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IEEE Transactions on Aerospace and Electronic Systems
Journal Prestige (SJR): 0.611
Citation Impact (citeScore): 3
Number of Followers: 301  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0018-9251
Published by IEEE Homepage  [228 journals]
  • IEEE Aerospace and Electronic Systems Society

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      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Modeling of Air Traffic Flow Using Cellular Automata

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      Authors: Han Yun-Xiang;Huang Xiao-Qiong;
      Pages: 2623 - 2631
      Abstract: Fast simulation technology is very important to explore the consequences of air traffic management decision. Although a variety of simulation tools have been developed to make decisions for air traffic controllers, the cognitive process of air traffic controllers is not effectively integrated into these tools. This article studies a probabilistic cellular automata (CA) model for air traffic flow simulation. By introducing the safety distance parameter into the CA model, the equilibrium property of air traffic system is studiedusing the statistical physics method. The simulation results show that the data are in good agreement with the measured results.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • AGAR: Array-Geometry-Aided Ambiguity Resolution for Baseline Growing With
           Global Navigation Satellite Systems

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      Authors: Yang Li;Xihua Zou;Bin Luo;Wei Pan;Lianshan Yan;Ronglei Kang;
      Pages: 2632 - 2648
      Abstract: Ambiguity resolution (AR) is a fundamental problem for carrier phase based signal processing tasks to leverage the superhigh precision of wavelength-level range and velocity measurements. With the elaborately designed waveform and coordinated running of the space-based satellite system, the antenna-array observations of global navigation satellite system (GNSS) signals feature a phase measurement model. In this article, the AR of baseline estimation with GNSS carrier phase measurements only in the AR step is examined from an array signal processing perspective. The array-geometry-aided ambiguity resolution approach, coined as AGAR, is proposed for growing the baseline estimation provided by a search-free algorithm to the accuracy of the aperture level in an effective way. First, the single-epoch and search-free $2q$-order AR method is further investigated in size and statistical independence. Second, the conventional phase beampattern is defined to characterize the similarity of carrier phase measurement vector of signals from different directions. Third, a simple and effective ambiguity-lookup-table approach after the conventional phase beampattern is proposed which fulfills the goal of baseline growing to the array aperture level. Fourth, the identifiability, success rate, Cramér–Rao bound (CRB), and computation complexity are analyzed. As a result, the phase-based and complex-based processings are distinguished, resulting in an alternative analytical prediction of outlier probability that well approximates AR’s success rate. The relationship between the success rate of AR and CRB is also clarified. Numerical simulations are carried out to verify the proposed analytical prediction and AR approach. The AR success rate increased from 10% to 93% at a relatively large measurement error of 0.05 cycle.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • LILO: A Novel Lidar–IMU SLAM System With Loop Optimization

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      Authors: Yi Zhang;
      Pages: 2649 - 2659
      Abstract: Light detection and ranging (Lidar) has become the core device in a simultaneous localization and mapping system, which has attracted much attention in recent years. However, the point clouds acquired by Lidar are sparse and mutually uncorrelated, making it difficult to calculate correspondences between consecutive frames and resulting in data drifting. In this situation, we propose a tightly coupled Lidar + IMU fusion system with loop optimization to address the above-mentioned problems. First, the ground Lidar points are segmented and removed. Second, under our framework, an inertial measurement unit is used to deskew the motion distortion of Lidar. Third, a voxel grid filtering process is implemented to further eliminate the redundant points, and feature matching is performed by identifying lines and planes. Finally, loop closure detection is realized to correct pose estimation and localization error. Experimental results on both public dataset and field test demonstrate the effectiveness of our algorithm.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Distributed Prescribed-Time Attitude Coordination for Multiple Spacecraft
           With Actuator Saturation Under Directed Graph

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      Authors: Chuang Xu;Baolin Wu;Danwei Wang;
      Pages: 2660 - 2672
      Abstract: This article studies the distributed prescribed-time coordination problem for the attitude system of multiple spacecraft subject to actuator saturation under the communication topology containing a directed spanning tree. The prescribed-time coordination requires that every spacecraft in a formation reaches an agreement state in a preset time. This preset time is set by the user and independent of any other control parameters and the initial state of spacecraft. To achieve this goal, we first design a distributed prescribed-time observer for every follower spacecraft to estimate the state of leader spacecraft. Next, a prescribed-time attitude control law is proposed by utilizing the estimated state of the leader spacecraft. In the proposed control law, an adaptive compensation law is used to compensate the input saturation. Furthermore, the prescribed-time stability of multispacecraft system subject to input saturation under the proposed scheme is analyzed in theory and simulation. The simulation results show the high reliability and effectiveness of the scheme.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • 3D ISAR for an Along-Track Airborne Radar

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      Authors: Chow Yii Pui;Brian Ng;Luke Rosenberg;Tri-Tan Cao;
      Pages: 2673 - 2686
      Abstract: In an airborne maritime radar, inverse synthetic aperture radar (ISAR) is used to image and classify non-cooperative targets. In this article, we investigate a 3D-ISAR as an alternative representation that can potentially improve the final target classification by automatically extracting key features from the radar data, such as the length, width, and height of a target. The technique works by estimating the target scatterers’ positions using measurements from multiple ISAR images. This has previously been achieved using a single receive channel that exploits the temporal motion of the target or with a multichannel dual-baseline interferometric system that uses the phase differences in both the along- and across-track directions. In this article, we combine aspects of these two techniques using a single along-track baseline suitable for airborne maritime radar systems.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Emitter Localization Algorithm Based on Passive Synthetic Aperture

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      Authors: Liting Zhang;Hao Huan;Ran Tao;Yue Wang;
      Pages: 2687 - 2701
      Abstract: Emitter localization is an active research topic in electronic reconnaissance. Recently, passive synthetic aperture (PSA) has been used to determine the azimuth and range distance of the emitter. However, the existing methods approximate the distance equation of the spaceborne model through the airborne model, resulting in a large positioning error. In this article, an emitter localization algorithm based on PSA in the spaceborne model is proposed. First, the phase of the received signal is accumulated by using the symmetry of the Doppler history of the received signal in long synthetic aperture time, improving the azimuth positioning accuracy. The effective velocity is then used to establish the nonlinear equations of range distance. A modulus function is used to solve the equations, correcting the range positioning error in the spaceborne model. Finally, the influence of noise, satellite position error, and satellite speed error on the positioning results is analyzed. The error matrix of the proposed method in wide swath is obtained. Simulation results show that the positioning accuracy of this method is one order of magnitude higher than that of traditional single-satellite positioning methods. The effectiveness of the proposed method is verified through actual satellite experiments.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Cybersecurity Attacks on Software Logic and Error Handling Within ADS-B
           Implementations: Systematic Testing of Resilience and Countermeasures

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      Authors: Syed Khandker;Hannu Turtiainen;Andrei Costin;Timo Hämäläinen;
      Pages: 2702 - 2719
      Abstract: Automatic-dependent surveillance-broadcast (ADS-B) is a cornerstone of the next-generation digital sky and is now mandated in several countries. However, there have been many reports of serious security vulnerabilities in the ADS-B architecture. In this article, we demonstrate and evaluate the impact of multiple cyberattacks on ADS-B via remote radio frequency links that affected various network, processing, and display subsystems used within the ADS-B ecosystem. Overall we implemented and tested 12 cyberattacks on ADS-B in a controlled environment, out of which 5 attacks were presented or implemented for the first time. For all these attacks, we developed a unique testbed that consists of 36 tested configurations. Each of the attacks was successful on various subsets of the tested configurations. In some attacks, we discovered wide qualitative variations and discrepancies in how particular configurations react to and treat ADS-B inputs that contain errors or contradicting flight information, with the main culprit almost always being the software implementation. In some other attacks, we managed to cause denial of service by remotely crashing/impacting more than 50% of the test set that corresponded to those attacks. We also implemented, and report some practical countermeasures to these attacks. We demonstrated that the strong relationship between the received signal strength and the distance-to-emitter might help verify the aircraft.s advertised ADS-B position and distance. For example, our best machine learning models achieved 90% accuracy in detecting attackers' spoofed ADS-B signals.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Reachable Set of Spacecraft With Finite Thrust Based on Grid Method

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      Authors: Bo Pang;Changxuan Wen;
      Pages: 2720 - 2731
      Abstract: Reachable sets are sets of position states that the spacecraft can reach from its initial state under mass and time constraints. In this study, a method to solve the reachable set of spacecraft with finite thrust is proposed. Solving reachable sets can be transformed into solving its boundary surface using the distance fields over grids method. A grid is established to represent the boundary surface, and each node on the grid can be determined by an optimal control problem. A modified sequential convex programming with nonlinear dynamic correction is used to solve optimal control problems with a theoretical proof of convergence. Moreover, the symmetry plane of the reachable set is found to reduce the computation in applications. The method is tested with two types of orbits, namely, geosynchronous and highly elliptical orbits, and the properties of the spacecraft’s reachability in two orbits are obtained. Numerical simulations show that the proposed method can succeed in solving reachable sets under mass and time constraints in two types of initial orbits even when a long period is considered.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Effect of Kinematics and Fluency in Adversarial Synthetic Data Generation
           for ASL Recognition With RF Sensors

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      Authors: Mohammad Mahbubur Rahman;Evie A. Malaia;Ali Cafer Gurbuz;Darrin J. Griffin;Chris Crawford;Sevgi Zubeyde Gurbuz;
      Pages: 2732 - 2745
      Abstract: RF sensors have been recently proposed as a new modality for sign language processing technology. They are noncontact, effective in the dark, and acquire a direct measurement of signing kinematic via exploitation of the micro-Doppler effect. First, this work provides an in depth comparative examination of the kinematic properties of signing as measured by RF sensors for both fluent ASL users and hearing imitation signers. Second, as ASL recognition techniques utilizing deep learning requires a large amount of training data, this work examines the effect of signing kinematics and subject fluency on adversarial learning techniques for data synthesis. The following two different approaches for the synthetic training data generation are proposed: 1) adversarial domain adaptation to minimize the differences between imitation signing and fluent signing data and 2) kinematically-constrained generative adversarial networks for accurate synthesis of RF signing signatures. The results show that the kinematic discrepancies between imitation signing and fluent signing are so significant that training on data directly synthesized from fluent RF signers offers greater performance (93% top-5 accuracy) than that produced by adaptation of imitation signing (88% top-5 accuracy) when classifying 100 ASL signs.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • On the Use of Reciprocal Filter Against WiFi Packets for Passive Radar

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      Authors: Fabiola Colone;Francesca Filippini;Marco Di Seglio;Kevin Chetty;
      Pages: 2746 - 2761
      Abstract: This article derives a novel unified signal processing scheme for WiFi-based passive radar in order to limit its complexity and enhance its suitability for short range civilian applications. To this purpose, the exploitation of a reciprocal filtering (RpF) strategy is investigated as an alternative to conventional matched filtering at the range compression stage. Along with the well-known advantage of a remarkable sidelobes control capability for the resulting range-Doppler response, the use of a RpF is shown to provide additional benefits for the specific sensor subject of this article. Specifically, it allows to streamline the disturbance cancellation stage and to implement a unified signal processing architecture which is capable to handle the different modulation schemes typically adopted in WiFi transmissions. Appropriate adjustments are also proposed to the theoretical RpF in order to cope with the inherent loss in terms of signal-to-noise power ratio. The effectiveness of the proposed signal processing scheme encompassing the RpF strategy is proved against both simulated and experimental datasets.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Joint Transmit Resource Management and Waveform Selection Strategy for
           Target Tracking in Distributed Phased Array Radar Network

