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Prof. Ratnesh Kumar’s research area is, “ESSeNCE: Embedded Software, Sensors, Networks, Cyberphysical, Energy”, spanning Sensors, Data Analytics, Networks, Controls, and Formal Methods for Correctness/Accuracy, Efficiency, Safety, Stability, Security, Resiliency, Diagnosability, and Prognosability, in Cyber-Physical (Hybrid) and Embedded and Real-time Systems, Model-based Software and Web-services, Agri-, Bio- and Envionmental Sensing, Wearables, and Power Grid and Energy Harvesting. For full list of publications, refer Ratnesh Kumar’s CV

Prof. Kumar has published extensively in the areas of ESSeNCE: 374 peer reviewed articles (139 Journal articles, 209 Conference articles, and 12 book-chapters, 1 Textbook, and 13 Patents—9 already awarded, and 5 already licensed by companies).


Sensors:

Agriculture Sensing

    • Kashyap, Bhuwan, and R. Kumar. “A Novel Multi-Set Differential Pulse Voltammetry Technique for Improving Precision in Electrochemical Sensing.” Biosensors and Bioelectronics, 2022.
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    • Kashyap, Bhuwan, and Ratnesh Kumar. “A Plug-and-Play Type Field-Deployable Bio-Agent-Free Salicylic Acid Sensing System.” IEEE Sensors Journal, vol. 21, no. 21, November 2021.
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    • Tabassum, Shawana, Divyesh P. Kumar, and Ratnesh Kumar. “Copper Complex-Coated Nanopatterned Fiber-Tip Guided Mode Resonance Device for Selective Detection of Ethylene.” IEEE Sensors Journal, vol. 21, no. 16, August 2021.
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    • Kashyap, Bhuwan, and Ratnesh Kumar. “Sensing Methodologies in Agriculture for Monitoring Biotic Stress in Plants Due to Pathogens and Pests.” Inventions, vol. 6, no. 2, April 2021.
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    • Kashyap, Bhuwan, and Ratnesh Kumar. “Sensing Methodologies in Agriculture for Soil Moisture and Nutrient Monitoring.” IEEE Access, vol. 9, 2021.
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    Development and deployment of sensing technologies is one of the main steps in achieving sustainability in crop production through precision agriculture. Key sensing methodologies developed for monitoring soil moisture and nutrients with recent advances in the sensing devices reported in literature using those techniques are overviewed in this article. The soil moisture determination has been divided into four main sections describing soil moisture measurement metrics and laboratory-based testing, followed by in-situ, remote and proximal sensing techniques. The application, advantages and limitations for each of the mentioned technologies are discussed. The nutrient monitoring methods are reviewed beginning with laboratory-based methods, ion-selective membrane based sensors, bio-sensors, spectroscopy-based methods, and capillary electrophoresis-based systems for inorganic ion detection. Attention has been given to the core principle of detection while reporting recent sensors developed using the mentioned concepts. The latest works reported on the different sensing methodologies point towards the trend of developing low-cost, easy to use, field-deployable or portable sensing systems aimed towards improving technology adoption in crop production leading to efficient site-specific soil and crop management which in turn will bring us closer to reaching sustainability in the practice of agriculture.

    • Kashyap, Bhuwan, Charles K. Sestok, Anand G. Dabak, Srinath Ramaswamy, and Ratnesh Kumar. “Ultra-Precision Liquid Level Sensing Using Impedance Spectroscopy and Data Analytics.” IEEE Sensors Journal, vol. 19, no. 20, October 2019.
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    • Tabassum, Shawana, Liang Dong, and Ratnesh Kumar. “Determination of Dynamic Variations in the Optical Properties of Graphene Oxide in Response to Gas Exposure Based on Thin-Film Interference.” Opt. Express, vol. 26, no. 5, March 2018.
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    • Tabassum, Shawana, Liang Dong, and Ratnesh Kumar. “Determination of Dynamic Variations in the Optical Properties of Graphene Oxide in Response to Gas Exposure Based on Thin-Film Interference.” Opt. Express, vol. 26, no. 5, March 2018.
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    We present an effective yet simple approach to study the dynamic variations in optical properties (such as the refractive index (RI)) of graphene oxide (GO) when exposed to gases in the visible spectral region, using the thin-film interference method. The dynamic variations in the complex refractive index of GO in response to exposure to a gas is an important factor affecting the performance of GO-based gas sensors. In contrast to the conventional ellipsometry, this method alleviates the need of selecting a dispersion model from among a list of model choices, which is limiting if an applicable model is not known a priori. In addition, the method used is computationally simpler, and does not need to employ any functional approximations. Further advantage over ellipsometry is that no bulky optics is required, and as a result it can be easily integrated into the sensing system, thereby allowing the reliable, simple, and dynamic evaluation of the optical performance of any GO-based gas sensor. In addition, the derived values of the dynamically changing RI values of the GO layer obtained from the method we have employed are corroborated by comparing with the values obtained from ellipsometry.

