Amplitude Constraints Research Articles

Finite-time time-varying formation control for marine surface vessels

This paper is dedicated to solving the time-varying formation control problem of multiple marine surface vehicles experiencing uncertainties, actuator faults and saturation constraints. At first, the transformed Euler-Lagrange dynamics of MSVs are presented for problem formulation. Based on such dynamics, a novel integral manifold possessing finite-time reachability is designed, and it follows that a time-varying formation tracking control scheme is proposed. Owing to the favorable properties of the Euler-Lagrange systems and the hyperbolic tangent function, amplitude constraints on the command control signals could be satisfied by just tuning the design parameters instead of complicated anti-saturation design. Then, the adverse effect arisen from uncertainties and actuator faults is suppressed by designed adaptive laws. Through Lyapunov stability analysis and homogenous theory, the globally finite-time stability of the closed-loop system is theoretically confirmed. Finally, numerical simulations are carried out to show the efficacy of the proposed algorithm.

Capacity-Achieving Input Distribution in Per-Sample Zero-Dispersion Model of Optical Fiber

The per-sample zero-dispersion channel model of the optical fiber is considered. It is shown that capacity is uniquely achieved by an input probability distribution that has continuous uniform phase and discrete amplitude that takes on finitely many values. This result holds when the channel is subject to general input cost constraints, that include a peak amplitude constraint and a joint average and peak amplitude constraint.

Robust spline-line energy management guidance algorithm with multiple constraints and uncertainties for solid rocket ascending

For the solid rocket with depletion shutdown system, effective energy management is significant to meet terminal constraints by exhausting excess energy. Several traditional energy management algorithms cannot satisfy the altitude constraint and path constraints are not sufficiently considered. The velocity adjustment capability of these algorithms is limited and the uncertainties are not considered. Based on the on-line programming of velocity capability curve, Spline-Line Energy Management (SLEM) guidance algorithm is proposed. It introduces lateral maneuvers to further consume the available velocity on the basis of longitudinal energy management. After expressing the constraints as several algebraic equations, the closed-loop guidance problem is converted to solving a system of nonlinear equations about the curve parameters in real time. The advantage is that the altitude constraint can be satisfied theoretically. The overload and control variable change rate and amplitude constraints are also considered during the flight by constructing the feasible boundary of velocity capability curve. To improve the robustness, it is further extended by estimating the actual uncertainties. The effectiveness and advantages of SLEM are demonstrated by simulations and comparisons with other energy management algorithms. Simulation results show that the proposed approach can satisfy multiple constraints with high precision under the condition of uncertainties.

Vibration and Position Control of Overhead Crane With Three-Dimensional Variable Length Cable Subject to Input Amplitude and Rate Constraints

In this paper, the modeling and control problem of an overhead crane equipped with a three-dimensional (3-D) variable length flexible cable is discussed. In order to achieve high control performance, a partial differential equation (PDE) model is deduced with exactly preserving high frequency modes of the original system. For the sake of dealing with the effect of input amplitude and rate constraints, a boundary control scheme is carried out to drive the payload to a desired position with the 3-D vibration reduction of the variable length cable by applying the backstepping technology. The exponential stability of the closed-loop system is demonstrated based on the Lyapunov's direct method. The simulation results verify the effectiveness of the proposed control strategy.

Trajectory tracking of under-actuated ships based on optimal sliding mode control with state observer

An optimal sliding mode control (SMC) with state observer is presented for trajectory tracking of under-actuated ships with the model uncertainties, environmental disturbances, input constraints and optimization. Firstly two backstepping virtual control laws are designed by the kinematic model to convert trajectory tracking into heading control and surge velocity control. Then, according to the Norrbin model and the correlation coefficient between surge velocity and propeller revolution, a heading model and a surge velocity model are established respectively. Meanwhile, two extended state observers are built based on the hyperbolic tangent function with clear bounded meaning, which estimate model uncertainties and disturbances. The nonlinear SMC is used to control heading and surge velocity, which embeds the control laws, namely rudder angle and propeller revolution, in a cost function. This cost function is solved with input limits to address the input optimization, amplitude and increment constraints. Finally, the stability analysis is provided, and the simulations show that the ship can track trajectory successfully in case of the disturbances and constraints. These results demonstrate the feasibility and effectiveness of this method.