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      Authors: Chenguang Shi;Yijie Wang;Sana Salous;Jianjiang Zhou;Junkun Yan;
      Pages: 2762 - 2778
      Abstract: In this article, a joint transmit resource management and waveform selection (JTRMWS) strategy is put forward for target tracking in distributed phased array radar network. We establish the problem of joint transmit resource and waveform optimization as a dual-objective optimization model. The key idea of the proposed JTRMWS scheme is to utilize the optimization technique to collaboratively coordinate the transmit power, dwell time, waveform bandwidth, and pulse length of each radar node in order to improve the target tracking accuracy and low probability of intercept (LPI) performance of distributed phased array radar network, subject to the illumination resource budgets and waveform library limitation. The analytical expressions for the predicted Bayesian Cramér–Rao lower bound and the probability of intercept are calculated and subsequently adopted as the metric functions to evaluate the target tracking accuracy and LPI performance, respectively. It is shown that the JTRMWS problem is a nonlinear and nonconvex optimization problem, where the above four adaptable parameters are all coupled in the objective functions and constraints. Combined with the particle swarm optimization algorithm, an efficient and fast three-stage-based solution technique is developed to deal with the resulting problem. Simulation results are provided to verify the effectiveness and superiority of the proposed JTRMWS algorithm compared with other state-of-the-art benchmarks.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Signal Tracking Algorithm With Adaptive Multipath Mitigation and
           Experimental Results for LTE Positioning Receivers in Urban Environments

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      Authors: Pai Wang;Yang Wang;Y. Jade Morton;
      Pages: 2779 - 2795
      Abstract: Positioning with cellular signals has been gaining attention in urban and indoor environments, where global navigation satellite system signals have limited availability due to interference, blockage, or multipath. However, accurate and reliable tracking of cellular signals under highly dynamic urban channel conditions remains a challenging task. This article presents a cellular long-term evolution (LTE) signal tracking algorithm implemented by an adaptive multipath estimating delay lock loop (AMEDLL) to achieve carrier phase synchronization and time-of-arrival (TOA) tracking under severe multipath propagation conditions. The analytical expression of the coherently integrated correlation result over multiple slots with the LTE cell-specific reference signal is derived. A multipath estimator along with a simple yet efficient multipath estimation monitoring approach is developed to estimate the parameters of all detected multipath signals. Several heuristic monitoring criteria based on historical multipath parameter estimations are established to enable adaptive adjustment of the estimated path number. Real LTE signals are collected in an urban environment for the signal tracking performance evaluation. This article presents two case studies with varying levels of multipath effects and signal power to illustrate the effectiveness of the developed signal tracking algorithm. Instead of a TOA truth reference, open-loop carrier phase estimations are used to analyze the TOA tracking error. Our analyses demonstrate that the AMEDLL-based tracking algorithm provides improved TOA estimation accuracy over the existing super-resolution-algorithm-based and delay-lock-loop-based tracking schemes.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Fault-Tolerant Formation Control for Heterogeneous Vehicles Via
           Reinforcement Learning

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      Authors: Wanbing Zhao;Hao Liu;Kimon P. Valavanis;Frank L. Lewis;
      Pages: 2796 - 2806
      Abstract: This article focuses on the formation control problem of multiple heterogeneous vehicles in air–ground coordination under communication link faults and actuator faults. To address communication link faults among heterogeneous vehicles, a distributed observer is first designed using the air and ground local vehicle information and its convergence is discussed. Using the outputs of the distributed observer and the states of the vehicles, fault-tolerant controller policies are designed for the team of heterogeneous vehicles via reinforcement learning but without knowledge of the vehicle dynamics. Simulation results are included to demonstrate the effectiveness of the proposed fault-tolerant controller.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Nonlinear Guidance Laws for Maneuvering Target Interception With Virtual
           Look Angle Constraint

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      Authors: Yaning Wang;Hui Wang;Defu Lin;Wei Wang;
      Pages: 2807 - 2822
      Abstract: For the problem of intercepting a maneuvering target with a desired terminal impact angle, we propose a guidance law in this article based on a nonlinear relative virtual guidance model in which the origin is attached to the target. In this way, the original maneuvering target is transformed to a stationary one. We introduce the idea of polynomial guidance in the range domain into the relative virtual guidance model, then the acceleration command is obtained considering the terminal line-of-sight angle constraint and the terminal virtual look angle constraint. After linearization, the proposed law turns to a similar structure with the trajectory shaping guidance law, which is the optimal guidance law in the linear system. Finally, the performance of the proposed guidance law is demonstrated through numerous nonlinear simulations.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • BeiDou Satellite Radiation Force Models for Precise Orbit Determination
           and Geodetic Applications

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      Authors: Bingbing Duan;Urs Hugentobler;Inga Selmke;Stefan Marz;Matthias Killian;Martin Rott;
      Pages: 2823 - 2836
      Abstract: China's BeiDou satellite navigation system (BDS) has completed its full constellation in orbit since June 2020. Services have been evolved from regional (BDS-2) to global (BDS-3). This contribution evaluates the impact of solar radiation pressure (SRP) modeling on satellite orbits and geodetic parameters. To that end, we process 2 years of BDS observations (2019-2021), collected by a network of 100 ground stations. A physical a priori box-wing model based on the estimated optical properties is introduced. Various physical effects, such as radiator emission and thermal radiation of solar panels are considered. The ECOM (Empirical CODE orbit Model), ECOM+along-track and ECOM2 models are employed on top in the experiment. We show that without the use of the a priori box-wing model, the ECOM+along-track model shows clear better orbit solutions during eclipse seasons for BDS-3 satellites. This is proven to be mainly due to the thermal radiation of the solar panels. However, the along-track acceleration is highly correlated with LOD (length of day) and ECOM parameters. LOD estimates in this case are contaminated. When using the physical a priori box-wing model satellite orbital errors are greatly reduced for all the ECOM models. For instance, orbit misclosures of BDS-3 CAST (China Academy of Space Technology) satellites improve by a factor of two for the ECOM model during eclipse seasons. Furthermore, the use of the a priori box-wing model mitigates a great majority of the spurious signals in the geodetic parameters.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Fuel-Optimal Guidance for End-to-End Human-Mars Entry, Powered-Descent,
           and Landing Mission

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      Authors: Changhuang Wan;Gangshan Jing;Ran Dai;Jeremy R. Rea;
      Pages: 2837 - 2854
      Abstract: This article investigates the fuel-optimal guidance problem of the end-to-end human-Mars entry, powered-descent, and landing (EDL) mission. It applies a unified modeling scheme and develops a computationally efficient new optimization algorithm to solve the multiphase optimal guidance problem. The end-to-end EDL guidance problem is first modeled as a multiphase optimal control problem with different dynamics and constraints at each phase. Via polynomial approximation and discretization techniques, this multiphase optimal control problem is then reformulated as a polynomial programming problem. By introducing intermediate variables and quadratic equality constraints, a polynomial program is equivalently converted into a nonconvex quadratically constrained quadratic program (QCQP). Then, a novel customized alternating direction method of multipliers (ADMM) is proposed to efficiently solve the large-scale QCQP with convergence proof to a local optimum under certain conditions on the algorithmic parameters. The fuel savings under the end-to-end human-Mars EDL guidance are verified by comparing to the fuel consumption using the separate phase guidance approach. Furthermore, the computational efficiency of the customized ADMM algorithm is validated by comparing to the state-of-the-art nonlinear programming method. The robustness of the customized ADMM algorithm is verified via extensive simulation cases with random initial conditions.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • HAPS Selection for Hybrid RF/FSO Satellite Networks

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      Authors: Olfa Ben Yahia;Eylem Erdogan;Gunes Karabulut Kurt;Ibrahim Altunbas;Halim Yanikomeroglu;
      Pages: 2855 - 2867
      Abstract: Nonterrestrial networks have been attracting much interest from the industry and academia. Satellites and high-altitude platform station (HAPS) systems are expected to be the key enablers of next-generation wireless networks. In this article, we introduce a novel downlink satellite communication (SatCom) model, where free-space optical (FSO) communication is adopted between a satellite and a HAPS node. A hybrid FSO/radio-frequency transmission model is used between the HAPS node and the ground station (GS). In the first phase of transmission, the satellite selects the HAPS node that provides the highest signal-to-noise ratio. In the second phase, the selected HAPS decodes and forwards the signal to the GS. To evaluate the performance of the proposed system, outage probability expressions are derived for exponentiated Weibull and shadowed-Rician fading models while considering the atmospheric turbulence, stratospheric attenuation, and attenuation due to scattering, path loss, and pointing errors. Additionally, asymptotic analysis is carried out, and diversity gain is provided. Furthermore, the impacts of the aperture averaging technique, temperature, and wind speed are investigated. We also provide some important guidelines that can be helpful for the design of practical HAPS-aided SatCom. Finally, the results show that the use of HAPS improves the system performance and that the proposed model performs better than all other existing models.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Strong Ionospheric Spatial Gradient Events Induced by Signal Propagation
           Paths Aligned With Equatorial Plasma Bubbles

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      Authors: Bruno Jacobini Affonso;Alison Moraes;Jonas Sousasantos;Leonardo Marini-Pereira;Sam Pullen;
      Pages: 2868 - 2879
      Abstract: Low-latitude ionospheric behavior directly interferes with a wide range of applications dependent on signals and information from satellites. The most severe and variable events are plasma bubbles and ionospheric scintillation. During plasma bubble events, large and steep plasma density gradients may intersect transionospheric signal from satellites, especially around the equatorial anomaly region. Large ionospheric spatial gradients (or decorrelations) are a critical component of ionospheric threat models for global navigation satellite systems augmentation systems; however, the models cannot assimilate abrupt changes in ionospheric behavior. In this article, an investigation of the relationship between plasma depletions, the occurrence of scintillation, and strong ionospheric spatial decorrelation events was conducted. The results indicate that strong scintillations occur when large gradients are verified. Additionally, the most critical ionospheric spatial gradients were verified mostly under certain conditions: when satellite signals are aligned with the plasma bubble propagation along geomagnetic field lines. Therefore, even though amplitude scintillation may degrade communications, the critical gradient events seem to be related to a particular configuration of satellite signal across the ionosphere. Thus, it is recommended that ionospheric threat models for augmentation systems in low-latitude regions consider this alignment aspect.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Fractional Ambiguity Function for the Generalized Wideband MIMO Radar

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      Authors: Chang Gao;Yongzhe Li;Ran Tao;
      Pages: 2880 - 2899
      Abstract: In this article, we define an ambiguity function (AF) for the generalized wideband multiple-input multiple-output (MIMO) radar, wherein the AF combines the signal processing in the fractional Fourier domain with all the functions of conventional AFs. We name it as the fractional AF for the wideband MIMO radar. In order to obtain the AF, we start from introducing the fractional order that relates to fractional signal processing into the matched-filter exploited by the AF, based on which we then derive the explicit expression of the AF. We provide explanations and implications of the fractional AF, and also derive its simplifications in terms of the case of slow-moving targets in far field. Moreover, we derive corresponding properties for the fractional AF, and meanwhile, we conduct analysis on the computational complexity of the AF. On the basis of the AF definition as well as its simplifications, we establish relationships of our proposed fractional AF to conventional AF forms. We show that our defined fractional AF can serve as a generalized AF form since conventional AFs are special cases of it. Our simulations show that the proper selection of fractional-orders can enable low sidelobe levels of the fractional AF for wideband MIMO radar.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Ground Moving Target Detection and Trajectory Reconstruction Methods for
           Multichannel Airborne Circular SAR

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      Authors: Beibei Ge;Daoxiang An;Leping Chen;Wu Wang;Dong Feng;Zhimin Zhou;
      Pages: 2900 - 2915
      Abstract: Synthetic aperture radar ground moving target indication (SAR-GMTI) is an attractive mode for radar system to obtain high-resolution regional images and detection of moving targets simultaneously. Moreover, the 360° observation capability of circular SAR (CSAR) makes it possible for moving target trajectory reconstruction. In order to address the problem that slow-moving targets, which are buried in strong stationary ground clutter, are difficult to be detected, a framework of multichannel SAR-GMTI is presented in this article. For ground moving target detection in the presence of stationary clutter, the proposed method first adopts clutter suppression interferometry and relaxation-based cyclic algorithm to suppress clutterand retrieve parameters (e.g., radial velocity and Doppler information). Then, to further reduce the false alarm rate, multiple moving target tracking algorithm is performed in range–Doppler domain. Finally, the moving target trajectory is reconstructed by using the proposed two-stage parameter estimation method based on Doppler characteristic and CSAR geometry, and the mathematical analysis of this method is performed. The proposed method is robust and insensitive to the signal-to-noise ratio. It does not rely on priori road information, so it has wide applicability, especially in military application. In addition, the framework is performed in echo domain and independent of imaging processing. The experimental results on simulated data are presented to evaluate the estimation accuracy of the proposed method, and the real data processing results are provided to demonstrate the validity and feasibility of the proposed method.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Accurate Modeling and Homing Control for Parafoil Delivery System Based on
           Wind Disturbance Rejection

