Active fault diagnosis provides an efficient means for incipient fault detection by injecting auxiliary signal or modifying controller, which, however, usually infringes on system performance. In this paper, an amicable active fault diagnosis method based on controller modification is developed for incipient fault diagnosis of closed-loop control systems. As any stabilizing controller can be equivalently realized in the observer based form, a switching controller based on a bank of observers is firstly constructed. Then, by making a good tradeoff between the sensitivity of a specific actuator fault and the robustness of other faults and disturbances with the help of an iterative algorithm, the observers in the controller are obtained with high sensitivity to fault, wherein the difference of the outputs are also utilized to enhance incipient fault diagnosis ability. Further, a switching mechanism of the controller is developed, based on which actively switching the observers in the controller can not only detect and isolate the incipient fault timely but also guarantee the system stability. An heating, ventilation and air conditioning (HVAC) system example is finally adopted to demonstrate the effectiveness and superiority of the proposed method.

This work investigates distributed state-of-charge (SOC) balancing for battery energy storage systems (BESSs). Existing predefined-time consensus designs, despite their explicit convergence-time guarantees, may exhibit singularity, induce transient overcurrents under large initial SOC mismatches, and rely on continuous communication. To overcome these limitations, a distributed adaptive predefined-time robust control framework with prescribed performance constraints is developed.Within this framework, a dynamic error envelope is constructed to shape the convergence profile under prescribed performance bounds. In this manner, the convergence time is prescribed a priori, whereas initial transients and the associated current peaks are limited to improve the safety margins of power electronic devices. To enforce the prescribed error evolution under disturbances, an event-triggered (ET)-based distributed predefined-time sliding mode controller is designed, in which a predefined-time adaptive law is incorporated to track mismatched disturbances, thereby mitigating high-frequency chattering while ensuring nonsingular dynamics. In addition, an ET-based model-free state observer with input-to-state stability is developed to support distributed implementation without continuous communication. Predefined-time stability is rigorously established via Lyapunov analysis. Multi-scenario simulations validate the proposed method and confirm reduced communication overhead, prescribed convergence time, and improved transient safety.

This paper focuses on the problem of adaptive predefined-time control for nonstrict-feedback nonlinear systems with sensor and actuator attacks under dynamic event-triggered framework. The property of the fuzzy logic system is employed to address the algebraic loop problem deriving from the nonstrict-feedback form. The command filter and the error compensation mechanism are devised to eliminate the “explosion of complexity” problem and the effect of filtered error in a predefined time, respectively. By means of the Nussbaum gain technique and modified coordinate transformation, the unknown control gains of the sensor and actuator induced by the deception attacks are resolved. By constructing a dynamic variable, a dynamic event-triggered mechanism is devised to reduce resource consumption. It is strictly proved that the closed-loop system is practically predefined-time stable and the output signal converges to a small region near the origin in a predefined time. Finally, a simulation example is utilized to testify the effectiveness and superiority of the proposed predefined-time control algorithm.

This article concentrates on the problem of practically time-synchronized tracking control for multi-input multi-output (MIMO) systems with unmatched nonlinearities and input saturations. Different from the existing approaches, a practically time-synchronized command filtered backstepping (CFB) control scheme is proposed. By integrating modified command filters and control signals designed with norm-normalized sign functions, the newly developed framework not only retains the advantages of the CFB control approach but also guarantees the property of time-synchronized convergence. Specifically, the "explosion of complexity" phenomenon and the influence of filtering errors are simultaneously addressed, and all components of the tracking error can achieve practically synchronous convergence to a small neighborhood of the origin in a finite time, despite the presence of unmatched nonlinearities in high-order systems. Furthermore, novel auxiliary systems are recursively embedded into each step of the time-synchronized CFB design to counteract the effect of input saturation. Rigorous theoretical analyses and comparative simulations demonstrate the rationality, effectiveness, and superiority of the proposed control scheme.

