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  • 1
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: Three-dimensional ultrasound imaging is a promising medical imaging technology because of its ease of use and improved accuracy in diagnosis. However, its high computational complexity and resulting high power consumption has precluded its use in hand-held applications. In this paper, we present a separable beamforming method that greatly reduces computational complexity. Our method is based on decomposing the delay term in a way that minimizes the root-mean-square error caused by the decomposition. We analyze tradeoffs between the approximation error caused by the decomposition and computational complexity. Then, we present enhancements to the Sonic Millip3De hardware accelerator for ultrasound beamforming to implement separable beamforming. Using hardware synthesis targeting standard cells in 45 nm, we show that the proposed method allows us to boost the Sonic Millip3De frame rate from 1–2 Hz to 32 Hz while maintaining power consumption at 15 W. We validate image quality of our method using cyst phantom simulations in Field II. Our evaluation demonstrates that the proposed separable beamforming method can produce 3-D images with high quality that are comparable to those generated by non-separable beamforming.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
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  • 2
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: For MIMO systems, due to the deployment of multiple antennas at both the transmitter and the receiver, the design variables, e.g., precoders, equalizers, and training sequences, are usually matrices. It is well known that matrix operations are usually more complicated compared with their vector counterparts. In order to overcome the high complexity resulting from matrix variables, in this paper, we investigate a class of elegant multi-objective optimization problems, namely matrix-monotonic optimization problems (MMOPs). In our work, various representative MIMO optimization problems are unified into a framework of matrix-monotonic optimization, which includes linear transceiver design, nonlinear transceiver design, training sequence design, radar waveform optimization, the corresponding robust design and so on as its special cases. Then, exploiting the framework of matrix-monotonic optimization the optimal structures of the considered matrix variables can be derived first. Based on the optimal structure, the matrix-variate optimization problems can be greatly simplified into the ones with only vector variables. In particular, the dimension of the new vector variable is equal to the minimum number of columns and rows of the original matrix variable. Finally, we also extend our work to some more general cases with multiple matrix variables.
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  • 3
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
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  • 4
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 5
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 6
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 7
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 8
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 9
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 10
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 11
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-11-08
    Beschreibung: RES, a regularized stochastic version of the Broyden–Fletcher–Goldfarb–Shanno (BFGS) quasi-Newton method, is proposed to solve strongly convex optimization problems with stochastic objectives. The use of stochastic gradient descent algorithms is widespread, but the number of iterations required to approximate optimal arguments can be prohibitive in high dimensional problems. Application of second-order methods, on the other hand, is impracticable because the computation of objective function Hessian inverses incurs excessive computational cost. BFGS modifies gradient descent by introducing a Hessian approximation matrix computed from finite gradient differences. RES utilizes stochastic gradients in lieu of deterministic gradients for both the determination of descent directions and the approximation of the objective function's curvature. Since stochastic gradients can be computed at manageable computational cost, RES is realizable and retains the convergence rate advantages of its deterministic counterparts. Convergence results show that lower and upper bounds on the Hessian eigenvalues of the sample functions are sufficient to guarantee almost sure convergence of a subsequence generated by RES and convergence of the sequence in expectation to optimal arguments. Numerical experiments showcase reductions in convergence time relative to stochastic gradient descent algorithms and non-regularized stochastic versions of BFGS. An application of RES to the implementation of support vector machines is developed.
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  • 12
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 13
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 14
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 15
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 16
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 17
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 18
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 19
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 20
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 21
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-13
    Beschreibung: 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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  • 22
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-17
    Beschreibung: This paper presents an optimized software implementation of a Successive Cancellation (SC) decoder for polar codes. Despite the strong data dependencies in SC decoding, a highly parallel software polar decoder is devised for x86 processor target. A high level of performance is achieved by exploiting the parallelism inherent in today's processor architectures (SIMD, multicore, etc.). Some optimizations that were originally thought for hardware implementation (memory reduction techniques and algorithmic simplifications) were also applied to enhance the throughput of the software implementation. Finally, some low level optimizations such as explicit assembly description or data packing are used to improve the throughput even more. The resulting decoder description is implemented on different x86 processor targets. An analysis of the decoder in terms of latency and throughput is proposed. The influence of several parameters on the throughput and the latency is investigated: the selected target, the code rate, the code length, the SIMD mode (SSE/AVX), the multithreading mode, etc. The energy per decoded bit is also estimated. The proposed software decoder compares favorably with state of the art software polar decoders. Extensive experimentations demonstrate that the proposed software polar decoder exceeds 1 Gb/s for code lengths $Nleq 2^{17}$ on a single core and reaches multi-Gb/s throughputs when using four cores in parallel in AVX mode.
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  • 23
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-17
    Beschreibung: This paper deals with the two-dimensional (2-D) direction-of-arrival (DOA) estimation of a mixture of noncoherent (including uncorrelated and partially correlated) and coherent (i.e., fully correlated) narrowband signals impinging on a planar sensor array composed of two parallel uniform linear arrays (ULAs). An oblique projection based approach for 2-D direction estimation (OPADE) is proposed by using some cross-correlations between the received array data. In the proposed OPADE, the oblique projection is utilized to isolate the coherent signals from the noncoherent ones and the effect of additive noise is alleviated, while the computationally intensive eigendecomposition is avoided, and the estimated elevation and azimuth angles are paired automatically. Further, an iterative alternating scheme is presented to improve the estimation accuracy of the oblique projector and hence that of the DOAs of coherent signals. The Cramér–Rao lower bound (CRB) for the mixture of noncoherent and coherent signals is also derived explicitly, where the prior knowledge of the signal correlation is incorporated into the 2-D DOA estimation of noncoherent signals. Finally the effectiveness of the OPADE and the theoretical analysis are substantiated through numerical examples.
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  • 24
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: Bounded Component Analysis (BCA) is a recent framework which enables development of methods for the separation of dependent as well as independent sources from their mixtures. This paper extends a recent geometric BCA approach introduced for the instantaneous mixing problem to the convolutive mixing problem. The paper proposes novel deterministic convolutive BCA frameworks for the blind source extraction and blind source separation of convolutive mixtures of sources which allows the sources to be potentially nonstationary. The global maximizers of the proposed deterministic BCA optimization settings are proved to be perfect separators. The paper also illustrates that the iterative algorithms corresponding to these frameworks are capable of extracting/separating convolutive mixtures of not only independent sources but also dependent (even correlated) sources in both component (space) and sample (time) dimensions through simulations based on a Copula distributed source system. In addition, even when the sources are independent, it is shown that the proposed BCA approach have the potential to provide improvement in separation performance especially for short data records based on the setups involving convolutive mixtures of digital communication sources.
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  • 25
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: This paper investigates the problem of frequency-specific (FS) model approximation of transfer functions using a min-max approach. The objective is to find an approximation model for a transfer function such that the maximum error gain over a specific frequency range is minimized. First, a linear matrix inequality condition characterizing the FS gain of a transfer function is derived by using the generalized Kalman-Yakubovich-Popov lemma, and then a simple iterative approach is proposed to optimize the approximation model. Numerical experiments show that the proposed approach can produce better approximation models over a specific frequency range than some existing approaches. Moreover, it is indicated how to apply the proposed approximation approach to the design problem of infinite impulsive response digital filters, and design examples clearly illustrate that the proposed design flow can generate filters comparable with the latest design method.
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  • 26
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: We address the problem of two-dimensional (2-D) phase retrieval from magnitude of the Fourier spectrum. We consider 2-D signals that are characterized by first-order difference equations, which have a parametric representation in the Fourier domain. We show that, under appropriate stability conditions, such signals can be reconstructed uniquely from the Fourier transform magnitude. We formulate the phase retrieval problem as one of computing the parameters that uniquely determine the signal. We show that the problem can be solved by employing the annihilating filter method, particularly for the case when the parameters are distinct. For the more general case of the repeating parameters, the annihilating filter method is not applicable. We circumvent the problem by employing the algebraically coupled matrix pencil (ACMP) method. In the noiseless measurement setup, exact phase retrieval is possible. We also establish a link between the proposed analysis and 2-D cepstrum. In the noisy case, we derive Cramér–Rao lower bounds (CRLBs) on the estimates of the parameters and present Monte Carlo performance analysis as a function of the noise level. Comparisons with state-of-the-art techniques in terms of signal reconstruction accuracy show that the proposed technique outperforms the Fienup and relaxed averaged alternating reflections (RAAR) algorithms in the presence of noise.
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  • 27
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: In this paper, shrinkage linear complex-valued least mean squares (SL-CLMS) and shrinkage widely linear complex-valued least mean squares (SWL-CLMS) algorithms are devised for adaptive beamforming. By exploiting the relationship between the noise-free a posteriori and a priori error signals, the SL-CLMS method is able to provide a variable step size to update the weight vector for the adaptive beamformer, significantly enhancing the convergence speed and decreasing the steady-state misadjustment. On the other hand, besides adopting a variable step size determined by minimizing the square of the augmented noise-free a posteriori errors, the SWL-CLMS approach exploits the noncircular properties of the signal of interest, which considerably improves the steady-state performance. Simulation results are presented to illustrate their superiority over the CLMS, complex-valued normalized LMS, variable step size, recursive least squares (RLS) algorithms and their corresponding widely linear-based schemes. Additionally, our proposed algorithms are more computationally efficient than the RLS solutions though they may have a slightly slower convergence rate.