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      Authors: Hao Sun;Qinglin Sun;Mingwei Sun;Jin Tao;Zengqiang Chen;
      Pages: 2916 - 2934
      Abstract: Parafoil delivery systems play an irreplaceable role in the area of the airdrop supply and aircraft recovery. Their main function is to transport the payload to the target position. The system applies a large flexible parafoil to provide the lift force and control the flight direction. The parafoil is strongly nonlinear and vulnerable to the wind disturbance. To solve this problem, in this study, we explore a novel flexible modeling method and a homing control methodology for the parafoil. First, an 8-degree-of-freedom dynamic model is built. By clarifying the functions of the different aerodynamic coefficients, the model can maximally simulate the flight states of the system. Then, a trajectory planning method based on a Gaussian pseudospectral method is presented to calculate the optimal reference trajectory by considering the influence of the constant wind. Next, the wind disturbance, such as constant wind and gusts, is compensated by an improved active disturbance rejection controller (ADRC) in the trajectory tracking. Finally, compared with the traditional PID and ADRC, the results of the flight experiment illustrate the correctness and feasibility of the proposed modeling and homing control methodology.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Multispectrally Constrained MIMO Radar Beampattern Design via Sequential
           Convex Approximation

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      Authors: Xianxiang Yu;Hui Qiu;Jing Yang;Wenqiang Wei;Guolong Cui;Lingjiang Kong;
      Pages: 2935 - 2949
      Abstract: This article deals with the multiple-input–multiple-output (MIMO) radar beampattern design in an effort to the coexistence with multiple communication systems. A waveform optimization model accounting for the minimization of the beampattern integrated sidelobe level (ISL) along with the mainlobe width, peak-to-average power ratio, and energy constraints, as well as multispectral requirements where the interference energy injected by the MIMO radar in each shared frequency band in a particular direction, is precisely controlled to ensure the desired quality of service at each communication system. Through an equivalent reformulation of the original nonconvex problem, a polynomial-time sequential convex approximation (SCA) procedure that involves the tackling of a series of constrained convex problems is proposed to monotonically decrease the ISL with the convergence guaranteed to a Karush–Kuhn–Tucker point. Herein, to speed up the convergence, a fast iterative algorithm based on the alternating-direction-method-of-multipliers framework is introduced to globally solve the convex problems during each iteration of the SCA procedure. Numerical results are provided to assess the proposed algorithm in terms of the computational complexity, the achieved beampattern, and spectral compatibility with some competitive counterparts available in the open literatures.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Similarity Relations of PID Flight Control Parameters of Scaled-Model and
           Full-Size Aircraft

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      Authors: Ting Yue;Xianshuai Zuo;Lixin Wang;Jianzhong Geng;Hong Zhang;
      Pages: 2950 - 2960
      Abstract: To carry out a scaled-model flight test of a high-gain aircraft with a proportional plus integral plus derivative (PID) flight control design, the similarity relations of the flight control law parameters of scaled-model and full-size aircraft must be systematically studied. In this article, the general similarity relations applicable to commonly used flight control law configurations and feedback signals are derived and analyzed. Based on the control principle, PID control parameters are divided into two types: feedback gains and series combined dynamic elements. The general similarity relations for the control parameters of these two types of elements are derived from system similarity theory. Finally, closed-loop flight control simulations of a fighter aircraft and its scaled model are completed. The simulation results show that the scaled-model and full-size aircraft with similar PID control law parameters are physically similar, validating the similarity relation conclusions proposed in this article.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Adaptive Distributed Target Detection for FDA-MIMO Radar in Gaussian
           Clutter Without Training Data

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      Authors: Bang Huang;Jiangwei Jian;Abdul Basit;Ronghua Gui;Wen-Qin Wang;
      Pages: 2961 - 2972
      Abstract: Since frequency diverse array multiple-input multiple-output (FDA-MIMO) radar possesses additional target range information for potential performance improvement, this article studies adaptive distributed targets detection for FDA-MIMO radar, where the targets are embedded in Gaussian clutter with unknown covariance matrix. The proposed FDA-MIMO radar detection model considers also the distributed targets occupying several secondary range cells, which is different from the classic detection models in multiple-input multiple-output (MIMO) and/or phase array (PA) radars that discuss only point-like targets. By exploiting the FDA-MIMO radar framework for distributed target detection, we propose the detector through a two-step generalized likelihood ratio test criteria without the need of training data and/or a priori covariance matrix. Moreover, closed-form expressions for the probability of false alarm and detection probability are derived, respectively. The proposed detector adheres to the property of a constant false alarm rate because its probability of false alarm is not restricted by the covariance matrix. The proposed method together with all theoretical analysis are verified by numerical results.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • On-Orbit Implementation of Discrete Isolation Schemes for Improved
           Reliability of Serial Communication Buses

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      Authors: Maximillian Holliday;Zachary Manchester;Debbie G. Senesky;
      Pages: 2973 - 2982
      Abstract: Serial communication buses are used in electronic systems to interconnect sensors and other devices, but two of the most widely used protocols, i.e., interintegrated circuit (I2C) and serial peripheral interface (SPI), are vulnerable to bus-wide failure if even one device on the bus malfunctions. For aerospace applications demanding increasingly more distributed processing and sensing capability, the compounding risk to system reliability as device count scales becomes a limiting factor in mission scope, performance, and lifetime. We propose a simple external circuit to be added to each node on a communication bus that automatically isolates the node in the event of device failure. By automatically isolating failed devices, the integrity of the bus is preserved without requiring additional signals or processing overhead from the host controller. In this article, I2C and SPI isolation circuits are simulated, fabricated, and experimentally verified to be effective at preserving bus integrity in the event of peripheral device failure. The isolation circuits were integrated into three spacecraft for the successful NASA V-R3x mission and found to significantly improve system reliability by eliminating single-point failure modes of the I2C and SPI buses. The developed protection schemes are a valuable tool for decoupling system reliability from serial bus device count and can readily be integrated into the existing aerospace systems.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • A Multipath Local Route Repair Scheme for Bidirectional Traffic in an
           Airborne Network of Multibeam FDD Nodes

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      Authors: Shreyas Devaraju;Moein Parsinia;Elizabeth Serena Bentley;Sunil Kumar;
      Pages: 2983 - 2995
      Abstract: A directional airborne network consisting of nodes equipped with multibeam antennas is considered. These nodes use the frequency division duplex mode of communication. This allows formation of multiple routes between a pair of source and destination nodes, where every forward and reverse route completely overlaps. Each of these routes supports the bidirectional traffic. These routes are formed using the bidirectional ad hoc on-demand multipath distance vector (BAOMDV) routing protocol. In this article, we propose a local route repair scheme, called BAOMDV-LR, when these routes break due to node mobility. The proposed route repair scheme preserves the overlapping and link-disjoint (or node-disjoint) characteristics of the routes, while reducing the need for expensive route rediscovery. The proposed scheme significantly improves the overall network performance for bidirectional traffic (in terms of packet delivery ratio, end-to-end delay, and routing overhead) as compared to the BAOMDV and other existing routing schemes, especially at higher node speeds and data rates.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Vector Trajectory Method for Obstacle Avoidance Constrained Planetary
           Landing Trajectory Optimization

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      Authors: Jiateng Long;Pingyuan Cui;Shengying Zhu;
      Pages: 2996 - 3010
      Abstract: Considering the requirement of avoiding obstacles in different planetary landing missions, this article presents a generalized method dealing with the obstacle avoidance constrained landing trajectory optimization problem with vectorized strategy, i.e., vector trajectory method (VTM). By introducing a trajectory direction constraint with vectorized description, the character of the obstacle avoidance trajectory can be more specifically depicted. Moreover, by satisfying proper trajectory direction constraint, the lander’s particular performances, such as the observation to the target or probability of a safe flight, can be improved. To this end, the VTM and relevant theorem are first developed, revealing the relationship between the two aspects of obstacle avoidance constraint (i.e., distance constraint and trajectory direction constraint). Then, both aspects of constraints are uniformly transformed as the auxiliary angle magnitude constraint with the vectorized strategy, which significantly simplifies the solving procedure of obstacle avoidance constrained trajectory optimization problem. Finally, the proposed VTM is illustrated in detail through the examples with the planetary landing background of atmospheric entry and powered descent landing.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • A Likelihood Ratio Detector for QTMS Radar and Noise Radar

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      Authors: David Luong;Bhashyam Balaji;Sreeraman Rajan;
      Pages: 3011 - 3020
      Abstract: We derive a detector function for quantum two-mode squeezing (QTMS) radar and noise radar that is based on the use of a generalized likelihood ratio (GLR) test for distinguishing between the presence and absence of a target. In addition to an explicit expression for the GLR detector, we derive a detector function which approximates the GLR detector in the limit where the target is small, far away, or otherwise difficult to detect. When the number of integrated samples is large, we derive a theoretical expression for the receiver operating characteristic (ROC) curve of the radar when the GLR detector is used. When the number of samples is small, we use simulations to understand the ROC curve behavior of the detector. One interesting finding is that there exists a parameter regime in which a previously-studied detector outperforms the GLR detector, contrary to the intuition that LR-based tests are optimal or nearly so. This is because neither the Neyman–Pearson lemma, nor the Karlin–Rubin theorem which generalizes the lemma to composite hypotheses, hold in this particular problem. However, the GLR detector remains a good choice for target detection in certain regimes.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Proportional-Integral-Type Event-Triggered Coupled Attitude and Orbit
           Tracking Control Using Dual Quaternions

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      Authors: Chunhui Li;Hengguang Zou;Dawei Shi;Jiliang Song;Junzheng Wang;
      Pages: 3021 - 3036
      Abstract: This article aims to investigate the coupled attitude and orbit tracking control problem of rigid spacecraft motion. A proportional-integral (PI)-type event-triggered active disturbance rejection control scheme is proposed for spacecraft coupled attitude and orbit control under the unknown internal uncertainties and external disturbances. First, the relative kinematics and dynamics are established using error dual quaternions to describe the attitude and orbit coupled motion of rigid spacecraft. Then, the PI-type event-triggering schemes are designed to reduce the communication rates between the pose sensors and the observers. Finally, the asymptotic stability of the closed-loop control system is proved. The simulation results show that the proposed closed-loop control system can achieve satisfactory tracking performance and reduce the occupancy of on-board communication resources to ensure the stable operation of the spacecraft.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Structure Priors Aided Visual-Inertial Navigation in Building Inspection
           Tasks With Auxiliary Line Features

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      Authors: Yang Lyu;Shenghai Yuan;Lihua Xie;
      Pages: 3037 - 3048
      Abstract: The article proposes a visual-inertial navigation method to support the autonomous operation of a quadrotor UAV during the building façade inspection tasks, where state-of-the-art vision-based localization methods may fail due to texture point feature insufficiency. Considering the appearance characteristics of the building façades, we additionally fuse line features and their corresponding structure prior information to the sliding-window-based estimator to improve localization reliability and accuracy. The contribution of the proposed method lies mainly in two aspects. First, we develop an informative feature selection mechanism according to the façade patterns and the inspection trajectory patterns to make a balance between localization accuracy and computation overheads. Second, we further utilize structure prior information, which is defined as line-to-line and point-to-line relationships, as another source of high-fidelity measurement to restrain the localization drifts. The proposed method is tested not only on public datasets, but also on an actual flight data package recorded in a building inspection task. Experimental results show that the proposed method can serve as a practical tool for navigating a robot in a building inspection task, with improved localization reliability and accuracy.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Agile Flight Control Under Multiple Disturbances for Quadrotor: Algorithms
           and Evaluation