This paper studies movable pinching-antenna (PA) assisted communications, where a single PA can be dynamically placed along a dielectric waveguide to serve multiple users via orthogonal or non-orthogonal multiple access (OMA/NOMA). In contrast to the ideal-lossless waveguide model commonly assumed, our work explicitly incorporates waveguide-power loss, thereby introducing a fundamental trade-off with free-space path loss that jointly determines system performance. By deriving the lower-bound-based suboptimal PA position for two- and three-user scenarios under both with and without waveguide-power loss, we establish a general positioning guideline applicable to multi-user scenarios. Furthermore, we perform a comparative analysis between the proposed single-PA scheme and a static multi-PA scheme. Analytical and simulation results derive the conditions determining which scheme is superior, revealing that the trade-off is fundamentally governed by the relative dominance between the waveguide-power loss and the free-space path loss. Simulation results validating our analytical derivations also confirm that the proposed PA positioning rule in NOMA-based PASS holds for both successive interference cancellation (SIC) decoding orders, demonstrating its robustness regardless of whether the near user decodes the far user’s signal first or vice versa.

In this letter, we investigate the wireless communication system assisted by hybrid intelligent reflecting surface (RIS), which is composed of both passive and active elements integrated reflection-type amplifiers. Different from conventional hybrid RIS system, the amplifying power used at active RIS is considered as one part of the total power for overall system. Under this condition, we present the exact closed-form expression of the outage probability (OP) and investigate the optimal allocations of the RIS elements and power budget for signal-to-interference-plus-noise ratio (SINR) maximization. In addition, we analyze the amplification factor and corresponding dynamic noise, as well as derive the threshold of the amplification factor for the proposed scheme. Finally, simulation and numerical results show that the proposed hybrid RIS scheme is significantly preferable over the conventional RIS scheme if the amplification factor of the proposed scheme is smaller than that of the threshold.

With the flourishing development of sixth-generation wireless networks, the demand of spectrum efficiency rapidly increases, in order to support the demands of high-quality data transmission and connections of massive users. Among various promising technologies, the technology of near-field communications provides a great potential to address such an issue due to the unique spherical-wave channels for electromagnetic (EM) propagation. In this article, multiple-input-single-output (MISO) near-field communications is comprehensively studied to clarify the influences of the shape and structure of uniform planar array (UPA) on the system performance, considering three cases with uniform linear array (ULA), rectangular UPA, and circular UPA. In particular, we reveal the properties of rapid deterioration for signal-to-noise ratio (SNR) from the reduced projection aperture in near-field communications and investigate the single spherical crown antenna design and spherical crown antenna array design in order to address this issue. Moreover, we also characterize the role of antenna projection aperture in detail, and theoretically analyze the shape of UPA, yielding the corresponding exact closed-form expressions for SNR and outage probability (OP). Based on these above analytical results, we find out that adjusting the spacing between adjacent antennas to control the relative angle between user and selected antennas is an efficient way to improve the projection aperture of antenna and SNR. Simulation results are shown to well match analytical results, which validate the correctness of our analysis, clarifying that our proposed designs outperform the conventional works and illustrating a better stability for angle variations.

Since adopting the spherical wave model in near-field, the imperfect resolution of beamfocusing has significantly enabled non-orthogonal multiple access (NOMA) technique to enhance spectrum efficiency, where one user’s beam can be served for additional users. However, as additional users sharing the same radio resources to enhance network density, physical layer security (PLS) becomes increasingly critical, especially in scenarios that eavesdroppers could potentially intercept communications intended for legitimate users. To address such issue, a comprehensive investigation of the resolution is proposed to distinguish NOMA users and eavesdroppers within a near-field communication (NFC) framework, considering both angular and distance domains. Furthermore, by leveraging the resolution capabilities, we individually consider the positions of NOMA users and eavesdroppers, which significantly impacts the power allocations, decoding orders and security performances. Moreover, our simulation results verify the analytical results and demonstrate the improvement of the average secrecy rate as well as secrecy outage probability (SOP), offering a novel perspective to enhance future NFC systems.

Feedback signal delays present a common challenge in the online decision-making processes of various real-world systems, such as real-time economic dispatch in power systems. These delays, primarily induced by limited computational capabilities or unknown parameter changes, can significantly hinder the performance or even effectiveness of online decision-making strategies. This study investigates distributed optimization over time-varying unbalanced networks with delayed feedback signals. We propose discrete-time distributed online algorithms for both constrained and unconstrained optimization problems. Each node in the network has access only to its individual time-varying local objective function with a delayed time sequence. At each decision-making step, each node selects the appropriate local online behavior, which depends on the information from its neighbor nodes, towards the minimization of global cumulative cost function value. We demonstrate that sublinear regrets can be ensured as long as the time-varying unbalanced communication networks maintain$\mathcal {B}$-strong connectivity. For a general convex or$\mu $-strongly convex local objective function, the network regret and individual regret grow as$\mathcal {O}((\ln (T))^{2})$and$\mathcal {O}(\sqrt {T})$, respectively, and are intrinsically related to the feedback delays and step sizes. To validate the proposed algorithms, numerical studies are carried out on constrained distributed time-varying economic dispatch problems.