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  • 28
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: Downsampling of signals living on a general weighted graph is not as trivial as of regular signals where we can simply keep every other samples. In this paper we propose a simple, yet effective downsampling scheme in which the underlying graph is approximated by a maximum spanning tree (MST) that naturally defines a graph multiresolution. This MST-based method significantly outperforms the two previous downsampling schemes, coloring-based and SVD-based, on both random and specific graphs in terms of computations and partition efficiency quantified by the graph cuts. The benefit of using MST-based downsampling for recently developed critical-sampling graph wavelet transforms in compression of graph signals is demonstrated.
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  • 29
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: We consider mesh networks composed of groups of relaying nodes which operate in decode-and-forward mode. Each node from a group relays information to all the nodes in the next group. We study these networks in two setups, one where the nodes have complete state information about the channels through which they receive the signals, and another when they only have the statistics of the channels. We derive recursive expressions for the probabilities of errors of the nodes and present several implementations of detectors used in these networks. We compare the mesh networks with multihop networks formed by a set of parallel sections of multiple relaying nodes. We demonstrate with numerous simulations that there are significant improvements in performance of mesh over multihop networks in various scenarios.
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  • 30
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: The resolution of many large-scale inverse problems using MCMC methods requires a step of drawing samples from a high dimensional Gaussian distribution. While direct Gaussian sampling techniques, such as those based on Cholesky factorization, induce an excessive numerical complexity and memory requirement, sequential coordinate sampling methods present a low rate of convergence. Based on the reversible jump Markov chain framework, this paper proposes an efficient Gaussian sampling algorithm having a reduced computation cost and memory usage, while maintaining the theoretical convergence of the sampler. The main feature of the algorithm is to perform an approximate resolution of a linear system with a truncation level adjusted using a self-tuning adaptive scheme allowing to achieve the minimal computation cost per effective sample. The connection between this algorithm and some existing strategies is given and its performance is illustrated on a linear inverse problem of image resolution enhancement.
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  • 31
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-12-06
    Beschreibung: In this paper, we develop verifiable sufficient conditions and computable performance bounds of $ell_{1}$ -minimization based sparse recovery algorithms in both the noise-free and noisy cases. We define a family of quality measures for arbitrary sensing matrices as a set of optimization problems, and design polynomial-time algorithms with theoretical global convergence guarantees to compute these quality measures. The proposed algorithms solve a series of second-order cone programs, or linear programs. We derive performance bounds on the recovery errors in terms of these quality measures. We also analytically demonstrate that the developed quality measures are non-degenerate for a large class of random sensing matrices, as long as the number of measurements is relatively large. Numerical experiments show that, compared with the restricted isometry based performance bounds, our error bounds apply to a wider range of problems and are tighter, when the sparsity levels of the signals are relatively low.
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  • 32
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: In this correspondence, we propose an efficient estimator of optimal memory (averaging interval) for discrete-time finite impulse response (FIR) filters in state-space. Its crucial property is that only real measurements and the filter output are involved with no reference and noise statistics. Testing by the two-state polynomial model has shown a very good correspondence with predicted values. Even in the worst case of the harmonic model, the estimator demonstrates practical applicability.
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  • 33
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: The JPEG compression method is among the most successful compression schemes since it readily provides good compressed results at a rather high compression ratio. However, the decompressed result of the standard JPEG decompression scheme usually contains some visible artifacts, such as blocking artifacts and Gibbs artifacts (ringing), especially when the compression ratio is rather high. In this paper, a novel artifact reducing approach for the JPEG decompression is proposed via sparse and redundant representations over a learned dictionary. Indeed, an effective two-step algorithm is developed. The first step involves dictionary learning and the second step involves the total variation regularization for decompressed images. Numerical experiments are performed to demonstrate that the proposed method outperforms the total variation and weighted total variation decompression methods in the measure of peak of signal to noise ratio, and structural similarity.
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  • 34
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Stochastic orders are binary relations defined on probability distributions which capture intuitive notions like being larger or being more variable. This paper introduces stochastic ordering of interference distributions in large-scale networks modeled as point processes. Interference is a major performance-limiting factor in most wireless networks, thus it is important to characterize its statistics. Since closed-form results for the distribution of interference for such networks are only available in limited cases, it is of interest to compare network interference using stochastic orders, for two different point processes with different fading or path-loss scenarios between the interferers and the receiver. In this paper, conditions on the fading distribution and path-loss model are given to establish stochastic ordering between interferences. Moreover, Laplace functional ordering is defined between point processes and applied for comparing interference. Monte-Carlo simulations are used to supplement our analytical results. The useful applications of this research are also provided.
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  • 35
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Screening is the problem of finding a superset of the set of non-zero entries in an unknown $p$ -dimensional vector $beta^*$ given $n$ noisy observations. Naturally, we want this superset to be as small as possible. We propose a novel framework for screening, which we refer to as Multiple Grouping (MuG), that groups variables, performs variable selection over the groups, and repeats this process multiple number of times to estimate a sequence of sets that contains the non-zero entries in $beta^*$ . Screening is done by taking an intersection of all these estimated sets. The MuG framework can be used in conjunction with any group based variable selection algorithm. In the high-dimensional setting, where $p gg n$ , we show that when MuG is used with the group Lasso estimator, screening can be consistently performed without using any tuning parameter. Our numerical simulations clearly show the merits of using the MuG framework in practice.
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  • 36
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: When designing optimal filters it is often unrealistic to assume that the statistical model is known perfectly. The issue is then to design a robust filter that is optimal relative to an uncertainty class of processes. Robust filter design has been treated from minimax (best worst-case performance) and Bayesian (best average performance) perspectives. Heretofore, the Bayesian approach has involved finding a model-specific optimal filter, one that is optimal for some model in the uncertainty class. Lifting this constraint, we optimize over the full class from which the original optimal filters were obtained, for instance, over all linear filters. By extending the original characteristics determining the filter, such as the power spectral density, to “effective characteristics” that apply across the uncertainty class, we demonstrate, for both linear and morphological filtering, that an “intrinsically optimal” Bayesian robust filter can be represented in the same form as the standard solution to the optimal filter, except via the effective characteristics. Solutions for intrinsic Bayesian robust filters are more transparent and intuitive than solutions for model-specific filters, and also less tedious, because effective characteristics push through the spectral theory into the Bayesian setting, whereas solutions in the model-specific case depend on grinding out the optimization.
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  • 37
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: We propose a novel decomposition framework for the distributed optimization of general nonconvex sum-utility functions arising naturally in the system design of wireless multi-user interfering systems. Our main contributions are i) the development of the first class of (inexact) Jacobi best-response algorithms with provable convergence, where all the users simultaneously and iteratively solve a suitably convexified version of the original sum-utility optimization problem; ii) the derivation of a general dynamic pricing mechanism that provides a unified view of existing pricing schemes that are based, instead, on heuristics; and iii) a framework that can be easily particularized to well-known applications, giving rise to very efficient practical (Jacobi or Gauss–Seidel) algorithms that outperform existing ad hoc methods proposed for very specific problems. Interestingly, our framework contains as special cases well-known gradient algorithms for nonconvex sum-utility problems, and many block-coordinate descent schemes for convex functions.
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  • 38
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: The ability to detect change-points in a dynamic network or a time series of graphs is an increasingly important task in many applications of the emerging discipline of graph signal processing. This paper formulates change-point detection as a hypothesis testing problem in terms of a generative latent position model, focusing on the special case of the Stochastic Block Model time series. We analyze two classes of scan statistics, based on distinct underlying locality statistics presented in the literature. Our main contribution is the derivation of the limiting properties and power characteristics of the competing scan statistics. Performance is compared theoretically, on synthetic data, and empirically, on the Enron email corpus.
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  • 39
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: In this paper, we propose opportunistic jammer selection in a wireless security system for increasing the secure degrees of freedom (DoF) between a transmitter and a legitimate receiver (say, Alice and Bob). There is a jammer group consisting of $S$ jammers among which Bob selects $K$ jammers. The selected jammers transmit independent and identically distributed Gaussian signals to hinder the eavesdropper (Eve). Since the channels of Bob and Eve are independent, we can select the jammers whose jamming channels are aligned at Bob, but not at Eve. As a result, Eve cannot obtain any DoF unless it has more than $KN_{j}$ receive antennas, where $N_{j}$ is the number of each jammer's transmit antenna, and hence $KN_{j}$ can be regarded as defensible dimensions against Eve. For the jamming signal alignment at Bob, we propose two opportunistic jammer selection schemes and find the scaling law of the required number of jammers for target secure DoF by a geometrical interpretation of the received signals.