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      Authors: Jindou Jia;Kexin Guo;Xiang Yu;Lei Guo;Lihua Xie;
      Pages: 3049 - 3062
      Abstract: In this article, a scheme of anti-disturbance agile flight control is developed for a maneuverable quadrotor unmanned aerial vehicle, subject to the aerodynamic drag, dynamic shift of center of gravity (CoG), and motor dynamics. A cascaded control framework is adopted. In the translational loop, an aerodynamic drag model that considers the drag surface change is developed, containing the deep coupling information between the aerodynamic drag and the system states. A disturbance observer based on the aerodynamic drag model is subsequently designed for suppressing the aerodynamic drag force. In the rotational loop, a full quaternion-based backstepping control is adopted and a nonlinear disturbance observer with consideration of motor dynamics is designed, which can handle the dynamic CoG shift and aerodynamic drag torque. Comparative studies on both simulations and experiments manifest that the agile ability can be ensured by the proposed control framework, especially in the presence of multiple disturbances.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Fixed-Time Formation Tracking for Heterogeneous Multiagent Systems Under
           Actuator Faults and Directed Topologies

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      Authors: Wanglei Cheng;Ke Zhang;Bin Jiang;Steven X. Ding;
      Pages: 3063 - 3077
      Abstract: This article investigates the problem of fixed-time formation tracking control for a heterogeneous multiagent system composed of unmanned aerial vehicles and unmanned ground vehicles in the presence of actuator faults, model uncertainties, and external disturbances. First, two fixed-time distributed observers are proposed, one of which is applied to detail-balanced directed graph and the other is applied to general directed graph. These two observers remove the requirements of global information and control signal of leader, as well as reduce communication flow. Second, a fixed-time disturbance observer is designed for each follower to estimate lumped uncertainties. Third, a Lyapunov-based formation controller is proposed to guarantee that the fixed-time synchronized formation is achieved for heterogeneous multiagent systems using estimation and backstepping technique. Furthermore, the obtained upper bound of convergence time only depends on the observer gains and controller parameters, which facilitates the adjustment of the settling time offline regardless of initial conditions under different formation requirements. Finally, the effectiveness of the proposed fixed-time protocol is verified using numerical simulations.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Transmit Code and Receive Filter Design for PMCW Radars in the Presence of
           One-Bit ADC

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      Authors: Foozie Foroozmehr;Mahmoud Modarres-Hashemi;Mohammad Mahdi Naghsh;
      Pages: 3078 - 3089
      Abstract: Phase-modulated continuous-wave (PMCW) radar is an emerging technology in various civilian applications. Due to the high bandwidth of the PMCW signal, it needs high-speed analog-to-digital converters (ADCs). High-resolution ADCs supporting this high bandwidth are expensive, have a big size on the chip, and consume high power, which are significant challenges for radar. A solution to deal with the aforementioned challenges is to use low-resolution, or in the most extreme case, one-bit ADCs. In this article, we aim at designing the transmit code and the receive filter for the PMCW radar in the presence of one-bit ADC at the receiver side. To this end, we introduce the mean integrated sidelobe level metric, called MISL. MISL generalizes the well-known ISL metric for nonideal ADC usage at the receiver side and takes the effect of noise and target backscattering coefficient into account. For mathematical tractability, we employ the maximum likelihood estimation of the target backscattering coefficient. This leads to casting an optimization problem that does not need knowledge about noise and target characteristics. We utilize the cyclic optimization procedure to optimize the transmit code and the receive filter. The filter design subproblem admits a closed-form solution, whereas we obtain a solution to transmit code design subproblem via the coordinate descent framework. Numerical examples illustrate the superior performance of the proposed method compared to benchmarks that design sequences assuming ideal ADC at the receiver.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Reward Factor-Based Multiple Agile Satellites Scheduling With Energy and
           Memory Constraints

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      Authors: Abhijit Chatterjee;Ratnasingham Tharmarasa;
      Pages: 3090 - 3103
      Abstract: Earth observing satellites (EOS) orbit around the earth to perform observation tasks specified by users. The additional maneuverability resulting from higher degrees of freedom than nonagile EOS (N-AEOS) provides agile EOS (AEOS) a significantly larger visible time window to complete the tasks. As a consequence, the task scheduling for AEOS is much more computationally complex than N-AEOS. In this article, a mixed-integer nonlinear optimization problem is formulated to find a near-optimal task allocation for a realistic AEOS scheduling problem. The satellite resources, such as energy and memory constraints, are considered in this problem. A reward factor is used to address the requirement of multiple scans in order to complete a task. A probability factor is also taken into consideration to incorporate the uncertainty of successful scans due to external factors, such as cloud coverage. An elitist mixed coded genetic algorithm-based satellite scheduling (EMCGA-SS) algorithm is proposed to solve the formulated problem. EMCGA-SS is extended to elitist mixed coded hybrid genetic algorithm-based satellite scheduling by combining a hill-climber mechanism in order to have better initialization. Experimental results to illustrate the performance of the algorithms and a comparison with some widely used methodologies are also presented.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Evaluation Model, Intelligent Assignment, and Cooperative Interception in
           Multimissile and Multitarget Engagement

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      Authors: Jianguo Guo;Guanjie Hu;Zongyi Guo;Min Zhou;
      Pages: 3104 - 3115
      Abstract: A complete engagement framework, including evaluation model, intelligent assignment, and cooperative interception is proposed to address the issue of multimissile and multitarget engagement (MME). The concepts of targets threat degree and missiles interception effective degree are included in the evaluation model, which fully considers both the offensive and defensive sides. Then, the multitarget assignment is carried out based on the obtained evaluation model, and a reinforcement learning-based intelligent assignment strategy is adopted. This scheme is capable of quickly generating the optimal assignment in the complex and variable engagement environment by virtue of the self-learning and reward mechanism. Following the optimal assignment, a cooperative interception technique is used to ensure the interception mission efficiently and accurately. Finally, simulation results illustrate the validity of the proposed engagement framework.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Fusion Recognition of Space Targets With Micromotion

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      Authors: Xudong Tian;Xueru Bai;Ruihang Xue;Ruoyu Qin;Feng Zhou;
      Pages: 3116 - 3125
      Abstract: During the observation of micromotion targets in space, inverse synthetic aperture radar usually obtains the narrowband and wideband echoes simultaneously. In order to exploit their rich information in target electromagnetic scattering, shape, structure, and motion, this article proposes a recognition method of space micromotion targets based on decision fusion. The proposed method extracts physical features from the radar cross section and the joint time–frequency distribution from narrowband echoes, while extracts the data features from high-resolution range profiles and range-instantaneous-Doppler image by convolution neural network. Finally, particle swarm optimization is adopted to decision-level fusion so as to realize high-precision recognition. The recognition results of electromagnetic simulated data under various conditions have demonstrated the effectiveness and robustness of the proposed method.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Feeder Link Precoding for Future Broadcasting Services

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      Authors: Alessandro Guidotti;Claudio Sacchi;Alessandro Vanelli-Coralli;
      Pages: 3126 - 3146
      Abstract: 5G systems are becoming a reality and the evolution toward beyond 5G and 6G systems is already being defined, also to cope with the ever increasing capacity demanded by on-ground users. This will pose challenging requirements on the feeder link of future satellite systems, which risks to become a bottleneck for the overall system performance. In this article, we propose a novel architecture of linear precoding for the feeder link of a broadcast satellite system operating with full frequency reuse to significantly enhance the achievable capacity. The architecture has been simulated and tested in a challenging multifrequency scenario, where Ku, Ka, Q/V, and W bands have been considered for transmission. The numerical performance analysis and the open issues related to the practical realization of the proposed architecture are also thoroughly discussed.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Factorized Geometrical Autofocus for UWB UHF-Band SAR With a GPS-Supported
           Linear Track Model

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      Authors: Jan Torgrimsson;Patrik Dammert;Hans Hellsten;Lars M. H. Ulander;
      Pages: 3147 - 3161
      Abstract: This article describes how to form a SAR image without proper motion quantities. That is within the scope of factorized geometrical autofocus (FGA). The FGA algorithm is a fast-factorized back-projection formulation with adjustable geometry parameters. Subapertures are tuned and merged pair-by-pair (base-2) and step-by-step. With this technique, we can correct an erroneous geometry and form a focused image. The FGA algorithm has been applied on two datasets, acquired by the UWB CARABAS 3 system at UHF-band. The tracks are measured accurately by means of a DGPS. We however adopt and modify a geometry model. Equidistant linear tracks at fixed altitudes are assumed. These tracks are then regulated via a two-stage search strategy and a reverseprocessing procedure. As this is a first experiment at UHF-band, we provide GPS-based length values for the subapertures, to simplify the search. Multiple geometry solutions are tested for each subaperture pair, i.e., at each resolution level. Resulting FGA images are compared to reference images and verified to be focused. This indicates that it is feasible to form a focused image with wavelength resolution at UHF-band, i.e., with minimum support from a motion measurement system.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • When Infrared Small Target Detection Meets Tensor Ring Decomposition: A
           Multiscale Morphological Framework

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      Authors: Lizhen Deng;Jie Song;Guoxia Xu;Hu Zhu;
      Pages: 3162 - 3176
      Abstract: Detecting the small targets from a heterogeneous background in an infrared image is a challenging problem, which has received extensive attention. In this article, we propose a method in terms of tensor ring (TR) decomposition and nonlinear multiscale morphological top-hat transformation for infrared small target detection (ISTD). First, a tensor model with prior knowledge is constructed for extracting the structural features of multiple infrared images. Then, the problem of small target detection is converted into a problem of minimizing the tensor rank with TR. Based on the TR decomposition model, we introduce the top-hat regularization into our model with multiple structural elements of different size to perform morphological operations. The corresponding morphological model exploits a more accurate ring top-hat regularization expression through adaptive nonlinear combination for the ISTD problem. Finally, the optimization of the model is realized by the closed solution given by the alternating direction method of multipliers algorithm. In order to verify the superior performance of our method, our method is compared with a number of advanced detection models. By analyzing the results of comparison experiments, the detection accuracy and precision of our model in the detection of small infrared targets have been improved. Even in complex background conditions, our model also maintain a good robustness.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Real-Time Adaptive Dwell Scheduling for Digital Array Radar Based on
           Virtual Dynamic Template

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      Authors: Ting Cheng;Zhongzhu Li;Qianqian Tan;Shaoxing Wang;Chengyu Yue;
      Pages: 3197 - 3208
      Abstract: According to the characteristics of signal processing in digital array radar (DAR), an adaptive dwell scheduling algorithm based on the virtual dynamic template is proposed, where a general pulse interleaving method with the overlap of receiving durations is involved. The virtual dynamic template is introduced to realize the general pulse interleaving among tracking tasks, where the tracking tasks with different numbers and repetition intervals of pulses may be interleaved under the time and energy constraints. The proposed dwell scheduling algorithm is a perfect combination of adaptive dwell scheduling technique and novel pulse interleaving based on the virtual dynamic template. It is developed based on the task model with multiple pulses and can realize real-time dwell scheduling, therefore, can be used in an actual radar system. Furthermore, to improve the efficiency of the proposed dwell scheduling algorithm, the efficient version of it is given. Simulation results demonstrate that the proposed algorithms can improve the scheduling performance effectively. Furthermore, the scheduling performance and efficiency can be balanced easily with the control of the utilization ratio threshold in the proposed efficient algorithm.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Finite-Time Prescribed Performance Control for Space Circumnavigation
           Mission With Input Constraints and Measurement Uncertainties

