Department of Electrical Engineering

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The α-η-κ-μ fading model is a very useful instrument to accurately describe various radio wave propagation scenarios. In this paper, we study the effective throughput performance of communication systems over the α-η-κ-μ fading channels. Novel and exact expressions for the effective throughput over α-η-κ-μ channels are derived, and the effective throughput of multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) systems over some widely used small-scale fading models are presented based on the derived results. To obtain more understandings on the impact of physical channel characteristics and system configuration on the effective throughput, closed-form expressions for the asymptotic effective throughput at high signal-to-noise ratio (SNR) regimes are also obtained. The results reveal the underlying connections between different physical channel parameters (e.g., scattering level, phase correlation, channel nonlinearity, multipath clustering, and channel imbalance) and the effective throughput. It is found that the effective throughput improves with the increase of channel nonlinearity and number of multipath clusters, and the high-SNR slope is only dependent on the channel nonlinearity and the number of multipath clusters present in the physical channel. © 2013 IEEE.

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IEEE Access

Effective Throughput Analysis of α-η-κ-μ Fading Channels

In this paper, a method for new controller design ensuring the arbitrary time of convergence is proposed. The sufficient condition for Lyapunov stability is also given for this arbitrary chosen time stable system. Disturbances have been taken care of by introducing sliding mode control in the design approach. Finally, the efficacy of the proposed method is illustrated through a practical system, viz., magnetic suspension system. © 2019 Elsevier Ltd

Automatica

Design of controllers with arbitrary convergence time

This paper proposes a new class of uniform continuous higher-order sliding mode algorithm (UCHOSMA) for the arbitrary relative degree systems. The proposed methodology is a combination of two controllers where one of the components is a uniform super-twisting control which acts as the disturbance compensator and the second part gives the uniform finite time convergence for the disturbance free system. This algorithm provides uniform finite time convergence of the output and its higher derivatives using an absolutely continuous control signal and thus alleviating the chattering phenomenon. The attractive feature of the proposed controller is that irrespective of the different initial conditions, the control is able to bring the states of the system to the equilibrium point uniformly in finite time. The effectiveness of the proposed controller has been demonstrated with both simulation and experimental results. © 2021 by ASME.

Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME

A New Class of Uniform Continuous Higher-Order Sliding Mode Controllers

Machine learning (ML) methods are popular in several application areas of multimedia signal processing. However, most existing solutions in the said area, including the popular least squares, rely on penalizing predictions that deviate from the target ground-truth values. In other words, uncertainty in the ground-truth data is simply ignored. As a result, optimization and validation overemphasize a single-target value when, in fact, human subjects themselves did not unanimously agree to it. This leads to an unreasonable scenario where the trained model is not allowed the benefit of the doubt in terms of prediction accuracy. The problem becomes even more significant in the context of more recent human-centric and immersive multimedia systems where user feedback and interaction are influenced by higher degrees of freedom (leading to higher levels of uncertainty in the ground truth). To ameliorate this drawback, we propose an uncertainty aware loss function (referred to as MSE*) that explicitly accounts for data uncertainty and is useful for both optimization (training) and validation. As examples, we demonstrate the utility of the proposed method for blind estimation of perceptual quality of audiovisual signals, panoramic images, and images affected by camera-induced distortions. The experimental results support the theoretical ideas in terms of reducing prediction errors. The proposed method is also relevant in the context of more recent paradigms, such as crowdsourcing, where larger uncertainty in ground truth is expected. IEEE

IEEE Transactions on Neural Networks and Learning Systems

Interval-Based Least Squares for Uncertainty-Aware Learning in Human-Centric Multimedia Systems

Authors’ Reply To: (CI 20-0229) Comments on Design of controllers with arbitrary convergence time [Automatica 108710]

Power converters, operating under fixed switching control, observe a substantial efficiency drop at light load owing to the associated fixed switching losses. To maintain the flat efficiency curve, varying the switching frequency depending on the load has been explored in the literature as a better alternative to fixed-frequency operation. This paper presents Event-triggered Sliding Mode Control (ETSMC) based variable frequency modulation scheme for power converters. The presented strategy leverage converter dynamics to execute control signal. This need-based switching technique ensures reduced switching losses and hence improved efficiency, without compromising on performance. Widely adopted switching reduction technique of Hysteresis modulation based SMC is established as a special case of ETSMC, thus highlighting the proposed scheme's generic nature. The scheme is demonstrated on an isolated half-bridge converter. Simulations, as well as experimentation results, are included to support the theory. © 2020

Control Engineering Practice

Event-triggered Sliding Mode Control for light load efficiency improvement in Power Converters