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  • 40
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: This paper is concerned with the distributed finite-horizon fusion Kalman filtering problem for a class of networked multi-sensor fusion systems (NMFSs) in a bandwidth and energy constrained wireless sensor network. To satisfy the finite communication bandwidth, only partial components of each local vector estimate are allowed to be transmitted to the fusion center (FC) at a particular time, while each sensor intermittently sends information to the FC for reducing energy consumptions. At the FC end, a novel compensation strategy is proposed to compensate the untransmitted components of each local estimates, then a recursively distributed fusion Kalman filter (DFKF) is derived in the linear minimum variance sense. Notice that the designed DFKF update does not need to know the transmitting situation of each component at a particular time, which means that the proposed fusion estimation algorithm is easily implemented for the addressed NMFSs. Since the performance of the designed DFKF is dependent on the selecting probability of each component, some criteria for the choice of probabilities are derived such that the mean squared errors (MSEs) of the designed DFKF are bounded or convergent. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method.
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  • 41
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: This paper addresses the joint design of MIMO precoding and decoding matrices for filter bank multicarrier (FBMC) systems based on OQAM, known as FBMC/OQAM. Existing solutions that support multi-stream transmission only give satisfactory performance in scenarios with high coherence bandwidth channels. To make progress towards the application of FBMC/OQAM to MIMO channels, we study the design of novel solutions that provide robustness against the channel frequency selectivity and support multi-stream transmission. To this end, two techniques have been devised under the criterion of minimizing the sum mean square error. The non-circular nature of the OQAM symbols has not been ignored, making evident the convenience of performing a widely linear processing. The first technique keeps the complexity at a reasonable level but in exchange the original problem is relaxed yielding a suboptimal solution. With the objective of performing closer to the optimum solution, the second option iteratively computes precoders and equalizers by resorting to an alternating optimization method, which is much more complex. We have demonstrated via simulations that the first technique nearly achieves the same results as the iterative design. Simulation results show that the proposed low-complexity solution outperforms existing MIMO-FBMC/OQAM schemes in terms of bit error rate. As for the comparison with OFDM, the numerical results highlight that FBMC/OQAM remains competitive, with and without perfect channel state information, while it provides spectral efficiency gains. Under highly frequency selective channels the proposed technique significantly outperforms OFDM.
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  • 42
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: Two adaptive Capon methods that jointly estimate the azimuth-angle and polarization of the sources in a closed-form are proposed. It is shown that the azimuth-angles of the sources may be estimated from the roots of a complex-valued polynomial or by rooting a real-valued polynomial, instead. The latter method is particularly useful in tracking arbitrarily polarized sources in a sequential snapshot-by-snapshot manner using root-tracking techniques. The proposed polynomial rooting based methods are applicable to polarization sensitive arrays regardless of the array geometry including conformal arrays, and take into account array nonidealities. A large-sample analysis of the polarimetric Capon method is also provided showing that it converges, up to a multiplicative factor that depends on the interference-plus-noise power, to the polarimetric MUSIC method in the high SINR regime. Such a result gives a new insight into the well-known Capon and MUSIC methods. This paper also shows that employing manifold separation in robust Capon beamforming as well as in transmit beamforming schemes leads to improved performance in terms of received SINR when array calibration measurements are used. Extensive numerical results employing real-world polarimetric arrays are given. Results show that employing manifold separation leads to improved performance in many array processing tasks.
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  • 43
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Channel statistics based secondary transmission strategy design has been studied intensively in the past. In this work, we consider the same problem but with a carrier sensing multiple access based primary networks, i.e., the primary users that would react to interference. In such primary networks, users always need to perform carrier sensing before accessing the channel. Such networks include 802.11 WLAN and 802.15 WPAN. The secondary transmission strategy design when the primary network uses carrier sensing based network access differs a lot from what has been considered in the literature. Here, we show through experiments with 802.11 networks that under secondary interference, the primary users can experience not only packet collisions but also transmission delay. Under long-term secondary interference, the primary users might even choose to transmit in another channel. This phenomenon is known as the channel capture effect. Next, with this in mind, we formulate a novel transmission strategy design problem that aims to maximize secondary transmission time with design constraints on the probability of packet collision or delay, as well as the probability that the primary user switches channel. Finally, we describe a software-defined radio device that we built to execute the designed transmission strategies on the 2.4 GHz band. The performance of both the primary and secondary users are studied. Results show that our consideration for the primary user reactions is necessary. In particular, the designed transmission strategy better protects the primary user transmission while maintaining secondary user performance.
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  • 44
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: We study distributed algorithms for adapting transmit beamformers and linear receiver filters in a Time-Division Duplex Multiple-Input Multiple-Output (MIMO) interference network. Each transmitter transmits a single beam, and neither the transmitters nor receivers have a priori Channel State Information (CSI). Given a fixed set of powers, we present an adaptive version of the Max-SINR algorithm: pilot symbols are alternately transmitted in the forward direction (transmitters to receivers) and in the reverse direction (receivers to transmitters). Unlike previous channel estimation schemes, transmissions in each direction are synchronized across the source or destination nodes, and the pilots are used to update the filters/beams directly using a least squares criterion. To improve the performance with limited training, we include exponential weighting of the least squares objective across data frames. In addition, bi-directional training can be used to implement analog interference pricing for power control: training in the forward direction is used to measure received signal-to-interference plus noise ratios (SINRs) and interference prices, and those estimates combined with synchronous backward training are used to update the powers. Given sufficient training this method achieves the same performance as interference pricing updates with perfect CSI. Numerical results are presented that illustrate the performance of these methods in different settings.
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  • 45
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Consider a multi-user orthogonal frequency division multiple access (OFDMA) system where multiple users share multiple discrete subcarriers, but at most one user is allowed to transmit power on each subcarrier. To adapt fast traffic and channel fluctuations and improve the spectrum efficiency, the system should have the ability to dynamically allocate subcarriers and power resources to users. Assuming perfect channel knowledge, two formulations for the joint subcarrier and power allocation problem are considered in this paper: the first is to minimize the total transmission power subject to the quality of service constraints and the OFDMA constraint, and the second is to maximize some system utility function subject to the total transmission power constraint per user and the OFDMA constraint. In spite of the existence of various heuristics approaches, little is known about the computational complexity status of the above problem. This paper aims at filling this theoretical gap, i.e., characterizing the complexity of the joint subcarrier and power allocation problem for the multi-user OFDMA system. It is shown in this paper that both formulations of the joint subcarrier and power allocation problem are strongly NP-hard. Several subclasses of the problem which can be solved efficiently in polynomial time are also identified. These complexity results suggest that there are not polynomial time algorithms that are able to solve the general joint subcarrier and power allocation problem to global optimality (unless ${rm P}={rm NP}$ ), and determining an approximately optimal subcarrier and power allocation strategy is more realistic in practice.
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  • 46
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Multicell cooperation has recently attracted tremendous attention because of its ability to eliminate intercell interference and increase spectral efficiency. However, the enormous amount of information being exchanged, including channel state information and user data, over backhaul links may deteriorate the network performance in a realistic system. This paper adopts a backhaul cost metric that considers the number of active directional cooperation links, which gives a first order measurement of the backhaul loading required in asymmetric Multiple-Input Multiple-Output (MIMO) cooperation. We focus on a downlink scenario for multi-antenna base stations and single-antenna mobile stations. The design problem is minimizing the number of active directional cooperation links and jointly optimizing the beamforming vectors among the cooperative BSs subject to signal-to-interference-and-noise-ratio (SINR) constraints at the mobile station. This problem is non-convex and solving it requires combinatorial search. A practical algorithm based on smooth approximation and semidefinite relaxation is proposed to solve the combinatorial problem efficiently. We show that semidefinite relaxation is tight with probability 1 in our algorithm and stationary convergence is guaranteed. Simulation results show the saving of backhaul cost and power consumption is notable compared with several baseline schemes and its effectiveness is demonstrated.
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  • 47
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: We develop new and optimal algorithms for distributed detection in sensor networks over fading channels with multiple receive antennas at the Fusion Centre (FC). Sensors observe a hidden physical phenomenon over fading channels and transmit their observations using the amplify-and-forward scheme over fading channels to the FC which is equipped with multiple antennas. We derive the optimal decision rules and the associated probabilities of detection and false alarm for three scenarios of Channel State Information (CSI) availability. For the most difficult case of unknown CSI, we develop two new algorithms to derive the optimal decision rule. The first is based on a Gaussian approximation method where we quantify the approximation error and its rate of convergence (to a true Normal distribution) via a multivariate version of the Berry-Esseen bound. The second is based on a multivariate Saddle-point (Laplace) approximation which is obtained via a non-convex optimisation problem which is solved efficiently via Bayesian Expectation-Maximisation method. We show under which system configuration which algorithm is suitable and should be used. For cases where the distribution of the optimal decision rule can not be derived exactly, we develop a Laguerre series expansion to approximate the resulting distribution. The performance of the proposed algorithms is evaluated via analytic bounds and numerical simulations. We show that the detection performance of the proposed algorithms is significantly superior to a local vote decision fusion based algorithms.
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  • 48
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: In this paper, we study the joint design of Doppler robust transmit sequence and receive filter to improve the performance of an active sensing system dealing with signal-dependent interference. The signal-to-noise-plus-interference (SINR) of the filter output is considered as the performance measure of the system. The design problem is cast as a max-min optimization problem to robustify the system SINR with respect to the unknown Doppler shifts of the targets. To tackle the design problem, which belongs to a class of NP-hard problems, we devise a novel method (which we call DESIDE) to obtain optimized pairs of transmit sequence and receive filter sharing the desired robustness property. The proposed method is based on a cyclic maximization of SINR expressions with relaxed rank-one constraints, and is followed by a novel synthesis stage. We devise synthesis algorithms to obtain high quality pairs of transmit sequence and receive filter that well approximate the behavior of the optimal SINR (of the relaxed problem) with respect to target Doppler shift. Several numerical examples are provided to analyze the performance obtained by DESIDE.