Reconfigurable Holographic Surface: Holographic Beamforming for Metasurface-Aided Wireless Communications

The future sixth generation (6G) wireless communications look forward to constructing a ubiquitous intelligent information network with high data rates. To fulfill such challenging visions, the reconfigurable holographic surface (RHS) is developed as a promising solution due to its capability of accurate multi-beam steering with low power consumption and hardware cost. Different from the conventional phase-controlled antennas, the RHS can control the radiation amplitude of the reference wave propagating on the metasurface by leveraging the holographic technique. The desired object waves can then be generated without complex phase-shifting circuits, enabling the convenient implementation of the transceiver. Such amplitude-controlled holographic beamforming triggers new challenges since a new beamforming scheme needs to be developed to handle the complex-domain optimization problem subject to the unconventional real-domain amplitude constraints, which makes the superposition of the radiation waves from different antenna elements difficult to tackle. In this letter, we consider an RHS-aided multi-user communication system with a base station equipped with an RHS. We formulate a sum rate maximization problem and design a novel amplitude-controlled algorithm to solve the problem. Simulation results verify the effectiveness of the proposed scheme.

GAMA/DEVILS: constraining the cosmic star formation history from improved measurements of the 0.3–2.2 μm extragalactic background light

ABSTRACT We present a revised measurement of the optical extragalactic background light (EBL), based on the contribution of resolved galaxies to the integrated galaxy light (IGL). The cosmic optical background radiation (COB), encodes the light generated by star formation, and provides a wealth of information about the cosmic star formation history (CSFH). We combine wide and deep galaxy number counts from the Galaxy And Mass Assembly survey (GAMA) and Deep Extragalactic VIsible Legacy Survey (DEVILS), along with the Hubble Space Telescope (HST) archive and other deep survey data sets, in nine multiwavelength filters to measure the COB in the range from 0.35 μm to 2.2 μm. We derive the luminosity density in each band independently and show good agreement with recent and complementary estimates of the optical-EBL from very high-energy (VHE) experiments. Our error analysis suggests that the IGL and γ-ray measurements are now fully consistent to within $\sim 10{{\ \rm per\ cent}}$, suggesting little need for any additional source of diffuse light beyond the known galaxy population. We use our revised IGL measurements to constrain the CSFH, and place amplitude constraints on a number of recent estimates. As a consistency check, we can now demonstrate convincingly, that the CSFH, stellar mass growth, and the optical-EBL provide a fully consistent picture of galaxy evolution. We conclude that the peak of star formation rate lies in the range 0.066–0.076 M⊙ yr−1 Mpc−3 at a lookback time of 9.1 to 10.9 Gyr.

Motion Planning and Adaptive Neural Tracking Control of an Uncertain Two-Link Rigid–Flexible Manipulator With Vibration Amplitude Constraint

This article deals with an uncertain two-link rigid-flexible manipulator with vibration amplitude constraint, intending to achieve its position control via motion planning and adaptive tracking approach. In motion planning, the motion trajectories for the two links of the manipulator are planned based on virtual damping and online trajectories correction techniques. The planned trajectories can not only guarantee that the two links can reach their desired angles, but also have the ability to suppress vibration, which can be adjusted to meet the vibration amplitude constraint by limiting the parameters of the planned trajectories. Then, the adaptive tracking controller is designed using the radial basis function neural network and the sliding mode control technique. The developed controller makes the two links of the manipulator track the planned trajectories under the uncertainties including unmodeled dynamics, parameter perturbations, and persistent external disturbances acting on the joint motors. The simulation results verify the effectiveness of the proposed control strategy and also demonstrate the superior performance of the motion planning and the tracking controller.

