problem via a residual video phase error term. This letter modifies the traditional maximum patch diameter expression to include effects of very high chirp rates View full abstract»

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  • Loop gain of a spacecraft switched shunt power system

    Publication Year: 1994 , Page(s): 1049 - 1053
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    A novel approach of deriving the loop gain of a spacecraft switched shunt power system is presented. The system hardware elements contain both the analog and the digital components. Transfer functions of the analog circuits are easily identified employing the conventional approach. Gain function of the digital block is however conceived following a quite unconventional route. The digital gain is shown to include the effects of comparator thresholds, digital clock, shift register, sinusoidal amplitude, and ac frequency. The dependence of the digital gain on voltage thresholds, clocking period, and the integrational property of threshold comparator is expected. The dependence on sinusoidal amplitude contradicts the traditional concept of small signal analysis. The overall loop gain in the analytic form yields a computational result that matches the actual measurement very well. This fact proves, to some extent, the validity of the digital gain function and the basis of its derivation View full abstract»

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  • A method for improving extended Kalman filter performance for angle-only passive ranging

    Publication Year: 1994 , Page(s): 1090 - 1093
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A relatively simple method is presented which eliminates previously reported (Oct. 1985) erratic estimation performance associated with Cartesian formulations of the extended Kalman filter (EKF) for the 2D angle-only emitter location problem. The technique is based on an initialization procedure which combines a priori probability density function (pdf) information with single measurement a posteriori pdf information in a manner which is more efficient than the EKF. Simulation results are presented which demonstrate the utility of the technique as compared with a previously offered modified gain EKF View full abstract»

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  • Eigenstructure assignment using output feedback

    Publication Year: 1994 , Page(s): 1129 - 1130
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    An eigenspace, achievable by gain output feedback, is proposed by Andry et al. (1983). One example contradicting the above conclusion is given by Kang and Lee (1992). The contradiction is due to the limitation of the result presented by Andry. This note derives the complete specification of the eigenspace which can be achieved by gain output feedback View full abstract»

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  • On the exact solutions of pseudorange equations

    Publication Year: 1994 , Page(s): 1021 - 1030
    Cited by:  Papers (17)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    Three formulations of exact solution algorithms to the system of determined pseudorange equations are derived. It is demonstrated that pseudorange equations are hyperbolic in nature and may have two solutions, even when the emitter configuration is nonsingular. Conditions for uniqueness and for the existence of multiple solutions are derived in terms of the Lorentz inner product. The bifurcation parameter for systems of pseudorange equations is also expressed in term of the Lorentz functional. The solution is expressed as a product of the geometric dilution of precision (GDOP) matrix, representing the linear part of the solution, and a vector of nonlinear term. Using this formulation stability of solutions is discussed View full abstract»

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  • Monopulse radar angle measurement in noise [Errata]

    Publication Year: 1994
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (32 KB)  

    A correction is given for the third sentence in the paragraph containing Equation (24) on Page 955, Column 2 View full abstract»

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  • Mutual coupling effects and their reduction in wideband direction of arrival estimation

    Publication Year: 1994 , Page(s): 1116 - 1122
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    The performance of multiple signal classification (MUSIC) algorithm using three different inputs over a wideband of frequencies is considered. These inputs are: 1) ideal voltages, 2) actual voltages which include coupling effects and are obtained with the method or moments, and 3) corrected voltages which are obtained from the actual voltages so that the mutual coupling effects are removed. Linear arrays of dipoles, sleeve dipoles, and spiral antennas are considered over 200 MHz to 400 MHz band View full abstract»

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  • Inherent bias assessment in height computation employing mixed-type radar data

    Publication Year: 1994 , Page(s): 1045 - 1049
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The objective here is the analysis of a systematic error inherently existing in aircraft geometric height monitoring under radar surveillance. This error is caused by the nonlinear processing of noisy measurements. The geometric height system under investigation uses mixed-type radar data, since the height is computed by referring range raw measurements to horizontal trajectory smoothed data View full abstract»

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  • Uses of electrodynamic forces in tethered satellite systems. II. Orbit-transfer

    Publication Year: 1994 , Page(s): 1039 - 1043
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Part II of this work presents electrodynamic forces used for orbit transfer. The system presented in Part I is to be transferred to a new orbit of a different radius while maintaining a nearly Earth-pointing orientation at all times. The maneuver is to be performed with electrodynamic forces without the use of thrusters. To accomplish this mission, the notion of synchronized impulses, that is, running electric current through the tether at precalculated instants and amplitudes, is presented View full abstract»

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  • Task allocation and reallocation for fault tolerance in multicomputer systems