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  • 49
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: We consider distributed optimization in random networks where $N$ nodes cooperatively minimize the sum $sum _{i=1}^{N} f_{i}(x)$ of their individual convex costs. Existing literature proposes distributed gradient-like methods that are computationally cheap and resilient to link failures, but have slow convergence rates. In this paper, we propose accelerated distributed gradient methods that 1) are resilient to link failures; 2) computationally cheap; and 3) improve convergence rates over other gradient methods. We model the network by a sequence of independent, identically distributed random matrices ${W(k)}$ drawn from the set of symmetric, stochastic matrices with positive diagonals. The network is connected on average and the cost functions are convex, differentiable, with Lipschitz continuous and bounded gradients. We design two distributed Nesterov-like gradient methods that modify the D–NG and D–NC methods that we proposed for static networks. We prove their convergence rates in terms of the expected optimality gap at the cost function. Let $k$ and $ {cal K}$ be the number of per-node gradient evaluations and per-node communications, respectively. Then the modified D–NG achieves rates $O(log k/k)$ and $O(log {cal K}/ {cal K})$ , and the modified D–NC rates $O(1/k^{2})$ and $O(1/ {cal K}^{2-xi })$ , where - tex Notation="TeX"〉$xi 〉0$ is arbitrarily small. For comparison, the standard distributed gradient method cannot do better than $Omega (1/k^{2/3})$ and $Omega (1/ {cal K}^{2/3})$ , on the same class of cost functions (even for static networks). Simulation examples illustrate our analytical findings.
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  • 50
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: We consider the problem of phase retrieval, namely, recovery of a signal from the magnitude of its Fourier transform, or of any other linear transform. Due to the loss of Fourier phase information, this problem is ill-posed. Therefore, prior information on the signal is needed in order to enable its recovery. In this work we consider the case in which the signal is known to be sparse, i.e., it consists of a small number of nonzero elements in an appropriate basis. We propose a fast local search method for recovering a sparse signal from measurements of its Fourier transform (or other linear transform) magnitude which we refer to as GESPAR: GrEedy Sparse PhAse Retrieval. Our algorithm does not require matrix lifting, unlike previous approaches, and therefore is potentially suitable for large scale problems such as images. Simulation results indicate that GESPAR is fast and more accurate than existing techniques in a variety of settings.
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  • 51
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: Cooperation between nodes sharing a wireless channel is becoming increasingly necessary to achieve higher throughputs in a wireless network. The problem of determining the feasibility and stability of cooperation between rational nodes in a wireless network is of great importance in understanding cooperative behavior. This paper addresses the stability of the grand coalition of transmitters signaling over a multiple access channel using the framework of cooperative game theory. The external interference experienced by each TX is represented accurately by modeling the cooperation game between the TXs in partition form. Single user decoding and successive interference cancelling strategies are examined at the receiver. Transmitter cooperation is stable, if and only if the core of the game (the set of all divisions of grand coalition utility such that no coalition deviates) is nonempty. Determining the stability of cooperation is a co-NP-complete problem in general. For a single user decoding receiver, transmitter cooperation is shown to be stable at both high and low SNRs, while for an interference cancelling receiver with a fixed decoding order, cooperation is stable only at low SNRs and unstable at high SNR. When time sharing is allowed between decoding orders, it is shown using an approximate lower bound to the utility function that TX cooperation is also stable at high SNRs. Thus, this paper demonstrates that ideal zero cost TX cooperation over a MAC is stable and improves achievable rates for each individual user.
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  • 52
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: Synthetic transmit aperture (STA) has been widely investigated in ultrasound system recently with characteristics of high frame rate and low hardware cost. Since the high-resolution image (HRI) of STA is formed by summation of low-resolution images (LRIs), it is susceptible to inter-firing motions. In this paper, we propose a low-complexity global motion compensation algorithm. We use the common region of interest $({rm ROI}_{{rm com}})$ between different transmissions of STA imaging to beamform backward and forward beam vectors. Then, the magnitude and direction of motion can be evaluated by cross-correlations between specific beam vectors in STA imaging. Compared with the uncompensated image in two-dimentional (2D) motion environment, the proposed motion compensation algorithm can improve the contrast ratio (CR) and contrast-to-noise ratio (CNR) by 13.73 and 2.04 dB, respectively. Also, the proposed algorithm improves the CR and CNR about 7.84 and 1.36 dB comparing with the reference work, respectively. In the Field II breath model, the proposed method also improves the CR and CNR about 6.65 and 1.04 dB than the reference method, respectively. Moreover, we propose a low-complexity delay generator in the architecture design to further reduce the computational complexity of the whole beamforming system. Finally, we verify the proposed low-complexity motion compensation beamforming engine by using the VLSI implementation with CMOS 90 nm technology. In the post-layout result, the core size is 2.39 mm $^2$ at 125 MHz operating frequency and the frame rate of the beamforming system is 42.23 frames per second.
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  • 53
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: With the electromagnetic theory as a basis, we present a sensor model for three-axis magnetometers suitable for localization and tracking as required in intelligent transportation systems and security applications. The model depends on a physical magnetic dipole model of the target and its relative position to the sensor. Both point target and extended target models are provided as well as a heading angle dependent model. The suitability of magnetometers for tracking is analyzed in terms of local observability and the Cramér–Rao lower bound as a function of the sensor positions in a two sensor scenario. The models are validated with real field test data taken from various road vehicles which indicate excellent localization as well as identification of the magnetic target model suitable for target classification. These sensor models can be combined with a standard motion model and a standard nonlinear filter to track metallic objects in a magnetometer network.
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  • 54
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Polarimetric weather radars provide additional measurements that allow better characterization of the targeted medium. Because ground clutter has different polarimetric characteristics from weather echoes, dual-polarization measurements can be used to distinguish one from the other. Ground clutter and weather signals also have different statistical properties which can be utilized to distinguish one from the other. A test statistic, obtained from the generalized likelihood ratio test (GLRT), and a simple Bayesian classifier (SBC), with inputs from the mean and covariance of the received signals, are developed to detect ground clutter in the presence of weather signals. It is found that the test statistic produces false detections caused by narrow-band zero-velocity weather signals while the SBC can effectively neutralize them. This work is aimed at detecting ground clutter based solely on data from each resolution volume. The performances of the test statistic and SBC are shown by applying them to radar data collected with the University of Oklahoma-Polarimetric Radar for Innovation in Meteorology and Engineering.
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  • 55
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: During the late 1990s, Huang introduced the algorithm called Empirical Mode Decomposition, which is widely used today to recursively decompose a signal into different modes of unknown but separate spectral bands. EMD is known for limitations like sensitivity to noise and sampling. These limitations could only partially be addressed by more mathematical attempts to this decomposition problem, like synchrosqueezing, empirical wavelets or recursive variational decomposition. Here, we propose an entirely non-recursive variational mode decomposition model, where the modes are extracted concurrently. The model looks for an ensemble of modes and their respective center frequencies, such that the modes collectively reproduce the input signal, while each being smooth after demodulation into baseband. In Fourier domain, this corresponds to a narrow-band prior. We show important relations to Wiener filter denoising. Indeed, the proposed method is a generalization of the classic Wiener filter into multiple, adaptive bands. Our model provides a solution to the decomposition problem that is theoretically well founded and still easy to understand. The variational model is efficiently optimized using an alternating direction method of multipliers approach. Preliminary results show attractive performance with respect to existing mode decomposition models. In particular, our proposed model is much more robust to sampling and noise. Finally, we show promising practical decomposition results on a series of artificial and real data.
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  • 56
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: In this paper, we present energy-efficient architectures for decoders of low-density parity check (LDPC) codes using the differential decoding with binary message passing (DD-BMP) algorithm and its modified variant (MDD-BMP). We also propose an improved differential binary (IDB) decoding algorithm. These algorithms offer significant intrinsic advantages in the energy domain: simple computations, low interconnect complexity, and very high throughput, while achieving error correction performance up to within 0.25 dB of the offset min-sum algorithm. We report on fully parallel decoder implementations of (273, 191), (1023, 781), and (4095, 3367) finite geometry-based LDPC codes in 65 nm CMOS. Using the MDD-BMP algorithm, these decoders achieve respective areas of 0.28 ${rm mm}^{2}$ , 1.38 ${rm mm}^{2}$ , and 15.37 ${rm mm}^{2}$ , average throughputs of 37 Gbps, 75 Gbps, and 141 Gbps, and energy efficiencies of 4.9 pJ/bit, 13.2 pJ/bit, and 37.9 pJ/bit with a 1.0 V supply voltage in post-layout simulations. At a reduced supply voltage of 0.8 V, these decoders achieve respective throughputs of 26 Gbps, 54 Gbps, and 94 Gbps, and energy efficiencies of 3.1 pJ/bit, 8.2 pJ/bit, and 23.5 pJ/bit. We also report on a fully parallel implementation of IDB for the (2048, 1723) LDPC code specified in the IEEE 802.3an (10GBASE-T) standard. This decoder achieves an area of 1.44 ${rm mm}^{2}$ , average throughput of 172 Gbps, and an energy efficiency of 2.8 pJ/bit with a 1.0 V supply voltage; at 0.8 V, it achieves throughput of 116 Gbps and energy efficiency of 1.7 pJ/bit.
