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IEEE Transactions on Aerospace and Electronic Systems
Journal Prestige (SJR): 0.611
Citation Impact (citeScore): 3
Number of Followers: 374  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0018-9251
Published by IEEE Homepage  [229 journals]
  • IEEE Aerospace and Electronic Systems Society
    • Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • HRRP Clutter Rejection Via One-Class Classifier With Hausdorff Distance
    • Pages: 2517 - 2526
      Abstract: Lots of detectors for high resolution range profile (HRRP) data are mainly based on the intensities of target echoes. When the intensities of outliers are as large as those of targets of interest, some false alarms will emerge during the detection stage. In this article, we propose a rejection algorithm for HRRP data between the detection stage and recognition stage to eliminate the false alarms occurring during the detection stage. In this method, the intensities and positions of the dominant scatterers are extracted as a joint feature. Then, the feature is used to develop the K-center one-class classifier based on Hausdorff distance. Experimental results on the measured HRRP data indicate that the proposed rejection algorithm can eliminate the false alarms remarkably well, and keep most of the target data as well. Meanwhile, the proposed method has better performance under different values of signal-to-noise ratio and different values of parameters than some other rejection methods.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Entry Trajectory Optimization With Virtual Motion Camouflage Principle
    • Pages: 2527 - 2536
      Abstract: This article proposes a bio-inspired algorithm called virtual motion camouflage (VMC) to reduce the dimension and computational cost of entry trajectory optimization problem for the reusable launch vehicle. In the VMC framework, the trajectory to be planned can be obtained by predefining the virtual prey motion according to the boundary conditions, then optimizing the reference point and path control parameters using sequential quadratic programming algorithm. Compared with Gauss pseudospectral method, due to the proposed approach reduce the number of discrete points and the equality constraints of the optimization model, it can improve the convergence speed and reduce computational cost effectively. Two minimum time entry examples, without and with no-fly-zone constraints, are presented to demonstrate the effectiveness of the proposed approach.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Electro-Mechanical-Thermal Performance and Stability of Aircraft Energy
           Networks With Pulse Power Loads
    • Pages: 2537 - 2547
      Abstract: Modern aircraft have an increasing need for pulse power loads which includes new weapon technologies and advanced avionics. These pulse power loads have thermal properties that couple to the electrical system and can lead to nonlinear destabilizing effects at low and high temperatures. These nonlinear electrical stability issues carry through to the mechanical and thermal systems of the aircraft and can damage components. The load is characterized by its duty cycle, period, and power level. For a given pulse load, the system is defined as metastable if there is a nonlinear limit cycle that remains bounded within the defined bus voltage limits. Regions of stability, metastability, marginal metastability, and instability are determined based on bus voltage transient tolerances. In this article a reduced-order nonlinear model of an aircraft's coupled electrical-mechanical-thermal (EMT) system is used to demonstrate the stability, metastability, and performance caused by the pulse load coupled with the EMT system.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Generalized Multifrequency GPS Carrier Tracking Architecture: Design and
           Performance Analysis
    • Pages: 2548 - 2563
      Abstract: This article presents a generalized multifrequency carrier tracking architecture applicable to multifrequency global navigation satellite system receivers operating in frequency-selective fading environments. This architecture unifies a conventional single-frequency-independent tracking (ST) mode, which only operates on measurements from a single carrier, a multifrequency joint tracking (JT) mode, which linearly combines measurements from multiple carriers, and a multifrequency optimal tracking (OT) mode, which incorporates signal intensity in multicarrier combinations via an aggregate Kalman filter. The analytical closed-form expressions of the tracking error variance for the ST, JT, and OT modes are derived for theoretical analysis and comparison. Their tracking performances are evaluated and quantified using a simulated triple-frequency GPS signal with varying combinations of signal strengths. To have a fair assessment in real-world scenarios, real data collected during strong ionospheric, tropospheric scintillations, and multipath reflections and scattering are also used for performance evaluations in ST, JT, and OT modes.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Expanding Window Dynamic-Programming-Based Track-Before-Detect With Order
           Statistics in Weibull Distributed Clutter
    • Pages: 2564 - 2575
      Abstract: This article considers radar detection and tracking of weak fluctuating targets using dynamic programming (DP)-based track-before-detect (TBD). The clutter is modeled using a Weibull distribution, and the well-known Swerling type 0, 1, and 3 targets are considered. An efficient algorithm is proposed, which employs order statistics in DP-based TBD to detect weak fluctuating targets. In addition, a novel expanding window track-before-detect (EW-TBD) technique for multiframe processing is presented to improve the detection performance with reasonable computational complexity compared to batch processing. It is shown that EW-TBD has lower complexity than existing multiframe processing techniques. Simulation results are presented, which confirm the superiority of the proposed expanding window technique in detecting targets even when they are not present in every scan in the window. In addition, the throughput of the proposed technique is higher than that with batch processing.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Moving Path Following With Prescribed Performance and Its Application on
           Automatic Carrier Landing
    • Pages: 2576 - 2590
      Abstract: This article studies the moving path following (MPF) problem where a desired path attached to a moving object must be followed. Focusing on the problem that the classical guidance vector field is not suitable for an MPF, we present a time-varying vector field guidance law, which is qualified for following a path expressed with respect to a moving target frame. Moreover, a prescribed performance method is embedded to the time-varying vector field law to further enhance the control performance. By combining the prescribed performance, the tracking errors are ensured not to exceed the predefined arbitrary small residual sets. Subsequently, the proposed guidance laws are applied to a typical MPF mission - the automatic carrier landing. An active disturbance rejection attitude controller is designed as the “low-level” controller with backstepping as the main frame. To eliminate the potential problem of external disturbances and parameter uncertainties, extended state observers are adopted in the controller. Besides, tracking differentiators are integrated with the controller to avoid complex derivative calculations in backstepping. Finally, comparative simulations are conducted, the results clarify and verify the proposed methods.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Learning Target Dynamics While Tracking Using Gaussian Processes
    • Pages: 2591 - 2602
      Abstract: Tracked targets often exhibit common behaviors due to influences from the surrounding environment, such as wind or obstacles, which are usually modeled as noise. Here, these influences are modeled using sparse Gaussian processes that are learned online together with the state inference using an extended Kalman filter. The method can also be applied to time-varying influences and identify simple dynamic systems. The method is evaluated with promising results in a simulation and a real-world application.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Optimal Predictive Inference and Noncoherent CFAR Detectors
    • Pages: 2603 - 2615
      Abstract: A Bayesian predictive inference approach, for the development of classical sliding window detection processes, is the focus of this article. It will be demonstrated that this methodology can produce such detectors with the constant false alarm rate (CFAR) property for clutter modeled by statistics, which are invariant with respect to a group of scale and power transformations. For such a clutter model, it will be shown that the derived detector achieves optimality in the sense of strong consistency. This implies that the Bayesian CFAR detector will have the best performance, in the class of CFAR detectors, for this specific clutter distribution. Although these Bayesian detectors are produced under the assumption of homogeneous clutter, they nonetheless provide the practical engineer with a benchmark on potential CFAR performance. To illustrate the results, the optimal CFAR detector for the Weibull-distributed clutter is derived. Although the Pareto Type I clutter model fits into the class of scale- and power-invariant distributions, there is complexity in the derivation of the Bayesian decision rule. Hence, this special case is also examined, and it will be shown that the Bayesian CFAR corresponds to a well-known detector for this clutter environment.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • High-Capacity FPGA Router for Satellite Backbone Network
    • Pages: 2616 - 2627