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      Authors: Hanlin Dong;Xuebo Yang;
      Pages: 3209 - 3222
      Abstract: This article presents a 6-DOF attitude-orbit synchronous control problem for the space circumnavigation (SCN) mission with parameter uncertainties, time-varying uncertainties, and input constraints. In particular, from the perspective of engineering application, time-varying measurement uncertainties are taken into account of the 6-DOF attitude–orbit coupling kinematics and dynamics, and the analytical solution of the desired attitude is derived based on the measured relative orbit information with measurement uncertainties. To drive the active spacecraft approach to the faulty target safely, a time-varying exponential prescribed convergence boundary is introduced into the sliding surface. A finite-time disturbance observer is involved in equivalent tracking errors for compensating the mismatched uncertainties. In addition, an auxiliary system is designed to overcome the instability danger caused by input constraints. The stability of the controlled system is discussed in the nonautonomous finite-time stable framework, which is proved via Lyapunov analysis that the attitude-orbit tracking errors converge to the equilibrium within finite time. The simulation experiment with mismatched uncertainties and prescribed constraints shows the superiority of the designed control scheme.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Principal–Agent Problem as a Principled Approach to Electronic
           Counter-Countermeasures in Radar

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      Authors: Anurag Gupta;Vikram Krishnamurthy;
      Pages: 3223 - 3235
      Abstract: Electronic countermeasures (ECMs) against a radar are actions taken by an adversarial jammer to mitigate the effective utilization of the electromagnetic spectrum by the radar. On the other hand, electronic counter-countermeasures (ECCMs) are actions taken by the radar to mitigate the impact of ECMs so that the radar can continue to operate effectively. The main idea of this article is to show that ECCMs involving a radar and a jammer can be formulated as a principal–agent problem (PAP)—a problem widely studied in microeconomics. With the radar as the principal and the jammer as the agent, we design a PAP to optimize the radar’s ECCM strategy in the presence of a jammer. The radar seeks to optimally trade off the signal-to-noise ratio of the target measurement with the measurement cost: cost for generating radiation power for the pulse to probe the target. We show that for a suitable choice of utility functions, the PAP is a convex optimization problem. Furthermore, we analyze the structure of the PAP and provide sufficient conditions under which the optimal solution is an increasing function of the jamming power observed by the radar; this enables computation of the radar’s optimal ECCM within the class of increasing affine functions at a low computation cost. Finally, we illustrate the PAP formulation of the radar’s ECCM problem via numerical simulations. We also use simulations to study a radar’s ECCM problem, wherein the radar and the jammer have mismatched information.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Multichannel Clutter Modeling, Analysis, and Suppression for Missile-Borne
           Radar Systems

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      Authors: Penghui Huang;Hao Yang;Zihao Zou;Xiang-Gen Xia;Guisheng Liao;
      Pages: 3236 - 3260
      Abstract: When a missile-borne radar system works in downward-looking surveillance mode, the broadened ground clutter signal in virtue of platform high-speed motion will be received by the radar receiver, which will cause difficulty in moving target detection and attacking. Unlike airborne and spaceborne platforms, a missile-borne platform exhibits some unique motion characteristics, such as diving, spinning, and coning, causing the clutter space–time distribution property significantly different from those of airborne and spaceborne radar platforms. In addition, the forward target striking requirements make the missile-borne clutter space–time spectrum further exhibit the severe range-dependent property. To deal with these issues, accurate motion modeling of a missile-borne radar platform is first carried out in this article, where the complex platform motions including forward-looking diving, spinning, and coning are considered. Then, the autocorrelation processing combined with iterative adaptive approach is applied to estimate the clutter angle-Doppler center frequencies, so as to effectively realize the clutter nonstationary compensation along spatial and temporal directions. Finally, a time-domain sliding window-based subspace projection method is proposed to achieve the robust clutter suppression. Both simulation and real-measured radar data processing results are presented to validate the effectiveness and feasibility of the proposed algorithm.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • The Strong Tracking Innovation Filter

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      Authors: Maryam Kiani;Reza Ahmadvand;
      Pages: 3261 - 3270
      Abstract: Sliding innovation filter (SIF) has recently been introduced as a robust strategy for estimation of linear systems. The SIF has been extended to nonlinear systems via analytical linearization. However, as the performance of the extended SIF (ESIF) degrades in the presence of severe nonlinearities, this article has initially developed a derivative-free cubature SIF (CSIF) that uses statistical linearization for the error propagation. In addition, the SIF gain has been reformed to incorporate the innovation covariance matrix, thus reducing the estimation error. Furthermore, the adaptive fading factor has been employed to strengthen the robustness and convergence properties of the CSIF against abrupt changes of state variables. Simulation results of the proposed estimation algorithm named the strong tracking innovation filter (STIF) have been compared to those of the ESIF and the CSIF in different conditions of the modeling error in the dynamic system and statistical characteristics of the system inputs. This comparison has demonstrated the superior performance of the STIF in terms of the convergence rate, estimation accuracy, and the chattering elimination. Integration of the STIF into a sliding mode controller for the concurrent estimation and control of a Mars lander has reconfirmed the robustness and accuracy of the proposed STIF.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Sliding-Mode Control and Strategic Thrust-Vectoring Based Aircraft Flat
           Spin Recovery With Altitude Loss Minimization

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      Authors: Salahudden Salahudden;Akash Taru Das;Ajoy Kanti Ghosh;
      Pages: 3271 - 3282
      Abstract: Spin recovery from a fully-developed-oscillatory-stable-flat spin is performed in this article using thrust vector control (TVC) and compared with the conventional mode of recovery. TVC dynamics is modeled and then added to the standard aircraft dynamics. TVC command is designed as a function of angle of attack in the pitch and yaw direction and optimally used with aircraft primary controls (APCs). The APC is designed using the sliding-mode control technique. The spin recovery profile is demonstrated on F-18 high alpha research vehicle to test the efficacy of the proposed algorithm. Results show that with the combined strategic use of TVC and APC, spin recovery time is drastically reduced because of reduced saturation of APC. Thus, altitude decrease during spin recovery also reduces, thereby gaining on final exit altitude to level flight, compared to recovery using only APC. Thus, TVC is proven in this article to be a powerful corrective contributor to spin recovery, increasing margin of safety in terms of excessive altitude loss.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Adaptive Radar Detection in the Presence of Missing-data

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      Authors: Augusto Aubry;Vincenzo Carotenuto;Antonio De Maio;Massimo Rosamilia;Stefano Marano;
      Pages: 3283 - 3296
      Abstract: This article deals with the problem of adaptive radar detection in a missing-data context, where the complete observations (i.e., downstream information loss mechanisms) are characterized by homogeneous Gaussian disturbance with an unknown but possibly structured covariance matrix. The detection problem, formulated as a composite hypothesis test, is tackled by resorting to suboptimal design strategies, leveraging the generalized likelihood ratio criterion demanding appropriate maximum likelihood estimates (MLEs) of the unknowns under both hypotheses. Capitalizing on some possible a priori knowledge about the interference covariance matrix structure, the optimization problems involved in the MLE computation are handled by employing the expectation–maximization (EM) algorithm or its expectation–conditional maximization and multicycle EM variants. At the analysis stage, the performance of the devised architectures is assessed both via Monte Carlo simulations and on measured data for some covariance matrix structures of practical interest.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • A Generalized Low-Rank Double-Tensor Nuclear Norm Completion Framework for
           Infrared Small Target Detection

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      Authors: Lizhen Deng;Dongyuan Xu;Guoxia Xu;Hu Zhu;
      Pages: 3297 - 3312
      Abstract: Infrared small target detection is a research hotspot in computer vision technology that plays an important role in infrared early warning systems. Specifically, infrared images with strong background clutter and noise pose a challenge to target detection technology. In this article, we propose a method for infrared small target detection based on the double nuclear norm and ring-structural elements over a generalized tensor framework. We use the double nuclear norm instead of the traditional single nuclear norm as the relaxation of the rank function, which solves the problem that the suboptimal solution deviates from the original solution and better approaches the rank minimization. In addition, we use weighted ring structural elements instead of traditional structural elements to make better use of the target information and its surrounding background. Experiments on six sequences of real images show that the proposed method can enhance the target and suppress the background effectively, and ensure a high detection probability and a low false alarm rate.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Dynamic Resource Allocation With Decentralized Multi-Task Assignment
           Approach for Perimeter Defense Problem

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      Authors: Shridhar Velhal;Suresh Sundaram;Narasimhan Sundararajan;
      Pages: 3313 - 3325
      Abstract: In this article, a dynamic resource allocation with decentralized multi-task assignment (DREAM) approach using a dynamic sized team of defenders is presented to protect a perimeter of a high-security area from heterogeneous intruders. In the DREAM approach, the spatio-temporal problem of neutralizing the heterogeneous intruders is converted into a decentralized time-ordered multi-task assignment problem. A single-step dynamic resource allocation algorithm based on the computed assignments determines an optimal number of defenders required. The DREAM approach adds more defenders to the team from the reserve stations or removes the excess defenders from the team such that it always utilizes minimal resources for protecting convex territory. A trajectory computation algorithm converts the optimal multi-task assignments to trajectories for the defenders. The working of the DREAM approach for a typical perimeter defense problem is illustrated using a simulated convex territory protection problem. Based on the results from the ablation study, it is seen that one needs to deploy a higher number of defenders in the team for a better success rate to handle highly maneuvering intruders. Furthermore, a higher defender-to-intruder speed ratio helps in better resource utilization. These results clearly indicate that the DREAM approach can protect any convex territory efficiently with minimal resources.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Dynamic Biasing for Improved On-Orbit Total-Dose Lifetimes of Commercial
           Electronic Devices

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      Authors: Maximillian Holliday;Thomas A. Heuser;Zachary Manchester;Debbie G. Senesky;
      Pages: 3326 - 3336
      Abstract: The survivability of microelectronic devices in ionizing radiation environments drives spacecraft design, capability, mission scope, and cost. This article exploits the periodic nature of many space radiation environments to extend device lifetimes without additional shielding or modifications to the semiconductor architecture. We propose a technique for improving component lifetimes through reduced total-dose accumulation by modulating device bias during periods of intense irradiation. Simulation of this “dynamic biasing” technique applied to single-transistor devices in a typical low-Earth orbit results in an increase in component lifetime from 114 to 477 days (318% improvement) at the expense of 5% down time (95% duty cycle). The biasing technique is also experimentally demonstrated using gamma radiation to study three commercial devices spanning a range of integrated circuit complexity in 109- and 256-rad/min dose rate conditions. The demonstrated improvements in device lifetimes using the proposed dynamic biasing technique lay a foundation for more effective use of modern microelectronics for space applications. Analogous to the role real-time temperature monitoring plays in maximizing modern processor performance, the proposed dynamic biasing technique is a means of intelligently responding to the radiation environment and capable of becoming an integral tool in optimizing component lifetimes in space.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Oscillation Phenomenon in Trust-Region-Based Sequential Convex Programming
           for the Nonlinear Trajectory Planning Problem

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      Authors: Lei Xie;Rui-Zhi He;Hong-Bo Zhang;Guo-Jian Tang;
      Pages: 3337 - 3352
      Abstract: The trust-region-based sequential convex programming (TSCP) method is designed to solve the nonlinear trajectory planning problem using successive linearization and trust region. The TSCP method has a good real-time performance suitable for onboard aerospace applications. However, the main challenge in practical applications is its poor convergence. In this article, we reveal an oscillation phenomenon, which is an important factor affecting the convergence. The main contribution of this article is threefold: 1) the oscillation phenomenon is proved to be an inherent property of the TSCP method for the nonlinear trajectory planning problem; 2) the oscillation condition that determines whether oscillation occurs is obtained; and 3) the oscillation-condition-based remedy to address the oscillation is presented. The effectiveness and robustness of the proposed remedy have been verified via a complex reentry trajectory planning problem.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Estimators for Space-Time Block-Coded ARTM CPM in Aeronautical Mobile
           Telemetry

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      Authors: Chad Josephson;Spencer Giddens;Erik Perrins;Willie K. Harrison;Michael Rice;
      Pages: 3353 - 3369
      Abstract: The use of space-time coded ARTM continuous phase modulation to solve the two-antenna problem in aeronautical mobile telemetry requires estimates of the parameters that define the propagation environment. The maximum likelihood estimator problem is defined and used to motivate reduced-complexity estimators suitable for use in a real system. A modified gradient descent algorithm performs the search required to find the delay parameters. An “inner” phase-lock loop operating with an “outer” frequency-lock loop computes decision-directed estimates of the frequency offset. Computer simulations were used to assess the impact on bit error rate performance introduced by the estimators. The simulation results show that the combined joint estimator for the delays, channel gains, and frequency offset imposes a 1.15-dB loss in performance.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Time-Correlated Window-Carrier-Phase-Aided GNSS Positioning Using Factor
           Graph Optimization for Urban Positioning

