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  • Articles  (861)
  • 2010-2014  (861)
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  • IEEE Transactions on Aerospace and Electronic Systems  (861)
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  • Electrical Engineering, Measurement and Control Technology  (861)
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  • 1
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    Bias analysis of maximum likelihood target location estimator (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: This paper investigates the bias of the maximum likelihood target location estimate resulting from the Gaussian data measurement noise and sensor position errors. The bias components from them are interrelated, except when they are independent and identically distributed. The bias behaviors of time of arrival, time difference of arrival, and angle of arrival positionings are contrasted, and geometric conditions under which the location bias becomes zero are elaborated.We illustrate the developed results for bias compensation in improving the performance of target tracking.
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  • 2
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    Target tracking in a collaborative sensor network (2014)
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    Publication Date: 2014-12-13
    Description: In a collaborative sensor network (CSN), the conventional target tracking algorithms employed are Kalman filtering (KF) or extended Kalman filtering (EKF). However, these techniques have a presumed probability distribution of the system noise and prediction noise. They also need some a priori information that may be unavailable in some circumstances. Therefore, the system is not flexible for a complicated scenario. With the help of a machine learning technique called expert prediction (EP), a novel target tracking approach for CSNs is developed. This scheme makes use of the aforementioned EP in parameter estimation course for the target of interest, instead of exploiting the filtering method as typically found in available literature. This idea is further unfolded with comparisons regarding the CSN using Kalman filters, extended Kalman filters, and decentralized sigma-point information filters (DSPIFs). The new tracking algorithm is investigated with both linear and nonlinear prediction methods. Simulation results demonstrate that this proposed measure will deliver forecasting output with more precision because of the built-in multimodel mode among different experts, the learning ability, and the self-perfection characteristic. Not only does this performance occur in a more robust way than those of the existing approaches – particularly in the presence of heavy clutter, highly maneuvering targets, and/or multiple targets – but it simultaneously requires the least a priori information and imposes the least limitation on the observation model.
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  • 3
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    Aerial-terrestrial communications: terrestrial cooperation and energy-efficient transmissions to aerial base stations (2014)
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    Publication Date: 2014-12-13
    Description: Hybrid aerial-terrestrial communication networks based on low-altitude platforms are expected to meet optimally the urgent communication needs of emergency relief and recovery operations for tackling large-scale natural disasters. The energy-efficient operation of such networks is important given that the entire network infrastructure, including the battery-operated ground terminals, exhibits requirements to operate under power-constrained situations. In this paper, we discuss the design and evaluation of an adaptive cooperative scheme intended to extend the survivability of the battery-operated aerial-terrestrial communication links. We propose and evaluate a real-time adaptive cooperative transmission strategy for dynamic selection between direct and cooperative links based on the channel conditions for improved energy efficiency. We show that the cooperation between mobile terrestrial terminals on the ground could improve energy efficiency in the uplink, depending on the temporal behavior of the terrestrial and aerial uplink channels. The corresponding delay in having cooperative (relay-based) communications with relay selection is also addressed. The simulation analysis corroborates that the adaptive transmission technique improves overall energy efficiency of the network whilst maintaining low latency, enabling real-time applications.
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  • 4
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    Direction finding algorithms based on joint iterative subspace optimization (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: In this paper, a reduced-rank scheme with joint iterative optimization is presented for direction of arrival estimation. A rank-reduction matrix and an auxiliary reduced-rank parameter vector are jointly optimized to calculate the output power with respect to each scanning angle. Subspace algorithms to estimate the rank-reduction matrix and the auxiliary vector are proposed. Simulations are performed to show that the proposed algorithms achieve enhanced performance over existing algorithms in the studied scenarios.
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  • 5
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    Formation flying with nonlinear partial integrated guidance and control (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: Using the dynamic inversion philosophy, a nonlinear partial integrated guidance and control approach is presented in this paper for formation flying. It is based on the evolving philosophy of integrated guidance and control. However, it also retains the advantages of the conventional guidance then control philosophy by retaining the timescale separation between translational and rotational dynamics explicitly. Simulation studies demonstrate that the proposed technique is effective in bringing the vehicles into formation quickly and maintaining the formation.
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  • 6
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    Near-far interference mitigation for pseudolites using double transmission (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: The use of ground-based transmitters (so-called pseudolites) for outdoor and indoor navigation has been under consideration since the origin of the Global Positioning System (GPS). However, one significant limitation of the use of code division multiple access (CDMA) was immediately obvious: one CDMA transmitter signal interferes with another CDMA transmitter signal. This is called the ""near-far problem."" Different methods have been studied in order to mitigate such jamming. This paper presents a new mitigation method based on a principle that can be summed up as follows: the signal and a delayed replica of the signal are broadcast by a ground transmitter antenna. At the receiver stage, the replica signal is used to eliminate the interference caused by the direct signal. This is called the double transmission technique (DTT), and it presents interesting performance features regarding interference mitigation. A signal processing technique corresponding to this method is presented in this paper, considering a GPS L1 C/A-code pseudolite. Performance simulations are also presented.
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  • 7
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    Relative pose estimation for cylinder-shaped spacecrafts using single image (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: This paper describes a novel framework to determine the relative pose and range of a solid-of-revolution-shaped spacecraft from a single image without any artificial beacons. The translation and the symmetry axis of the spacecraft can be estimated from the imaged cross sections of the spacecraft body. Then the pose and range of the spacecraft are fully determined by means of the images of its solar panels and asymmetric feature. Our method has been validated by both synthetic and real images.
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  • 8
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    Approximate evaluation of marginal association probabilities with belief propagation (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: Data association, the problem of reasoning over correspondence between targets and measurements, is a fundamental problem in tracking. This paper presents a graphical model formulation of data association and applies an approximate inference method, belief propagation (BP), to obtain estimates of marginal association probabilities. We prove that BP is guaranteed to converge, and bound the number of iterations necessary. Experiments reveal a favourable comparison to prior methods in terms of accuracy and computational complexity.
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  • 9
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    Demonstration of cognitive radar for target localization under interference (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: An ultrawideband (UWB) multiple input/multiple output (MIMO) cognitive radar has been developed and demonstrated for the first time. Field-programmable gate array (FPGA) is used for waveform-level computing, while waveform optimization is accomplished in CPU. Working as a closed loop, convex optimization is applied to jointly design (arbitrary) transmitted waveforms and the receiving filters in response to the varying wireless environment. Multiple targets localization in the presence of interference is demonstrated. Shown in the experiment, performance improvement is obvious in all interference patterns.
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  • 10
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    Extreme-value analysis for ML-PMHT, Part 1: threshold determination (2014)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2014-12-13
    Description: The Maximum Likelihood Probabilistic Multi-Hypothesis Tracker (ML-PMHT) can be used as a powerful multisensor, low-observable, multitarget active sonar tracker. It is a non-Bayesian algorithm that uses a generalized likelihood ratio test to differentiate between clutter and targets. Prior to this paper, the detection threshold used for target discrimination was determined either through trial and error or with lengthy Monte Carlo simulations.We present a new method for determining this threshold by assuming that clutter is uniformly distributed in the search space (which is one of the basic assumptions of the ML-PMHT algorithm) and then treating the log-likelihood ratio (LLR) as a random variable transformation. In this manner we can obtain an expression for the value of any random point on the likelihood surface caused by clutter. We then use extreme value theory to obtain an expression for the probability density function (PDF) of the peak point of the LLR surface due to clutter. From this peak PDF, we can then calculate a threshold based on some desired (small) false track acceptance probability.
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  • 11
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    Extreme-value analysis for mlML-PMHT, Part 2: target trackability (2014)
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    Publication Date: 2014-12-13
    Description: The Maximum Likelihood Probabilistic Multi-Hypothesis Tracker (ML-PMHT) can be used as a powerful multisensor, low-observable, multitarget active tracker. It is a non-Bayesian algorithm that uses a generalized likelihood ratio test (GLRT) to differentiate between clutter and targets. We use a new method, initially developed to obtain the probability density function (pdf) of the maximum point in theML-PMHT log-likelihood ratio (LLR) due to clutter, to now develop a pdf for the maximum value of the ML-PMHT LLR caused by a target. With expressions for the pdfs of the maximum points caused by both clutter (developed in a companion article) and a target, we can, for a given set of tracking parameters (signal-to-noise ratio, search volume, target measurement probability of detection, etc.), develop ML-PMHT "tracker operating characteristic" curves, similar to receiver operating characteristic curves for a detector. Since ML-PMHT can be thought of as an optimal algorithm in the sense that, as long as the target and the environment match the algorithm???s assumptions, all the information from all the available measurements can be used, and no approximations are necessary to get the algorithm to function, the analysis presented in this paper offers for the first time part of the answer to the fundamental question: Can a particular target be tracked?
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  • 12
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    Efficient target detection using an adaptive compressive imager (2014)
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    Publication Date: 2014-12-13
    Description: The goal of a target detection system is to determine the location of potential targets in the field of view of the sensor. Traditionally, this is done using high-quality images from a conventional imager. For wide-field-of-view scenarios, this can pose a challenge for both data acquisition and system bandwidth. In this paper, we discuss a compressive sensing technique for target detection that dramatically reduces the number of measurements that is required to perform the task, as compared with the number of pixels in conventional images. This, in turn, can reduce the data rate from the sensor electronics, and along with it, the cost, complexity, and the bandwidth requirements of the system. Specifically, we discuss a two-stage approach that, first, adaptively searches a large area using shift-invariant masks to determine the locations of potential targets (i.e., the regions of interest) and then revisits each location to discriminate between target and clutter using a different set of specialized masks.We show that the overall process is not only highly efficient (i.e., dramatically reduces the number of measurements as compared with the number of pixels) but does so without appreciable loss in target detection performance.
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  • 13
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    Singular perturbationlike approach to compensation of actuator dynamics effect in missile control (2014)
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    Publication Date: 2014-12-13
    Description: Our recently developed nonlinear autopilot controller can make the input???output (I/O) dynamic characteristics of the nonlinear bank-to-turn (BTT) missile system linear and independent of flight conditions. However, relatively slow actuator dynamics can degrade its performance significantly. The proposed compensation method can nearly eliminate the effect of slow actuator dynamics while maintaining the desired linear I/O dynamic characteristics. It considers fully the nonminimum-phase nonlinear BTT missile dynamics but requires no differentiations of noisy variables, unlike other existing control methods.