Reduced-order diagnostic observer (RODO) is more desirable in the monitoring of electrical systems due to the advantages of low computation consumption and flexible structure, while its tradeoff design remains a longstanding unsettled issue in model-based fault diagnosis research. In this paper, an integrated design scheme of RODO is developed for event-triggered systems, making, for the first time, a direct tradeoff between false alarm rate (FAR) and fault detection rate (FDR). Firstly, by considering the effects of disturbance, fault and event-triggered transmission error on the residual, along with the principle of residual evaluation, the event-triggered FAR and FDR are defined and their relationship is established. Then, by introducing the so-called quasi-Luenberger constraints, the Luenberger equality challenges in the optimization of performance tradeoff are removed and an iterative algorithm is developed for the tradeoff design of full-order or high-order diagnostic observer. Based on this, the deviations between the quasi-Luenberger and Luenberger equalities are further eliminated with the assistance of another iterative algorithm to achieve the tradeoff of RODO. Finally, a DC microgrid simulation is adopted to demonstrate the effectiveness of the proposed design scheme as well as its advantages over other schemes.

This article investigates the problem of removing the peaking phenomenon in the stabilization of a class of nonlinear cascaded systems using linear partial state feedback within a quadratic program (QP) framework. By appropriately designing the QP and selecting its parameters, the inter-subsystem cascaded input terms are effectively constrained within a desirable control-invariant set, thereby eliminating undesirable transient peaks. Semi-global stabilization of the overall system is achieved through only minimal modifications to the nominal linear feedback controllers. Owing to the simplicity of the resulting controller structure and the real-time efficiency of QP solvers, the proposed method is readily applicable to practical systems. Numerical examples from previous studies are revisited to demonstrate the effectiveness and robustness of the proposed control strategy.

This article focuses on the problem of predefined-time adaptive output-feedback tracking control with prescribed performance for a quadrotor unmanned aerial vehicle (QUAV). Fuzzy logic systems (FLSs) are utilized to identify the unknown nonlinear dynamics of QUAV, and a fuzzy state observer is devised to estimate immeasurable states. By using the command filter, the problem of “explosion of complexity” is successfully averted, meanwhile the influence of filtered error is eliminated by way of the fractional power error compensation mechanism. The issue of singularity is effectively tackled by the hyperbolic tangent function's property and L'Hospital's rule. A predefined-time performance function is inserted into the control scheme to ensure that the tracking errors are restricted to the preassigned performance bounds. It is strictly proven that the closed-loop system is practically predefined-time stable, and the position and attitude tracking errors are driven into a small region around zero in a predefined time. Finally, a comparative simulation example is provided to show the validity and superiority of the proposed predefined-time adaptive control algorithm.

With the further investigation and utilization of the extremely large-scale antenna array (ELAA) and Terahertz (THz) band, as well as the increasingly stringent standards of regulatory agencies, the near-field communications are evolving into the norm of intelligent transportation systems. In this work, we propose a novel beamfocusing scheme to improve the system performance for the reconfigurable intelligent surface (RIS)-aided hybrid near- and far-field communications with multi-unmanned aerial vehicle (UAV). Compared to conventional schemes without considering the near-field beam pattern with a finite depth, in our proposed scheme, the RIS only serves one UAV, while other UAVs are within the radiation range of the concentrated signal energy by beamfocusing. Specifically, we study the polar radius and angular deviations between UAVs with a given beamfocusing gain, aiming to reveal the impact of RIS structure on beamfocusing gain. We also make a fair comparison between the proposed scheme and allocated RIS scheme, deriving the feasible reference distance. In addition, we study the feasibility for different RIS structures focusing on the beamfocusing gain, which has the potential to improve the system performance. Simulation results demonstrate that the proposed scheme is always superior than that of the allocated RIS scheme within the feasible reference distance.