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  • 57
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-18
    Beschreibung: Energy efficiency optimization of wireless systems has become urgently important due to its impact on the global carbon footprint. In this paper we investigate energy efficient multicell multiuser precoding design and consider a new criterion of weighted sum energy efficiency, which is defined as the weighted sum of the energy efficiencies of multiple cells. This objective is more general than the existing methods and can satisfy heterogeneous requirements from different kinds of cells, but it is hard to tackle due to its sum-of-ratio form. In order to address this non-convex problem, the user rate is first formulated as a polynomial optimization problem with the test conditional probabilities to be optimized. Based on that, the sum-of-ratio form of the energy efficient precoding problem is transformed into a parameterized polynomial form optimization problem, by which a solution in closed form is achieved through a two-layer optimization. We also show that the proposed iterative algorithm is guaranteed to converge. Numerical results are finally provided to confirm the effectiveness of our energy efficient beamforming algorithm. It is observed that in the low signal-to-noise ratio (SNR) region, the optimal energy efficiency and the optimal sum rate are simultaneously achieved by our algorithm; while in the middle-high SNR region, a certain performance loss in terms of the sum rate is suffered to guarantee the weighed sum energy efficiency.
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  • 58
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: We present a new class of highly effective and low complexity digital filters for processing very wideband signals. Digital filtering for wideband signals is often limited by the number of arithmetic operations that has to be performed per input sampling interval. We will show the new architecture permits filtering to be performed on partitioned spectral segments of the input signal at significantly reduced sample rate. The digital filtering will be shown to include various tasks such as linear/non-linear phase finite impulse response (FIR) filtering, fractional delay filter among others. The proposed technique utilizes the framework of non-maximally decimated filter banks (NMDFBs) with perfect reconstruction (PR) property, which makes the filter bank design simpler and more flexible. Compact representation for the generalized DFT based NMDFBs as well as its efficient polyphase implementation will be provided. The digital filtering is made possible by incorporating the desired intermediate processing elements in between the analysis and synthesis filter banks. We will show this embedded intermediate processing elements can achieve spectral shaping/signal manipulation task, which is a generalization of the concept of manipulating a digital filter in the frequency domain. We also analyze both analytically and experimentally, the spectral shaping accuracy based on different design strategies.
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  • 59
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-01-22
    Beschreibung: Long-time coherent integration technique is one of the most important methods for the improvement of radar detection ability of a weak maneuvering target, whereas the integration performance may be greatly influenced by the across range unit (ARU) and Doppler frequency migration (DFM) effects. In this paper, a novel representation known as Radon-fractional Fourier transform (RFRFT) is proposed and investigated to solve the above problems simultaneously. It can not only eliminate the effect of DFM by selecting a proper rotation angle but also achieve long-time coherent integration without ARU effect. The RFRFT can be regarded as a special Doppler filter bank composed of filters with different rotation angles, which indicates a generalization of the traditional moving target detection (MTD) and FRFT methods. Some useful properties and the likelihood ratio test detector of RFRFT are derived for maneuvering target detection. Finally, numerical experiments of aerial target and marine target detection are carried out using simulated and real radar datasets. The results demonstrate that for integration gain and detection ability, the proposed method is superior to MTD, FRFT, and Radon-Fourier transform under low signal-to-clutter/noise ratio (SCR/SNR) environments. Moreover, the trajectory of target can be easily obtained via RFRFT as well.
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  • 60
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: A new optimization method for the design of fullband and lowpass IIR digital differentiators is proposed. In the new method, the passband phase-response error is minimized under the constraint that the maximum passband amplitude-response relative error is below a prescribed level. For lowpass IIR differentiators, an additional constraint is introduced to limit the average squared amplitude response in the stopband so as to minimize any high-frequency noise that may be present. Extensive experimental results are included, which show that the differentiators designed using the proposed method have much smaller maximum phase-response error for the same passband amplitude-response error and stopband constraints when compared with several differentiators designed using state-of-the-art competing methods.
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  • 61
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: Although many sparse recovery algorithms have been proposed recently in compressed sensing (CS), it is well known that the performance of any sparse recovery algorithm depends on many parameters like dimension of the sparse signal, level of sparsity, and measurement noise power. It has been observed that a satisfactory performance of the sparse recovery algorithms requires a minimum number of measurements. This minimum number is different for different algorithms. In many applications, the number of measurements is unlikely to meet this requirement and any scheme to improve performance with fewer measurements is of significant interest in CS. Empirically, it has also been observed that the performance of the sparse recovery algorithms also depends on the underlying statistical distribution of the nonzero elements of the signal, which may not be known a priori in practice. Interestingly, it can be observed that the performance degradation of the sparse recovery algorithms in these cases does not always imply a complete failure. In this paper, we study this scenario and show that by fusing the estimates of multiple sparse recovery algorithms, which work with different principles, we can improve the sparse signal recovery. We present the theoretical analysis to derive sufficient conditions for performance improvement of the proposed schemes. We demonstrate the advantage of the proposed methods through numerical simulations for both synthetic and real signals.
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  • 62
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: We consider algorithms and recovery guarantees for the analysis sparse model in which the signal is sparse with respect to a highly coherent frame. We consider the use of a monotone version of the fast iterative shrinkage-thresholding algorithm (MFISTA) to solve the analysis sparse recovery problem. Since the proximal operator in MFISTA does not have a closed-form solution for the analysis model, it cannot be applied directly. Instead, we examine two alternatives based on smoothing and decomposition transformations that relax the original sparse recovery problem, and then implement MFISTA on the relaxed formulation. We refer to these two methods as smoothing-based and decomposition-based MFISTA. We analyze the convergence of both algorithms and establish that smoothing-based MFISTA converges more rapidly when applied to general nonsmooth optimization problems. We then derive a performance bound on the reconstruction error using these techniques. The bound proves that our methods can recover a signal sparse in a redundant tight frame when the measurement matrix satisfies a properly adapted restricted isometry property. Numerical examples demonstrate the performance of our methods and show that smoothing-based MFISTA converges faster than the decomposition-based alternative in real applications, such as MRI image reconstruction.
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  • 63
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: We investigate the problem of a monostatic pulse-Doppler radar transceiver trying to detect targets sparsely populated in the radar's unambiguous time-frequency region. Several past works employ compressed sensing (CS) algorithms to this type of problem but either do not address sample rate reduction, impose constraints on the radar transmitter, propose CS recovery methods with prohibitive dictionary size, or perform poorly in noisy conditions. Here, we describe a sub-Nyquist sampling and recovery approach called Doppler focusing, which addresses all of these problems: it performs low rate sampling and digital processing, imposes no restrictions on the transmitter, and uses a CS dictionary with size, which does not increase with increasing number of pulses $P$ . Furthermore, in the presence of noise, Doppler focusing enjoys a signal-to-noise ratio (SNR) improvement, which scales linearly with $P$ , obtaining good detection performance even at SNR as low as ${-}$ 25 dB. The recovery is based on the Xampling framework, which allows reduction of the number of samples needed to accurately represent the signal, directly in the analog-to-digital conversion process. After sampling, the entire digital recovery process is performed on the low rate samples without having to return to the Nyquist rate. Finally, our approach can be implemented in hardware using a previously suggested Xampling radar prototype.
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  • 64
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    Publikationsdatum: 2014-03-14
    Beschreibung: In this paper, a deterministic blind identification approach is proposed for linear output-switching systems, which are modeled by multiple infinite impulse-response (IIR) dynamic functions. By adopting a new over-sampling strategy, the concerned single-input–single-output (SISO) output-switching system is equivalently transformed into a time-invariant multi- input–multi-output (MIMO) system. Further, by exploring the mutual relations among the multiple inputs, the time-invariant MIMO system model and subsequently the output-switching system model are identified uniquely up to a scalar constant using the proposed identification approach. Sufficient identifiability conditions are provided for output-switching systems and numerical simulations are carried out to validate the proposed approach.
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  • 65
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    Publikationsdatum: 2014-03-14
    Beschreibung: In this paper, we address the problem of interference alignment (IA) over MIMO interference channels with limited channel state information (CSI) feedback based on quantization codebooks. Due to limited feedback and, hence, imperfect IA, there are residual interferences across different links and different data streams. As a result, the performance of IA is greatly related to the CSI accuracy (namely number of feedback bits) and the number of data streams (namely transmission mode). In order to improve the performance of IA, it makes sense to optimize the system parameters according to the channel conditions. Motivated by this, we first give a quantitative performance analysis for IA under limited feedback and derive a closed-form expression for the average transmission rate in terms of feedback bits and transmission mode. By maximizing the average transmission rate, we obtain an adaptive feedback allocation scheme, as well as a dynamic mode selection scheme. Furthermore, through asymptotic analysis, we obtain several clear insights on the system performance and provide some guidelines on the system design. Finally, simulation results validate our theoretical claims and show that obvious performance gain can be obtained by adjusting feedback bits dynamically or selecting transmission mode adaptively.