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  • 14
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    GPS-based attitude determination for a spinning rocket (2014)
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    Publication Date: 2014-12-13
    Description: An algorithm is developed for determining the attitude of a spinning sounding rocket. This algorithm is able to track global positioning system (GPS) signals with intermittent availability but with enough accuracy to yield phase observables for the precise, three-axis attitude determination of a nutating rocket. Raw, single-frequency GPS RF front-end data are processed by several filters to accomplish this task. First, a Levenberg-Marquardt algorithm (LMA) estimates GPS observables for multiple satellites by performing a least-squares fit to the accumulation outputs of a bank of correlators. These observables are then used as measurements in a Rauch-Tung-Striebel smoother that optimizes estimates of carrier phase, Doppler shift, and code phase. Finally, attitude determination is carried out by another batch filter that uses the single-differenced optimized carrier phase estimates between two antennas and an Euler dynamics model for the torque-free attitude motion of the spinning rocket. This second batch filter implements a combination of a substantially modified form of the LMA and the least-squares ambiguity decorrelation adjustment (LAMBDA) method. This design enables it to deal with integer ambiguities that change over long data gaps between times of carrier phase availability. The algorithm presented in this paper is applied to recorded RF data from a spinning sounding rocket mission to produce attitude quaternion and spin-rate estimates using a pair of antennas separated by a 0.3-m baseline. These results are confirmed by another set of quaternions and spin-rate vectors independently estimated from magnetometer and horizon crossing indicator data. Attitude precision on the order of several degrees has been demonstrated.
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  • 15
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    Modal estimation by FBG for flexible structures attitude control (2014)
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    Publication Date: 2014-12-13
    Description: This work investigates an online mode shape estimation method to estimate the time-varying modal properties and correct IMU readings in real time using distributed strain measurements of FBG sensor arrays. Compared to the notch filter approach, the proposed method removes structural vibration information without adding phase lag or transient dynamics. Numerical simulations on a flexible rocket attitude control and the experiments on a vertical test beam with configurable mass distribution are used for demonstration.
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  • 16
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    Sensor selection for nonlinear systems in large sensor networks (2014)
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    Publication Date: 2014-12-13
    Description: In this paper, we consider multistage look-ahead sensor selection problems for nonlinear dynamic systems such as radar target tracking systems. We investigate the problem for large sensor networks for both independent and dependent Gaussian measurement noises in the presence of temporally separable as well as inseparable constraints, e.g., energy constraints. First, when the measurement noises are uncorrelated between sensors, we derive the optimal solution for sensor selection when the constraints are temporally separable. When constraints are temporally inseparable, we can obtain near-optimal solutions by relaxing the nonconvex problem formulation to a linear programming problem so that the sensor selection problem for a large sensor network can be solved in a computationally efficient manner. For illustration, a radar target tracking problem is considered where it is shown that the new method presented for nonlinear dynamic systems performs better than the method based on linearizing the nonlinear equations and using previous sensor selection methods for large sensor networks. Finally, when the measurement noises are correlated between the sensors, the sensor selection problem with temporally inseparable constraints can be relaxed to a Boolean quadratic programming problem problem,,which can be efficiently solved by a Gaussian randomization procedure along with solving a semidefinite programming problem. Numerical examples show that the proposed method that includes consideration of dependence performs much better than the method that ignores dependence of noises.
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  • 17
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    Pylon line spatial correlation assisted transmission line detection (2014)
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    Publication Date: 2014-12-13
    Description: A transmission line is one of the most hazardous objects to low altitude flying aircraft. Due to its extremely tiny size and unsalient visual features, transmission line detection (TLD) is a well-recognized problem. In this paper, a novel TLD method is proposed with the assistance of the spatial correlation between pylon and line for TLD. First, a unidirectional spatial mapping is built up to describe the pylon line spatial correlation. Then, the proposed pylon line spatial correlation and other line features are integrated into a Bayesian framework, which is trained in advance and used to estimate the probability of one line segment belonging to a transmission line. Compared with three other line-based TLD methods, the experimental results demonstrate that the proposed method can obtain better detection performance with higher detection rates and much lower false alarm rates.
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  • 18
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    Modeling of extended objects based on support functions and extended Gaussian images for target tracking (2014)
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    Publication Date: 2014-12-13
    Description: This paper considers tracking of extended objects using the measurements of down-range and cross-range extent. This type of measurement can be naturally and intuitively expressed in terms of support functions. Based on support functions, we propose a general approach to model smooth shapes of objects. Another approach based on extended Gaussian image is proposed to model nonsmooth shapes such as polygons. Compared with existing approaches, a larger range of object shapes can be modeled by the proposed approaches, which have concise mathematical forms and favorable properties. Specifically for elliptical and rectangular objects, our approaches can be implemented easily utilizing simple parametric representations without the need to assume that the major axis of the object is parallel to its velocity vector. Based on these models, a Bayesian algorithm for extended object tracking is easily obtained, where the kinematic state and object extension can be jointly estimated effectively. The benefits of the proposed modeling approaches are illustrated by simulation results.
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  • 19
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    Quadrature Bandpass Sampling Rules for Single- and Multiband Communications and Satellite Navigation Receivers (2011)
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    Publication Date: 2011-12-06
    Description: In this paper, we examine how existing rules for bandpass sampling rates can be applied to quadrature bandpass sampling. We find that there are significantly more allowable sampling rates and that the minimum rate can be reduced.
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  • 20
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    X-Ray Pulsar-Based Relative Navigation using Epoch Folding (2011)
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    Publication Date: 2011-12-06
    Description: How the relative position between two spacecraft can be estimated utilizing signals emitted from X-ray pulsars is explained. The mathematical models of X-ray pulsar signals are developed, and the pulse delay estimation problem is formulated. The Cramér-Rao lower bound (CRLB) for any unbiased estimator of the pulse delay is presented. To retrieve the pulsar photon intensity function, the epoch folding procedure is characterized. Based on epoch folding, two different pulse delay estimators are introduced, and their performance against the CRLB is studied. One is obtained by solving a least squares problem, and the other uses the cross correlation function between the empirical rate function and the true one. The effect of absolute velocity errors on position estimation is also studied. Numerical simulations are performed to verify the theoretical results.
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  • 21
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    Optimizations of Multisite Radar System with MIMO Radars for Target Detection (2011)
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    Publication Date: 2011-12-06
    Description: This paper proposes a novel multisite radar system (MSRS) with multiple-input and multiple-output (MIMO) radars, i.e., MIMO-MSRS system, to improve the detection performance of fluctuating targets. The proposed MIMO-MSRS system increases the local signal-to-noise ratio (SNR) by using digital beamforming (DBF) among all transmitting and receiving channels in a single site. Then it smoothes the target's fluctuation via spatial diversity among the DBF outputs of different sites. For the MIMO-MSRS system, we derive the likelihood ratio test (LRT) detector at first based on the proposed signal model and spatial diversity conditions. Furthermore, with the derived statistics of the LRT detector in the fixed noise background, three optimization problems are discussed on the MIMO-MSRS system configurations, i.e., the numbers of sites and collocated channels in different sites. The first problem is to detect the lowest SNR target with a given probability of false alarm ( PF ), probability of detection ( PD ) and total system degrees of freedom (DOF). The second is to detect a target with the highest PD for a given PF , target SNR, and system DOF. The third is on the minimal system DOF to detect a target with a given PF , PD , and target SNR. For the uniform MIMO-MSRS system, both the standard optimal site number, i.e., the diversity DOF, and its closed-form approximation of the above three problems are obtained. Finally, some numerical results are also provided to demonstrate the effectiveness of the proposed MIMO-MSRS systems.
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    Multitarget Tracking using Probability Hypothesis Density Smoothing (2011)
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    Publication Date: 2011-12-06
    Description: In general, for multitarget problems where the number of targets and their states are time varying, the optimal Bayesian multitarget tracking is computationally demanding. The Probability Hypothesis Density (PHD) filter, which is the first-order moment approximation of the optimal one, is a computationally tractable alternative. By evaluating the PHD, the number of targets as well as their individual states can be extracted. Recent sequential Monte Carlo (SMC) implementations of the PHD filter have paved the way to its application to realistic nonlinear non-Gaussian problems. It is observed that the particle implementation of the PHD filter is dependent on current measurements, especially in the case of low observable target problems (i.e., estimates are sensitive to missed detections and false alarms). In this paper a PHD smoothing algorithm is proposed to improve the capability of PHD-based tracking system. It involves forward multitarget filtering using the standard PHD filter recursion followed by backward smoothing recursion using a novel recursive formula. Smoothing, which produces delayed estimates, results in better estimates for target states and a better estimate for the number of targets. Multiple model PHD (MMPHD) smoothing, which is an extension of the proposed technique to maneuvering targets, is also provided. Simulations are performed with the proposed method on a multitarget scenario. Simulation results confirm improved performance of the proposed algorithm.
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  • 23
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    Joint Multitarget Tracking and Sensor Localization in Collaborative Sensor Networks (2011)
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    Publication Date: 2011-12-06
    Description: Multitarget tracking methods in a sensor network often assume the knowledge of the locations of the sensor nodes. However, in reality sensor nodes are randomly deployed with no prior knowledge about their positions. We propose a method to track an unknown and variable number of targets in the presence of false detections with the positions of sensor nodes estimated jointly to avoid the need of extra localization hardware. Moreover, as low-power consumption is a requirement in sensor networks, a collaborative estimation scheme is presented. For each target in the field under observation there is only a small set of sensor nodes that are active while the others remain in an idle state. The proposed technique is based on a Rao-Blackwellized sequential Monte Carlo (SMC) method that takes advantage of the fact that the state space of the unknown variables is separable. Therefore the problem is divided in two parts. The first one generates samples to estimate the number of targets and solves the association uncertainty between measurements and targets; while the second one is a multiple target tracking problem that can be solved with a modified unscented Kalman filter (MUKF) for each sample. It is shown through simulations that it is possible to track the multiple targets and also get accurate estimates of the unknown locations of the sensor nodes.
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    Persymmetric Adaptive Radar Detectors (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In the general framework of radar detection, estimation of the Gaussian or non-Gaussian clutter covariance matrix is an important point. This matrix commonly exhibits a particular structure: for instance, this is the case for active systems using a symmetrically spaced linear array with constant pulse repetition interval. We propose using the particular persymmetric structure of the covariance matrix to improve the detection performance. In this context, this work provides two new adaptive detectors for Gaussian additive noise and non-Gaussian additive noise which is modeled by the spherically invariant random vector (SIRV). Their statistical properties are then derived and compared with simulations. The vast improvement in their detection performance is demonstrated by way of simulations or experimental ground clutter data. This allows for the analysis of the proposed detectors on both real Gaussian and non-Gaussian data.