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      Authors: Xiwei Bai;Weisong Wen;Li-Ta Hsu;
      Pages: 3370 - 3384
      Abstract: This article proposes an improved global navigation satellite system (GNSS) positioning method that explores the time correlation between consecutive epochs of the code and carrier-phase measurements, which significantly increases the robustness against outlier measurements. Instead of relying on the time difference carrier phase which only considers two neighboring epochs using an extended Kalman filter estimator, this article proposed to employ the carrier-phase measurements inside a window, the so-called window carrier phase (WCP), to constrain the states inside a factor graph. A left null space matrix is employed to eliminate the shared unknown ambiguity variables and, therefore, correlate the associated states inside the WCP. Then, the pseudorange, Doppler, and the constructed WCP measurements are integrated simultaneously using factor graph optimization to estimate the state of the GNSS receiver. We evaluated the performance of the proposed method in two typical urban canyons in Hong Kong, achieving the mean positioning errors of 1.76 and 2.96 m, respectively, using the automobile-level GNSS receiver. Meanwhile, the effectiveness of the proposed method is further evaluated using a low-cost smartphone-level GNSS receiver, and similar improvement is also obtained when compared with several existing GNSS positioning methods.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Semidefinite Programming Solutions for Elliptic Localization in
           Asynchronous Radar Networks

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      Authors: Xiaoping Wu;Yana Shen;Xuefen Zhu;Qinman Lin;
      Pages: 3385 - 3398
      Abstract: In this article, semidefinite programming (SDP) solutions are proposed for the elliptic localization problem in asynchronous radar networks, where the transmitters are subject to clock offsets. Relaxing the nonconvex problem into different convex forms, we design tight SDP (TSDP) and global SDP (GSDP) solutions for this problem. The TSDP solution includes several SDP cones to solve the problem, and the correlation is not considered. Hence, the TSDP solution performs poorly in the presence of correlated noise. We further put forward the GSDP solution to improve the performance by introducing a new GSDP form, which includes only one SDP cone to handle the correlated noise. We also theoretically prove that the GSDP problem is tight enough so that its performance is able to sufficiently approach the Cramér–Rao lower bound (CRLB) accuracy. The simulated results show that the TSDP solution can provide the comparable performance with the GSDP in the absence of related noise. The performance of the GSDP solution can almost attain the CRLB accuracy using less receivers.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Frequency-Variable Resonant Self-Heating Technique for Lithium-Ion
           Batteries at Low Temperature

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      Authors: Sang-Hyeon Ha;Jae-In Lee;Hyunki Yoon;Tae-Ryong Park;Jaeill Baek;Jae-Sang Kim;Gun-Woo Moon;
      Pages: 3399 - 3410
      Abstract: This article presents a frequency-variable resonant self-heating technique for improving the heating speed of lithium-ion batteries at very low temperatures. In contrast to the conventional heating method with a fixed current and frequency, the proposed technique can increase the battery heating current by determining the minimum impedance of the lithium-ion batteries. Then, through a variable charging/discharging frequency operation, this technique can increase the heating speed without inducing a temperature plateau because of impedance reduction. A lithium-ion battery with improved self-heating performance at low temperatures was developed and used to verify the proposed self-heating technique. A simulation model and self-heating device (dc/dc converters) were also designed and tested at –30-°C ambient temperature. The proposed frequency-variable resonant self-heating technique achieved a heating speed four times faster (from 2784 s to 717 s) than the conventional self-heating technique. Thus, lithium-ion batteries can be used at cryogenic temperatures (–30 °C) by quickly raising the battery temperature with this technique.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Multiple-Kernelized-Correlation-Filter-Based Track-Before-Detect Algorithm
           for Tracking Weak and Extended Target in Marine Radar Systems

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      Authors: Yi Zhou;Hang Su;Shuai Tian;Xiaoming Liu;Jidong Suo;
      Pages: 3411 - 3426
      Abstract: This article addresses the problem of tracking weak and extended targets in the clutter for marine radar systems. In the proposal, multiple kernelized correlation filters (MKCFs) incorporate a low-threshold constant false alarm rate and segmentation model under the principle of multiframe track before detect (MF-TBD). By setting the similarity score of the correlation filter as the test statistic, the maximization of the integration over frames can be solved by the essentially exhaustive searching of the MKCF. Since the correlation filter measures the similarity of the intensity distributions in the extended templates, the proposed method can differentiate the weak target from the surrounding clutter and other targets at a close range. Compared to other amplitude-based MF-TBD methods, it performs better in detecting and tracking extended targets in the real-radar data with heavy clutter caused by floating sea ice and the simulations with Rayleigh and $K$-distributed sea clutters.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Accurate Clutter Synthesis for Heterogeneous Textures and Dynamic Radar
           Environments

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      Authors: Donghoon Kim;Andrew Junghoon Park;Ui-Suk Suh;Dongwoo Goo;Donghwan Kim;Boram Yoon;Won-Sang Ra;Sanghoek Kim;
      Pages: 3427 - 3445
      Abstract: This article proposes an accurate clutter synthesis method for a dynamic radar under various environmental conditions. Previous clutter synthesis methods mostly rely on empirical clutter models fitting the measurement results obtained from the limited conditions of observations. Inherently, these models have difficulties synthesizing clutter for unexplored environments and operational conditions. The method presented in this article overcomes this limitation by creating and summing the clutter patch by patch. The clutters of individual patches are synthesized by the clutter model corresponding to each patch’s specific conditions, such as the grazing angle, ground texture, and wind velocity. It enables one to synthesize clutter signals under various observation scenarios accurately. For example, this work demonstrates the synthesis of clutter signals from heterogeneous textures for an aircraft radar on a mission. Also, the clutter signals for a monopulse radar are synthesized and included in the radar simulation to evaluate the performance of a detection algorithm. Potentially, this method can be utilized to design a robust radar algorithm against the clutter environment of interests. For a given condition of measurement, it is shown that the synthesized clutters agree well with the actual measured data in their statistical characteristics. The program is freely available through the open code.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Development of an Aircraft Electric Power Architecture With Integrated
           Ground Power Unit

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      Authors: Chen-Wei Yang;Min-Ze Lu;Chang-Ming Liaw;
      Pages: 3446 - 3459
      Abstract: This article presents a switch-mode rectifier-based electric power architecture with an integrated ground power unit for more electric aircraft. The well-regulated high-voltage dc-bus is established from the aircraft generator. And the conventional major 270-Vdc, 28-Vdc, and 115-Vac/400-Hz buses are also preserved. In landed conditions, the ground power unit function powered by the mains is inherently possessed thanks to the proposed integrated schematic. First, the developed switch-mode rectifier using a silicon-carbide device with a wide frequency range covering utility line frequency and aircraft generated varied high frequency is presented. The allowable energy storage inductances using the embedded generator armature winding are derived. Good generator armature power quality and well-regulated dc output voltage are preserved by the designed current and voltage control schemes. Next, the utility grid-powered ground power unit established by the embedded schematic is introduced. Finally, the inverter for generating the 115-Vac/400-Hz three-phase source and the dc–dc converter for establishing the 270-Vdc bus are constructed. Normal operations, good dynamic, and steady-state performances of all the constructed power stages are verified experimentally, which can confirm the feasibility of the proposed aircraft power architecture.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Flow Field Reconstructions With GANs Based on Radial Basis Functions

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      Authors: Liwei Hu;Wenyong Wang;Yu Xiang;Jun Zhang;
      Pages: 3460 - 3476
      Abstract: Nonlinear sparse data regression and generation have been a long-term challenge in the field of aerodynamics, flow field reconstruction is an area of specific interest in this article. The high computational costs of computational fluid dynamics (CFD) make large scale CFD data production expensive, which is the reason why cheaper methods are needed. Traditional reduced-order models were promising but they cannot generate a large amount of full domain flow field data (FFD) to execute high-precision flow field reconstructions. Motivated by the problem of existing approaches, and inspired by the success of generative adversarial networks (GANs) in the field of computer vision, we prove a theorem that shows the optimal approximation to a GAN discriminator is a radial basis function neural network when engaged in with nonlinear sparse FFD regression and generation. Based on this theorem, a radial basis function-based GAN (RBF-GAN) and a RBF cluster-based GAN (RBFC-GAN) are proposed for regression and generation purposes. Three different datasets are applied to verify the feasibility of our models. The results show that the performance of RBF-GAN and RBFC-GAN are better than that of GANs and conditional GANs (cGANs) by both the mean square error and the MSPE measurements. In addition, compared with GANs/cGANs, the stability of the RBF-GAN and the RBFC-GAN are improved by 34.62 and 72.31%, respectively. Consequently, our proposed models can be used to generate full domain FFD from limited and sparse datasets to meet the requirements of high-precision flow field reconstructions.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Concept Design and Intelligent Control of Solar Sail With Numerous
           Discrete Elements

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      Authors: Lin Chen;Tong Luo;Ming Xu;Xiaoyu Zuo;
      Pages: 3477 - 3491
      Abstract: Solar sail appears to be promising and effective spacecraft in interplanetary missions; however, performance degradation is inevitable during its long-term voyage, caused by materials wastage and accidents. This study designed a solar sail with numerous discrete elements (SSNDE) and an intelligent attitude control strategy (IACS) to prevent performance degradation and decrease its harmful effect. Structural analysis of SSNDE revealed improvement in reduction of system errors caused by irregular blade deformation and mechanical abrasion via employing numerous discrete elements with rigid boundaries. Furthermore, IACS enables SSNDE to maintain control ability despite the invalidation of a quarter of blades, which can be verified by simulation results. The SSNDE design and its IACS endow an effective solution to decrease performance degradation against material wastage and unpredictable accidents in interplanetary missions. Moreover, they reveal the potential of intelligent strategy in the future aerospace industry.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Natural Landing Simulations on Generated Local Rocky Terrains for Asteroid
           Cubic Lander

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      Authors: Xiangyuan Zeng;Tongge Wen;Ziwen Li;Kyle T. Alfriend;
      Pages: 3492 - 3508
      Abstract: Recent missions reveal that rubble-pile asteroids usually have a wide distribution of bare rocks in various scales. The dynamical evolution of a lander interacting with such rough surfaces is still an open problem. This article investigates the influence of the explicitly refined rocky terrains on the natural landing motion of a cuboid asteroid lander. The methodology for constructing the local terrains with centimeter-sized to meter-sized rocks is developed based on manipulating the original polyhedron shape model. Local rocky terrains refined with different-sized rocks (20 cm, 40 cm, 80c m, and 1 m) are generated. Moreover, hypothetical local terrains in different numbers of 1-m-sized rocks are presented to assess their influence on the landing motion. Numerical simulations are performed to characterize the dynamical behavior of the lander in rocky terrains. The distributions of the first and second touchdown positions, the transfer time, and the locomotion distance are taken as the three key indicators for examining the motion difference in these rocky terrains. The mechanism for the landing motion is analyzed by considering the collision slope. The results are expected to provide guidelines for the lander deployment and the path planning of a rover on rocky asteroids .
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Probe Dynamics Direct Control for Aerial Recovery With Preassigned Docking
           Performance

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      Authors: Zikang Su;Yiheng Liu;Honglun Wang;
      Pages: 3509 - 3523
      Abstract: Aiming at the probe docking control problem in aerial recovery, this article proposes a neural-adaptive probe dynamics direct control algorithm with preassigned docking performance for the unmanned aerial vehicle (UAV) to be recovered, even under multiple ambient airflow disturbances and initial docking deviations. The affine nonlinear dynamics of the probe in the inertial axis are formulated, together with the UAV's 6-DOF dynamics, for the convenience of the direct nonlinear docking control design. To compensate UAV's unmeasurable nonlinear dynamics with better approximation property and lower computational burden, the minimal learning parameter (MLP) technique based echo state network (ESN) approximators are constructed by employing the system state approximation errors to adaptively update neural weights learning. Then, to guarantee the preassigned docking performance required by the recovery safety, a finite-time prescribed performance control algorithm incorporated backstepping control law is developed to achieve the desired docking. Both the docking trajectory and forward docking velocity are not only always constrained within the preassigned performance constraints but also finely controlled to achieve accurate rendezvous with the target drogue. The closed-loop stability is discussed with Lyapunov analysis. Numerical simulations are conducted to validate the performance of the docking control algorithm.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Modeling and Control of Spacecraft with Multiple Active Pointing
           Ultra-Quiet Platforms