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  • 66
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    Publikationsdatum: 2014-03-14
    Beschreibung: In decentralized consensus optimization, a connected network of agents collaboratively minimize the sum of their local objective functions over a common decision variable, where their information exchange is restricted between the neighbors. To this end, one can first obtain a problem reformulation and then apply the alternating direction method of multipliers (ADMM). The method applies iterative computation at the individual agents and information exchange between the neighbors. This approach has been observed to converge quickly and deemed powerful. This paper establishes its linear convergence rate for the decentralized consensus optimization problem with strongly convex local objective functions. The theoretical convergence rate is explicitly given in terms of the network topology, the properties of local objective functions, and the algorithm parameter. This result is not only a performance guarantee but also a guideline toward accelerating the ADMM convergence.
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  • 67
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: A guiding principle for data reduction in statistical inference is the sufficiency principle. This paper extends the classical sufficiency principle to decentralized inference, i.e., data reduction needs to be achieved in a decentralized manner. We examine the notions of local and global sufficient statistics and the relationship between the two for decentralized inference under different observation models. We then consider the impact of quantization on decentralized data reduction, which is often needed when communications among sensors are subject to finite capacity constraints. The central question we intend to ask is: if each node in a decentralized inference system has to summarize its data using a finite number of bits, is it still optimal to implement data reduction using global sufficient statistics prior to quantization? We show that the answer is negative using a simple example and proceed to identify conditions under which sufficiency based data reduction followed by quantization is indeed optimal. They include the well known case when the data at decentralized nodes are conditionally independent as well as a class of problems with conditionally dependent observations that admit conditional independence structure through the introduction of an appropriately chosen hidden variable.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: Port-starboard ambiguity is an important issue in underwater tracking systems with anti-submarine warfare applications, especially for wireless sensor networks based upon autonomous underwater vehicles. In monostatic systems this ambiguity leads to a ghost track of the target symmetrically displaced with respect to the sensor. Removal of such artifacts is usually made by rough and heuristic approaches. In the context of Bayesian filtering approximated by means of particle filtering techniques, we show that optimal disambiguation can be pursued by deriving the full Bayesian posterior distribution of the target state. The analysis is corroborated by simulations that show the effectiveness of the particle-filtering tracking. A full validation of the approach relies upon real-world experiments conducted by the NATO Science and Technology Organization – Centre for Maritime Research and Experimentation during the sea trials Generic Littoral Interoperable Network Technology 2011 and Exercise Proud Manta 2012, results which are also reported.
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  • 69
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: Most of the existing beamforming methods are based on the Minimum Variance (MV) criterion. The MV approach is statistically optimal only when the signal, interferences and the noise are Gaussian-distributed. However, non-Gaussian signals arise in a variety of practical applications. In this paper, Minimum Dispersion Distortionless Response (MDDR) beamforming, which minimizes the $ell_p$ -norm of the output while constraining the desired signal response to be unity, is devised for non-Gaussian signals. It is shown that the MDDR beamformer, which implicitly exploits non-Gaussianity, can improve the performance significantly if $p 〉 2$ for sub-Gaussian signals or $p 〈 2$ for super-Gaussian signals. Three efficient algorithms, the Iteratively Reweighted Minimum Variance Distortionless Response (IR-MVDR), complex-valued full Newton's and partial Newton's methods, are developed to solve the resulting $ell_p$ -norm minimization with a linear constraint. Furthermore, the MDDR beamformer with a single constraint is generalized to the Linearly Constrained Minimum Dispersion (LCMD) beamformer with multiple linear constraints, which exhibits robustness against steering vector mismatch. The LCMD beamformer yields significant performance improvement over the conventional Linearly Constrained Minimum Variance (LCMV) beamformer. Simulation results are provided to demonstrate the superior performance of the proposed minimum dispersion beamforming approaches.
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  • 70
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: In this work, we propose algorithms to perform Blind Source Separation (BSS) for the linear-quadratic mixing model. The linear-quadratic model is less studied in the literature than the linear one. In this paper, we propose original methods that are based on Non-negative Matrix Factorization (NMF). This class of methods is well suited to many applications where the data are non-negative. We are here particularly interested in spectral unmixing (extracting reflectance spectra of materials present in pixels and associated abundance fractions) for urban hyperspectral images. The originality of our work is that we developed extensions of NMF, which is initially suited to the linear model, for the linear-quadratic model. The proposed algorithms are tested with simulated hyperspectral images using real reflectance spectra and the obtained results are very satisfactory.
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  • 71
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: In traditional multicarrier systems, the pilot carriers used to estimate the channel are placed as uniform as possible over the bandwidth. However, with the raise of cognitive radio systems, where the multicarrier system is used by the secondary users, parts of the bandwidth are not available for transmission as primary users are active in these bands. Therefore, the multicarrier system must introduce guard bands in which the carriers may not be used. Hence, a problem might occur when placing the pilot carriers. In this paper, we investigate the effect of the positions of the pilot carriers on the MSE performance of channel estimation, and look for the pilot carrier placement that minimizes the MSE. We do not restrict our attention to multicarrier systems with a cyclic prefix, but we also consider other types of guard interval that are used for multicarrier transmission. It is known that an equidistantly-spaced distribution of the pilot carriers is in general not the optimal placement of the pilot carriers, as the corresponding MSE can become very high. In this paper, we use a heuristic algorithm to search for the best pilot placement, which is able to deliver a pilot carrier placement that outperforms the maximum distance distribution from [S. Song and A. C. Singer, “Pilot-Aided OFDM Channel Estimation in the Presence of the Guard Band,” IEEE Trans. Commun., vol. 55, no. 8, pp. 1459–1465, Aug. 2008] in terms of the MSE, and results in an MSE that is close to the case where no guard bands are present. Based on the results of the algorithm, we can derive some simple rules of thumb to select the positions of the pilot carriers.
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  • 72
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: The dual use of radio signal for simultaneous wireless information and power transfer (SWIPT) has recently drawn significant attention. To meet the practical requirement that the energy receiver (ER) operates with significantly higher received power as compared to the conventional information receiver (IR), ERs need to be deployed in more proximity to the transmitter than IRs in the SWIPT system. However, due to the broadcast nature of wireless channels, one critical issue arises that the messages sent to IRs can be eavesdropped by ERs, which possess better channels from the transmitter. In this paper, we address this new physical-layer security problem in a multiuser multiple-input single-output (MISO) SWIPT system where one multi-antenna transmitter sends information and energy simultaneously to an IR and multiple ERs, each with one single antenna. Two problems are investigated with different practical aims: the first problem maximizes the secrecy rate for the IR subject to individual harvested energy constraints of ERs, while the second problem maximizes the weighted sum-energy transferred to ERs subject to a secrecy rate constraint for IR. We solve these two non-convex problems optimally by a general two-stage procedure. First, by fixing the signal-to-interference-plus-noise ratio (SINR) target for ERs or IR, we obtain the optimal transmit beamforming and power allocation solution by applying the technique of semidefinite relaxation (SDR). Then, each of the two problems is solved by a one-dimension search over the optimal SINR target for ERs or IR. Furthermore, for each problem, suboptimal solutions of lower complexity are proposed.
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  • 73
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-03-14
    Beschreibung: In this paper, a robust linear programming beamformer (RLPB) is proposed for non-Gaussian signals in the presence of steering vector uncertainties. Unlike most of the existing beamforming techniques based on the minimum variance criterion, the proposed RLPB minimizes the $ell_{infty}$ -norm of the output to exploit the non-Gaussianity. We make use of a new definition of the $ell_{p}$ -norm $(1leq pleqinfty)$ of a complex-valued vector, which is based on the $ell_{p}$ -modulus of complex numbers. To achieve robustness against steering vector mismatch, the proposed method constrains the $ell_{infty}$ -modulus of the response of any steering vector within a specified uncertainty set to exceed unity. The uncertainty set is modeled as a rhombus, which differs from the spherical or ellipsoidal uncertainty region widely adopted in the literature. The resulting optimization problem is cast as a linear programming and hence can be solved efficiently. The proposed RLPB is computationally simpler than its robust counterparts requiring solution to a second-order cone programming. We also address the issue of appropriately choosing the uncertainty region size. Simulation results demonstrate the superiority of the proposed RLPB over several state-of-the-art robust beamformers and show that its performance can approach the optimal performance bounds.
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  • 74
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Interest in parameterized time-frequency analysis for non-stationary signal processing is increasing steadily. An important advantage of such analysis is to provide highly concentrated time-frequency representation with signal-dependent resolution. In this paper, a general scheme, named as general parameterized time-frequency transform (GPTF transform), is proposed for carrying out parameterized time-frequency analysis. The GPTF transform is defined by applying generalized kernel based rotation operator and shift operator. It provides the availability of a single generalized time-frequency transform for applications on signals of different natures. Furthermore, by replacing kernel function, it facilitates the implementation of various parameterized time – frequency transforms from the same standpoint. The desirable properties and the dual definition in the frequency domain of GPTF transform are also described in this paper. One of the advantages of the GPTF transform is that the generalized kernel can be customized to characterize the time – frequency signature of non-stationary signal. As different kernel formulation has bias toward the signal to be analyzed, a proper kernel is vital to the GPTF. Thus, several potential kernels are provided and discussed in this paper to develop the desired parameterized time – frequency transforms. In real applications, it is desired to identify proper kernel with respect to the considered signal. This motivates us to propose an effective method to identify the kernel for the GPTF.