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    Detection and Mitigation of Reference Receiver Faults in Differential Carrier Phase Navigation Systems (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In this paper, a methodology is developed to evaluate differential carrier phase navigation architectures subject to reference receiver faults. Carrier phase measurements can be used to provide high accuracy estimates of a user's position. But in applications that involve safety-of-life, such as in precision approach for autonomous shipboard landing, integrity also plays a critical role. One source of integrity risk is the potential for GPS reference receiver failure. Integrity risk in these situations is typically mitigated by equipping the reference station with redundant receivers. However, various approaches to utilize redundant carrier phase measurements from multiple reference receivers are possible. In this paper, we describe two new methods: an averaging approach where different position solutions are averaged in the position domain, and a coupled estimation approach where the measurements from all reference receivers are coupled in the range domain and used to estimate a unified position solution. Furthermore, we investigate the impact of using these methods on accuracy and integrity from several perspectives, including availability performance, cycle resolution capabilities, implementation complexity, and computational efficiency.
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    Optimal Flow Models for Multiscan Data Association (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Multiscan data association can significantly enhance tracking performance in critical radar surveillance scenarios involving multiple targets, low detection probability, high false alarm probability, evasive target maneuvers, and finite radar resolution. Unfortunately, however, this approach is affected by the curse of dimensionality which hinders its real-time application for tracking problems with short scan periods and/or a high number of scans of the association logics and/or many measurements per scan. It is shown here how the formulation of the multiscan association as a multi-commodity or single-commodity flow optimization problem allows a relaxation of the association problem which, on one hand, provides close-to-optimal association performance and, on the other hand, implies a significant reduction of the computational load.
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    A Robust Nonlinear Control Approach for Tip Position Tracking of Flexible Spacecraft (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In this paper, the problem of attitude control of a 3D nonlinear flexible spacecraft is investigated. Two nonlinear controllers are presented. The first controller is based on dynamic inversion, while the second approach is composed of dynamic inversion and γ-synthesis schemes. The extension of dynamic inversion approach to flexible spacecraft is impeded by the nonminimum phase characteristics when the panel tip position is taken as the output of the system. To overcome this problem, the controllers are designed by utilizing the modified output redefinition approach. It is assumed that only three torques in three directions on the hub are used. Actuator saturation is also considered in the design of controllers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. The performances of the proposed controllers are compared in terms of nominal performance, robustness to uncertainties, vibration suppression of panel, sensitivity to measurement noise, environment disturbance, and nonlinearity in large maneuvers. Simulation results confirm the ability of the proposed controller in tracking the attitude trajectory while damping the panel vibration. It is also verified that the perturbations, environment disturbances, and measurement errors have only slight effects on the tracking and damping performances.
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    Hierarchical Fault Diagnosis and Fuzzy Rule-Based Reasoning for Satellites Formation Flight (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Formation flying is an emerging area in the Earth and space science and technology domains that utilize multiple inexpensive spacecraft by distributing the functionalities of a single platform spacecraft among miniature inexpensive platforms. Traditional spacecraft fault diagnosis and health monitoring practices involve around-the-clock monitoring, threshold checking, and trend analysis of a large amount of telemetry data by human experts that do not scale well for multiple space platforms. A novel hierarchical fault diagnosis framework and methodology is presented here that enables a systematic utilization of fuzzy rule-based reasoning to enhance the level of autonomy achievable in fault diagnosis at ground stations. Fuzzy rule-based fault diagnosis schemes for satellite formation flight are developed and investigated at different levels in the hierarchy for a leader-follower architecture. Our formation level fault diagnosis is found to be useful as a supervisory diagnosis scheme that can prompt the operators to have a closer look at the potential faulty components to determine the sources of a fault. Effectiveness of our proposed fault diagnosis methodology is demonstrated by utilizing synthetic formation flying data of five satellites that are configured in the leader-follower architecture, and are subjected to nonabrupt intermittent faults in the attitude control subsystem (ACS) and the electrical power subsystem (EPS) of the follower satellites.
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    Optimal Maneuvers for Aircraft Conflict Resolution Based on Efficient Genetic Webs (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: The problem of designing optimal conflict-free maneuvers for planar multiple aircraft encounters is studied. The maneuvers propose suitable heading changes for aircraft in a cooperative manner. The new mathematical approach provides optimal aircraft trajectories to resolve a wide variety of conflicts, especially in the presence of high-altitude clear air turbulence (CAT), normally encountered during en-route flights. The proposed approach effectively uses Genetic Algorithms (GA), together with modified webs, to quickly find conflict-resolving maneuvers. Different case studies show the method is fast enough to be used for real-time applications when resolving conflicts involving two aircraft. It is also efficient enough to resolve conflicts involving as many as 26 aircraft, which would be helpful in designing acrobatic maneuvers or in congested airspaces where emergency plans are needed.
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    Radon-Fourier Transform for Radar Target Detection (II): Blind Speed Sidelobe Suppression (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: This paper gives a detailed performance analysis for the novel radar long-time coherent integration method, i.e., Radon-Fourier transforms (RFT). Some important properties of RFT, e.g., two-dimensional (2D) impulse response, 2D translational invariance, multitarget linear additivity, linear signal-to-noise ratio gain in additive white Gaussian noise (AWGN), as well as the 2D correlation function of transformed AWGN, are derived for continuous and discrete RFT, respectively. However, because of discrete pulse sampling, finite range resolution, and limited integration time, the "blind-speed sidelobes (BSSL)" of discrete RFT may inevitably appear in real applications. Although the BSSL are reduced with the increase of the blind-speed integer, they may still lead to false alarms or loss detections in a real multitarget scenario. Based on the analytic expression derived for BSSL, the causes of BSSL are analyzed and the effective BSSL suppression methods are proposed. Finally, numerical experiments are also provided to demonstrate the effectiveness of the proposed methods.
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    A Nonlinear-Phase Model-Based Human Detector for Radar (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Radar offers unique advantages over other sensors for the detection of humans, such as remote operation during virtually all weather and lighting conditions, increased range, and better coverage. Many current radar-based human detection systems employ some type of Fourier analysis, such as Doppler processing. However, in many environments, the signal-to-noise ratio (SNR) of human returns is quite low. Furthermore, Fourier-based techniques assume a linear variation in target phase over the aperture, whereas human targets have a highly nonlinear phase history. The resulting phase mismatch causes significant SNR loss in the detector itself. In this paper, human target modeling is used to derive a more accurate nonlinear approximation to the true target phase history. The likelihood ratio is optimized over unknown model parameters to enhance detection performance. Cramer-Rao bounds on parameter estimates and receiver operating characteristic curves are used to validate analytically the performance of the proposed method and to evaluate simulation results.
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    A Near-Optimal Iterative Algorithm via Alternately Optimizing Sensor and Fusion Rules in Distributed Decision Systems (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: For parallel distributed sensor systems with statistically independent sensor decision rules, Chair and Varshney in [2] has obtained the optimal fusion rule. On the other hand, under a given fusion rule, the optimal sensor compression rules have been proposed by Zhu et al. in [21], [23] for generally distributed and dependent sensor observations. An open problem is how to simultaneously obtain an optimal fusion rule and optimal sensor compression rules for general parallel distributed sensor decision systems. Obviously, the exhaustive method for searching for the optimal fusion rule is computationally intractable. For general parallel distributed sensor decision systems, we provide necessary conditions of an optimal fusion rule and optimal sensor compression rules and propose a computationally efficient iterative algorithm to simultaneously/alternately search for a fusion rule and sensor compression rules by combining both Zhu's and Chair and Varshney's methods. Moreover, the algorithm is extended to multiple bit compression and Network decision systems. Numerical examples show that the fusion rule obtained by the algorithm is in most cases the same as the optimal fusion rule obtained by the exhaustive method, therefore, it is effective and near optimal.
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    Near-Optimal Terrain Collision Avoidance Trajectories using Elevation Maps (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so-called "quad-tree forms." The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the "cost map," lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different simulations show the method is applicable wherever there is no need for sharp changes in flight level. Nevertheless, the current method could be expanded to three-dimensional terrain avoidance/terrain following flights.
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    Maritime ATR using Classifier Combination and High Resolution Range Profiles (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: A maritime automatic target recognition system is developed that performs ship classification using one-dimensional high resolution range profiles. Five physically based features are defined and are extracted from both VV and HH polarizations resulting in a 10-dimensional feature vector. A nonlinear classifier combination approach involving a neural network combiner along with three individual classifiers (Bayes, nearest neighbor, and neural network) is proposed. A decision confidence measure based on the classifier discriminants is developed using a nonparametric estimation approach. The confidence measure enables the system to reject samples that have a low decision confidence. The performance of the proposed neural network based combination is compared with individual classifiers and a number of other combination rules. The results show that this combination can provide high recognition accuracy along with a high probability of declaration. The performance in the presence of samples from not-before-seen classes is also investigated. A new nearest neighbor confidence thresholding approach is developed to aid the neural network combiner in rejecting these samples.
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    Aircraft Power System Stability Study Including Effect of Voltage Control and Actuators Dynamic (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: This paper describes a stability analysis of aircraft ac frequency-wild power systems with constant power loads (CPL). In contrast to previous publications, the proposed analysis method employs the dq modeling approach instead of the state-space averaging (SSA) and average-value modeling (AVM) methods to derive power-electronic converter models for stability studies. This results in lower order models and allows the modeling of vector-controlled converter elements where the SSA and AVM methods are not easily applicable. The resulting model can be combined with models of other power system elements expressed in terms of synchronously rotating frames (generators, front-end converters, vector-controlled drives, etc.). The paper analyzes the stability of frequency-wild power systems for both load and parameter variations and takes into account controlled generator voltage dynamics and electromechanical actuator dynamics. The stability margins are assessed and compared with those for power systems with the ideal voltage source and the ideal CPLs. The study is supported by intensive time domain simulations that support the theory.