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      Authors: Liang Tang;Xiao Feng;Xin Guan;Renjian Hao;Youyi Wang;
      Pages: 3524 - 3537
      Abstract: Future high-resolution space-based astronomical observation and remote sensing require space telescope with long focal length or space interferometer with long baseline. In these systems, multiple payloads will be placed over a large spacecraft structure and work in coordination to fulfill the mission tasks. However, structure flexibility and various disturbances present challenges for precision control of the payloads. In this article, each payload is placed on an active pointing ultra-quiet platform for simultaneous steering and active/passive vibration isolation, and the associated modeling and control problems are addressed. First, dynamic equations are formulated for a flexible spacecraft with $N$ platforms. In these equations, relative motion variables are used for the platforms, so that the equations are simple yet suitable for control design and analysis. Then, two typical coordination schemes for the platforms are identified, and the corresponding control goals are defined. Finally, the controllers for both the schemes are designed based on the disturbance observer technique, and their performance, including steady-state disturbance rejection and transient-state agility, is evaluated via numerical simulation.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Nonfragile Quantitative Prescribed Performance Control of Waverider
           Vehicles With Actuator Saturation

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      Authors: Xiangwei Bu;Baoxu Jiang;Humin Lei;
      Pages: 3538 - 3548
      Abstract: The existing prescribed performance control (PPC) strategies exhibit the fragility and nonguarantee of the prescribed performance when they are applied to dynamic systems with actuator saturation, and moreover, all of them are unable to quantitatively design prescribed performance. This article aims at remedying those deficiencies by proposing a new nonfragile PPC method for waverider vehicles (WVs) such that the quantitative prescribed performance can be guaranteed for tracking errors in the presence of actuator saturation. First, readjusting performance functions are developed to achieve quantitative prescribed performance and prevent the fragile problem. Then, low-complexity fuzzy neural control protocols are presented for velocity subsystem and altitude subsystem of WVs, while there is no need of recursive back-stepping design. Furthermore, auxiliary systems are designed to generate effective compensations on control constraints, which contributes to the guarantee of the desired prescribed performance, being proved via Lyapunov synthese. Finally, compared simulation results are given to validate the superiority.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • DNCNet: Deep Radar Signal Denoising and Recognition

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      Authors: Mingyang Du;Ping Zhong;Xiaohao Cai;Daping Bi;
      Pages: 3549 - 3562
      Abstract: Deep learning with its rapid development and advancement has achieved unparalleled performance in many areas like computer vision as well as cognitive radio and signal recognition. However, the performance of most deep neural networks would suffer from degradation in the data mismatch scenario, e.g., the test dataset has a related but nonidentical distribution with the training dataset. Considering the noise corruption, a classifier’s accuracy might drop sharply when it is tested on a dataset with much lower signal-to-noise ratio compared to its training dataset. To address this dilemma, in this work, we propose an efficient denoising and classification network (DNCNet) for radar signals. The DNCNet consists of denoising and classification subnetworks. First, a radar signal detection and synthetic mechanism is designed to generate pairwise clean data and noisy data for the DNCNet to train its denoising subnetwork. Then, a two-phase training procedure is proposed to train the denoising subnetwork in the first phase and strengthen the mapping between the denoising results and perceptual representation in the second. Experiments on synthetic and benchmark datasets validate the excellent performance of the proposed DNCNet against state-of-the-art methods in terms of both signal restoration quality and classification accuracy.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Stiffness Mitigation in Stochastic Particle Flow Filters

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      Authors: Liyi Dai;Fred Daum;
      Pages: 3563 - 3577
      Abstract: The linear convex log-homotopy has been used in the derivation of particle flow filters. One natural question is whether it is beneficial to consider other forms of homotopy. We revisit this question by considering a general linear form of log-homotopy for which we derive particle flow filters, validate the distribution of flows, and obtain conditions for the stability of particle flows. We then formulate the problem of stiffness mitigation as an optimal control problem by minimizing the condition number of the Hessian matrix of the posterior density function. The optimal homotopy can be efficiently obtained by solving a 1-D second-order two-point boundary value problem. Compared with traditional matrix analysis based approaches to improving condition numbers, this approach explicitly exploits the special structure of the stochastic differential equations in particle flow filters. The effectiveness of the proposed approach is demonstrated by numerical examples.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Observability Criteron Guidance for Passive Towed Array Sonar Tracking

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      Authors: Tom Northardt;
      Pages: 3578 - 3585
      Abstract: Nonlinear sonar contact tracking always presents a significant observability challenge. Observability as it relates to sonar tracking is the metric used to determine if a state estimate is uniquely identifiable given a history of measurements. Poor observability is troublesome to all nonlinear tracking filters to varying degrees. Observability criteria are used to assess the degree of observability and many observability criteria require, in some way, an observer maneuver. But when observability criteria are evaluated with real data they are evaluated in the presence of “micromaneuvers” due to unmodeled forces. The issue associated with these micromaneuvers is that they satisfy, mathematically, observability criteria but hold little practical value for obtaining trustworthy state estimates. This article chooses a recent observability criterion and examines its utility for passive sonar tracking with a towed array. The analysis performed provides guidance to all similar observability criteria when applied to the passive sonar tracking with a towed array and implies such criteria will be most valuable in applications with minimal navigation perturbations.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Automatic Carrier Landing System With Fixed Time Control

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      Authors: Haibin Duan;Yang Yuan;Zhigang Zeng;
      Pages: 3586 - 3600
      Abstract: Automatic Carrier Landing System With Fixed Time Control
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • On Polarization, Combining, and Equalization in Aeronautical Mobile
           Telemetry

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      Authors: Farah Arabian;Michael Rice;
      Pages: 3601 - 3612
      Abstract: In this article, we explore the relationship between an equalizer and a combiner operating on the available polarization states of a received signal in aeronautical mobile telemetry. The maximum likelihood combiner is derived and shown to be equivalent to summing the outputs of two filters matched to the channels in the horizontal and vertical polarization states. For historical reasons, current systems combine right-hand and left-hand circularly polarized antenna feed outputs using a maximum ratio combiner. To compare the two combining approaches, the aeronautical telemetry multipath channel is extended to include polarization state information. The channel extension is used in computer simulations. The simulations results for SOQPSK-TG with a constant modulus algorithm equalizer show that the postequalizer bit error rate for the two approaches is the same.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Integrated Power, Attitude, and Vibration Control of Gyroelastic Body

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      Authors: Chuandong Guo;Quan Hu;Yao Zhang;Jun Zhang;Gongjun Li;
      Pages: 3613 - 3623
      Abstract: Gyroelastic body refers to a flexible structure with distributed angular momentum exchange devices, such as variable speeds control moment gyros (VSCMGs). A VSCMG contains a rotor with high rotating speeds. The direction and the magnitude of the rotor’s angular momentum can be simultaneously tuned.When distributing a set of VSCMGs on a flexible structure, they could simultaneously produce control torques for attitude control and modal forces for vibration suppression. Meanwhile, the high spinning rotor in the VSCMGs can be used for energy storage. Thus, an integrated power, attitude, and vibration control system (IPAVCS) for a free flexible structure can be obtained. In this work, the control scheme for the IPAVCS is developed. A nonlinear controller is first designed to calculate the desired attitude control torques and vibration suppression modal forces for attitude stabilization and vibration suppression. Then, a robust pseudoinverse gimbal steering law and a pseudoinverse rotor acceleration law are developed to generate the desired control input and meet the power requirement, respectively. Numerical examples are conducted to verify the effectiveness of the proposed control scheme.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • A Time–Frequency Representation Approach of Undersampled Signals With
           Multiple Periodic FM Components

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      Authors: Yuetao Ren;Yongfeng Zhi;Kai Feng;Huan Gao;Jun Zhang;
      Pages: 3624 - 3632
      Abstract: Periodic frequency-modulated (FM) interference signals, commonly employed by jammers and radars, may lead to the performance degradation or even failure of global navigation satellite systems and wireless communications. Time–frequency (TF) representations play an essential role in FM signal analysis and instantaneous frequency (IF) estimation, which is the basis of many nonstationary interference suppression algorithms. This article provides a TF representation approach for signals with multiple periodic FM components in the presence of sample loss. The proposed approach utilizes the periodicity and the sparsity of signal components in the TF domain to suppress cross-terms and artifacts. We reconstruct TF distributions of each component by time-averaging Wigner–Ville distribution. Then, the residual artifacts are eliminated by a low-complexity sparse-based adaptive directional TF filtering method. Simulation results confirm that the proposed approach provides an outstanding suppression of cross-terms and artifacts. The proposed TF representation approach can effectively improve the accuracy of the IF estimation of each signal component.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Distributed Confidentiality Fusion Estimation Against Eavesdroppers

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      Authors: Xinhao Yan;Yuchen Zhang;Daxing Xu;Bo Chen;
      Pages: 3633 - 3642
      Abstract: This article is concerned with the distributed confidentiality fusion estimation problem for cyber-physical systems in the presence of eavesdroppers. A novel active contamination strategy is proposed to guarantee the confidentiality of local state estimates (LSEs) that are transmitted to the fusion center (FC) over communication channels. Here, the LSEs are actively contaminated by the contaminating vectors, which are related to the weighting fusion process. Meanwhile, the selecting matrices that denote whether the components are contaminated are, respectively, designed for linear and nonlinear systems by maximizing the mean square errors of eavesdropper’s estimator. Under this contamination strategy, the confidentiality of systems can be effectively guaranteed when the eavesdropper tries to obtain the real state by fusing the contaminated estimates, because the estimation error covariance of the eavesdropper is large. At the same time, the corresponding compensation strategy is employed in the FC to compensate the performance loss caused by the proposed contamination method. Finally, two illustrative examples are exploited to demonstrate the effectiveness of the proposed methods.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Trajectory Approximation of a Solar Sail With Constant Pitch Angle and
           Optical Degradation

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      Authors: Lorenzo Niccolai;Alessandro A. Quarta;Giovanni Mengali;
      Pages: 3643 - 3649
      Abstract: The aim of this article is to analyze the 2-D heliocentric trajectory of a solar sail with constant attitude in the presence of reflective film optical degradation. The proposed procedure starts from the results obtained for a nondegrading flat sail, and taking into account the film optical degradation, obtains an analytical (although approximate) form of both the polar trajectory and the osculating orbit characteristics. In this context, the solar sail state vector is modeled through a set of nonsingular elements, and the heliocentric dynamics is analyzed with the aid of the perturbation theory, where the propulsive acceleration represents the (small) perturbative term. The soundness of the mathematical model is discussed for a propulsion system whose performance is consistent with the current solar sail technology.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Iterative Pose Estimation for a Planar Object Using Virtual Sphere

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      Authors: Cuicui Jiang;Qinglei Hu;
      Pages: 3650 - 3657
      Abstract: This article proposed an iterative pose estimation for the planar object to deal with the pose ambiguity in the Perspective n Points (PnP) problem. Specifically, by utilizing the unit virtual sphere, the PnP pose estimation problem can be performed as a minimization of the error function with three independent transitional parameters, referred to as the coupling position. Then, Levenberg–Marquardt (LM) optimization algorithm is applied to acquire the coupling position of the first local minimum. Furthermore, the coupling position is represented as the two Euler angles and the vector length, which are combined with the planar points to compute the second local minimum approximation as the initialization of the second LM algorithm. Consequently, once the global coupling position in the two local minimum is decided by the lower error, the orientation and position are directly decoupled by using the singular value decomposition. It is shown that the designed pose estimation is able to achieve prescribed performance for locating and distinguishing two local minimum, and meanwhile guarantee the superior computation behavior under the pose ambiguity for the planar object. Finally, numerical simulation and physical experiment are conducted to validate the effectiveness of the proposed method, compared with the state-of-the-art PnP methods.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • High-Accuracy DOA Estimation Algorithm at Low SNR Through Exploiting a
           Supervised Index