An Efficient Low-Complexity Method to Calculate Hybrid Beamforming Matrices for mmWave Massive MIMO Systems

In the context of a massive MIMO system, the number of RF chains increases prohibitively. To solve the problem, hybrid beamforming (BF) has been proposed. Nevertheless, the amplitude constraint of the analog part in hybrid BF limits achieving the optimal performance given by the optimal digital BF. Some studies have been conducted recently to relax the amplitude constraint by deploying multiple phase shifters and switches (that select phase shifters) in the hybrid beamforming structures. The tremendous number of switches in the structure makes the problem of switch state selection very complex. In this paper, we propose an efficient low-complexity algorithm to obtain the optimal switch states. In the proposed algorithm, we decompose the main problem into sub-ones to reduce the complexity and solve the problem using a finite search space. The results of our study suggest that the optimal solution will be attainable by searching through less than 1% of the search space, if the number of phase levels exceeds 14. Moreover, the proposed algorithm has the potential to perfectly implement linear beamformers, designed for fully digital architectures, in a hybrid structure, while applying the minimum number of RF chains. Finally, the simulation results prove the efficiency of the algorithm and confirm the sufficiency of the analog part of the BF to achieve the optimal digital BF performance just by applying a few number of fixed phase shifters.

A Study on Stability Boundary of Highly Flexible Aircraft With Saturation Constraint

This paper deals with investigating the closed-loop stability boundary of the highly flexible aircraft with structural flexibility and input saturation constraint. A method is presented to analyze the stable region based on the system features of the open-loop instability. In this paper, a dynamic model of highly flexible aircraft is made and the dynamic characteristics are analyzed and the long period mode and stability are investigated in terms of the trimmed model. Considering the saturation constraint of elevator deflection, the closed-loop stability boundary of the system under saturation constraint is discussed by combining the open-loop instability features of highly flexible aircraft. The analysis indicates that the boundary is related to the left eigenvector consistent with the amplitude constraint and the unstable poles of the control signals. Based on the long period instability of the aircraft, the formula of closed-loop stability boundary is analytically obtained. The convergence region of highly flexible aircraft is verified in terms of the LQR controller. The influence of structural flexibility and saturation constraint amplitude of elevator on the stability boundary of highly flexible aircraft is analyzed based on state constraints, which is also compared with the rigid aircraft. The simulation results show that the closed-loop stability of the system is restricted by the open-loop characteristic of the system and the control input saturation constraint.

Stochastic radiation field optimization for microwave staring correlated imaging via spatial correlation minimization

Microwave staring correlated imaging (MSCI) is a staring high-resolution microwave imaging technique, employing the temporal–spatial stochastic radiation field (TSSRF). The imaging capability of MSCI depends on the spatial correlation of the TSSRF, which is equivalent to the incoherence of the sensing matrix in discrete form. A waveform design method for MSCI using multifrequency signals to reduce the spatial correlation of the TSSRF is proposed. The amplitude of each frequency component in the multifrequency signals serves as the design variable. Considering the power and the amplitude constraints in the practical radar system, we first form the waveform design as a constrained optimization problem. Then, it is reformulated as a nonsmooth unconstrained optimization problem by the penalty function method. With the smoothing approximation, the reformulated problem is solved by alternating minimization. Numerical experiments show that the proposed method can decrease the spatial correlation of the TSSRF and improve the imaging performance of MSCI as a result.