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    Throughput per Pass for Data Aggregation from a Wireless Sensor Network via a UAV (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Data retrieval from a sensor field by means of unmanned aerial vehicle (UAV) has increasing interests for both commercial, military, and homeland security applications. In these situations, the design of energy-efficient communication links between sensor field and UAV is crucial, owing to battery powered sensor nodes. We propose an energy-efficient cooperative transmission scheme for wireless sensor networks (WSNs) where data gathered by sensor nodes need to be collected into a far receiver. In particular, we consider a network composed of sensor nodes that share a common message that has to be transmitted asynchronously toward a fusion center onboard a UAV. We consider that the communication channels between the nodes and the fusion center are subject to fading and noise. Due to the far communication distance and energy constraint at each node, the fusion center must be able to reliably receive the weak and noisy signals. In our approach the fusion center consists of a Rake receiver capable of collecting multiple replicas of the same information from the nodes in the WSN. The performance of the proposed cooperative diversity scheme is then studied in terms of throughput, bit error probability, and energy efficiency. The results obtained show that, as the number of nodes increases, the proposed approach increases network lifetime, communication reliability, and throughput.
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    Delayed PIC for Postcorrelation Mitigation of Continuous Wave and Multiple Access Interference in GPS Receivers (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Several techniques are available to mitigate the problem of multiple access interference (MAI) caused by the limited dynamic range of the 1023-chip global positioning system (GPS) coarse acquisition Gold codes. MAI causes difficulties in several high-sensitivity applications, including indoor GPS and the use of pseudolites for GPS augmentation. This paper provides details on a variation on the existing techniques of successive interference cancellation (SIC) and parallel interference cancellation (PIC), but with the advantage of being more readily applied. This postcorrelation method is suitable for use in both hardware and software GPS receivers and is able to use commercially available GPS front-end chips employing 2-bit quantization of the received radio signal. The method can also be used to cancel some forms of continuous wave (CW) interference. Simulation results providing statistics on the effectiveness of the technique are provided, as well as results obtained when the technique was implemented in hardware on a GPS receiver based on a field programmable gate array correlator. The proposed method is also compared to some other MAI-mitigating techniques.
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    High Resolution ISAR Imaging of Targets with Rotating Parts (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: For a target with rotating parts, the ISAR image of its main body may be overshadowed by micro-Doppler signals, which are traditionally treated as interference and removed from radar echoes. However, it is potentially useful to perform imaging using micro-Doppler signals because they contain information on the geometrical structure of the rotating part. Inspired by the inverse Radon transform, well-known in the image processing community, this paper creates a data-recording model for two-dimensional (2D) ISAR imaging of rotating parts. Based on this model, the real-valued inverse Radon transform is applied to image formation in the range-slow time domain. Then we put forward a complex-valued inverse Radon transform for imaging of rotating parts, which utilizes both the sinusoidal modulus and the phase of the radar echoes. Additionally, we analyze possible problems when applying these algorithms in real world situations and provide corresponding solutions. Finally, the effectiveness of the algorithms is demonstrated using simulated and measured data.
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    Cooperative Search by UAV Teams: A Model Predictive Approach using Dynamic Graphs (2011)
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    Publication Date: 2011-12-06
    Description: A receding-horizon cooperative search algorithm is presented that jointly optimizes routes and sensor orientations for a team of autonomous agents searching for a mobile target in a closed and bounded region. By sampling this region at locations with high target probability at each time step, we reduce the continuous search problem to a sequence of optimizations on a finite, dynamically updated graph whose vertices represent waypoints for the searchers and whose edges indicate potential connections between the waypoints. Paths are computed on this graph using a receding-horizon approach, in which the horizon is a fixed number of graph vertices. To facilitate a fair comparison between paths of varying length on nonuniform graphs, the optimization criterion measures the probability of finding the target per unit travel time. Using this algorithm, we show that the team discovers the target in finite time with probability one. Simulations verify that this algorithm makes effective use of agents and outperforms previously proposed search algorithms. We have successfully hardware tested this algorithm in two small unmanned aerial vehicles (UAVs) with gimbaled video cameras.
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    Multipath Insensitive Delay Lock Loop in GNSS Receivers (2011)
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    Publication Date: 2011-12-06
    Description: The code measurement suffers from multiple error sources and especially multipath. The latter is unpredictable and changes in space and over time. Many interesting multipath mitigation techniques have been proposed. Most of them are not sufficiently effective for precise positioning using the code measurement. This paper presents a multipath insensitive delay lock loop that aims to improve the pseudorange measurement precision in the presence of multipath. This code loop is simple and does not require postprocessing of observables. Simulation and real implementation results showed that the proposed code loop dramatically improves the tracking error due to multipaths. Tracking error is limited to 1 m on pseudorange in typical multipath environments. This loop is more sensitive than the standard delay lock loop to thermal noise and applies predominantly to strong GNSS signals.
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    Joint DOA, Range, and Polarization Estimation in the Fresnel Region (2011)
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    Publication Date: 2011-12-06
    Description: A new algorithm of joint direction-of-arrival (DOA), range, and polarization estimation is proposed to localize multiple polarized sources in the Fresnel region. The algorithm is based on a sparse linear array composed of dual-polarization sensors with symmetric subarray partition. By the symmetric property of sparse linear array, the steering vector of the polarized array can be expressed as the product of a complex matrix with the signal's DOA and a complex matrix with the signal's range and a complex vector with the signal's polarization. A spectral rank reduction (RARE) algorithm is presented to estimate the DOA independent from the range and polarization. With each estimated DOA, the range of each source is accordingly estimated by defining the 1-D range RARE function. For each DOA and range of source, a MUSIC algorithm is finally adopted for the signal's polarization. The DOA and range identifiability of the proposed algorithm are discussed, and the range ambiguity issues caused by sparse linear array are analyzed. The proposed algorithm employs only second-order statistics and 1-D search so that its computational burden is reduced. The limitation of inter-element spacing ( d ≤ λ/4) is overcome. By numerical examples, it is shown that the proposed algorithm can enhance the angle resolution even with the limited number of sensors.
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    Analysis of the Robustness of Bistatic Inverse Synthetic Aperture Radar in the Presence of Phase Synchronisation Errors (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Bistatic inverse synthetic aperture radar (B-ISAR) has the potential to become the radar imaging tool for obtaining noncooperative target images in arbitrary bistatic configurations. A monostatic ISAR processor is used here to form B-ISAR images and its robustness is tested with respect to phase synchronisation errors and rapidly time-varying bistatic configurations. Specifically, the B-ISAR point spread function (PSF) is analytically derived and the problem of B-ISAR image autofocusing is reformulated in such conditions. It is shown that, in most bistatic scenarios, the range-Doppler (RD) based monostatic ISAR processor is able to form focussed B-ISAR images. Simulation results are used to support the theoretical results.
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    Highly-Dynamic Cross-Layered Aeronautical Network Architecture (2011)
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    Publication Date: 2011-12-06
    Description: Highly-dynamic wireless environments present unique challenges to end-to-end communication networks, caused by the time-varying connectivity of high-velocity nodes combined with the unreliability of the wireless communication channel. Such conditions are found in a variety of networks, including those used for tactical communications and aeronautical telemetry. Addressing these challenges requires the design of new protocols and mechanisms specific to this environment. We present a new domain-specific architecture and protocol suite, including cross-layer optimizations between the physical, MAC, network, and transport layers. This provides selectable reliability for multiple applications within highly mobile tactical airborne networks. Our contributions for this environment include the transmission control protocol (TCP)-friendly transport protocol, AeroTP; the IP-compatible network layer, AeroNP; and the geolocation aware routing protocol AeroRP. Through simulations we show significant performance improvement over the traditional TCP/IP/MANET protocol stack.
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    On Accumulated State Densities with Applications to Out-of-Sequence Measurement Processing (2011)
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    Publication Date: 2011-12-06
    Description: In target tracking applications, the full information on the kinematic target states accumulated over a certain time window up to the present time is contained in the joint probability density function of these state vectors, given the time series of all sensor data. This joint density may also be called an accumulated state density (ASD) and provides a unified treatment of filtering and retrodiction insofar as by marginalizing the ASD, the standard filtering and retrodiction densities are obtained. In addition, ASDs fully describe the posterior correlations between the states at different instants of time. The notion of ASDs and closed formulae for calculating them are discussed. The practical usefulness of considering ASDs is illustrated by applications, where out-of-sequence (OoS) measurements are to be processed within the framework of a centralized measurement fusion architecture, i.e., when the sensor data do not arrive in the temporal order, in which they were produced. The approach can be applied to Kalman, multiple hypothesis tracking (MHT), and interacting multiple model (IMM) filtering.
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    Probabilistic Validation of Simplified Models of Spacecraft Formations near Libration Points (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: This paper introduces a method to probabilistically evaluate the validity of dynamics model approximations, and applies this method to simplified models of satellite formation dynamics near the Sun-Earth/Moon L2 libration point. The method uses a Monte Carlo scheme similar to a sampling importance resampling (SIR) filter to evolve state probability densities through several satellite dynamics models of differing complexity. The evolved densities are fit with a Gaussian mixture model and compared probabilistically to evaluate the validity of the simplified dynamics models over time. With this method, analysis of a formation flying mission on a halo orbit near the Sun/Earth-Moon L2 point reveals a 2 hr window of validity in which the relative satellite dynamics are indistinguishable from a double integrator (DI) and initial relative velocities drive model uncertainty.
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    A Nonlinear Observer-Based Strategy for Aircraft Oscillatory Failure Detection: A380 Case Study (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Robust and early detection of oscillatory failures in the electrical flight control system of an aircraft is a crucial issue. Oscillatory failures, if not detected and passivated in time, can lead to strong interactions with loads and aeroelasticity and may potentially lead to structural damages. A nonlinear observer-based solution to detect such failures with small amplitude at a very early stage is presented. The stability and convergence proofs are given and experimental results with real A380 flight data are presented.
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    Specific Length Trajectories Optimised for Maximum Acceleration using Conic Parameterised Clothoids (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: One current method of aircraft flightpath generation employs multi-segmented straight trajectories with each consecutive pair of segments filleted with arcs of constant radius. A difficulty of infeasibility immediately arises. In order for an aircraft to make the transition from a straight to a curved path segment (or vice versa) there is a physical requirement for a step acceleration, implying an infinite jerk. Clothoid curves provide a solution and have been investigated to fillet the consecutive segments. However, in this case, the mathematical definition of the clothoid is in terms of an integral that precludes closed-form solutions for critical guidance parameters. The attractiveness of the clothoid is to solve the physical infeasibility problem, however the mathematical intractability inherent in the approach has attracted limited attention despite being recognised as a major concern through early experiments. A method is presented here where double clothoid curves are used to fillet consecutive segments. This work goes beyond present practice to provide closed form solutions by using the hyperbola as a clothoid facsimile. Acceleration constraints have been enforced, both accumulative and maximum, and both the reference bank angle and bank angle rate have been expressed analytically in closed-form in terms of hyperbolic parameters. The solution can be optimised in terms of accumulative acceleration and path length, whilst simultaneously enforcing maximum acceleration constraints. This method of trajectory generation is attractive for implementation with air traffic management separation assurance, tunnel-in-the-sky, and other proposed cockpit display systems.