    Publication Year: 1994 , Page(s): 1094 - 1104
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    The goal of task allocation in a set of interconnected processors (computers) is to maximize the efficient use of resources and thus reduce the job turnaround time. Proposed is a simple yet effective method to allocate the tasks in multicomputer systems for minimizing the interprocessor communication cost subject to resource limitations defined by the system and designer. The limitations can be viewed as results from the load balancing since the execution time of each task, the number of available processors, processor speed, and memory capacity are known to the system or designer. As the number of processors increases, the probability of a failure existing somewhere in the systems at any time also increases. Very few established task allocation models have considered the reliability property. In multicomputer systems, we define system reliability as the probability that the system can run the tasks successfully. After the (nonredundant) task scheduling strategy is defined, tasks are then reallocated to processors statically and redundantly. This is a form of time redundancy, in which if some processors fail during the execution, all tasks can be completed on the remaining processors (but at a longer time). Due to static preallocation of tasks this method is simpler and thus more practical than well-known dynamic reconfiguration and rollback recovery techniques in multicomputer systems. We demonstrate the effectiveness of the task allocation and reallocation for hardware fault tolerance by illustrations of applying the methods to different examples and practical communications network multiprocessor system View full abstract»

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  • Further results on adaptive filtering with embedded CFAR

    Publication Year: 1994 , Page(s): 1009 - 1020
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    Among the few known adaptive filtering algorithms which have an embedded (integrated) constant false alarm rate (CFAR) performance feature, the generalized likelihood ratio (GLR) test algorithm has been found to be robust in non-Gaussian clutter. This paper examines the detection performance of the GLR algorithm in nonhomogeneous/nonstationary clutter environments which lead to nonidentical distribution of secondary (training) data. For two common types of nonhomogeneity, i.e., the so-called “signal contamination” and “clutter edge”, the asymptotic detection performance is derived and compared with simulations. These asymptotic results are relatively simple to use and they predict the GLR performance in nonhomogeneous environments quite well. The GLR performance loss due to the nonhomogeneity is also evaluated. It is found that the “generalized angle” between the desired and contaminating signal plays an important role in the study of the effects of signal contamination. It is also found that the performance degradation due to the clutter edge depends largely on the width of the clutter spectrum and target-clutter Doppler separation View full abstract»

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  • Requirements for optimal glint reduction by diversity methods

    Publication Year: 1994 , Page(s): 1108 - 1114
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    Target “glint” (the difference between the phase-front gradient of the scattered field and the true target direction vector) is related to the analytic properties of the scattered field. The resulting model is used to reinterpret diversity methods for glint reduction and to more accurately specify system requirements. A relationship for estimating the best possible improvement in target bearing estimation is also developed View full abstract»

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  • Antenna sidelobes in the presence of flat reflectors

    Publication Year: 1994 , Page(s): 1122 - 1125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Reflecting surfaces near the antenna may produce surprisingly large sidelobes even if the designed free-space sidelobes in the directions of these surfaces are very small. Calculations of such sidelobes are presented for an example of a linear aperture with a parabolic weighting function for the received signal amplitude View full abstract»

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  • Attitude determination using dedicated and nondedicated multiantenna GPS sensors

    Publication Year: 1994 , Page(s): 1053 - 1058
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    We show that the use of nondedicated Global Positioning System (GPS) sensors to determine the attitude parameters of a vessel yields the same level of performance as the use of a dedicated multiantenna receiver, namely an agreement of the order of 0.1° (1σ). The test platform is a survey launch operating at cruising speeds of 10 to 15 kt. The dedicated multiantenna receiver is a four-antenna Ashtech 3DF unit, while the nondedicated sensor array consists of three NovAtel GPSCardTM receivers. The approach used to resolve the relative carrier phase integer ambiguities between the antennas is discussed and the use of antenna baseline constraints is analyzed. A least-squares procedure which utilizes all the position information from the antennas for the estimation of the attitude parameters and their accuracy is presented. The attitude determination results from the two configurations tested are intercompared View full abstract»

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  • Authors' reply [Computational complexity of matrix inversion]

    Publication Year: 1994
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    The purpose of our two-page communication was to study the computational complexity of a matrix inversion formula with the intention of showing its improvement over the naive method of computing the inverse separately. We did not intend to claim that the matrix inversion formula is our discovery. However, it is true that this point was not made clear in our short paper View full abstract»

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  • Electrodynamic forces in tethered satellite systems. I. System control

    Publication Year: 1994 , Page(s): 1031 - 1038
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    Part I of this work deals with the use of electrodynamic forces for control of tethered satellite system. A system formed by two massive end-bodies connected to each other by a current carrying tether is to be kept in an Earth-pointing orientation by means of joint actions of thrusters on one of the end-bodies and electrodynamic forces acting on the tether View full abstract»

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  • Reduction of interference from DGPS transmissions in the MF band using a GMSK modulation scheme

    Publication Year: 1994 , Page(s): 1104 - 1108
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB)  

    The accuracy of the Global Positioning System (GPS) can be improved by differential techniques. For maritime applications a DGPS service with transmissions by maritime radiobeacons in the MF band is provided. It offers a position accuracy of approximately 5 m. For the data link a minimum shift keying (MSK) modulation scheme has been recommended. The adjacent channel interference at the maximum transmission rate might not be consistent with existing frequency plans View full abstract»

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  • The case for like-sensor predetection fusion

    Publication Year: 1994 , Page(s): 986 - 1000
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1268 KB)  