      Abstract: Satellite backbone networks provide a viable means of establishing broadband connectivity for remote, sparsely populated areas. In addition, satellite communication systems are well suited for airborne, maritime, and disaster relief environments. Technologies for links are continuing to improve in performance and power efficiency, making onboard regeneration and routing feasible within spacecraft power envelope. In this article, we implement and analyze a spaceborne router design integrated on a field-programmable gate array (FPGA). FPGA provides a flexibility needed to circumvent space radiation effects on chip circuitry, as they can be reconfigured at runtime. We explored scalability of the high-end state-of-the art FPGA chip family, and its ability to support high bit-rate satellite links: 10 Gbps satellite-to-ground links and 100 Gbps intersatellite links. Through implementation and testing, we confirm that the current FPGA technology can support space routers with very high data throughput.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Understandings of Classical and Incremental Backstepping Controllers With
           Model Uncertainties
    • Pages: 2628 - 2641
      Abstract: This article suggests closed-loop analysis results for both classical and incremental backstepping controllers considering model uncertainties. First, transfer functions with each control algorithm under the model uncertainties, are compared with the ones for the nominal case. The effects of the model uncertainties on the closed-loop systems are critically assessed via investigations on stability conditions and performance metrics. Second, closed-loop characteristics with classical and incremental backstepping controllers under the model uncertainties are directly compared using derived common metrics from their transfer functions. This comparative study clarifies how the effects of the model uncertainties on the closed-loop system become different depending on the applied control algorithm. It also enables an understanding of the effects of additional measurements in the incremental algorithm. Third, case studies are conducted assuming that the uncertainty exists only in one aerodynamic derivative estimate while the other estimates have true values. This facilitates systematic interpretations on the impacts of the uncertainty on the specific aerodynamic derivative estimate to the closed-loop system.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Fast Generation of Optimal Asteroid Landing Trajectories Using Deep Neural
           Networks
    • Pages: 2642 - 2655
      Abstract: To improve the autonomy and reliability of asteroid landings, an intelligent approach to fast and reliable generation of optimal landing trajectories is proposed. Unfortunately, the indirect methods require good initial guesses for shootings. To address this issue, deep neural networks (DNNs) are developed to approximate the costates of the indirect methods and supply good initial solutions to achieve high success rate of shootings. This article focuses on the following three contributions. First, the original asteroid landing problems are connected with two-dimensional (2-D) asteroid-free transfer problems using model continuation and state transformation techniques. Second, DNNs are developed and optimized to approximate the costates of the 2-D transfers with high accuracy. Third, a systematical solution for asteroid landing trajectory optimization is developed, wherein the DNNs provide good initial solutions, and the accurate solutions for landings are obtained through a solution continuation process. Additionally, an alternative solution supplying strategy based on error statistics of DNN approximation is presented to take over the solution supplying when the predictions of DNNs fail to converge to the optima. Evaluations of the DNNs for solution supplying and simulations of landings on 433 Eros and 101955 Bennu are given to substantiate the effectiveness of the proposed techniques and demonstrate the performance of the developed algorithm.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • A Gaussian Uniform Mixture Model for Robust Kalman Filtering
    • Pages: 2656 - 2665
      Abstract: This article presents a Kalman-type recursive estimator for discrete-time systems with a measurement noise modeled by a Gaussian-uniform mixture. The objective is to deal with data containing outliers that degrade the performance of the regular Kalman filter. The proposed non-Gaussian noise model takes into account the reliability of the measurement with respect to erroneous data. The Kalman-type estimator is based on Masreliez's formulation which copes with non-Gaussian noise models. Results in different simulated conditions are displayed to evaluate the performance of the newly-presented algorithm and to compare it to state-of-art alternatives.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • A Novel Low-Cost TMR-Without-Voter Based HIS-Insensitive and MNU-Tolerant
           Latch Design for Aerospace Applications
    • Pages: 2666 - 2676
      Abstract: With complementary metal oxide semiconductor (CMOS) technology scaling down, radiation induced multiple-node upsets (MNUs) that include double-node-upsets and triple-node upsets (TNUs) are becoming more and more an issue in storage cells used for applications constrained by their environment, such as aerospace applications confronted to radiations. This article presents a novel triple-modular redundancy without voter based high-impedance state (HIS) insensitive and MNU-tolerant latch design, namely TMHIMNT, to ensure both high reliability and low cost. The TMHIMNT latch mainly comprises triple clock-gating (CG) based dual-interlocked-storage-cells (DICEs) and four inverters. Through three internal inverters, the values stored in DICEs converge to a common node feeding an output-level inverter, enabling the TMHIMNT latch to tolerate any possible MNU. Simulation results demonstrate the MNU tolerance of the proposed TMHIMNT latch. Due to the disuse of C-elements, the proposed TMHIMNT latch is insensitive to the HIS, making the latch more reliable for aerospace applications. Moreover, compared with the state-of-the-art TNU hardened latch, due to the use of a high-speed path, CG technologies, and fewer transistors, the proposed TMHIMNT latch can achieve 98% delay, 17% power, and 29% area reductions, respectively.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Observability-Based Navigation Using Optical and Radiometric Measurements
           for Asteroid Proximity
    • Pages: 2677 - 2688
      Abstract: In this article, to improve navigation performance, observability-based navigation using optical and radiometric measurements for asteroid approach phase is proposed in tandem with the optimization of the configuration of spacecraft formation. By introducing the relative range and range-rate between spacecraft measured by radiometric sensors, the position and velocity of the two spacecraft are estimated, and the estimation performance degradation at the end of asteroid approach phase is reduced. A better observability of the integrated navigation system has been proven based on a novel geometry measurement model. Furthermore, a configuration optimization method is developed based on the lower bound of the Cramer-Rao inequality and the observability degree of the navigation system. By optimizing the configuration of spacecraft formation, the observability and estimation accuracy of the navigation system have been improved. Three cases of different configurations of spacecraft formation are established for numerical simulation, demonstrating the improvement in the accuracy of the navigation method.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Cooperative Relative UAV Attitude Estimation Using DoA and RF Polarization
    • Pages: 2689 - 2700
      Abstract: Relative unmanned aerial vehicle attitude is estimated using only on-board radio-frequency signaling. The method uses a direction-of-arrival (DoA) vector estimate to determine two degrees-of-freedom (DoFs), a polarimetric narrowband multiple-input multiple-output (MIMO) channel estimate to specify the third DoF to within a $180^circ$ ambiguity, and one of the several potential methods for ambiguity resolution. Simulation results demonstrate that the method accurately determines aircraft attitude, with errors proportional to DoA and MIMO channel estimate errors. This approach is useful for cooperative navigation when external navigation aids are not available, such as in GPS-denied environments.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Energy-Optimal Waypoint-Following Guidance Considering Autopilot Dynamics
    • Pages: 2701 - 2717
      Abstract: This article addresses the problem of energy-optimal waypoint-following guidance for an unmanned aerial vehicle, considering a general autopilot dynamics model. The proposed guidance law is derived as a solution of a linear-quadratic optimal control problem in conjunction with a linearized kinematics model. The algorithm developed integrates path planning and path following into a single step, and can be applied to a general waypoint-following mission. Theoretical analysis reveals that previously suggested optimal point-to-point guidance laws are special cases of the proposed approach. Nonlinear numerical simulations clearly demonstrate the effectiveness of the proposed formulations.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Performance Analysis of Integrated Satellite-Terrestrial Multiantenna
           Relay Networks With Multiuser Scheduling
    • Pages: 2718 - 2731
      Abstract: In this article, we investigate the performance of a multiuser integrated satellite-terrestrial relay network (ISTRN) with the threshold-based decode-and-forward protocol, where the satellite-relay link undergoes shadowed-Rician (SR) fading, while the relay-user links experience Nakagami-m fading. We first formulate a constrained optimization problem with an objective to maximize the system capacity in order to determine the beamforming weight vectors at the relay and thereby develop two multiuser scheduling schemes, namely, best user scheduling and user fairness scheduling. Then, we present a closed-form expression for the probability density function (PDF) of the square sum of independent and identically distributed SR random variables, which is more accurate and concise than the existing solutions. Based on the new PDF results, we derive closed-form expressions for the outage probability (OP) and ergodic capacity of the considered network using the two scheduling schemes. Furthermore, the asymptotic OP expressions at high signal-to-noise ratio are also deduced to reveal the asymptotic behavior of the considered ISTRN. Finally, simulation results are provided to validate our theoretical analysis and show the impact of various parameters on the system performance.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • One-Bit LFMCW Radar: Spectrum Analysis and Target Detection