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    Effect of Estimation on the Performance of an Integrated Missile Guidance and Control System (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Motivated by spectral separation, guidance and control systems of interceptors are traditionally designed separately. However, interception of highly maneuverable targets and increased interception accuracy requirements lead to intense maneuvering during the last phase of the engagement, thus violating the spectral separation assumption of the conventional two-loop design. This has boosted the interest in integrated guidance-control designs that demonstrate superior interception accuracies by accounting for the coupling between the kinematics and dynamics of the problem. One of the approaches used for the integrated design is the sliding mode control (SMC) methodology. The results presented so far assumed full state information. We examine the effect of estimation on the performance of the integrated sliding mode controller design. In particular, a sliding mode observer/differentiator (SMOD) is used to estimate the target states. Through an intensive numerical study it is shown that the integrated guidance-control approach has a clear advantage over a conventional separated two-loop design. This advantage is attributed to the robustness of the integrated sliding mode controller design that better deals with the estimation errors and measurements noises.
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    Automatic Understanding of ATC Speech: Study of Prospectives and Field Experiments for Several Controller Positions (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Although there has been a lot of interest in recognizing and understanding air traffic control (ATC) speech, none of the published works have obtained detailed field data results. We have developed a system able to identify the language spoken and recognize and understand sentences in both Spanish and English. We also present field results for several in-tower controller positions. To the best of our knowledge, this is the first time that field ATC speech (not simulated) is captured, processed, and analyzed. The use of stochastic grammars allows variations in the standard phraseology that appear in field data. The robust understanding algorithm developed has 95% concept accuracy from ATC text input. It also allows changes in the presentation order of the concepts and the correction of errors created by the speech recognition engine improving it by 17% and 25%, respectively, absolute in the percentage of fully correctly understood sentences for English and Spanish in relation to the percentages of fully correctly recognized sentences. The analysis of errors due to the spontaneity of the speech and its comparison to read speech is also carried out. A 96% word accuracy for read speech is reduced to 86% word accuracy for field ATC data for Spanish for the "clearances" task confirming that field data is needed to estimate the performance of a system. A literature review and a critical discussion on the possibilities of speech recognition and understanding technology applied to ATC speech are also given.
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    Novel Technique for Vision-Based UAV Navigation (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: We describe a novel technique for vision-based UAV (unmanned aerial vehicle) navigation. In this technique, the navigation (position estimation) problem is formulated as a tracking problem and solved by a particle filter. The state and observation models of the particle filter are established based on a stereo analysis of the image sequence generated by the UAV's video camera in connection with a DEM (digital elevation map) of the area of the flight, which helps to control estimation error accumulation. The efficacy of this technique is demonstrated by simulation results.
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    The Modified Riccati Equation for Amplitude-Aided Target Tracking in Heavy-Tailed Clutter (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: The performance of tracking methods can most often only be assessed by means of Monte-Carlo simulations. An exception to this rule is the popular probabilistic data association filter (PDAF), whose root mean square error (RMSE) can be predicted by means of the modified Riccati equation (MRE). To the best of our knowledge, the first treatment along these lines for the PDAF with amplitude information (PDAFAI) is presented here. We evaluate the MRE with amplitude information (AI) for the case of a Swerling I target in heavy-tailed, or more precisely K -distributed, background noise. The MRE can be used to determine an optimal nominal false alarm rate. To the best of our knowledge, the first systematic approach to the determination of false alarm rates in heavy-tailed clutter is presented here. In particular, it is indicated that the PDAFAI can safely operate in the presence of very abundant clutter, while the PDAF only can cope with limited amounts of clutter.
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    Rapid Fine Strapdown INS Alignment Method under Marine Mooring Condition (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In order to solve the strapdown inertial navigation system (INS) alignment problem under the marine mooring condition, the rapid strapdown INS fine alignment method is proposed. This method uses the gravity in the inertial frame to deal with the lineal and angular disturbances. Also the forward and backward processes for strapdown INS calculation and filter estimation are designed. Making use of the forward and backward processes to repeatedly process the saved inertial measurement unit (IMU) data sequence could quickly obtain the initial strapdown attitude matrix. Simulation and trial test validate the performance of the proposed rapid fine strapdown INS alignment.
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    Range Doppler and Image Autofocusing for FMCW Inverse Synthetic Aperture Radar (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Inverse synthetic aperture radar (ISAR) is a well-known technique for obtaining high-resolution radar images. ISAR techniques have been successfully applied in the recent past in combination with pulsed coherent radar. In order to be more appealing to both civilian and military fields, imaging sensors are required to be low cost, low powered, and compact. Coherent pulsed radars do not account for these requirements as much as frequency modulated continuous wave (FMCW) radars. However, FMCW radars transmit a linear frequency modulated (LFM) sweep in a relatively long time interval when compared with the pulse length of a coherent pulse radar. During such an interval the assumption of stop&go is no longer valid, that is the target cannot be considered stationary during the acquisition of the entire sweep echo. Therefore, the target motion within the sweep must be taken into account. Such a problem is formulated and solved for ISAR systems, where the target is noncooperative and additional unknowns are added to the signal model. In the present work, the authors define a complete FMCW-ISAR received signal model, propose an ISAR image formation technique suitable for FMCW radar and derive the point spread function (PSF) of the imaging system. Finally, the proposed FMCW ISAR autofocusing algorithm is tested on simulated and real data.
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    An Autoregressive Formulation for SAR Backprojection Imaging (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: We present a recursive backprojection-based procedure for synthetic aperture imaging. In traditional synthetic aperture radar (SAR) imaging, radar measurements are processed in blocks of contiguous azimuth angle measurements. In continuous imaging applications, block processing generally entails significant computational overhead, in part due to overlapped processing of azimuth intervals. We consider a novel recursive update approach, in which the SAR image is updated using an autoregressive-based algorithm as new measurements are taken. In this approach, the SAR image is found as a linear combination of a small number of previous images and a term containing the current radar measurement. The computational and memory requirements of the recursive imaging approach are modest-on the order of M · N 2 , where M is the recursion order (typically ≤ 3) and N 2 is the image size. In addition, we investigate the crossrange sidelobes realized by the autoregressive (AR) imaging approach. We show that a first-order autoregression of the image gives crossrange sidelobes similar to a rectangular azimuth window, while a third-order autoregression gives sidelobes comparable to those obtained from widely-used windows in block-processing image formation. We compare images obtained from the recursive and block-processing techniques, both for a synthetic scene and for X-band SAR measurements from the Gotcha data set.
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    Interval-Based Localization using RSSI Comparison in MANETs (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: The knowledge of node positions is essential to many applications of wireless sensor networks. We propose an original model-free technique for localization in mobile ad hoc sensor networks (MANETs). Region constraints are set by a comparison of the received signal strength indicators (RSSIs) at both anchors and nonanchor nodes. The accuracy of this method remains in the way that it overcomes the use of the channel pathloss model. It is thus naturally adapted to nonstationary environments. The proposed approach uses interval analysis and constraints satisfaction techniques to compute accurate locations in a guaranteed way. Simulations are performed on group trajectories of sensors whose movements are generated using a reference point group mobility model. The simulation results confirm the efficiency of the proposed method and show that it outperforms the anchor-based methods in terms of accuracy and estimation errors.
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    Intent Inference and Syntactic Tracking with GMTI Measurements (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In conventional target tracking systems, human operators use the estimated target tracks to make higher level inference of the target behaviour/intent. The work presented here develops syntactic filtering algorithms that assist human operators by extracting spatial patterns from target tracks to identify suspicious/anomalous spatial trajectories. The targets' spatial trajectories are modeled by a stochastic context free grammar (SCFG) and a switched mode state space model. Bayesian filtering algorithms for SCFGs are presented for extracting the syntactic structure and illustrated for a ground moving target indicator (GMTI) radar example. The performance of the algorithms is tested with the experimental data collected using DRDC Ottawa's X-band Wideband Experimental Airborne Radar (XWEAR).
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    Threshold Optimization for Tracking a Nonmaneuvering Target (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: A promising line of research attempts to bridge the gap between radar detector and radar tracker by means of considering jointly optimal parameter settings for both of these subsystems. We consider the problem of detection threshold optimization in a tracker-aware manner so that a feedback from the tracker to the detector is formed to maximize the overall system performance. We explore the research space for tracker-aware detector threshold optimization schemes and compare various approaches in a theoretical and experimental framework. In particular, we consider the optimization schemes which rely on two nonsimulation performance prediction (NSPP) algorithms for the probabilistic data association filter (PDAF), namely, the modified Riccati equation (MRE) and hybrid conditional averaging (HYCA). The study identifies a number of algorithmic and experimental evaluation gaps in this space and we propose to fill these gaps. Simulation results on relevant tracking scenarios demonstrate and discuss the behavior of the existing and proposed methods in terms of steady-state and transient tracking performance.
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    Overlap Area Assisted Call Admission Control Scheme for Communications System (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In this paper we propose a novel call admission control scheme named overlap area assisted new call blocking scheme (NCBS-OA) for High Altitude Platform (HAP) based communications systems, which utilizes both the geographical information and the overlap area to intelligently decide when to block a new call to help avoid possible handover failure. An approximate analytical model is derived to estimate the new call blocking performance of the new scheme, which is verified by simulation results. Research results show that the NCBS-OA can improve the new call blocking probability significantly (by a minimum of 25% for the system model with the parameter values chosen) while maintaining a zero handover call dropping probability seen with the time-based channel reservation algorithm (TCRA), and that the greater the cell radius and the more the number of connections considered in the overlap area of a virtual cell, the better the new call blocking performance.
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    Cramer-Rao Bounds and Selection of Bistatic Channels for Multistatic Radar Systems (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In this paper we deal with the problem of calculating the Cramer-Rao lower bounds (CRLBs) for bistatic radar channels. To this purpose we exploited the relation between the ambiguity function (AF) and the CRLB. The bistatic CRLBs are analyzed and compared with the monostatic counterparts as a function of the bistatic geometric parameters. In the bistatic case both geometry factors and transmitted waveforms play an important role in the shape of the AF, and therefore in the estimation accuracy of the target range and velocity. In particular, the CRLBs depend on the target direction of arrival (DOA), the bistatic baseline length (BBL), and the distance between the target and the receiver. The CRLBs are then used to select the "optimum" bistatic channel (or set of channels) for the tracking of a radar target moving along a trajectory in a multistatic scenario.