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      Authors: Kaijie Xu;Mengdao Xing;Rui Zhang;Hanyu E;Minghui Sha;Weike Nie;Yinghui Quan;
      Pages: 3658 - 3665
      Abstract: Performance of direction of arrival (DOA) estimation is one of the most important issues in array signal processing. Subspace-based algorithms provide a good compromise between the estimation accuracy and computational complexity. However, these methods are exposed to performance breakdown at low SNR scenarios. A major reason for such performance breakdown is the subspace swap phenomenon (intersubspace leakage). In this article, we elaborate on a novel modified signal subspace model through exploiting a supervised index for the estimation of DOA. With the developed model we refine the signal subspace so as to enhance the performance of the DOA estimation. In the proposed scheme, we define a fuzzy similarity matrix for the eigenvalues of the array output correlation matrix to capture the distribution of the eigenvalues. Then, we build up a transformation matrix between the fuzzy similarity matrix and the eigenspace of the correlation matrix, and construct a nonlinear transformation function to adjust the fuzzy similarity matrix. Subsequently, we define a supervised evaluation index named signal subspace reconstruction error for DOA estimation and construct a cost function of the signal subspace to develop a supervised model for the signal subspace. The signal subspace can be modified through adjusting the parameter in the nonlinear transformation function and optimizing the abovementioned cost function. Finally, the performance of DOA estimation can be enhanced with the modified signal subspace. The main characteristic of the proposed model is circularly applied feedback of the estimated DOA for refining the estimated subspace. It is a closed loop and supervised method not reported before. This article opens a specific way for improving the performance of the DOA estimation in array signal processing by a supervised index. However, the proposed method is still unsatisfying in some scopes of signal-to-noise ratio. We believe that exploiting a validity index for DOA e-timation in array signal processing is still a general and interesting problem.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • An IGGM-Based Poisson Multi-Bernoulli Filter and its Application to
           Distributed Multisensor Fusion

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      Authors: Guchong Li;
      Pages: 3666 - 3677
      Abstract: This article proposes a joint estimate approach in terms of target states and target cardinality as well as detection probability based on the Poisson multi-Bernoulli (PMB) filter. For the situations, where the detection probability is unknown or unreliable, the usual tracking methods often fail to work, so online estimation of the detection probability is indispensable.To depict the unknown detection probability, an inverse gamma Gaussian mixture (IGGM) implementation is adopted to propagate nonnegative features, including signal amplitude and signal-to-noise ratio (SNR). The IGGM-based PMB filter, abbreviated as IGGM-PMB, is proposed to solve the multitarget tracking (MTT) along with the unknown and time-varying detection profile. Specifically, the Poisson random finite set (RFS) intensity is approximated as an IGGM, while the density of Bernoulli RFS is approximated as a single inverse gamma Gaussian component (IGGC). Then, the proposed IGGM-PMB filter is applied to distributed multisensor fusion, wherein the estimated detection probabilities are used as a choice of the fusion ordering. Simulation results demonstrate the effectiveness and superiority of the proposed approach via comparisons with state-of-the-art approaches.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Improvement of a Sample Clock Offset Estimation Method Used in Passive
           Radar

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      Authors: Stephen Searle;Kutluyil Doğançay;
      Pages: 3678 - 3685
      Abstract: Sample clock offset must be estimated in order to correctly demodulate an OFDM signal. Estimates are also required in passive radar processing, to produce a reference signal, which is properly matched to the transmission. A recently proposed clock offset estimation method for passive radar is found to be overly sensitive to measurement noise. However, the radar ambiguity surface is found to be unaffected by the specific errors engendered by this noise. The reasons for this are explored. An updated method based on state-space modeling and Kalman smoothing is proposed. This is found to restore clock offset estimation performance in cases of higher noise, achieving this with low processing latency. These improvements enable the method to be employed for other applications requiring high quality, time-critical clock offset estimation.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Nonsingular Fixed-Time Tracking Guidance for Mars Aerocapture With Neural
           Compensation

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      Authors: Qijia Yao;Hongwei Han;Dong Qiao;
      Pages: 3686 - 3696
      Abstract: Mars aerocapture is one of the most concerned technologies for future Mars sample-return and manned exploration missions. This article investigates the challenging problem of the reference trajectory tracking guidance for Mars aerocapture under uncertainties. Based on an integral sliding surface, a fixed-time neural adaptive tracking guidance law is synthesized by incorporating the neural network (NN) approximation into the fixed-time integral sliding mode control approach. Benefiting from the integral sliding surface design, the proposed tracking guidance law has no singularity problem inherently existing in terminal sliding mode control. By adopting the NN approximation to compensate for the lumped uncertain term in the feedforward loop, the proposed tracking guidance law is strongly robust against aerodynamic coefficient uncertainties and atmospheric density uncertainty. Stability analysis shows that the radial distance tracking error and its time derivative can stabilize to the small neighborhoods around the origin in fixed time under the proposed tracking guidance law. Finally, the effectiveness and advantages of the proposed tracking guidance law are illustrated through simulations and comparisons.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Asymptotic Performance Analysis of Distributed Non-Bayesian Quickest
           Change Detection With Energy Harvesting Sensors

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      Authors: Sinchan Biswas;Subhrakanti Dey;
      Pages: 3697 - 3707
      Abstract: This article focuses on the distributed non-Bayesian quickest change detection based on the cumulative sum (CUSUM) algorithm in an energy harvesting wireless sensor network, where the distributions before and after the change point are assumed to be known. Each sensor is powered by randomly available harvested energy from the surroundings. It samples the observation signal and computes the log-likelihood ratios (LLRs) of the aforementioned two distributions if enough energy is available in its battery for sensing and processing the sample ($E_{s}$). Otherwise, the sensor decides to abstain from the sensing process during that time slot and waits until it accumulates enough energy to perform the sensing and processing of a sample. This LLR is used for performing the CUSUM test to arrive at local decisions about the change point, which are then combined at the fusion center (FC) by a predecided fusion rule to arrive at a global decision. In this article, we derive the asymptotic expressions (as the average time to a false alarm goes to infinity) for the expected detection delay and the expected time to a false alarm at the FC for three common fusion rules, namely, or, and, and $r$ out of $N$ majority rule, respectively, by considering the scenario, where the average harvested energy at each sensor is greater than the energy required for sensing and processing a sample $E_{s}$. To this end, we use the theory of order statistics and the asymptotic distribution of the first passage times of the local decisions. Numerical results are also provided to support the theoretical claims.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • $mathcal+{L}{}_{1}$ +Adaptive+Path-Following+of+Small+Fixed-Wing+Unmanned+Aerial+Vehicles+in+Wind&rft.title=IEEE+Transactions+on+Aerospace+and+Electronic+Systems&rft.issn=0018-9251&rft.date=2022&rft.volume=58&rft.spage=3708&rft.epage=3716&rft.aulast=Souanef;&rft.aufirst=Toufik&rft.au=Toufik+Souanef;">$mathcal {L}{}_{1}$ Adaptive Path-Following of Small Fixed-Wing Unmanned
           Aerial Vehicles in Wind

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      Authors: Toufik Souanef;
      Pages: 3708 - 3716
      Abstract: This article proposes an adaptive path-following controller of small fixed-wing unmanned aerial vehicles (UAVs) in the presence of wind disturbances, which explicitly considers that wind speed is time-varying. The main idea was to formulate UAVs path-following as control design for systems with parametric uncertainties and external disturbances. Assuming that there is no prior information on wind, the proposed solution is based on the $mathcal {L}{}_{1}$ adaptive control, using linearized model dynamics. This approach makes clear statements for performance specifications of the controller and relaxes the common constant wind velocity assumption. This makes the design more realistic and the analysis more rigorous, because in practice wind is usually time varying (windshear, turbulence, and gusting). The path-following controller was demonstrated in flight under wind speed up to $10 text{ m/s}$, representing 50% of the nominal UAV airspeed.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Refracting RIS-Aided Hybrid Satellite-Terrestrial Relay Networks: Joint
           Beamforming Design and Optimization

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      Authors: Zhi Lin;Hehao Niu;Kang An;Yong Wang;Gan Zheng;Symeon Chatzinotas;Yihua Hu;
      Pages: 3717 - 3724
      Abstract: Reconfigurable intelligent surface (RIS) has been viewed as a promising solution in constructing reconfigurable radio environment of the propagation channel and boosting the received signal power by smartly coordinating the passive elements’ phase shifts at the RIS. Inspired by this emerging technique, this article focuses on joint beamforming design and optimization for RIS-aided hybrid satellite-terrestrial relay networks, where the links from the satellite and base station (BS) to multiple users are blocked. Specifically, a refracting RIS cooperates with a BS, where the latter operates as a half-duplex decode-and-forward relay, in order to strengthen the desired satellite signals at the blocked users. Considering the limited onboard power resource, the design objective is to minimize the total transmit power of both the satellite and BS while guaranteeing the rate requirements of users. Since the optimized beamforming weight vectors at the satellite and BS, and phase shifters at the RIS are coupled, leading to a mathematically intractable optimization problem, we propose an alternating optimization scheme by utilizing singular value decomposition and uplink–downlink duality to optimize beamforming weight vectors, and using Taylor expansion and penalty function methods to optimize phase shifters iteratively. Finally, simulation results are provided to verify the superiority of the proposed scheme compared to the benchmark schemes.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Joint STO and DFO Estimation for SEFDM in Low-Earth-Orbit Satellite
           Communications

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      Authors: Xiaohu Liang;Hehao Niu;Aijun Liu;Zhixiang Gao;Yunyang Zhang;
      Pages: 3725 - 3729
      Abstract: In this article, a joint symbol timing offset (STO) and Doppler frequency offset (DFO) estimation algorithm is proposed for spectrally efficient frequency division multiplexing (SEFDM) system in the downlink of low-earth-orbit (LEO) satellite communications. Considering the nonorthogonality of SEFDM, the proposed algorithm is derived by maximizing likelihood function. To reduce computation complexity of STO estimator, all unnecessary terms in likelihood function are ignored. Further, the proposed CFO estimator is simplified by replacing the inverse trigonometric function with polynomial approximation. According to relevant standards issued by the International Telecommunications Union and the 3rd Generation Partnership Project, simulation parameters are set to evaluate the estimation performance. Simulation results show that the proposed algorithm is robust to different packing factors of SEFDM, and outperforms traditional estimation methods.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • LEO Satellite Networks: When Do All Shortest Distance Paths Belong to
           Minimum Hop Path Set'

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      Authors: Quan Chen;Lei Yang;Deke Guo;Bangbang Ren;Jianming Guo;Xiaoqian Chen;
      Pages: 3730 - 3734
      Abstract: A low Earth orbit (LEO) satellite constellationnetwork (SCN) has become a promising solution for nonterrestrial networks. In LEO-SCNs, the shortest distance path (SDP) and the minimum hop path (MHP) are two types of important paths. This letter focuses on the proposition that all the SDPs belong to the MHP set and studies the conditions when the proposition holds or not. Based on the topological regularity and link distance variation patterns, this letter proves several simplified equivalent propositions and derives a discriminant function to judge if the proposition holds in an arbitrary constellation. Simulations verify the judging method and find that all the SDPs belong to the MHP set in constellations with small inclinations (less than 68$^circ$) or large phasing offsets. The propositions can help to simplify the calculation of the SDP.
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
  • Corrections to “Robust Modeling of GNSS Tropospheric Delay
           Dynamics”

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      Authors: Elisa Gallon;Mathieu Joerger;Boris Pervan;
      Pages: 3735 - 3739
      PubDate: Aug. 2022
      Issue No: Vol. 58, No. 4 (2022)
       
 
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