    • Pages: 2732 - 2750
      Abstract: One-bit radar, performing signal sampling and quantization by a 1-bit analog-to-digital converter, is a promising technology for many civilian applications due to its low-cost and low-power consumptions. In this article, problems encountered by a 1-bit linear-frequency-modulated continuous-wave (LFMCW) radar are studied, and a two-stage target detection method termed as the dimension-reduced generalized approximate message passing (DR-GAMP) approach is proposed. First, the spectrum of 1-bit quantized signals in a scenario with multiple targets is analyzed. It is indicated that high-order harmonics may result in false alarms and cannot be neglected. Second, based on the spectrum analysis, the DR-GAMP approach is proposed to carry out target detection. Specifically, linear preprocessing methods and target predetection are first adopted to perform the dimension reduction, and then, the generalized approximate message passing algorithm is utilized to suppress high-order harmonics and recover true targets. Finally, numerical simulations are conducted to evaluate the performance of the 1-bit LFMCW radar under typical parameters. It is shown that compared to the conventional radar applying linear processing methods, the 1-bit LFMCW radar has about 1.3-dB performance gain when the input signal-to-noise ratios of targets are low. In the presence of a strong target, it has about 1.0-dB performance loss.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Receding Horizon Scheduling of On-Demand Urban Air Mobility With
           Heterogeneous Fleet
    • Pages: 2751 - 2761
      Abstract: Mobility on demand (MoD) is a new paradigm of personal mobility that responds to passengers' demands in real time, and urban air mobility (UAM) is an area of MoD enabled by advances in electric vertical take-off and landing aircraft. This demand-responsive nature of MoD poses a challenge for optimally scheduling vehicles, and it has attracted much attention in recent years. However, there is a lack of research in the MoD scheduling literature: a homogeneous fleet is assumed, but it is not necessarily true all the time. Hence, this article proposes a novel formulation of the scheduling problem for UAM with a heterogeneous fleet and presents particle swarm optimization and a genetic algorithm that utilize a greedy algorithm to keep solutions feasible. The proposed algorithms are implemented with a model-predictive control scheme to effectively manage the demand-responsive nature. As a result, the proposed algorithms can find a near-optimal solution in a short time. Using the algorithms, a numerical experiment with six different fleet mixes is conducted, and impacts of fleet heterogeneity are analyzed. As a result, it is shown that the fleet heterogeneity affects both the quality of service and operational efficiency, and there is a tradeoff: the more vehicles and seats, the better the service, but the less efficient it is.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Fast Optimization Algorithm for Evanescent-Mode Cavity Tuner Optimization
           and Timing Reduction in Software-Defined Radar Implementation
    • Pages: 2762 - 2778
      Abstract: Dynamic spectrum allocation will require cognitive radar transmitters to change operating frequency and bandwidth in real time. This will require high-power reconfigurable circuitry to improve radar performance by simultaneously increasing 1) the output power of the transmit waveform and 2) the power-added efficiency of the power amplifier. This circuitry is also used to mitigate cochannel interference by maintaining sufficiently linear performance so that the output waveform conforms to a given spectral mask. In this approach, a 90-W evanescent-mode cavity tuner is reconfigured using a specially designed gradient search to find the best combination of resonant cavity position numbers. This approach will be much more flexible for field use than typical Smith-chart-based load-pull searches, which require a characterization that is susceptible to drift. Experimental results are presented showing that the efficiency, output power, spectral performance, and estimated maximum radar detection range are improved significantly by retuning the matching network at each operating frequency. Additionally, this article discusses innovations to reduce or eliminate time bottlenecks in a cognitive radar system for impedance tuning, reducing the time needed for complete impedance tuning searches from minutes to seconds. This significant timing reduction makes tunable power amplifiers a feasible option for future use in spectrum sharing by cognitive radar systems.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Hose-Drum-Unit Modeling and Control for Probe-and-Drogue Autonomous Aerial
           Refueling
    • Pages: 2779 - 2791
      Abstract: Probe-and-drogue aerial refueling has been widely adopted because of its flexibility, but the drogue is susceptible to wind disturbances, especially the receiver forebody bow wave disturbance and the excessive contact on the drogue. The docking process must be accurate, and a submeter error may result in failure. Thus, it is important for the docking task to understand the dynamics of the drogue under wind disturbances and improve safety after excessive contact happens. In this article, based on the previous work on drogue dynamic modeling, an improved integrated model is proposed by adding the hose-drum unit to describe the behavior of the drogue under wind disturbances more accurately. For the convenience of docking controller design of the receiver aircraft, the simplified drogue dynamic model with the hose-drum unit is obtained through system identification. Finally, to avoid the hose whipping phenomenon after excessive contact on the drogue, a control method is proposed to monitor the state of the hose and control the hose length to stabilize the drogue movement. Simulations and comparisons indicate that the motion of the drogue generated by the proposed modeling method is in good agreement with the real experimental results, and the proposed control method can significantly reduce the effect of the hose whipping phenomenon and improve the safety of probe-and-drogue aerial refueling systems.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Active Fault-Tolerant Control With Imperfect Fault Detection Information:
           Applications to UAVs
    • Pages: 2792 - 2805
      Abstract: A major issue in active fault-tolerant control (FTC) is having to rely on uncertain information provided by the fault detection and identification (FDI) algorithm. To achieve a reliable FTC, the controller needs to be robust against FDI uncertainties, namely missed “small” faults and fault detection delays. In this article, the FDI system only needs to indicate which actuator is faulty after a predefined amount of time, but does not need to estimate the actuator fault value or its faulty position. The goal is to design a FTC, which is robust against potentially undetected “small” actuator faults and which guarantees boundedness of the unstable poles for all possible actuator fault types. An adapted μ analysis is developed to analyze the unstable system poles, due to the presence of a fault. It is integrated within a DK-iteration approach to synthesize a controller in a robust control framework with H∞-design objectives. The synthesis is shown on a fixed-wing UAV, where fault-tolerance against single-actuator faults is achieved. Real flight experiments of a UAV with aileron and flap faults show the validity of the approach.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • High Resolution FDMA MIMO Radar
    • Pages: 2806 - 2822
      Abstract: Traditional multiple-input multiple-output (MIMO) radars, which transmit orthogonal coded waveforms, suffer from range–azimuth resolution tradeoff. In this article, we adopt a frequency division multiple access (FDMA) approach that breaks this conflict. We combine narrow individual bandwidth for high azimuth resolution and large overall total bandwidth for high range resolution. We process all channels jointly to overcome the FDMA range resolution limitation to a single bandwidth, and address range–azimuth coupling using a random array configuration.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Modeling and Control of a Tilting Quadcopter
    • Pages: 2823 - 2834
      Abstract: This article addresses modeling and tracking control for a tilting quadcopter in the presence of parametric uncertainties and external disturbances. We propose the novel concept of a tilting quadcopter, which suggests that the rotational and translational movements can be controlled independently. A complete dynamic model is developed, where parametric uncertainties and external disturbances are taken into consideration. Then, an adaptive fast finite-time control is proposed to provide robust, chattering-free, and fast convergence tracking performances. All the tracking errors can fast converge into arbitrary small neighborhoods around the origin in finite-time proved by a modified Lyapunov finite-time stability theory, and an adaptive scheme is synthesized to compensate for the effect of uncertainties. Finally, comparative simulations are carried out to illustrate the effectiveness and the robustness of the proposed controller.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Range-Doppler Sidelobe Suppression for Pulse-Diverse Waveforms
    • Pages: 2835 - 2849
      Abstract: Waveform diversity, which can be used to obtain synthetic bandwidth or mitigate range ambiguity, interference, and folded clutters, has attracted a great deal of attention in recent years. However, the range sidelobe modulation effect between agile pulses yields high range-Doppler sidelobes in pulse-Doppler (PD) radar applications, because of which traditional window functions or mismatched filters (MMFs) do not apply. In this article, a Doppler-tuned matched filter is used to equivalently obtain the PD result. Then, to mitigate the high range-Doppler sidelobes, a two-dimensional MMF (2-D MMF) is proposed, and the relevant signal-to-noise ratio (SNR) loss is deduced. A cyclic algorithm is also designed to calculate the 2-D MMF for suppressing sidelobes over desired range-Doppler regions with constrained SNR loss and mainlobe width. Several simulations and an experiment based on real measured data of an airborne platform are conducted to illustrate the effectiveness of the proposed 2-D MMF.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Interference Environment Model Recognition for Robust Adaptive Detection