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    Efficient Real-Time Generation of Bit-Wise Parallel Representations of Oversampled Carrier Replicas (2011)
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    Publication Date: 2011-12-06
    Description: An algorithm has been developed that efficiently generates in-phase and quadrature carrier replicas over a range of Doppler shift frequencies and initial phase offsets. This algorithm provides a new method that aids in bit-wise parallel baseband mixing of signals in software radios, specifically targeted at GNSS radios. Bit-wise parallel correlation, of which one step is baseband mixing, provides a processing time speed-up when correlating signals that are digitized to a low number of bits, as opposed to the standard multiply-and-accumulate correlation. The new algorithm makes use of the small phase differences between a set of signals that have a large ratio of the IF to the Doppler shift frequency. It uses specially-designed look-up tables to generate carrier replicas on-the-fly. This new algorithm can efficiently generate bit-packed carrier replicas using a small look-up table (10-100 s of kBytes).
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    Coordinate Registration Method based on Sea/Land Transitions Identification for Over-the-Horizon Sky-Wave Radar: Numerical Model and Basic Performance Requirements (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: We propose an approach to the problem of range coordinate registration (CR) for HF band over-the-horizon sky-wave radar (OTHR-SW) signals on a single pulse basis. The approach is based on the a priori knowledge of the displacement of the sea/land transitions within the area illuminated by the radar antenna beam. It takes advantage of the geomorphological structure of the surveillance area, which is exploited to build a surface correlation mask that is in turn used as a geographic reference for the received radar echo. The method is based on the maximization of the cross-correlation between the received radar echo and the surface mask signatures. We describe first an extended numerical model of the whole HF OTHR-SW scenario for simulating the received signal, then we show the results of the application of the method under simplifying operative hypotheses that allow to point out the minimum requirements in terms of received signal-to-noise ratio (SNR) and differential sea/land backscattering coefficient for achieving given accuracies in the range estimates.
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    Update to the Hybrid Conditional Averaging Performance Prediction of the IMM Algorithm (2011)
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    Publication Date: 2011-12-06
    Description: Traditionally the performance evaluation of a target tracking algorithm is accomplished via Monte Carlo simulations for each specific scenario of interest. For some applications, the time and computational resource requirements of performing the necessary simulations for algorithm design is excessive; so the need for performance prediction becomes paramount. One method of performance prediction developed during the early 1990s is the hybrid conditional averaging (HYCA) technique, which can be used to predict the performance of the interacting multiple model (IMM) algorithm. Applying the HYCA technique to the IMM algorithm as originally developed leads to poor performance prediction in certain situations. A new extension used in these circumstances is shown to lead to superior performance prediction without an increase in computational complexity compared with the originally developed algorithm for such situations.
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    Optimization of Satellite Laser Communication Subject to Log-Square-Hoyt Fading (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: In the existing studies of satellite laser communications, the variances in the azimuth and elevation axes of a swaying transmitter are usually assumed to be identical. In this correspondence, the analysis is extended to the general case in which these two variances are not the same. It is shown that the transmitter radial pointing error angle follows the Hoyt distribution. Furthermore, we prove that the instantaneous signal-to-noise ratio (SNR) follows the log-square-Hoyt distribution. Based on these results, we establish an optimization model to minimize the outage probability, subject to a specified transmitter power, by adjusting some system parameters such as the transmitter gain. A closed form of the solution is obtained and a set of representative curves are presented.
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    Efficient Time-Domain Image Formation with Precise Topography Accommodation for General Bistatic SAR Configurations (2011)
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    Publication Date: 2011-12-06
    Description: Due to the lack of an appropriate symmetry in the acquisition geometry, general bistatic synthetic aperture radar (SAR) cannot benefit from the two main properties of low-to-moderate resolution monostatic SAR: azimuth-invariance and topography-insensitivity. The precise accommodation of azimuth-variance and topography is a real challenge for efficent image formation algorithms working in the Fourier domain, but can be quite naturally handled by time-domain approaches. We present an efficient and practical implementation of a generalised bistatic SAR image formation algorithm with an accurate accommodation of these two effects. The algorithm has a common structure with the monostatic fast-factorised backprojection (FFBP), and is therefore based on subaperture processing. The images computed over the different subapertures are displayed in an advantageous elliptical coordinate system capable of incorporating the topographic information of the imaged scene in an analogous manner as topography-dependent monostatic SAR algorithms do. Analytical expressions for the Nyquist requirements using this coordinate system are derived. The overall discussion includes practical implementation hints and a realistic computational burden estimation. The algorithm is tested with both simulated and actual bistatic SAR data. The actual data correspond to the spaceborne-airborne experiment between TerraSAR-X and F-SAR performed in 2007 and to the DLR-ONERA airborne experiment carried out in 2003. The presented approach proves its suitability for the precise SAR focussing of the data acquired in general bistatic configurations.
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    A Kullback-Leibler Methodology for Unconditional ML DOA Estimation in Unknown Nonuniform Noise (2011)
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    Publication Date: 2011-12-06
    Description: Maximum likelihood (ML) direction-of arrival (DOA) estimation of multiple narrowband sources in unknown nonuniform white noise is considered. A new iterative algorithm for stochastic ML DOA estimation is presented. The stepwise concentration of the log-likelihood (LL) function with respect to the signal and noise nuisance parameters is derived by alternating minimization of the Kullback-Leibler divergence between a model family of probability distributions defined on the unconditional model and a desired family of probability distributions constrained to be concentrated on the observed data. The new algorithm presents the advantage to provide closed-form expressions for the signal and noise nuisance parameter estimates which results in a substantial reduction of the parameter space required for numerical optimization. The proposed algorithm converges only after a few iterations and its effectiveness is confirmed in a simulation example.
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    Interacting Methods for Manoeuvre Handling in the GM-PHD Filter (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Probability hypothesis density (PHD) filter implementations with jump Markov linear system (JMLS) manoeuvre handling are well known. A new derivation, following the method of the popular interacting multiple model (IMM) filter from single target tracking, is presented and is shown to be equivalent to existing implementations. The resulting filter is shown to reduce to the optimal Bayes solution for jointly estimating target state and motion mode in the single target, linear, and Gaussian case.
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    Examination of a Popular Out-of-Sequence Measurement Update Algorithm (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: We examine an out-of-sequence measurement (OoSM) update algorithm by Bar-Shalom. We demonstrate that "Algorithm C" is mathematically equivalent to initializing a track with the OoSM, predicting that track to the current time without process noise, then using the OoSM track as a pseudomeasurement to update the system track. We argue that a more reasonable approximation includes process noise in the OoSM prediction. Like Algorithm C, the proposed algorithm makes use only of current track information.
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    New Approach for SAR Doppler Ambiguity Resolution in Compressed Range Time and Scaled Azimuth Time Domain (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: A new approach is addressed for Doppler ambiguity resolution. This method exploits the fact that, in compressed range time and special scaled azimuth time domain, all the trajectories exhibit the same slope, which is proportional to the Doppler ambiguity number. The method can directly estimate the ambiguity number without a priori knowledge on the baseband Doppler centroid. It is confirmed that this approach is robust to the partially exposed strong targets in azimuth, ground slowly moving targets and the motion variation of platform in realistic scenarios. Results of real measured data processing show that this method works well in medium- to high-contrast scenes and can basically (not always) provide the right estimate in low-contrast scenes.
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    Performance Analysis of Noncoherent Pulse Compression Technique (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Noncoherent pulse compression (NCPC) is a recently investigated variant of the classical (coherent) coded pulse compression technique [1-5]. The performance of NCPC under various signal-to-noise ratio (SNR) conditions is investigated and compared with coherent pulse compression (CPC). Various performance measurement approaches are used to quantify NCPC performance. All of them indicate very similar performance trends. It was found that, as the SNR of received signal decreases, the advantage of pulse compression in terms of improved SNR, gets diminished. It is therefore argued that NCPC is not well suited for low input SNR conditions, and for applications requiring large pulse compression gain.
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    Aircraft Attenuation Measurements and Radio Interference Scenarios Between In-Cabin and Terrestrial Cellular Networks (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: This paper presents an outdoor-to-aircraft measurement campaign conducted inside a long range Airbus A340-300 aircraft. The attenuation induced by the hull of the aircraft for various operational frequencies is determined and these results are utilized to perform interference studies and assess whether the aircraft mobile terminal interferes to the ground base station and the opposite.
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    Parameter Selection in Sparsity-Driven SAR Imaging (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: We consider a recently developed sparsity-driven synthetic aperture radar (SAR) imaging approach which can produce superresolution, feature-enhanced images. However, this regularization-based approach requires the selection of a hyper-parameter in order to generate such high-quality images. In this paper we present a number of techniques for automatically selecting the hyper-parameter involved in this problem. We propose and develop numerical procedures for the use of Stein's unbiased risk estimation, generalized cross-validation, and L-curve techniques for automatic parameter choice. We demonstrate and compare the effectiveness of these procedures through experiments based on both simple synthetic scenes, as well as electromagnetically simulated realistic data. Our results suggest that sparsity-driven SAR imaging coupled with the proposed automatic parameter choice procedures offers significant improvements over conventional SAR imaging.
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    How Many Low-Precision Sensors are Enough for Reliable Detection? (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: This paper investigates the problem of achieving any given detection performance through combining multiple independent low-precision sensors with uncertain parameters. It shows that the achievability is robustly guaranteed when the number of sensors is above some level. An example is used to demonstrate the effectiveness of the obtained results.
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    A Multi-Dimensional Hough Transform-Based Track-Before-Detect Technique for Detecting Weak Targets in Strong Clutter Backgrounds (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: The Hough transform (HT) algorithm detects straight-line features in two-dimensional data. This correspondence extends the HT to N -dimensional data to efficiently combine multiple first-threshold crossings from moving targets. The data dimensions can be the target position, its range and range-rate, and/or the first-threshold crossing times. This multi-dimensional HT (MHT) technique can be applied to enhance the detection of targets in random clutter backgrounds through the application of track-before-detect (TBD) processing.