An Artificial-Noise-Based Approach for the Secrecy Rate Maximization of MISO VLC Wiretap Channel With Multi-Eves

In this paper, we consider improving the secure performance of multiple-input single-output visible light communication channel in the presence of multiple eavesdroppers with multiple photodiodes. Our goal is to design an optimal artificial-noise (AN) aided transmission strategy to maximize the achievable secrecy rate subject to both sum power constraint and peak amplitude constraint. We consider a joint optimization of the transmit covariance and AN covariance for the non-convex secrecy rate maximization (SRM) problem. In order to solve it, the SRM problem is transformed into a series of single-variable semidefinite programming (SDP) problems without losing any optimality, and a one-dimensional search based algorithm is proposed to handle the converted problem, with polynomial complexity. By exploiting Karush-Kuhn-Tucker conditions of the problem, beamforming is found to be optimal for the confidential information transmission. Simulation results show the superior performance of the proposed AN-aided method compared with two other AN-aided methods and no AN-aided method.

Multi-User Precoder Designs for RGB Visible Light Communication Systems.

In this paper, we design linear precoders for the downlink of a visible light communication (VLC) system that simultaneously serves multiple users. Instead of using phosphor-coated white light-emitting diodes (PWLEDs), we focus on Red-Green-Blue light-emitting diodes (RGB-LEDs) that allow modulating three separate data streams on the three primary colors of the RGB-LEDs. For this system, we design a zero-forcing (ZF) precoder that maximizes the weighted sum rate for a multilevel pulse amplitude modulation (M-PAM). The precoding design in RGB-based systems presents some challenges due to the system constraints, such as the limited power, the non-negative amplitude constraints per light-emitting diode (LED), and the need to guarantee white light emission while transmitting with RGB-LEDs. For comparison purposes, we also consider the ZF design for a PWLED-based system and evaluate the performance of both a PWLED- and an RGB-based system.

Mars entry guidance for mid-lift-to-drag ratio vehicle with control constraints

With the control constraints taken into account, the Mars entry guidance problem of the entry vehicle with a mid-lift-to-drag ratio is investigated in this paper. A dual-loop guidance framework is proposed that the bank angle command is generated in the outer loop and tracked in the inner loop. An innovative energy-based mathematical model is firstly derived. Then, the switching mode of longitudinal guidance and lateral guidance is used in the outer loop, which is based on the velocity. The former is a time-varying sliding mode anti-saturation guidance law considering the amplitude constraint of bank angle, and the latter is obtained by feedback linearization of the heading angle. Hereafter, the heading angle error threshold, which is linear with velocity, is given, and the logic of the bank angle sign is designed to control the lateral motion. Furthermore, the cascade-saturation PD controller is used in the inner loop to meet the angular rate and angular acceleration constraints of bank angle, and the non-overshoot tracking can be realized by reasonably selecting the parameters to satisfy the bank angle amplitude constraint. Numerical examples are presented to demonstrate that the guidance law developed in this paper has a clear physical meaning, a small deviation from the expected state on the basis of meeting the terminal energy requirements, and strong robustness, which is convenient for engineering application.

Demonstration of a Reflectarray With Near-Field Amplitude and Phase Constraints as Compact Antenna Test Range Probe for 5G New Radio Devices

In this work, a reflectarray is proposed to be used as a probe of reduced and portable compact-antenna-test range for 5G new radio devices. The reflectarray works at 28 GHz and produces a quiet zone in the near-field region of the antenna. Considering that the quiet zone specifications are established in terms of the amplitude and phase ripple, a synthesis technique is presented to optimize the near field in the Fresnel region of a reflectarray with amplitude and phase constraints. The proposed technique is based on the generalized intersection approach using the Levenberg–Marquardt algorithm as its backward projector obtaining a novel technique in near-field synthesis. This technique is applied to improve the quiet zone radiated by the proposed reflectarray, overcoming the amplitude and phase limitations of the initial configuration. The solution provided by this process is used to design and manufacture a reflectarray based on a three-parallel-dipole cell. Finally, the prototype is measured in a near-field planar range facility in order to evaluate the radiated quiet zone and demonstrate the methodology. The prototype satisfies the tight requirements in amplitude and phase, obtaining promising results.

Modeling Two Dimensional Touch Pointing.