    • Pages: 2850 - 2861
      Abstract: The recognition of the interference environment for adaptive radar detection is addressed in this article. Typically, detectors are designed in one specific scenario which may not be appropriate for the varying interference environment, especially for the airborne and space-based radar system. In this article, the considered recognition task is cast in terms of multiple hypothesis tests and the theory of model order selection (MOS) techniques are exploited to devise suitable decision rules. The interference environments are divided into homogeneity, partial homogeneity, and spherically invariant random process. Three MOS techniques, namely, the Akaike information criterion (AIC), generalized information criterion, and corrected AIC, are adopted. At the analysis stage, illustrating examples for the influence of the environment model parameters on the recognition accuracy of the MOS rules are presented. Numerical experiments show the AIC rule has the most robust recognition performance.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Global Navigation Satellite Systems Fault Detection and Exclusion: A
           Parameterized Quadratic Programming Approach
    • Pages: 2862 - 2871
      Abstract: In this article, the problem of detecting and excluding faulty global navigation satellite systems (GNSSs) measurements at the receiver end is formulated as a parameterized quadratic programming (PQP) problem. Compared to the existing fault detection and exclusion (FDE) methods, which mostly rely on exhaustive search, the PQP method is computationally efficient for finding the outliers even when the number of outliers is moderate or large. In the context of multiconstellation GNSS where the probability of multiple simultaneous faults is increased, the PQP method is ideal for the task of fault exclusion since the computation time does not increase with the number of fault hypotheses. It is noted that this article addresses the computational load due to the exclusion function only. The integrity risk bound and continuity risk bound are of fundamental importance to assess the performance of FDE algorithms for safety-critical applications. With the aim to benefit safety-critical applications, the PQP method is integrated with the integrity risk bound and the continuity risk bound derived for FDE using Chi-squared receiver autonomous integrity monitoring (RAIM). It is emphasized that the integration of the PQP method and the integrity and continuity risk bounds do not make the PQP method a practical integrity monitoring method. This is because the computation of the integrity risk bound is still combinatorial and the resulting integrity risk bound is rather conversative. Instead, the integration allows for the opportunity to refine the PQP method so that it can be considered a practical integrity monitoring method. In particular, improvements to reduce the computational load for the Chi-squared RAIM FDE integrity risk bound calculation can readily be applied to the integrity risk bound calculation for the PQP method. Also, further research on PQP parameter tuning can be pursued to tighten the integrity risk bound.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Extended-State-Observer-Based Event-Triggered Orbit-Attitude Tracking for
           Low-Thrust Spacecraft
    • Pages: 2872 - 2883
      Abstract: This article addresses the coupled orbit-attitude tracking problem using low-thrust propulsion while aiming to minimize on-board spacecraft system communication. An adaptive controller is proposed by employing an event-triggered control and an extended-state-observer, where a simple strategy to tune the observer parameters is provided. Moreover, the event-triggering strategy updates and allocates the control signal to the thrusters at prescribed discrete events and is shown to significantly reduce the data-rate requirement. Finally, the performance of the controller is illustrated through numerical examples.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Multiemitter Two-Dimensional Angle-of-Arrival Estimator via Compressive
           Sensing
    • Pages: 2884 - 2895
      Abstract: This article introduces a multiemitter 2-D angle-of-arrival (AoA) estimation scheme. It consists of an AoA estimation algorithm based on impinging signal spatial sparsity, Dantzig selector (an l1-norm minimization solution), and a six-element nonuniformly random-spaced 2-D array. The new scheme can identify more signals than the number of sensors without requiring a priori knowledge of signals and in a low signal-to-noise ratio (SNR) environment. It is demonstrated from 2 to 18 GHz with ten simultaneous incoming signals within 500 MHz instantaneous bandwidth. The number of signals, bandwidth, and frequency range are determined by the performance of digital receivers and are not limited by the compressive sensing (CS)-based 2D-AoA estimation scheme. Note that the random selection of element locations plays a vital role in ensuring that the new scheme achieves a highly successful estimation rate (SER). This is because random sensing is one of the key factors in CS. The only constraint of element locations is the spacing between elements, which has to be bigger than the diameter of cavity-backed-spiral-antenna. Simulation results show that the 2D-AoA estimator has more than 69%, 82%, and 90% SER if the measurement error is less than or equal to 1°, 2°, and 4°, respectively, when SNR is between -10 and 10 dB.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Optimal Guidance for Planetary Landing in Hazardous Terrains
    • Pages: 2896 - 2909
      Abstract: In this article, a minimum-fuel powered-descent optimal guidance algorithm that incorporates obstacle avoidance is presented. The approach is based on convex optimization that includes the obstacles using nonconvex functions. To convert these nonconvex obstacle constraints to convex ones, a simple linearization procedure is employed. It is proved that the optimal solution of the convex relaxation problem is also optimal for the original nonconvex one. The sensitivity of the multiobstacle avoidance method to the relaxation factor and its effectiveness under different conditions are also investigated through simulations.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Geo-registration and Geo-location Using Two Airborne Video Sensors
    • Pages: 2910 - 2921
      Abstract: Geo-registration and geo-location of data collected by video sensors such as electro-optical and infrared cameras are two fundamental steps in the airborne surveillance of ground targets. With the availability of high-resolution imaging sensors and detailed mapping or terrain data sources, video data plays an increasingly important role in modern surveillance platforms like unmanned aerial vehicles and airborne, ground, or maritime surveillance systems. Surveillance systems without any compensation for the inevitable sensor registration errors, i.e., biases, may make geo-location erroneous and render the surveillance platform less effective for precision targeting. This article deals with the modeling of sensor biases in geo-location and proposes a method to estimate them. The proposed method leads to a minimization problem with a nonlinear cost function. Detailed derivation of the bias model is given along with an algorithm to find the bias parameters. The achievable lower bounds for debiased geo-location are provided and simulations are used to demonstrate the validity of the proposed method.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • HSLTP—An LTP Variant for High-Speed Links and Memory Constrained
           Nodes
    • Pages: 2922 - 2933
      Abstract: Delay/disruption-tolerant networking architecture relies on the use of Licklider Transmission Protocol (LTP) on interplanetary links. LTP loss recovery is based on automatic repeat request retransmissions, which, when the propagation delay is very long, are costly. Alternatively, losses could be recovered by using Packet Layer Forward Error Correcting codes, as done by the authors in ECLSA (error Coding Link Service Adapter), recently presented in a companion paper, where LTP segment retransmissions are limited to the unlikely case of decoding failures. However, on high bandwidth-delay-product links, the very possibility of segment retransmission requires that a huge number of Rx buffers be available. To resolve this problem, high-speed LTP, presented here, has a more disruptive approach than ECLSA: it enforces almost one-to-one correspondence between LTP blocks and FEC codewords, and never requires LTP segment retransmissions. In the unlikely case of a FEC failure, the partially received block is discarded and its bundles are resent directly by the bundle protocol. The advantages and disadvantages of this approach are explored in the article. On nodes limited in memory, the results are significantly improved.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Study on the Optimal Access Orbiter Selection Algorithm in Mars Automatic
           Relay Communications
    • Pages: 2934 - 2946