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    Efficient Velocity Filter Implementations for Dim Target Detection (2011)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2011-12-06
    Description: Efficient frequency domain and recursive spatiotemporal (RST) velocity filter implementations are presented. In the frequency domain, the sliding discrete Fourier transform (SDFT) is exploited to yield a track-before-detect (TBD) algorithm with a complexity that is independent of the filter integration time. The performance of the filters is examined using simulation and real sensor data. When processing the real data, the SDFT implementation is approximately 3 times faster than the equivalent fast Fourier transform (FFT) implementation and 16 times faster than the corresponding spatiotemporal (ST) implementation. The RST filter outperformed all other implementations when simulated data were used.
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    Flatness-Based Trajectory Planning/Replanning for a Quadrotor Unmanned Aerial Vehicle (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: A flatness-based flight trajectory planning/replanning strategy is proposed for a quadrotor unmanned aerial vehicle (UAV). In the nominal situation (fault-free case), the objective is to drive the system from an initial position to a final one without hitting the actuator constraints while minimizing the total time of the mission or minimizing the total energy spent. When actuator faults occur, fault-tolerant control (FTC) is combined with trajectory replanning to change the reference trajectory in function of the remaining resources in the system. The approach employs differential flatness to express the control inputs to be applied in the function of the desired trajectories and formulates the trajectory planning/replanning problem as a constrained optimization problem.
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    Iterative Maximum Likelihood Estimators for High-Dynamic GNSS Signal Tracking (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: This paper presents novel signal-tracking algorithms for global navigation satellite system (GNSS) receivers using a maximum likelihood estimation (MLE) technique to carry out robust signal tracking under severe signal environments, such as high dynamics for maneuvering users. The cost function of the MLE of signal parameters such as code delay, carrier phase, and Doppler frequency is used to derive a discriminator function and thus generate error signals based on incoming and reference signals. Two distinct forms of algorithms are derived by means of mathematical programming using an iterative approach, which is based on the log-likelihood MLE cost function that assumes various signal parameters as unknown constants over an observation interval. First, the Levenberg-Marquardt method is employed using gradient and Hessian matrices. Second, a conventional nonlinear least-square estimation method is applied to determine the MLE cost function, assuming additive white Gaussian noise. An efficient and practical approach to Doppler frequency tracking is also derived based on the assumption of a code-free signal (i.e., a signal from which the code has been wipe off). The use of MLE for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited to various GNSS signals that have the same tracking module structure. Finally, performance of the receivers, in terms of robustness under dynamic stress, computational efficiency, accuracy, computational burden, and response speed, is assessed using analytical and/or numerical techniques.
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    Out-of-Sequence Measurement Processing for Particle Filter: Exact Bayesian Solution (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: The problem of out-of-sequence measurement (OOSM) processing when the filtering technique used at the tracker is the particle filter (PF) is considered. First, an exact Bayesian algorithm for updating with OOSMs is derived. Then, the PF implementation of the exact Bayesian algorithm, called A-PF, is developed. Since A-PF is rooted in exact Bayesian inference, if the number of particles is sufficiently large, A-PF is the one (and the only one) that is able to achieve the optimal performance obtained from the in-sequence processing. This is confirmed by the simulation results. Also, it is shown that the performance of A-PF is always superior to previous (heuristic) PF-based algorithms with the same number of particles.
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    GPS Signal-in-Space Integrity Performance Evolution in the Last Decade (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Knowledge of the Global Positioning System (GPS) signal-in-space (SIS) anomalies in history has a great importance for not only assessing the general performance of GPS SIS integrity but also validating the fundamental assumption of receiver autonomous integrity monitoring (RAIM): at most one satellite fault at a time. The main purpose of this paper is to screen out all potential SIS anomalies in the last decade by comparing broadcast ephemerides and clocks with precise ones. Validated broadcast navigation messages are generated from 397,044,414 navigation messages logged by on average 410 International GNSS Service (IGS) stations during the period 6/1/2000??8/31/2010. Both IGS and National Geospatial-Intelligence Agency (NGA) precise ephemerides/clocks are used as truth references. Finally, 1256 potential SIS anomalies are screened out. These anomalies show an improving SIS integrity performance in the last decade, from tens or hundreds of anomalies per year before 2003 to on average two anomalies per year after 2008. Moreover, the fundamental assumption of RAIM is valid because never have two SIS anomalies or more occurred simultaneously since 2004.
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    High Efficiency Satellite Multiple Access Scheme for Machine-to-Machine Communications (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: The work presented here describes the key design drivers and performance of a high efficiency satellite mobile messaging system well adapted to the machine-to-machine communication services targeting, in particular, the vehicular market. It is shown that the proposed return link multiple access solution is providing a random access channel (RACH) aggregated spectral efficiency around 2 bit/s/Hz in the presence of power unbalance with reliable packet delivery over typical land mobile satellite (LMS) channels.
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    Automatic Radar Antenna Scan Type Recognition in Electronic Warfare (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: We propose a novel and robust algorithm for antenna scan type (AST) recognition in electronic warfare (EW). The stages of the algorithm are scan period estimation, preprocessing (normalization, resampling, averaging), feature extraction, and classification. Naive Bayes (NB), decision-tree (DT), artificial neural network (ANN), and support vector machine (SVM) classifiers are used to classify five different ASTs in simulation and real experiments. Classifiers are compared based on their accuracy, noise robustness, and computational complexity. DT classifiers are found to outperform the others.
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    RFS MCMC Predetection Fusion Applied to Multistatic Sonar Data (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Predetection fusion can be indispensable for multisensor/multitarget tracking using large networks of low quality sensors. Previously we derived both the "optimal" generalized likelihood ratio test (GLRT) and a more practicable contact-sifting variant. Unfortunately, the gaps between the two in terms both of computation time and performance are not inconsiderable. In this paper we propose an approach, based on random finite sets (RFS) and implemented by Markov chain Monte Carlo (MCMC) simulation, that offers a good balance between run time and metrics for the tracking results.
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    Optimality of Linear Time-Varying Guidance for Impact Angle Control (2012)
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    Publication Date: 2012-10-09
    Description: The work presented here demonstrates optimality of linear time-varying guidance laws for controlling impact angles as well as terminal misses using the inverse problem of optimal control theory. Under the assumptions of a stationary target and a lag-free missile with a constant speed and a small flight path angle, it is shown that a generalized linear time-varying guidance law with an arbitrary pair of guidance coefficients can minimize a certain quadratic performance index subject to the terminal constraints. Feasible sets of the guidance coefficients for capturability are investigated and explicitly stated by yielding the closed-form solutions of the guidance loop in this paper. These results imply that it is possible for more realistic settings of the guidance coefficients either to improve the guidance performance or to achieve some specific guidance objectives in practical environments. Furthermore, the time-to-go calculation methods, which consider the closed-loop solutions for arbitrary guidance coefficients, are included for implementation of the guidance law. Linear and nonlinear simulations are performed to validate the proposed approach.
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    Micro-Range/Micro-Doppler Decomposition of Human Radar Signatures (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Recently, the use of micro-Doppler radar signatures for target classification has become an area of focus, in particular for the case of dynamic targets where many components are interacting over time. To fully exploit the signature information, individual scattering centers may be automatically extracted and associated over the full target observation. The availability of ultrafine radar range resolution, or micro-range resolution, aids this process immensely. This paper proposes one such algorithm. The proposed method uses the well-known nonlinear least squares (NLS) and expectation-maximization (EM) algorithms. As shown, leveraging fine range and Doppler resolution allows human signatures to be decomposed into the responses of constituent body parts. The algorithm is experimentally validated against a number of measured human-radar data sets.
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    Integration of a Triaxial Magnetometer into a Helicopter UAV GPS-Aided INS (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: The University of Alberta's Applied Nonlinear Controls Lab (ANCL) helicopter unmanned aerial vehicle's (UAV's) existing GPS-aided inertial navigation system (INS) does not provide observability of heading angle during hover. This motivates the integration of a triaxial magnetometer aiding sensor into the extended Kalman filter (EKF)-based navigation algorithm. A novel magnetometer calibration procedure is implemented and compared with conventional approaches. Experimental results in ground and flight testing confirm that the observability issue is resolved and demonstrate improvements in attitude estimation.
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    Recursive Least-Squares Source Tracking using One Acoustic Vector Sensor (2012)
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    Publication Date: 2012-10-09
    Description: An acoustic vector-sensor (a.k.a. vector-hydrophone) is composed of three acoustic velocity-sensors, plus a collocated pressure-sensor, all collocated in space. The velocity-sensors are identical, but orthogonally oriented, each measuring a different Cartesian component of the three-dimensional particle-velocity field. This acoustic vector-sensor offers an azimuth-elevation response that is invariant with respect to the source's center frequency or bandwidth. This acoustic vector-sensor is adopted here for recursive least-squares (RLS) adaptation, to track a single mobile source, in the absence of any multipath fading and any directional interference. A formula is derived to preset the RLS forgetting factor, based on the prior knowledge of only the incident signal power, the incident source's spatial random walk variance, and the additive noise power. The work presented here further advances a multiple-forgetting-factor (MFF) version of the RLS adaptive tracking algorithm, that requires no prior knowledge of these aforementioned source statistics or noise statistics. Monte Carlo simulations demonstrate the tracking performance and computational load of the proposed algorithms.
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    Optimal Update with Multiple Out-of-Sequence Measurements with Arbitrary Arriving Order (2012)
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    Publication Date: 2012-10-09
    Description: In multisensor target tracking systems receiving out-of-sequence measurements (OOSMs) from local sensors is a common situation. In the last decade many algorithms have been proposed to update with an OOSM optimally or suboptimally. However, what one faces in the real world is the multiple OOSMs, which arrive at the fusion center in, generally, arbitrary orders, e.g., in succession or interleaved with in-sequence measurements. A straightforward approach to deal with this multi-OOSM problem is by sequentially applying a given OOSM algorithm; however, this simple solution does not guarantee the optimal update under the multi-OOSM scenario. The work presented here discusses the differences between the single-OOSM processing and the multi-OOSM processing, and presents the general solution to the multi-OOSM problem, which is called the complete in-sequence information (CISI) approach. Given an OOSM, in addition to updating the state at the most recent time, the CISI approach also updates the states between the OOSM time and the most recent time, including the state at the OOSM time. Three novel CISI methods are developed in this paper: the information filter-equivalent measurement (IF-EqM) method, the CISI fixed-point smoothing (CISI-FPS) method and the CISI fixed-interval smoothing (CISI-FIS) method. Numerical examples are given to illustrate the optimality of these CISI methods under various multi-OOSM scenarios.