    There has been a great deal of theoretical study into decentralized detection networks composed of similar (often identical), independent sensors, and this has produced a number of satisfying theoretical results. At this point it is perhaps worth asking whether or not there is a great deal of point to such study-certainly two sensors can provide twice the illumination of one, but what does this really translate to in terms of performance? We take as our metric the ground area covered with a specified Neyman-Pearson detection performance. To be fair, the comparison will be of a multisensor network to a single-sensor system where both have the same aggregate transmitter power. The situations examined are by no means exhaustive but are, we believe, representative. Is there a case? The answer, as might be expected, is “sometimes.” When the statistical situation is well behaved there is very little benefit to a fused system; however, when the environment is hostile the gains can be significant. We see, depending on the situation, gains from colocation, gains from separation, optimal gains from operation at a “fusion range,” and sometimes no gains at all View full abstract»

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  • Relationship between navigation vertical error, VDOP, and pseudo-range error in GPS

    Publication Year: 1994 , Page(s): 1138 - 1142
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    At a specified position and time, vertical position error is related to satellite ranging errors by the relationship Z=VDOP*URE where URE is the user range equivalent error, VDOP is the vertical dilution of precision, and Z is the vertical position error. This relationship is developed and it is shown that it is statistically correct even when position and time are variables. Expressions are given for the density, cumulative distribution, and standard deviation of Z in terms of the distributions of VDOP and URE. Vertical position error is investigated at several locations and the results compared with published work. A simple method for converting VDOP distributions to distributions of vertical accuracy as an alternative to computer simulation is presented View full abstract»

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  • Precise navigation using adaptive FIR filtering and time domain spectral estimation

    Publication Year: 1994 , Page(s): 1071 - 1076
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    This paper introduces a new low cost, short range, positioning system based on adaptive finite impulse response (FIR) filtering and time domain spectral estimation. The system can determine absolute positions with a high degree of accuracy and is well suited for real time navigation. The approach is based upon signal processing techniques and a priori knowledge of the system transfer function. The first step is to measure the phase response of the linear transfer function and then using a FIR filter the time response of the system can be determined. The FIR filter computes the time response by performing a deconvolution between the measured phase response, and the complex conjugate of the transfer function. By correlating the known input impulse response with the output of the FIR filter, an error term is generated. The time delay of the system is determined by adjusting the FIR filter coefficients to minimize the error term. Simulated analysis of the system indicates a worst case error of ±16 cm View full abstract»

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  • Enhancing filter robustness in cascaded GPS-INS integrations

    Publication Year: 1994 , Page(s): 1001 - 1008
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    Filter robustness is defined herein as the ability of the Global Positioning System/Inertial Navigation System (GPS-INS) Kalman filter to cope with adverse environments and input conditions, to successfully identify such conditions and to take evasive action. The formulation of two such techniques for a cascaded GPS-INS Kalman filter integration is discussed This is an integration in which the navigation solution from a GPS receiver is used as a measurement in the filter to estimate inertial errors and instrument biases. The first technique presented discusses the handling of GPS position biases. These are due to errors in the GPS satellite segment, and are known to be unobservable. They change levels when a satellite constellation change occurs, at which point they introduce undesirable filter response transients. A method of suppressing these transients is presented. The second technique presented deals with the proper identification of the filter measurement noise. Successful formulation of the noise statistics is a factor vital to the healthy estimation of the filter gains and operation. Furthermore, confidence in the formulation of these statistics can lead to the proper screening and rejection of bad data in the filter. A method of formulating the filter noise statistics dynamically based on inputs from the GPS and the INS is discussed View full abstract»

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  • Ambiguity resolution of multiple targets using pulse-Doppler waveforms

    Publication Year: 1994 , Page(s): 1130 - 1137
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    To cancel clutter, both medium-PRF waveforms which are ambiguous in both range and Doppler and high-PRF waveforms which are ambiguous in range but unambiguous in ambiguities, a previous paper has shown that superior results for a single target can be achieved by using a clustering algorithm. Here, the problem of multiple targets is considered. A maximum likelihood (ML) technique which incorporates the clustering algorithm is developed for the multiple target problem. Simulation results show that four targets which have the same speed but are at different ranges can be resolved by using a medium-PRF waveform and employing the ML resolution technique View full abstract»

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  • On cross-ambiguity properties of Welch-Costas arrays

    Publication Year: 1994 , Page(s): 1063 - 1071
    Cited by:  Papers (8)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    We discuss cross-ambiguity properties of a specific family of Costas arrays called Welch-Costas (W-C) arrays. These properties are of interest in multiuser radar and sonar system, especially since Costas arrays are known to possess ideal auto-ambiguity functions. The theory of W-C arrays is reviewed. It is then proved that only pairs of W-C arrays can have at most two hits in their cross-ambiguity function (best possible case). The maximum number of hits in the cross-ambiguity functions of a family of W-C arrays is shown to be a function of the number of W-C arrays in the family. The upper bound on the number of hits in the cross ambiguity functions for a family of W-C arrays is also derived. Specific examples of how reducing the number of W-C arrays improves the cross-ambiguity properties are given for various types of prime numbers 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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Editor-in-Chief
Lance Kaplan
Army Research Laboratory