      Abstract: In current Mars relay communications, the Consultative Committee for Space Data Systems (CCSDS) Proximity-1 protocol is simple and efficient but it exhibits low flexibility in optimal access orbiter selection. Once connected with the first successful hailing orbiter, the rover would not switch to other better orbiters until the end of that connection, which makes it difficult to provide more convenient and efficient data relay services. The entire system cost is essential for optimal access orbiter selection, which includes both the Proximity-1 links' transmission cost concerned with the data transmission energy consumption and the orbiters' storage cost concerned with the data buffering energy consumption, thus minimizing the system cost on unit data volume could reduce energy consumption and extend the deep space vehicle's life. We employ long-term simulations of the single rover, simultaneously tracking two orbiters utilizing the improved Hotelling oligopoly model, and reveal the potential improvements for the current “first-come first-serve” selection strategy. In this article, a complete solution is proposed to solve the optimal access orbiter selection issues, including the geometric model, orbit design, oligopoly model, storage cost, and optimal selection algorithms. Simulation results show that our new algorithm outperforms current CCSDS Proximity-1 protocols and distance-dependent selection algorithm in the system cost on unit data volume with the selection gains $36.14%$ and $ 29.59%$, respectively, which could be used as the rover's optimal access orbiter selection algorithm in Mars automatic relay communications.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Bounding Fault Probabilities for Advanced RAIM
    • Pages: 2947 - 2958
      Abstract: Advanced receiver autonomous integrity monitoring (ARAIM) is under development to support both lateral and vertical guidance. A key component of ARAIM is the integrity support message (ISM), which contains validated input parameters including the probabilities of satellite and constellation failure. A service commitment for the former is provided in the global positioning system (GPS) performance standards, whereas further commitments from GLONASS, Galileo, and Beidou are expected to follow. However, air navigation service providers may demand some flexibility in setting the ISM. This article presents a procedure for setting ISM parameters employing a means to determine the a priori probabilities using the Bayesian inference of a Poisson process model given in the literature. This method and a novel way to accumulate the service history are used to analyze the effects of satellite block and age. Results show that while the type and age of satellite are clearly drivers in the likelihood of a fault; such effects may be accounted for without significant impact on the broadcast values. This article also addresses the probability of unscheduled satellite outages using the new method. Finally, this article gives a high-level scheme of how the validity of the ISM parameters may be assured.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Coalitional Graph Game for Air-to-Air and Air-to-Ground Cognitive Spectrum
           Sharing
    • Pages: 2959 - 2977
      Abstract: The aeronautical spectrum band for air-to-ground (A/G) communications is severely underutilized at less than 12.5%, and yet anticipating scarcity in the near future because of the explosive growth in aeronautical service data. Air-to-air (A/A) communications allow aircraft in close proximity to communicate with each other directly without ground stations or satellites, and are regarded as an effective complement for A/G communications in terms of the spectrum utilization efficiency. In this article, to enable such spectral efficiency that A/A links reuse the spectrum of A/G communications, we propose a cognitive solution that A/A communications are regarded as secondary users which sense idle primary A/G communication channels and transmit data on these channels wherever possible. This results in two major issues: spectrum sensing and sharing between A/A and A/G communications. A coalitional manner is devised in which some A/A links are grouped together to perform cooperative spectrum sensing and sharing while an interference graph is used to address the interference that arises from spectrum sharing within a group. We then formulate the cooperative spectrum sensing and sharing into a coalitional graph game played by all the A/A links involved. Finally, a distributed coalitional graph game algorithm is developed to maximize the utility so as to optimize the schedule of the A/A transmissions on the available A/G channels. Extensive simulations show that the achievable sum rate approaches the results of the optimal exhausted searching with relatively low complexity.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Battery Management System With State-of-Charge and Opportunistic
           State-of-Health for a Miniaturized Satellite
    • Pages: 2978 - 2989
      Abstract: The lifespan of a satellite is primarily dependent on its battery performance. Thus, proper management and monitoring of the battery is important. Most miniaturized satellites of cubeSat and nanosatellite primarily rely on battery voltage readings for monitoring and seldom provide battery health status in a satellite. As the voltage readings can be affected by satellite operating conditions such as temperature and battery lifespan, it can give unreliable readings that might jeopardize satellite operation. The availability of the battery health status can prevent unexpected battery failures and provide useful insights into the planning of satellite operations. In this article, the battery management system of a satellite with state-of-charge (SOC) and state-of-health (SOH) monitoring is presented. For SOC estimation, a scaled unscented Kalman filter (UKF) is proposed. When compared to the existing UKF approach, it requires fewer sigma points and the positive weights used in the scaled unscented transform ensure the positive semidefiniteness of the covariance matrix leading to the improved numerical stability of the filter. Conversely, SOH monitoring is achieved by taking advantage of the opportunity arising from the satellite operations. The battery parameters are extracted without artificially injecting charge and discharge pulses. To validate the performance of the BMS, the experimental prelaunch tests and the actual in-flight data of the VELOX-II satellite is used as an example. From the results, the SOC estimation error is approximately 1% and the SOH estimation is consistent with the manufacturer's datasheet.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Design of a Compact, Multifrequency, Multiconstellation GNSS Precise Point
           Positioning Correction Format
    • Pages: 2990 - 2998
      Abstract: High-accuracy, high-precision global navigation satellite systems (GNSSs) have been utilized by specialized user markets for over two decades. Traditional high-accuracy GNSS systems are not scalable as they require local infrastructure. Precise point positioning (PPP) is a GNSS position estimation technique that allows positioning and navigation with centimetre-level accuracy without local infrastructure. The caveat of PPP is the timely transmission of corrections to errors in the GNSS signals. Next-generation GNSS satellites such as Galileo, BeiDou, QZSS, and other local systems have plans to broadcast corrections for PPP services broadcast corrections for PPP services. However, since these services are expected to have limited channel capacity, the development of efficient formats for PPP corrections is needed. In this article, a messaging strategy for PPP corrections and testing its performance, in terms of data rate and obtained positioning accuracy, is proposed. Message formats in the literature require 522 bps or more to transmit corrections for 70 satellites. By contrast, the message format proposed in this article can transmit information corrections for more than 70 satellites using 52% of the standard satellite-based augmentation system channel's 212 bps capacity, while incurring less than 1 cm of positioning accuracy degradation.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Rao Detector for Passive MIMO Radar With Direct-Path Interference
    • Pages: 2999 - 3009
      Abstract: This article deals with the problem of target detection in a passive multiple-input multiple-output (MIMO) radar network involving noncooperative illuminators of opportunity (IOs) and geographically dispersed multichannel receivers. The signal model considers the direct-path interference (DPI). We employ the Rao test to solve the problem and derive a closed-form detector. Then, by considering the properties of the ambiguity functions of most IO waveforms, an approximated version of the detector with a simpler form is derived. Two detectors in the case of an active MIMO network are also provided as the upper bounds of the passive situations. Moreover, considering target echo signal fluctuation, we have analyzed the performance of the detectors in terms of probability of miss-detection when being used in a multistatic configuration and have specified the conditions under which the full diversity gain is achieved. Numerical results verify the effectiveness of the proposed detectors and demonstrate that the proposed detectors have performance very close to the active situation.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Intrusion Detection System for the MIL-STD-1553 Communication Bus
    • Pages: 3010 - 3027
      Abstract: MIL-STD-1553 is a military standard that defines the specification of a serial communication bus that has been implemented in military and aerospace avionic platforms for over 40 years. MIL-STD-1553 was designed for a high level of fault tolerance while less attention was paid to cyber security issues. Thus, as indicated in recent studies, it is exposed to various threats. In this article, we suggest enhancing the security of MIL-STD-1553 communication buses by integrating a machine learning-based intrusion detection system (IDS); such anIDS will be capable of detecting cyber attacks in real time. The IDS consists of two modules: 1) a remote terminal (RT) authentication module that detects illegitimately connected components and data transfers and 2) a sequence-based anomaly detection module that detects anomalies in the operation of the system. The IDS showed high detection rates for both normal and abnormal behavior when evaluated in a testbed using real 1553 hardware, as well as a very fast and accurate training process using logs from a real system. The RT authentication module managed to authenticate RTs with +0.99 precision and +0.98 recall; and detect illegitimate component (or a legitimate component that impersonates other components) with +0.98 precision and +0.99 recall. The sequence-based anomaly detection module managed to perfectly detect both normal and abnormal behavior. Moreover, the sequencebased anomaly detection module managed to accurately (i.e., zero false positives) model the normal behavior of a real system in a short period of time (~22 s).