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  • 75
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: In bistatic synthetic aperture radar (BSAR) with one-stationary station, azimuth variation is a major problem. In this paper, based on the two-dimensional (2D) spatial linearization of the accurate analytical point target reference spectrum, an Omega-K imaging algorithm to deal with this problem is proposed. Different from the traditional Omega-K algorithms for monostatic SAR and translational invariant BSAR, the approach uses a 2D Stolt frequency transformation. In addition, a compensation method for the phase error caused by the linearization and the related geometry registration are also discussed. Numerical simulations verify the effectiveness of the proposed method.
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  • 76
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Doppler spectrum in an aeronautical channel is modeled with dual-Doppler shift instead of classical Jakes model. Orthogonal frequency division multiplexing (OFDM)-based systems are sensitive to Doppler shifts/spread, since the time variation of the channel causes inter-carrier interference (ICI). ICI analysis is provided here for OFDM-based systems in the aeronautical channel. The effect of ICI on the received signal is presented and its power is derived. As compared with terrestrial channels, where ICI is generally overcome by increasing the subcarrier spacing and bounding the normalized Doppler frequency (NDF), we propose to mitigate the effect of Doppler shifts in aeronautical channels, as follows. First, we use parametric spectrum estimation methods to extract the Doppler shifts by exploiting the predictable number of paths. Then, a beamforming-based method is introduced to resolve the incoming rays by separating them individually. Finally, paths are Doppler-compensated and combined using diversity combining techniques. Computer simulations are performed to provide numerical results. It is shown that a mean square error (MSE) performance ofis achieved with the parametric estimation methods, and bit error rate (BER) performance approaching the no-Doppler scenario is obtained with the beamforming-based mitigation method.
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  • 77
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: The reduction of COemissions, and therefore the increase of ecoefficiency, is one of the most important challenges for the aircraft industry. An approach could be the more electric aircraft concept. Within this concept, the traditional auxiliary power unit could be replaced by a multifunctional fuel cell system. For integration into the ±270 Vgrid, it is necessary to convert the load-dependent fuel cell output voltage using a direct current-to-direct current converter. The converter usually is designed for the maximum available fuel cell power. This paper deals with an adaption of the fuel cell output voltage to achieve downsizing of the converter. The proposed converter structure with an additional bypass has weight-saving effects and improves overall system efficiency.
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  • 78
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: This paper presents the 2D close-range navigation sensor for cooperative spacecraft developed in the framework of the experiment ARCADE. The sensor exploits an infrared LED transmitter mounted on the target, and two photodiode receivers mounted on the chaser. Laboratory tests were performed to assess the sensor performance and range of application. The accuracies of estimates were, on average, 1.9 mm for distance and 1.0 deg for yaw angle, in ranges of [0.20, 0.42] m and [-40, 40] deg, respectively.
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  • 79
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: The performances of Marcum's (signal + noise) - noise ((S+N)-N) integration scheme are analyzed for SW1 and SW2 fluctuating targets. This lesser known integration concept was not treated by Swerling when he extended Marcum's main signal + noise integration to four cases of fluctuating targets. We present closed-form probability density (pdfs) functions confirmed and extended by simulations. We show typical signal-to-noise ratio (SNR) loss of 1 dB for both SW1 and SW2, agreeing with Marcum's result for SW0. (S+N)-N integration is inherent in our work on noncoherent pulse compression, hence the renewed interest.
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  • 80
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: We present a fast implementation of the optimal linear processor for “chirp” signals with O() computational load for data length. The method is technically an approximation since it has an interpolation step but we show that the errors are negligible. In simulations it performs up to 20 times faster than the existing method using radix-2 fast Fourier transform (FFT) and has significantly lower threshold signal-to-noise ratio (SNR) against noise and interference compared with a leading fast method.
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  • 81
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: We present a new approach for simultaneous tracking and segmentation of multiple targets in low frame rate aerial video. We focus on building an accurate background model that accounts for both global camera motion and moving objects in the scene. We then apply a probabilistic framework for simultaneous tracking and segmentation that incorporates this background model. By using a background model, we are able to track the object through dramatic appearance changes caused by shadows and lighting changes. Furthermore, the incorporation of segmentation into the tracking algorithm reduces the impact of common tracking problems, such as drift and partial occlusion. Results are shown for the Columbus Large Image Format (CLIF) 2007 data set, demonstrating successful tracking under significant occlusions, target appearance changes, and near similar moving objects.
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  • 82
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: We focus in the work presented here on in the estimation of a target trajectory defined by whether a time constant parameter is a simple stochastic process or a random walk with binary observations. The binary observations come from binary derivative sensors, that is, the target is getting closer or moving away. Such a binary observation has a time property that will be used to ensure the quality of the velocity estimation, through single index model or classification for the constant velocity movement. In the second part of this work we present a new algorithm for target tracking within a binary sensor network when the target trajectory is assumed to be modelled by a random walk. For a given target this algorithm provides an estimation of its velocity and its position. The greatest improvements are made through a position correction and velocity analysis.
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  • 83
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Target motion analysis (TMA) with wideband passive sonar has received much attention. Maximum likelihood probabilistic data association (ML-PDA) represents an asymptotically efficient estimator for deterministic target motion, and is especially well suited for low-observable targets; the results presented here apply to situations with higher signal-to-noise ratio as well, including of course the situation of a deterministic target observed via “clean” measurements without false alarms or missed detections. Here we study the inverse problem, namely, how to identify the observing platform (following a “two-leg” motion model) from the results of the target estimation process, i.e., the estimated target state and the Fisher information matrix (FIM), quantities we assume an eavesdropper might intercept. We tackle the problem and we present observability properties, with supporting simulation results.
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  • 84
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: A generalized inter-satellite tracking problem, maneuver-aided active satellite tracking, is addressed here. An active satellite has uncooperative maneuver, which shortens the tracking window and worsens the tracking precision. For tracking an active target satellite, a spacecraft maneuver-aided tracking strategy (SMATS) is proposed. Consisting of a robust tracking algorithm, an osculating-orbit-based coordinate matching scheme, a six-degree-of-freedom (six-DOF) maneuver control law and a transfer function of tracking attitude, the proposed approach can not only achieve precise tracking, but also keep a chaser satellite autonomously staying with the desired position and attitude to guarantee the tracking continuity. Based on sufficient stability conditions derived from system error analysis, a six-DOF optimal dynamic inversion control (ODIC) law is developed. As a precise nonlinear optimal solution, it provides the most adequate control performance with minimum impact to the tracking result. Both formation and hovering keeping of active satellites are simulated to illustrate the efficiency of the proposed SMATS and the advantages of the ODIC law.
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  • 85
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: The purpose of the work presented have is to employ space-time block codes (STBC) to eliminate the cross-correlation effects among parallelly transmitted probing signals of a multiple-input multiple-output (MIMO) radar imaging system. By exploiting the diversity offered by the transmission scheme, the hardware requirement can be substantially reduced compared with conventional technology.
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  • 86
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Surveillance systems typically incorporate multitarget tracking algorithms for sequential estimation of kinematic states (e.g. positions, velocities) of moving objects in the surveillance domain of interest. This letter proposes an algorithm for online detection of anomalies in the motion and the count of objects, using the output of a multiobject tracking algorithm. The surveillance area is partitioned by a square grid and the kinematic states that fall inside each cell of the grid are modelled by a Poisson point process. During the unsupervised learning phase, the parameters of the Poisson point process are estimated for each cell. The testing phase is performed sequentially by threshold detection at a specified level of significance. The performance of the algorithm is illustrated using the Automatic Identification System (AIS) dataset in the context of maritime surveillance.
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  • 87
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Provides a listing of current committee members and society officers.
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  • 88
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Pseudolites, or pseudosatellites, are ground-based transmitters of global navigation satellite system (GNSS)-like signals. Pseudolite signal modulations often include a pulsing scheme that is adopted to reduce interference with nonparticipating GNSS receivers, mitigate the near-far problem, and allow time division multiple access. For these reasons, an effective pulsing scheme design is crucial for the proper functioning of a pseudolite based system. In this paper, the requirements that a pseudolite pulsing scheme has to satisfy are first identified, and a general pulsing scheme based on random permutations is proposed. The spectral and temporal characteristics of the proposed scheme are determined and thoroughly analyzed. From the analysis, it emerges that the proposed scheme meets all identified requirements, making the suggested solution an effective tool for pseudolite signal design. Finally, the proposed approach is compared with a number of existing pulsing schemes from the literature and found to provide significant benefits with respect to most existing schemes.
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  • 89
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: The random hypersurface model (RHM) is introduced for estimating a shape approximation of an extended object in addition to its kinematic state. An RHM represents the spatial extent by means of randomly scaled versions of the shape boundary. In doing so, the shape parameters and the measurements are related via a measurement equation that serves as the basis for a Gaussian state estimator. Specific estimators are derived for elliptic and star-convex shapes.