Modeling touch pointing is essential to touchscreen interface development and research, as pointing is one of the most basic and common touch actions users perform on touchscreen devices. Finger-Fitts Law [4] revised the conventional Fitts' law into a 1D (one-dimensional) pointing model for finger touch by explicitly accounting for the fat finger ambiguity (absolute error) problem which was unaccounted for in the original Fitts' law. We generalize Finger-Fitts law to 2D touch pointing by solving two critical problems. First, we extend two of the most successful 2D Fitts law forms to accommodate finger ambiguity. Second, we discovered that using nominal target width and height is a conceptually simple yet effective approach for defining amplitude and directional constraints for 2D touch pointing across different movement directions. The evaluation shows our derived 2D Finger-Fitts law models can be both principled and powerful. Specifically, they outperformed the existing 2D Fitts' laws, as measured by the regression coefficient and model selection information criteria (e.g., Akaike Information Criterion) considering the number of parameters. Finally, 2D Finger-Fitts laws also advance our understanding of touch pointing and thereby serve as the basis for touch interface designs.

A Backstepping Control of Plant Protection Boom System Considering Input Constraints

Aiming at the plant protection machine boom system with input constraints, uncertain disturbances and various nonlinear factors, a backstepping controller considering input saturation uncertain interference is proposed. The method introduces an auxiliary system, realizes the compensation of control saturation by designing new error variables, and solves the amplitude constraint problem of the control input. By constructing the appropriate Lyapunov function, the stability of the planter boom system is guaranteed. The simulation results show that the designed controller has good tracking performance and robustness.

Optimum Design of Robust Adaptive Controller with Actuator Constraints

In this paper, a direct optimal adaptive nonlinear tracking control method for a class of uncertain Multi-Input Multi-Output (MIMO) nonlinear systems with actuator amplitude constraints in presence of unknown disturbance is developed. In order to handle parametric model uncertainties and external disturbance, an adaptive controller is presented. Particle Swarm Optimization (PSO) algorithm is employed to prevent constraints violation through determining the optimal adaptive controller parameters. The performance of this control approach is studied using a new index function in time-domain, and the stability analysis is conducted by Lyapunov theory. In addition, indicative robot examples are provided to illustrate how investigated method effectively stabilizes system and confines tracking error to prescribed bounds without control input saturation, particularly with large parametric uncertainties.

Ptychography imaging by 1-D scanning with a diffuser

It is beneficial to improve the resolution by a diffuser in imaging systems, because higher frequency information could be involved into the captured patterns via scattering effect. In this paper, a lensless imaging method is designed by 1-D scanning. A diffuser is placed upstream of the object, which is translated in a one-dimensional path and corresponding positions are corrected by cross-correlation. Our method requires a diffraction pattern of the object without a diffuser to speed up convergence and improve resolution. In field reconstruction, the amplitude constraint is added into the iterative phase retrieval algorithm. The high-quality complex-valued images can be obtained with ∼15 patterns. As a ptychography, the proposed method only needs a 1-D device, which could simplify the experimental equipment for reducing costs and measurement time.

A transformed proportional-integral-derivative controller for a multi-vectored propeller aerostat with independent actuator magnitude and rate saturations.

The problem of designing a controller for a multi-vectored propeller airship with independent amplitude and rate saturations is addressed. First, a linear Proportional-Integral-Derivative (PID) controller is introduced for position control without considering the input saturations. Then, two design methods are applied to the traditional PID control output to satisfy the independent amplitude and rate constraints: the nested saturated PID controller (N-PID) and the transformed PID controller (T-PID). The bounded magnitudes and rate outputs of the modified controllers are given. Simulation results showed both controllers have good tracking performance while satisfying independent amplitude and rate saturations. However, the transformed PID controller has the advantage of expressing explicitly the relationship of the actuator magnitude and rate saturations with the parameters of the transformed function such that the actuator saturations are suppressed by calculation but not by trial and error.