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Reel-Based Tension Control of Tethered Space Robots
    • Pages: 3028 - 3043
      Abstract: This article elaborates on the tension control design of tethered space robots for debris removal. The novel approach is to change the tether natural length via a reel. With only the tension sensing, we leverage a Kalman filter and a recursive least-squares algorithm to estimate the actual length and the debris mass, which are fed back to a model-predictive controller to generate the optimal tangential velocity of the reel. Simulations show that the stiff tether exhibits better tension-tracking performance which is robust to the tumbling debris.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Particle Filtering-Based Low-Elevation Target Tracking With Multipath
           Interference Over the Ocean Surface
    • Pages: 3044 - 3054
      Abstract: As radar signals propagate above the ocean surface to determine the trajectory of a target, the signals that are reflected directly from the target arrive at the receiver along with indirect signals reflected from the ocean surface. These unwanted signals must be properly filtered; otherwise, their interference may mislead the signal receiver and significantly degrade the tracking performance of the radar. To this end, we propose a low-elevation target tracking mechanism considering the specular and diffuse reflection effects of multipath propagation over the ocean surface simultaneously. The proposed mechanism consists of a state-space model and a particle filtering algorithm and promises considerable improvements in the capacity and accuracy of the radar tracking systems. The efficiency and accuracy of the developed target tracking method are tested and compared with an unscented Kalman filtering method in two- and three-dimensional space using a series of simulation experiments.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Star Identification Based on Spider-Web Image and Hierarchical CNN
    • Pages: 3055 - 3062
      Abstract: Unlike the traditional star pattern recognition algorithms that extract star features as a vector to be matched in a database, in this article, a spider-web image is constructed and a hierarchical convolution neural network (CNN) model is proposed to recognize this spider-web image. Stars are linked with different color lines based on the angle distance to enhance the discrimination of the spider-web images. A training dataset and testing dataset are constructed based on spider-web images for CNN model training. A hierarchical CNN model with two stages, which are designed to perform first step identification and recognize similar spider-web images, respectively, is proposed. Experiment results show that, compared with other algorithms, the proposed algorithm is more robust toward the position noise, magnitude noise, small numbers of stars in the field of view, and the presence of false stars.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Post-Newtonian Equations for Laser Links in Space
    • Pages: 3063 - 3079
      Abstract: The purpose of this article is threefold. We first show that the second-order post-Newtonian (p-N) equations for the Earth exterior Schwarzschild field introduced in this article are the equations that, unlike those of the first p-N order, allow the space-based pointing, acquisition, and tracking laser systems to substantially reduce the size of the p-N corrections to the Newtonian location from the systems of middle size targets in orbit about the Earth. To achieve this goal the trackers must be endowed with very narrow laser beams and atomic clocks. Second, we show that these corrections can be used to speed up the trackers' shooting systems in any scenario where this kind of beam may be involved. In fact, since the first step in any procedure aimed to achieve this goal is to accurately determine the ranging and shooting directions to the targets from the lines of sight, the computation of the second p-N relative orbits of the targets with respect to the trackers must be carried out in real time. Then, the solution of these equations for the target of interest can be uploaded in the closed-loop control system on board the tracker involved, in order to initiate the control process of the respective ranging and shooting direction, as well as to reinitiate it, as soon as the target ceases to be hidden for the tracker due to the Earth. Third, we to show that these equations will be very useful for autonomous trackers to carry out two demanding tasks, namely 1) to steadily maintain intersatellite optical links and 2) to perform laser ablation of middle size LEO debris objects at operative distances.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Simultaneous Measurement of Radial and Transversal Velocities Using
           Interferometric Radar
    • Pages: 3080 - 3098
      Abstract: The linear velocity of an arbitrary moving object comprises two orthogonal components with reference to the observing radar, which are radial velocity and transversal velocity. Simultaneous measurement of both the radial and transversal velocities can provide a complete 2-D movement information for further target detection, tracking, and classification. The interferometric radar is capable of measuring the 2-D velocity of an arbitrary moving object simultaneously, regardless of the trajectory. However, the radial velocities and transversal velocities are coupled in the interferometric measurement due to the nonlinear processing when there are multiple moving objects in the radar field of view (FoV), thus the conventional time-frequency analysis fails to measure the transversal velocities. In this article, we first derive and analyze the signal distortion caused by the nonlinear interferometric operation. We then propose two new methods of combining the inverse Radon transform (IRT) and short-time Fourier transform (STFT), which can concentrate a sinusoidally frequency-modulated waveform from time-frequency domain into a point in the parameter domain, thus separating the transversal velocity measurements of different objects with rigid-body rotations. Simulation and experimental results are provided to validate the effectiveness of the proposed methods.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • High-Resolution Range-Doppler Maps by Coherent Extension of Narrowband
           Pulses
    • Pages: 3099 - 3112
      Abstract: The range resolution of radar is inversely proportional to the swept bandwidth. However, this bandwidth may not be available due to a variety of reasons, including spectrum congestion and lack of instantaneous bandwidth despite access to a larger tunable bandwidth. Existing approaches to achieving high-range resolution include bandwidth extrapolation, ultrawideband coherent processing, and spectral splicing of narrowband stepped-frequency pulses. In this article, we achieve high-range resolution of a wideband chirp from a sequence of narrowband pulses using coherent-phase extension of the beat tones of an FMCW dechirper. By phase matching the beat tones across pulse boundaries, the algorithm trades a longer observation interval for a smaller swept bandwidth. Phase matching of the short beat tones is applied in two steps to first obtain the coarse estimate of the beat frequencies which are then used as the starting point in the formation of the range-Doppler map that now enjoys the two-dimensional fast-Fourier transform (2-D-FFT) gain. With this approach, a fraction of the total bandwidth to obtain a range resolution of a wideband chirp is used. Using both simulations and experimental data, the proposed high-resolution algorithm is applied to a narrowband chirp sequence with bandwidth B to generate range-Doppler maps with range resolution corresponding to a wideband chirp sequence of bandwidth NB.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Multipoint Contact Dynamics and the Detumbling Strategy for a
           Fast-Tumbling Target
    • Pages: 3113 - 3122
      Abstract: To ensure the safety of operations with a fast-tumbling target, a detumbling strategy implemented by a dual-arm space robot with finger-type end effectors is proposed to attenuate the target rotation. A detumbling system that consists of the robot and the target is established. Through the contact effects between the two parts, the energy of the target is gradually dissipated. Evaluated by the detumbling duration, energy consumed, and the target movement, the contact strategy is developed. Through numerical simulations, the multipoint contact detumbling is verified feasible to detumble a fast-tumbling target. With suitable parameters, the kinematic response of the detumbling system could be bounded and steady, which makes further operation for the target easier.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Closed-Form Solution for Elliptic Localization in Distributed MIMO Radar
           Systems With Minimum Number of Sensors
    • Pages: 3123 - 3133
      Abstract: In this article, the problem of 3-D target localization from bistatic range measurements in multiple-input-multiple-output (MIMO) radars with distributed antennas is considered. A closed-form two-stage weighted least squares solution is developed, which is able to uniquely determine the target position with a smaller number of sensors (transmitters or receivers) compared to the other existing closed-form methods. The proposed method employs several weighted least-squares minimizations and does not require any initial solution guesses to give the target position estimate. A detailed theoretical performance analysis associated with the method as well as the Cramer-Rao lower bound (CRLB) are provided. The proposed estimator is shown theoretically to achieve the CRLB accuracy under small Gaussian noise. Computer simulations are included to corroborate the theoretical development and to compare the estimator performance with several previous approaches. The proposed algorithm in the considered example is shown to outperform the existing closed-form estimators. In the 3-D and in the case of a minimum number of sensors (i.e., two transmitters and two receivers) in a MIMO radar, the proposed method is also shown to be able to localize a target with high accuracy while the previous closed-form methods cannot uniquely determine the target position.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Discriminant Analysis for Radar Signal Classification
    • Pages: 3134 - 3148