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    Extended Object Tracking Based on Set-Theoretic and Stochastic Fusion (2012)
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    Publication Date: 2012-10-09
    Description: A novel approach for extended object tracking is presented. In contrast to existing approaches, no statistical assumptions about the location of the measurement sources on the extended target object are made. As a consequence, a combined set-theoretic and stochastic estimator is obtained that is robust to systematic errors in the target model. The benefits of the new approach is demonstrated by means of simulations.
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    Hovering Quad-Rotor Control: A Comparison of Nonlinear Controllers using Visual Feedback (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: This article presents a comparison of three control techniques: nested saturations, backstepping, and sliding modes. The control objective consists of obtaining the best control strategy to stabilize the position of a quad-rotor unmanned aerial vehicle (UAV) when using visual feedback. We propose a vision-based method to measure translational speed as well as the UAV 3D position in a local frame. The three selected controllers were implemented and tested in real-time experiments. The obtained results demonstrate the performance of such methodologies applied to the quad-rotor system.
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    Improved Estimation of Kinematic State of Reentry Ballistic Targets with Modeling of Colored and Nonstationary Seeker Noise (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: A method is presented for modeling the nonstationary and correlated noise of the RF seeker for estimating the target acceleration and the relative kinematics for endo-atmospheric engagement. The estimator also incorporates the dynamics of the seeker track loop. The state model estimates the acceleration of the target directly along with relative position and velocity. This model also include the ratio of the air density and the ballistic coefficient and its time derivatives as elements of the state vector to account for the aerodynamic drag in the endo-atmospheric phase. Such formulations obviate the need for priori empirical models of air density and drag coefficient. Performance results of the proposed method have been compared with a well-known model from the literature with and without the model of the measurement dynamics and the nonstationary, correlated measurement noise under closed-loop guidance employing the augmented proportional navigation (APN) law for endo-atmospheric ballistic target tracking. It is clearly seen that the proposed method yields more accurate estimates of target acceleration and the relative kinematics.
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    Spread-Spectrum Continuous-Phase-Modulated Signals for Satellite Navigation (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Spread-spectrum continuous-phase-modulated (SS-CPM) signals are investigated with application to satellite navigation. In particular, focus is devoted to the special subclasses of SS-CPM with semi-integer modulation index $h$ greater than one. This constitutes a novelty with respect to traditional navigation signal design on one hand (which is based on direct-sequence spread-spectrum (DS-SS) signals with rectangular pulse) and with traditional communication SS-CPM with $hgt1$ on the other. Main output is that setting the modulation index $hlt1$ to semi-integer values allows the SS-CPM signals to behave like having subcarriers, exactly in the same way as it happens for the binary offset carrier (BOC) modulation. The main advantage is that CPM ensures a constant envelope at the transmission side, thus being appealing when these features are required at the system level. After a description of signal properties, focus is devoted to ranging code synchronization, by exploitation of the theory on time-delay estimation (TDE). A few delay-lock loop schemes are also presented, based on an offset quadrature phase-shift keying (OQPSK) approximation of the signal at the receiver side, achieved by Laurent's decomposition at the receiver side. Proposed loops performance are analyzed in terms of Cramer-Rao bound (CRB), rms tracking error, and multipath robustness. An application of SS-CPM for a two-rate-service scheme is proposed.
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    MIMO SAR using Chirp Diverse Waveform for Wide-Swath Remote Sensing (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Synthetic aperture radar (SAR) is a well-proven remote sensing technique; however, current single-antenna SAR systems cannot fulfill the increasing demands of future remote sensing in high-resolution and wide-swath imaging performance. This paper presents a scheme of multiple-input and multiple-output (MIMO) SAR using chirp diverse waveform for wide-swath remote sensing. This approach employs MIMO antenna configuration in elevation which is divided into multiple subpertures. In this way, multiple pairs of transmit-receive virtual beams directing to different subswathes are formed simultaneously. Equivalently a large swath is synthesized. The corresponding system scheme, chirp diverse waveform design, multi-beam forming algorithm and range ambiguity performance are investigated. A chirp-scaling-based image formation algorithm is presented to focus the MIMO SAR simulation data. Comprehensive numerical simulation examples are performed. It is shown that the proposed method enables the SAR systems to operate with high flexibility and reconfigurability which is particularly attractive for next generation remote sensing technique.
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    Extended Target Tracking using a Gaussian-Mixture PHD Filter (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: This paper presents a Gaussian-mixture (GM) implementation of the probability hypothesis density (PHD) filter for tracking extended targets. The exact filter requires processing of all possible measurement set partitions, which is generally infeasible to implement. A method is proposed for limiting the number of considered partitions and possible alternatives are discussed. The implementation is used on simulated data and in experiments with real laser data, and the advantage of the filter is illustrated. Suitable remedies are given to handle spatially close targets and target occlusion.
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    Prediction Error Based Adaptive Jacobian Tracking for Free-Floating Space Manipulators (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: The work presented here investigates task-space trajectory tracking control for free-floating space robots with uncertain kinematics and dynamics. To deal with these two kinds of uncertainties, we propose a prediction error based adaptive Jacobian controller, which includes a modified task-space computed torque controller and two modified least-squares estimators. By defining a new variable that is termed as the estimate of the spacecraft angular acceleration, the proposed controller can work without requiring measurement of the spacecraft angular acceleration. The kinematic and dynamic parameter adaptations are driven by prediction errors. Using input-output stability analysis, we obtain explicit stability results of the closed-loop system and show the asymptotic convergence of the end-effector motion tracking errors of the free-floating manipulator. Furthermore, it is shown that the performance of the proposed controller has a tight relationship with the estimated generalized Jacobians of free-floating manipulators. Simulation results are presented to show the performance of the proposed controller, and in addition some implementation issues of the proposed control algorithm are discussed.
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    Sliding Mode and Inertial Delay Control Based Missile Guidance (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: A novel formulation of sliding mode control (SMC) based proportional navigation (PN) guidance law is presented. Unlike conventional SMC-based guidance laws, the law presented here does not need any knowledge of bounds of target acceleration. The target acceleration is estimated using the so-called inertial delay control (IDC). Closed-loop stability for the guidance loop is established. Simulations are carried out by considering highly-maneuvering targets and constant as well as varying missile velocity and the results are presented to demonstrate the effectiveness of the proposed formulation.
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    On Transmit Beamforming for MIMO Radar (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Methods for transmit beamforming in multiple-input multiple-output (MIMO) radar based on the design of multiple correlated waveforms have been proposed. This paper points out that this approach couples the spatial (beamformer) and temporal (waveform) parts of the problem, significantly complicating the design. It is shown here that the most general form of transmit beamforming can be achieved in a decoupled form, using orthogonal (uncorrelated) waveforms and a multi-rank transmit beamformer. This formulation allows the use of standard beamformer design procedures. Examples are provided to illustrate the design of multi-rank beamformers for search and tracking applications. The examples include single and multiple beamformers, adaptive beamformers, and wide beams for illumination. These examples are illustrated by simulation results.
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    Modeling and Simulation of Coherent Sea Clutter (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: This paper describes a new technique for modeling and simulating the coherent returns from radar sea clutter, based on the compound K-distribution model for clutter amplitude statistics. Using observations of recorded Doppler spectra, a simple method is proposed for characterizing the temporal variations of the Doppler spectrum observed in a single-range cell. It is shown that simulations based on this model can reproduce the main statistical features observed in real measurements.
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    Electronic Warfare Receiver with Multiple FFT Frame Sizes (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: An electronic warfare (EW) receiver based on fast Fourier transforms (FFTs) with different frame sizes is presented. With a given sampling frequency, an FFT-based EW receiver can improve its frequency estimation by increasing the FFT frame size; however, such an increase has detrimental effects on its time-of-arrival and pulse width estimations. By applying multiple FFTs with different frame sizes, the proposed EW receiver can achieve high time and frequency resolutions simultaneously.
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    Robust Multisensor Multitarget Tracker with Application to Passive Multistatic Radar Tracking (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: This paper presents a novel approach to multitarget multisensor tracking, based on the combination of a probability hypothesis density (PHD) smoother and hard multisensor multiscan data association (MMDA) used in a feedback connection. The PHD smoother allows to initiate target tracks without resorting to complicated measurement-to-measurement association procedures while the feedback from the hard MMDA, besides providing track labeling, makes the PHD smoother, and hence the overall tracker, more robust to missed detections and false alarms. An application of the proposed tracker to passive multistatic radar tracking is worked out in order to demonstrate its effectiveness in critical situations where the lack of single-sensor observability prevents the use of traditional track initiation methods. As a further contribution, an extension to the multisensor case of the multicommodity approach to multiscan data association, originally presented for the single-sensor case, is provided.
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    Spaceborne Reflector SAR Systems with Digital Beamforming (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: Spaceborne synthetic aperture radar (SAR) imaging enters an era where increasingly short revisit times, or large swath widths, respectively, and high spatial resolutions are requested. These requirements impose contradicting constraints on conventional SAR systems using analog beamforming technology. The development for future radar satellites is therefore towards digital beamforming (DBF) systems where the analogous receiver hardware is replaced by digital components. Concerning the SAR antenna the innovative concept of a parabolic mesh reflector in conjunction with a digital feed array is becoming a promising architecture for this new SAR system generation. These antennas, already a mature technique for communication satellites, have the potential to outperform planar array antennas in terms of gain at a moderate hardware effort. This article provides a hardware concept study based on a design in X-band. Focus is put on DBF algorithms adopted to the SAR case and important performance figures are derived.
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    Distributed Tracking with Energy Management in Wireless Sensor Networks (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2012-10-09
    Description: We consider a wireless sensor network (WSN) tasked with tracking a process using a set of distributed nodes. Here multiple remote sensor nodes estimate the physical process (viz., a moving object) and transmit quantized estimates to a fusion center for processing. At the fusion node a BLUE (best linear unbiased estimation) approach is used to combine the sensor estimates and to create a final estimate of the state. In this framework the uncertainty of the overall estimate is derived and shown to depend on the individual sensor transmit energy and quantization levels, as well as the Kalman tracker uncertainty at the node. Since power and bandwidth are critically constrained resources in battery operated sensor nodes, we attempt to quantify the trade-off between the lifetime of the network and the estimation quality over time. Three different convex formulations of the underlying nonconvex mixed integer nonlinear optimization problem are presented. Unlike previous work this effort incorporates the operating state of the nodes into the decisions of the optimum bits and the transmission power levels based on a heuristic. Simulation results for all formulations demonstrate the quality of the state estimate as well as the extended lifetime of the WSN.
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