This article focuses on the predefined-time adaptive fuzzy bipartite consensus control problem for multiquadrotors (MQs) under malicious attacks. The unknown nonlinear dynamics of MQs are effectively identified via the approximation capability of fuzzy logic systems. By integrating the command filter and the error compensation mechanism into the backstepping design procedure, the “explosion of complexity” issue and the effect of filtered error are concurrently eliminated. Additionally, the problem of singularity is skillfully surmounted by the feature of hyperbolic tangent functions and L'Hospital's rule. To deal with unknown malicious attacks, the quadratic-fraction actual controllers for MQs are devised based on the adaptive technique, where the lower bounds of attack signals are not required. It is proven that the closed-loop system is practically predefined-time stable, and the bipartite consensus errors converge into a small neighborhood of the origin within a predefined time. A simulation example is conducted to verify the effectiveness and superiority of the developed predefined-time control strategy.

An approach with multi-rate samplings has been proposed to deal with the uncontrollable challenge of nonholonomic system's linearization around equilibrium in its stabilization problem. Concerning unknown nonlinearities, one scaling factor has been introduced to guarantee global asymptotic stability using techniques of linear feedback domination. Due to the interplay between this scaling factor and system's sampling period under multi-rate samplings, not only controllability of the whole nonholonomic systems has been guaranteed but also flexibility of choosing different sampling periods has been increased. Stabilization of uncertain unicycle under different sampling periods is also presented to demonstrate our proposed scheme and verify the established theoretical results.

This study concentrates on the differential private distributed optimization problem with an event-triggered mechanism, whose goals include preserving the privacy of agents’ initial states and local cost functions and improving communication efficiency. A distributed event-triggered mechanism is integrated into the differentially private subgradient-push distributed optimization algorithm and then a new algorithm named as DP-ETSP is designed, where the real-time information propagation among agents is avoided. Additionally, under the proposed event-triggered mechanism, an analysis of mean-square consensus and optimality over time-varying directed networks is made when the added Laplace noises meet some specific decaying conditions. Convergence rate results are further established under a specific stepsize, which are equal to the rate of stochastic gradient-push algorithm without event-triggered communication. Moreover, the differential privacy preservation performance is analyzed and the rule for selecting privacy level is discussed. Finally, the feasibility and effectiveness of DP-ETSP are verified in two simulation cases.

Due to the inherent broadcast characteristics of wireless communications, the data transmission is difficult to be shielded from unintended recipients. Secure communications over wireless channel is regarded as an effective way to overcome this issue in the design of wireless networks. In this paper, a new cooperative relaying system based on partial non-orthogonal multiple access (P-NOMA) is proposed, where two relays help the communications between the source and destination nodes in the presence of an eavesdropper (Eve). Specifically, after receiving the P-NOMA signals transmitted from the base station, the relay nodes decode and forward the receptions under the attack of a passive Eve. To improve the physical layer security (PLS) of the proposed system, we design four cooperative schemes for signals decoded at the relays and destination, where maximum ratio combination (MRC) technique is adopted to both destination and Eve to construe the worst case for achievable secrecy rate. Without lose of generality, the channel conditions (weak or strong), new power allocations, decoding principles and Eve locations are considered in designing forwarding schemes. In particular, to further improve the achievable secrecy rate, we also propose that, if the Eve locating near to the weak relay node, the weak relay only forwards the signal with lower power allocation factor at the base station. The closed-form expressions of the achievable secrecy rates are derived for the proposed schemes over Rayleigh fading and Nakagami-$m$fading channels, which well match the simulation results. By means of the numerical result, it corroborates the superiority of the proposed P-NOMA schemes over the conventional NOMA schemes. It is also revealed that, with an increasing overlap ratio, the advantage in terms of the secrecy rate becomes more remarkable.

In this paper, we study a distributed convex optimization problem with inequality constraints. Each agent is associated with its cost function, and can only exchange information with its neighbors. It is assumed that each cost function is convex and the optimization variable is subject to an inequality constraint. The objective is to make all the agents reach consensus, and meanwhile converge to the minimum point of the sum of local cost functions. A distributed protocol is proposed to guarantee that all agents can reach consensus in finite time and converge to the optimal point within the inequality constraints. Based on the ideas of parameter projection, the protocol includes two decent directions. One makes the cost function decrease, and the other makes agents step forward to the constraint set. It is shown that the proposed protocol solves the problem under connected undirected graphs without using a Lagrange multiplier technique. Especially, all of the agents could reach the constraint sets in finite time and stay in there after. The method could also be used in the centralized optimization problems.