      Abstract: Discriminant analysis is a technique used in statistics and machine learning to separate two or more classes of objects or events. We introduce linear, quadratic, and mixture discriminant analysis methods into radar signal classification. However, the selection of an appropriate discriminant analysis method can be difficult and no comparison study of these discriminant analyses for radar signal classification can be found in the open literature. This article presents a theoretical analysis and practical comparison of these three discriminant analysis methods for radar signal classification. The theoretical analysis is derived from Bayes' theorem. The practical comparison study is performed on a dataset consisting of five radars emissions. The advantages and drawbacks of each discriminant analysis method are highlighted. This study demonstrates that quadratic discriminant analysis (QDA) is predominantly a better method for radar signal classification using our radar dataset. On average, it demonstrates 95%, 93%, and 86.6% classification accuracy for three, four, and five radar emitters in our radar dataset, respectively. Linear discriminant analysis (LDA) achieves on average 88.7%, 84.9%, and 79.2% classification accuracy for three, four, and five radar emitters, respectively. Mixture discriminant analysis (MDA) also achieves the same classification performance as QDA. Theoretical analysis shows that both LDA and QDA are a special case of MDA and that MDA can set up more decision boundaries than LDA and QDA if the feature distribution in the dataset is an ensemble of Gaussian distributions. Therefore, MDA is recommended for radar signal classification.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • High-Latitude OTHR Adaptive Beamforming: Preserving Angle-Doppler Coupled
           Clutter
    • Pages: 3149 - 3161
      Abstract: Over-the-horizon radars (OTHRs) often operate in the presence of interference that is nonstationary over the coherent processing interval (CPI). In this case, effective adaptive beamforming requires intra-CPI updates to the spatial weight vector to track changes in the interference spatial structure. However, these weight vector changes must be constrained to prevent modulating the clutter signal and drastically reducing subclutter visibility. These additional constraints require a model of the clutter signal. Existing adaptive beamforming algorithms either explicitly or implicitly rely on a scalar multivariate autoregressive (MVAR) model, which is based on typical observations made by mid-latitude OTHRs. However, high-latitude OTHRs often observe angle-Doppler coupled clutter, for which the scalar MVAR model does not apply. This article investigates the ramifications of angle-Doppler coupling for spatial adaptive processing (SAP), which results in the proposal of a new SAP algorithm. The efficacy of the new algorithm is compared to existing methods through simulation.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Automatic Scheduling for Earth Observation Satellite With Temporal
           Specifications
    • Pages: 3162 - 3169
      Abstract: This article investigates a mission scheduling problem for earth observation satellite (EOS) with specific and temporal requirements. As is well known, the challenge is how to automatically generate an optimal actionable sequence for EOS given various physical constraints and temporal/spatial specifications that are often too intuitive to reason. To this end, we propose an automatic scheduling algorithm for EOS with the help of a linear temporal logic (LTL). In particular, LTL semantics are introduced to automate the constraints as well as temporal specifications, such that the argument of the mission specifications can be properly formulated. Toward this, we proceed to construct the state transition system by abstracting the mission objectives and specifications into a directed graph with weighted edges, and the automata theory is applied to obtain the observation sequence that satisfies the said specifications. Numerical examples verified the performance of the proposed strategy.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Integer Ambiguity Resolution by Mixture Kalman Filter for Improved GNSS
           Precision
    • Pages: 3170 - 3181
      Abstract: Accurate carrier-phase integer ambiguity resolution is fundamental to high-precision global navigation satellite systems (GNSSs). Real-time GNSSs typically resolve the ambiguities by a combination of recursive estimators and integer least-squares solvers, which need to be reset when satellites are added or cycle slip occurs. In this article, we propose a mixture Kalman filter solution to integer ambiguity resolution. By marginalizing out the set of ambiguities and exploiting a likelihood proposal for generating the ambiguities, we can bound the possible values to a tight and dense set of integers. Thus, we extract the state and integer estimates from a mixture Kalman filter. The proposed approach yields an integrated method to detect cycle slip and initialize new satellites. Numerical analysis and experimental results indicate that the proposed method achieves reliable position estimates, repeatedly finds the correct integers in cases when other methods may fail, and is more robust to cycle slip.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Output-Feedback Image-Based Visual Servoing for Multirotor Unmanned Aerial
           Vehicle Line Following
    • Pages: 3182 - 3196
      Abstract: This article considers visual servoing-based motion control of multirotor unmanned aerial vehicles. We employ output feedback and image-based visual servoing to control the vehicle's pose with respect to a static planar visual target with a linear structure (e.g., electric transmission lines or pipelines). The method uses measurements from inexpensive sensors typically found on-board: an inertial measurement unit, and a monocular computer vision system. Unlike existing work, it does not require linear velocity, position measurements, or an optical flow sensor. The method directly controls the relative pose to the visual target and does not require global navigation satellite system measurements of the vehicle or target. The visual servoing method ensures the vehicle flies centered above the lines at specified height and yaw. Such motion control is important in a number of applications such as efficient data collection for infrastructure inspection. Our article exploits the inherent robustness of an image-based approach where feature error is computed directly in the image plane. A virtual camera is combined with output feedback and convergence of the closed loop is proven. The method is adaptive to vehicle mass, thrust constant, desired depth, and a constant disturbance force. Simulation and experimental results illustrate the method's performance and robustness to model uncertainty.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Motion Classification Using Kinematically Sifted ACGAN-Synthesized Radar
           Micro-Doppler Signatures
    • Pages: 3197 - 3213
      Abstract: Deep neural networks have recently received a great deal of attention in applications requiring classification of radar returns, including radar-based human activity recognition for security, smart homes, assisted living, and biomedicine. However, acquiring a sufficiently large training dataset remains a daunting task due to the high human costs and resources required for radar data collection. In this article, an extended approach to adversarial learning is proposed for generation of synthetic radar micro-Doppler signatures that are well adapted to different environments. The synthetic data are evaluated using visual interpretation, analysis of kinematic consistency, data diversity, dimensions of the latent space, and saliency maps. A principle-component analysis-based kinematic-sifting algorithm is introduced to ensure that synthetic signatures are consistent with physically possible human motions. The synthetic dataset is used to train a 19-layer deep convolutional neural network to classify micro-Doppler signatures acquired from an environment different from that of the dataset supplied to the adversarial network. An overall accuracy of 93% is achieved on a dataset that contains multiple aspect angles (0$^{circ }$, 30$^{circ }$, and 45$^{circ }$ as well as 60$^{circ }$), with 9% improvement as a result of kinematic sifting.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Detecting Hazardous Spatial Gradients at Satellite Acquisition in GBAS
    • Pages: 3214 - 3230
      Abstract: In this article, we develop a ground monitor capable of detecting anomalous signal-in-space spatial gradients for rising, newly acquired, and reacquired satellites in the ground-based augmentation system using either single or dual frequency. These gradients can be caused by satellite orbit ephemeris faults and ionospheric fronts. The monitor utilizes differential code and carrier phase measurements across multiple reference receiver antennas as the basis for detection. We show that the new monitor significantly improves performance over existing detection algorithms and is capable of meeting Category III precision approach and landing requirements.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Synthetic-Range-Profile-Based Training Library Construction for Ship
           Target Recognition Purposes of Scanning Radar Systems
    • Pages: 3231 - 3245
      Abstract: The quantity and quality of range profiles in a training library play a significant role in target recognition. Classifier structures should be built up by experiencing a sufficient amount of range profiles in order to enhance classification accuracy. On the other hand, there might be insufficient measuremental range profiles especially for the targets rarely cruising. Therefore, training libraries should be enriched for these types of targets. In this article, the suitability and efficiency of creating a training library with synthetic range profiles are investigated for maritime target recognition purposes of scanning radar systems. In this context, synthetic range profiles are generated for six different ship targets, and the compatibility of these profiles with measuremental ones has been analyzed from different points of view. Moreover, a novel approach on generating synthetic range profiles is introduced. In the sense of compatibility studies, first, correlation analyses have been performed directly between range profiles and then between spatial- and velocity-based features. It is seen that the proposed approach has the ability to generate more compatible range profiles than the conventional methodology. In addition to similarity analyses, classification examinations have been performed for different feature use cases by employing synthetic profiles in the training set and the measuremental ones in the test set. At this step, a k-nearest-neighbor-based classifier that benefits by the discrimination ability of length- and velocity-based features is proposed to obtain higher classification rates. The results of the classification examinations show that synthetic profiles could be used either to construct an offline training library from scratch or to enrich a nonhomogenous and lacking library for ship target recognition.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Unified Backstepping Sliding Mode Framework for Airship Control Design