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  • 90
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: The multiple hypothesis tracking (MHT) approach has been proven to be successful in multiple target tracking applications, however, its computational complexity remains a major hurdle to its practical implementation. This paper presents an efficient MHT implementation, referred to as “GRASP-MHT”, which integrates a greedy randomized adaptive search procedure (GRASP) within a track-oriented MHT framework. The hypothesis generating problem arising in the MHT framework is formulated as a maximum weighted independent set problem, and a GRASP module is designed to generate multiple high-quality hypotheses. An extensive simulation study was carried out to compare the performance of the proposed GRASP-MHT against several well-known multitarget tracking algorithms, and multiple metrics were considered in order to make the performance evaluation more comprehensive. Experimental results indicate that, by efficiently generating and fusing multiple high-quality global hypotheses in the data association process, GRASP-MHT is able to achieve better overall tracking performance than other algorithms, especially in a closely-spaced multitarget scenario.
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  • 91
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: A moving target indication, noncoherent change detection algorithm is introduced to detect moving targets inside buildings. The proposed algorithm is designed to attenuate image artifacts observed in coherent change detection images by utilizing noncoherent change detection, a positive threshold operation, and sidelobe minimization. The proposed algorithm is compared with coherent change detection for three moving target scenarios. It is shown that the proposed algorithm significantly reduces imaging artifacts while preserving the moving target signature.
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  • 92
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Feature extraction from high-dimensional synthetic aperture radar images is one of the key steps for SAR automatic target recognition. In this paper, we propose a new approach to SAR image feature extraction that is named neighborhood geometric center scaling embedding, which is based on manifold learning theory. In our framework, neighborhood geometric center scaling is introduced to construct neighborhood relationships. The samples are endowed with clear clustering directions in dimensionality reduction, and the classification is better conducted in the feature space than in the original space. Moreover, by introducing neighborhood geometric center scaling, the influence of neighbor parameters on recognition performance is reduced effectively. The experiment based on the Moving and Stationary Target Acquisition and Recognition database shows that the proposed method has better recognition performance and higher stability than other methods.
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  • 93
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: The work presented in this paper makes two contributions for exploiting Doppler (range rate) measurements in tracking systems. First, a new linear filter, the converted Doppler measurement Kalman filter (CDMKF), is presented to extract nonlinear pseudostates from converted Doppler measurements (i.e., the product of the range measurements and Doppler measurements). The pseudostates are constructed from the converted Doppler and its derivatives. The linearly evolving equations of the pseudostates are derived for common target motion models. The second contribution of this paper is using the CDMKF along with the converted position measurement Kalman filter (CPMKF), in which only the position measurements are used, to establish a new filtering structure, statically fused converted measurement Kalman filters (SF-CMKF). The resulting states of CPMKF and CDMKF are combined by a static minimum mean squared error (MMSE) estimator, where the nonlinearity and correlation between the pseudostates and the Cartesian states are handled simultaneously, to yield the final state estimates. The dynamic nonlinear estimation problem is converted into dynamic linear estimation followed by static nonlinear fusion. The estimation accuracy can be enhanced by incorporating the Doppler measurements via the linear CDMKF, while the filtering stability can be improved by dealing with nonlinearity outside the filtering recursions. Monte Carlo simulations and comparison with the posterior Cramer-Rao bound demonstrate the effectiveness of the CDMKF and SF-CMKF.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: A coordinated standoff target tracking strategy using path shaping for multiple unmanned aerial vehicles (UAVs) is presented. In performing a tracking mission of a ground target of interest, UAVs are to approach a target and to keep a standoff distance from it with a prescribed inter-vehicle angular separation around the target in order to track it while acquiring accurate target information. Since fixed-wing UAVs without hovering capability fly efficiently at a nominal airspeed, it is desirable that they can keep angular separation between vehicles while holding a constant velocity in a mission duration point of view. The work presented here introduces a new path shaping technique using two constant curvature segments satisfying the turn radius constraint and having more flexibility and fewer discontinuous points on a curvature command compared with the Dubins path at the expense of the path length. Moreover, a simultaneous arrival concept is introduced as a coordinated tracking strategy for multiple UAVs, which initialises UAVs on a standoff orbit with a desired angular separation. In order to address arrival time delay or failure of the UAV, a two-orbit approach is proposed in which UAVs first arrive at the outer orbit and subsequently shrink to the desired inner orbit at different times, while adjusting the angular separation between constant-speed UAVs. The feasibility and benefits of the proposed approach are evaluated via numerical simulations for a ground target using two cooperative UAVs.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Air-traffic controllers cannot identify air vehicles flying with a defective or nonexistent transponder. Primary radar does not help, because it cannot classify air vehicles from echoes. Passive radar offers a potential solution, the main difficulty lying in the analysis of the data. We present a novel, automatic object-target recognition system capable of classifying air vehicles observed with passive radar. We describe the testbed we deployed near Orly Airport, and the data it provided over 10 days. A preliminary experiment involving three broad classes, and using a grid of parallel classifiers, gives a promising correct recognition rate of 71%.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: Collection of radar sea-clutter is typically performed from the top of a cliff looking out to sea, as it is relatively simple and inexpensive. This constrains the radar look direction with respect to the wind and limits the grazing angle. To improve our understanding at high grazing angles in the range 15° to 45°, the Defence Science and Technology Organisation's Ingara airborne X-band fully polarimetric radar has been used to collect 12 days worth of sea-clutter data. It has previously been shown that Walker's mean Doppler spectrum model is not suitable at these grazing angles; hence, a new two-component model is proposed that captures both the slow Bragg component and the fast non-Bragg component of the radar backscatter. A temporal decorrelation model is then presented that can be used to provide realistic performance prediction modeling.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: This paper proposes novel models of silent-watch of a combat vehicle (CV) and their application for a mission-aware energy management strategy (MAEMS). The MAEMS minimizes unnecessary battery discharge of a CV by controlling the power states of systems according to the mission needs and available battery capacity. Initial experiments show that the MAEMS consumes 3% less energy than the baseline energy management strategy (EMS) for one scenario and 1.8% less for the second scenario.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: This paper provides an approach for the deconfliction problem for a pair of constant altitude, constant speed unmanned aerial vehicles (UAVs) modeled as unicycles in the presence of static constraints. We use a combination of navigation and swirling functions to direct the unicycle vehicles along the planned trajectories while avoiding intervehicle collisions. The main feature of our contribution is proposing means of designing a deconfliction algorithm for unicycle vehicles that more closely capture the dynamics of constant speed UAVs as opposed to double integrator models. Specifically, we consider the issue of UAV turn-rate constraints and proceed to explore the selection of key algorithmic parameters in order to minimize undesirable trajectories and overshoots induced by the avoidance algorithm. The avoidance and convergence analysis of the proposed algorithm is then performed for two cooperative UAVs and simulation results are provided to support the viability of the proposed framework for more general mission scenarios.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: This paper develops and analyzes the performance of a structured covariance matrix estimate for the important practical problem of radar space-time adaptive processing in the face of severely limited training data. Traditional maximum likelihood (ML) estimators are effective when training data are abundant, but they lead to poor estimates, degraded false alarm rates, and detection loss in the realistic regime of limited training. The problem is exacerbated by recent advances, which have led to high-dimensionalof the observations arising from increased antenna elements, as well as higher temporal resolution (time epochs and finally=). This work addresses the problem by incorporating constraints in the ML estimation problem obtained from the geometry and physics of the airborne phased array radar scenario. In particular, we exploit the structure of the disturbance covariance and, importantly, knowledge of the clutter rank to derive a new rank-constrained maximum likelihood (RCML) estimator of clutter and disturbance covariance. We demonstrate that despite the presence of the challenging rank constraint, the estimation can be transformed to a convex problem and derive closed-form expressions for the estimated covariance matrix. Performance analysis using the knowledge-aided sensor signal processing and expert reasoning data set (where ground truth covariance is made available) shows that the proposed estimator outperforms state-of-the-art alternatives in the sense of a higher normalized signal-to-interference and noise ratio. Crucially, the RCML estimator excels for low training, including the notoriously difficult regime of K≤N training samples.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2014-05-07
    Beschreibung: We present a target tracking system for passive radar suitable for a digital audio/video broadcast (DAB/DVB) network with orthogonal frequency division multiplexing (OFDM) illuminators of opportunity. In this system bistatic range and range-rate are available as a measurement while angular information is assumed unavailable or of very poor quality. There is also a novel association ambiguity between the signals and illuminators, this in addition to the usual one between the signals and targets, and hence an interesting data association problem. Our intention is to provide tracks directly in the geographic space (3-D Cartesian domain). Here, four filters are suggested. The first two are the extended Kalman filter (EKF) and unscented Kalman filter (UKF) based on a joint probabilistic data association (JPDA) modified to incorporate the additional assignment complexity. The other two filters are a bootstrap particle filter (BPF) and an auxiliary particle filter (APF) based on the data association under the probabilistic multi-hypothesis tracker (PMHT) measurement model, which means that each measurement's assignment is independent of all others. Simulation results show that these four filters can work properly, albeit naturally with different performance characteristics and complexity.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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