Inverter connected single-phase AC loads cause second-order oscillations in source currents and DC bus voltage. These oscillations degrade the efficiency and reliability of the dc microgrid. In this paper, an adaptive sliding mode control based output impedance shaping (ASMC-OIS) methodology is proposed for voltage regulation, proportional load sharing, and second-order ripple management in a dc microgrid. By using the proposed control method, the magnitude of the output impedance of the source interfacing converter is increased at 2fac programmably, which results in the reduction of second-order ripple currents propagating through the converter. Instead, it is propagated to the dc-link capacitor or towards the nodes which consists of some ripple absorption active or passive filter. This leads to an increase in the energy density of the ripple filters. The dynamic consensus-based secondary control is incorporated to ensure proportional load current sharing. A graph theoretical analysis is presented to analyze per unit load sharing among all the nodes. Stability of the proposed controller is analyzed considering multiple source nodes using Lyapunov's approach. A dc microgrid consisting of parallel-connected dc-dc boost converters, dc load, and inverter load is simulated to verify the proposed control strategy. The proposed ASMC-OIS methodology is validated through experimentation. © 2010-2012 IEEE.

IEEE Transactions on Sustainable Energy

Adaptive-SMC Based Output Impedance Shaping in DC Microgrids Affected by Inverter Loads

Reducing the operating voltage and processing temperature are the crucial factors in the progression of organic field-effect transistors (OFETs) in flexible portable applications. Here, we have demonstrated RF sputtering deposited Ba0.5Sr0.5TiO3(BST) as high-k dielectric material for high performance operationally stable flexible low voltage operated OFETs. It was found that the BST deposition parameters can enormously affect the film properties like dielectric constant, surface morphology, and the crystallinity. The room-temperature-deposited BST films were found to be amorphous in nature with low leakage current, high dielectric constant, smoother surface morphology and high electromechanical stability. The fabricated flexible OFETs with optimized BST film have shown excellent electrical performance with max. field-effect mobility (μmax) of 1.01 cm2 V-1s-1 with near zero threshold voltage (VTH) and Ion/Ioff of ?105 while operating at -5 V. The fabricated devices were found to be operationally and electromechanically stable when subjected to various electrical and mechanical stress. The investigation has demonstrated that the proposed room-temperature-deposited BST is a suitable candidate for gate dielectric in low voltage operated, long-term electromechanical stable flexible OFETs. Copyright © 2020 American Chemical Society.

ACS Applied Electronic Materials

High Performance Flexible Organic Field-Effect Transistors with Barium Strontium Titanate Gate Dielectric Deposited at Room Temperature

We report an ultralow power consuming and forming-free hybrid flexible resistive random access memory device fabricated with poly(4-vinylphenol) (PVP):MoS 2 composite and HfO x bilayer, exhibiting threshold switching with ultralow ON-current of 500 nA. While the higher concentration of MoS 2 imparted the higher leakage current in the devices, the lower concentration devices exhibited decent switching with set and reset powers as low as 270 and 0.1 nW, respectively. The ultralow switching current indicates the formation of multiple weak nanosized conductive filaments created due to electromigration of Ag atoms under external bias. Moreover, heating temperature-dependent study of switching behavior confirms the metallic nature of the filament as the low resistance state (LRS) current falls significantly with rising temperature. Furthermore, these devices exhibited remarkable mechanical strength on flexible substrate with demonstration of nondestructive switching characteristics at a bending radius as low as 2.5 mm and after 100 consecutive compressive and tensile strain cycles at ±5-mm radius. The ultralow switching current with high flexibility indicates the capability of devices for advancement toward future low-power flexible memories and computing systems. © 1963-2012 IEEE.

IEEE Transactions on Electron Devices

Ultralow Current Switching in Flexible Hybrid PVP:MoS 2 /HfO x Bilayer Devices

Flexible devices have been in focus for their applications in wearable electronics, displays, sensors, and memory. PVP/HfOx based hybrid resistive random access memory devices were demonstrated on flexible PET substrates to study their resistive switching characteristics and memory application. These RRAM devices exhibited decent repeatability of more than 100 cycles with excellent Ion/Ioff of 106 at 0.2 V as read voltage. With retention time of more than 6000 s and reliable switching operation, the fabricated devices have potential to be embedded in flexible electronic applications. Moreover, conduction mechanism in devices was found to be ohmic at lower voltage levels in high resistance state (HRS) and space charge limited conduction at higher voltage levels, occurring mainly due to traps sites available in PVP and HfOx. The AFM image confirms the presence of pinholes at PVP surface which will eventually assist in filament formation. © 2020 IEEE.