    • Pages: 3246 - 3258
      Abstract: This article presents a new kind of vectorial backstepping sliding mode control (BSMC) for the positioning and trajectory tracking of an autonomous robotic airship. Also, a unified framework basis for the design/analysis of vectorial BSMC, as well as sliding mode control and backstepping control for a system in lower triangular block form is derived. The design framework makes the theoretical-based comparative analysis of performances/robustness easier between the three nonlinear control approaches. Simulation results for the positioning and tracking of the autonomous airship illustrate the proposal.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • End-to-End Simulations of Coded Transmissions in Space Links Affected by
           Solar Scintillation
    • Pages: 3259 - 3275
      Abstract: In this article, coded space communication links impaired by solar scintillation are investigated followed by a comprehensive end-to-end approach. With respect to baseband analyses, this allows for a more realistic modeling of actual communication links in these scenarios, though at the cost of longer simulation times and higher minimum values of the error rates assessable. The effect of solar scintillation on both signal amplitude and phase is studied, by considering the potential use of noncoherent demodulation to withstand phase synchronization impairments. This article allows optimizing some receiver parameters, such as the phase-locked loop bandwidth, in a way to face critical contingency scenarios as well.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Persymmetric Subspace Detectors With Multiple Observations in Homogeneous
           Environments
    • Pages: 3276 - 3284
      Abstract: In this article, a target detection problem in homogeneous Gaussian noise with unknown covariance matrix is examined using multiple observations, which may be collected from multiple range cells, bands, and/or coherent processing intervals. In order to take into consideration mismatches of the target steering vector, we adopt a subspace model where the target steering vector is assumed to lie in a subspace spanned by the column vectors of a known matrix with unknown target coordinates. By exploiting persymmetric structures, we propose several adaptive detectors according to ad hoc modifications of generalized likelihood ratio test (GLRT), Rao test, and Wald test. It is found that the Rao test does not exist, whereas the two-step Wald test shares the same form as the two-step GLRT. Numerical examples show that the robustness of the proposed detectors is better than that of their counterparts in general. In particular, the proposed one-step GLRT is the most robust in most cases, and the proposed two-step GLRT and one-step Wald test can be more robust than the one-step GLRT in the case where the number of training data is small.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Opportunistic UAV Navigation With Carrier Phase Measurements From
           Asynchronous Cellular Signals
    • Pages: 3285 - 3301
      Abstract: This article presents a framework for opportunistic unmanned aerial vehicle (UAV) navigation by exploiting carrier phase measurements from ambient cellular signals of opportunity. In the proposed framework, the cellular base transceiver stations (BTSs) are not assumed to be synchronous. A complete framework that employs an extended Kalman filter (EKF) is presented, including filter initialization and process and measurement noise covariance selection. The EKF estimates the position and velocity of the UAV, as well as the differences between the UAV-mounted receiver and each of the BTSs' clock bias and clock drift. The observability of the estimation framework is analyzed, and the boundedness of the EKF's errors is studied. It is shown that the system is observable given a class of vehicle and receiver clock dynamics. A lower bound for the EKF estimation error covariance is derived, and it is shown that the covariance remains bounded. Monte Carlo simulations are conducted to study the effect of the number of BTSs, the initial UAV speed, and the receiver's oscillator quality, on the estimation performance. Two sets of experimental results are presented demonstrating UAVs navigating exclusively with cellular carrier phase measurements via the developed framework, achieving a total position root-mean-squared error of 2.94 and 5.99 m for UAV trajectories of 2.6 and 2.9 km, respectively.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Distributed Kalman Filter for Cooperative Localization With Integrated
           Measurements
    • Pages: 3302 - 3310
      Abstract: This correspondence is concerned with the problem of distributed Kalman filtering for cooperative localization with absolute and relative measurements. Each target state is estimated by using locally available absolute measurements and relative measurements with other targets in the neighborhood. Two distributed Kalman filters are developed by enforcing each target to transmit its local estimates to the neighbors in a directed graph. A sufficient condition is established to guarantee the stability of the error dynamics. Numerical simulations are provided to verify the effectiveness of the proposed filters.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Reduced-DOF Three-Dimensional STAP via Subarray Synthesis for
           Nonsidelooking Planar Array Airborne Radar
    • Pages: 3311 - 3325
      Abstract: Compared with conventional two-dimensional space-time adaptive processing (2D-STAP) methods, the elevation-azimuth-Doppler three-dimensional space-time adaptive processing (3D-STAP) method has the advantage of suppressing nonstationary clutter. Thereby, it is suitable for nonsidelooking airborne radar (non-SLAR) applications. However, its huge training data requirements and computational load are often beyond radar's ability in practical clutter environments. In this correspondence, we develop a simple but efficient reduced-degree-of-freedom (DOF) 3D-STAP method that significantly reduces the required training data and the computational complexity while maintaining the suboptimal clutter suppression performance. The proposed method transforms the planar array data into linear array data in azimuth and in elevation, respectively, thereby beamforming an equivalent cross-shape array prior to STAP. In consequence, only a few spatial DOFs, including azimuth and elevation dimension, are used for STAP directly resulting in the potential advantage for nonstationary clutter suppression and drastically reducing training data requirements and computational load. Furthermore, the clutter rank estimation rules of the planar array and the transformed cross-shape array are derived, and the required elevation DOFs of the proposed method are further discussed in detail. Simulations for clutter suppression of non-SLAR show that the proposed STAP method outperforms the state-of-the-art 3D-STAP method in terms of convergence and computational complexity.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Compressive TDOA Estimation: Cramér–Rao Bound and Incoherent
           Processing
    • Pages: 3326 - 3331
      Abstract: Estimation of time-difference-of-arrival (TDOA) between a signal and its time-shifted version has many applications, mostly in localization. Because compressive sensing (CS) can reduce the sampling rate and data volume, TDOA estimation from CS samples (CS-TDOA) has become a subject of interest. Generally, CS-TDOA has lower estimation accuracy, and the Cramér–Rao bound (CRB) can quantify this degradation. The first part of this correspondence derives the CRB for CS-TDOA estimation, and the second part proposes an incoherent processing scheme for CS-TDOA estimation using partial Fourier coefficients. This results in the reduction of the number of sampling channels needed to acquire those coefficients. Simulation results are given to corroborate the theoretical development.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Single-Bit Consensus With Finite-Time Convergence: Theory and Applications
    • Pages: 3332 - 3338
      Abstract: In this article, a new consensus protocol based on the sign of innovations is proposed. Based on this protocol, each agent requires only a single-bit of information about its relative state to its neighboring agents. This is significant in real-time applications, since it requires less computation and/or communication load on agents. Using Lyapunov stability theorem, the convergence is proved for networks having a spanning tree. Furthermore, the convergence is shown to be in finite time, which is significant as compared to most asymptotic protocols in the literature. Time-variant network topologies are also considered in this article, and final consensus value is derived for undirected networks. Applications of the proposed consensus protocol in two-dimensional (2-D)/3-D rendezvous task, distributed estimation distributed optimization, and formation control are considered and the significance of applying this protocol is discussed. Numerical simulations are provided to compare the protocol with those existing in the literature.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
  • Double Differential Modulation for LEO-Based Land Mobile Satellite
           Communication
    • Pages: 3339 - 3346
      Abstract: In this article, we propose a double differential (DD) modulation technique for low earth orbit (LEO)-based land mobile satellite (LMS) communication to overcome the carrier frequency offset, which is an inevitable effect with the LEO satellites. The symbol error rate (SER) expressions for the considered scheme over Shadowed-Rician fading channels with phase-shift keying (PSK) constellations are presented. Since a closed-form expression cannot be derived for quadrature PSK and higher order PSK constellations, an upper bound and a lower bound of SER are derived. The error performance of the DD modulated LMS system is compared to that of coherent modulation-based and single differential modulation-based LMS systems, and a significant performance gain of the proposed DD modulation-based system is observed. Furthermore, we have also studied the effects of elevation angle and LEO trajectory on the error performance of the considered system.
      PubDate: Aug. 2020
      Issue No: Vol. 56, No. 4 (2020)
       
 
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