    • Pandey, Gunjan, Robert J. Weber, and Ratnesh Kumar. “Agricultural Cyber-Physical System: In-Situ Soil Moisture and Salinity Estimation by Dielectric Mixing.” IEEE Access, vol. 6, 2018.
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    • Tabassum, Shawana, Ratnesh Kumar, and Liang Dong. “Nanopatterned Optical Fiber Tip for Guided Mode Resonance and Application to Gas Sensing.” IEEE Sensors Journal, vol. 17, no. 22, November 2017.
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    • Tabassum, Shawana, Ratnesh Kumar, and Liang Dong. “Plasmonic Crystal-Based Gas Sensor Toward an Optical Nose Design.” IEEE Sensors Journal, vol. 17, no. 19, October 2017.
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    • Xu, Zhen, Xinran Wang, Robert J. Weber, Ratnesh Kumar, and Liang Dong. “Nutrient Sensing Using Chip Scale Electrophoresis and In Situ Soil Solution Extraction.” IEEE Sensors Journal, vol. 17, no. 14, July 2017.
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    • Ali, Md. Azahar, Huawei Jiang, Navreet K. Mahal, Robert J. Weber, Ratnesh Kumar, Michael J. Castellano, and Liang Dong. “Microfluidic Impedimetric Sensor for Soil Nitrate Detection Using Graphene Oxide and Conductive Nanofibers Enabled Sensing Interface.” Sensors and Actuators B: Chemical, vol. 239, February 2017.
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    This paper reports on a microfluidic impedimetric nitrate sensor using a graphene oxide (GO) nanosheets and poly(3,4-ethylenedioxythiophene) nanofibers (PEDOT-NFs) enabled electrochemical sensing interface. The sensor has demonstrated the ability to accurately detect and quantify nitrate ions in real samples extracted from soil. The PEDOT NFs-GO composite serves as an effective matrix for immobilization of nitrate reductase enzyme molecules. The oxygenated functional groups available at GO allows an increased charge transfer resistance of the electrochemical electrode. Microscopic, spectroscopic, and electrochemical studies were systematically conducted to illustrate synergic interactions between the GO and PEDOT NFs. The sensor provides a sensitivity of 61.15Ω/(mg/L)/cm2 within a wide concentration range of 0.44–442mg/L for nitrate ions in agricultural soils. The detection limit of the sensor is 0.135mg/L with good specificity, reliability, and reproducibility.

    • Ali, Md. Azahar, Huawei Jiang, Navreet K. Mahal, Robert J. Weber, Ratnesh Kumar, Michael J. Castellano, and Liang Dong. “Microfluidic Impedimetric Sensor for Soil Nitrate Detection Using Graphene Oxide and Conductive Nanofibers Enabled Sensing Interface.” Sensors and Actuators B: Chemical, vol. 239, 2017.
    • BibTeX
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    This paper reports on a microfluidic impedimetric nitrate sensor using a graphene oxide (GO) nanosheets and poly(3,4-ethylenedioxythiophene) nanofibers (PEDOT-NFs) enabled electrochemical sensing interface. The sensor has demonstrated the ability to accurately detect and quantify nitrate ions in real samples extracted from soil. The PEDOT NFs-GO composite serves as an effective matrix for immobilization of nitrate reductase enzyme molecules. The oxygenated functional groups available at GO allows an increased charge transfer resistance of the electrochemical electrode. Microscopic, spectroscopic, and electrochemical studies were systematically conducted to illustrate synergic interactions between the GO and PEDOT NFs. The sensor provides a sensitivity of 61.15Ω/(mg/L)/cm2 within a wide concentration range of 0.44–442mg/L for nitrate ions in agricultural soils. The detection limit of the sensor is 0.135mg/L with good specificity, reliability, and reproducibility.

    • Pandey, Gunjan, Ratnesh Kumar, and Robert J. Weber. “A Low RF-Band Impedance Spectroscopy Based Sensor for In Situ, Wireless Soil Sensing.” IEEE Sensors Journal, vol. 14, no. 6, June 2014.
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Bio-Sensors

    • Kashyap, Bhuwan, and R. Kumar. “A Novel Multi-Set Differential Pulse Voltammetry Technique for Improving Precision in Electrochemical Sensing.” Biosensors and Bioelectronics, 2022.
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    • Kundu, Souvik, Shawana Tabassum, and Ratnesh Kumar. “Plasmonic Point-of-Care Device for Sepsis Biomarker Detection.” IEEE Sensors Journal, vol. 21, no. 17, September 2021.
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    • Kundu, Souvik, Shawana Tabassum, and Ratnesh Kumar. “A Perspective on Sepsis Pathogenesis, Biomarkers and Diagnosis: A Concise Survey.” Med Devices Sens DEVICES & SENSORS, vol. 3, no. 4, June 2020.
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    • Tabassum, Shawana, and Ratnesh Kumar. “Advances in Fiber-Optic Technology for Point-of-Care Diagnosis and In Vivo Biosensing.” Advanced Materials Technologies, vol. 5, no. 5, 2020.
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    • Ali, Md. Azahar, Shawana Tabassum, Qiugu Wang, Yifei Wang, Ratnesh Kumar, and Liang Dong. “Integrated Dual-Modality Microfluidic Sensor for Biomarker Detection Using Lithographic Plasmonic Crystal.” Lab Chip, vol. 18, no. 5, 2018.
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    • Xu, Zhen, Xinran Wang, Robert J. Weber, Ratnesh Kumar, and Liang Dong. “Nutrient Sensing Using Chip Scale Electrophoresis and In Situ Soil Solution Extraction.” IEEE Sensors Journal, vol. 17, no. 14, July 2017.
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Energy:

Energy Harvesting

    • Pathak, Madhav, Cheng Huang, and Ratnesh Kumar. “Start-up Circuit for Synchronous Switched Energy Extraction from Triboelectric Energy Harvesters.” 2023 IEEE 16th Dallas Circuits and Systems Conference (DCAS), 2023.
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    Ambient triboelectric vibration energy harvesters used for self-powering IoT sensor nodes provide enhanced power output when interfaced with synchronous switched energy extraction circuits. However, these active interface circuits require overhead power for their switching actions and may suffer from cold-start issue, for example, in batteryless IoT system. This work develops a start-up circuit that initiates energy extraction via passive full-wave-rectification path and on accumulation of enough energy for control actions, autonomously toggles to an active synchronous switched optimal path, maximizing the energy extraction from the harvester. We integrate the here developed start-up circuit with our previously demonstrated multi-shot synchronous charge extraction (MS-SCE) circuit. The resultant self-starting end-to-end power management circuit is designed and simulated in TSMC 70V 0.18μm BCD process and its operation is validated in a triboelectric energy harvester powered batteryless IoT setting. The transition from passive to active optimal steady-state mode is achieved in 41.1 seconds and the start-up circuit’s overhead/parasitic-loss is only 3.43 μW or 6.7% of the harvested power in the steady-state.

    • Pathak, Madhav, Shuo Xie, Cheng Huang, and Ratnesh Kumar. “High-Voltage Triboelectric Energy Harvesting Using Multi-Shot Energy Extraction in 70-V BCD Process.” IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 69, no. 5, May 2022.
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    Triboelectric Nanogenerators (TENG) suitable for mechanical energy harvesting typically have ultra-high open-circuit voltage in several hundreds of volts, challenging the energy extraction circuit (EEC) design required for charging load battery/capacitor. Here, we present a novel multi-shot switched EEC that extracts energy in multiple discrete steps to regulate the TENG voltage below the breakdown limit of the technology (70 V in our case), making it suitable for Integrated Circuit (IC) implementation. The proposed strategy maintains high TENG voltage just below the breakdown limit to offer a high electrostatic retardation, enhancing the work done against it by the mechanical source in the form of transduced electrical energy. Mathematical derivation of the circuit’s output shows a constant transduction power at all load voltages, fully eliminating Maximum Power Point (MPP) Tracking and saving power for the same. The design and simulation of the proposed EEC in TSMC 0.18 μm BCD process achieve a maximum power conversion efficiency of 63.3% and a 1.91x gain over even an ideal conventional Full Wave Rectifier (FWR) circuit at its optimal MPP load (gain will be higher for a real FWR implementation).

    • Pathak, Madhav, and Ratnesh Kumar. “Synchronous Pre-Biasing of Triboelectric Nanogenerator for Enhanced Energy Extraction.” IEEE Transactions on Power Electronics, 2022.
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    Triboelectric Nanogenerator (TENG) is a class of ambient mechanical energy harvesters used to augment the battery life of electronic devices such as sensors in implantables, wearables, and Internet of Things (IoT) applications. In this work, the fundamentals of pre-biasing (pre-charging) the TENG at the start of the operation cycle to enhance the per-cycle extracted energy is presented. The energy gain is mathematically formulated, and the optimum pre-biasing voltage (equivalently charge) is derived by analyzing the energy exchange between the mechanical and the electrical domain over a periodic cycle. Further, a novel Energy Extraction Circuit (EEC) termed as "Pre-biased Synchronous Charge Extraction (pSCE)" is introduced to 1) Realize synchronous pre-biasing of TENG using the load battery itself and 2) Achieve enhanced energy extraction from TENG. Energy output per-cycle is derived analytically for the pSCE circuit and compared to the state of the art Synchronous Charge Extraction (SCE) circuit. The experimental implementation is performed for the proposed pSCE circuit that shows a 6.65 fold gain over the Full Wave Rectifier (standard EEC) and 1.45 over the SCE circuit for a 5V battery load.

    • Pathak, Madhav, and Ratnesh Kumar. “Self-Propelled Pre-Biased Synchronous Charge Extraction Circuit for Triboelectric Nanogenerator.” IEEE Journal of Emerging and Selected Topics in Power Electronics, 2022.
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    Triboelectric Nanogenerators (TENGs) are suitable for harvesting ambient mechanical energy to increase the battery life of Internet of Things (IoT) devices. Energy Extraction Circuits (EECs) are required as an interface between TENG and the onboard battery load to rectify and improve the energy transfer efficiency. Here, for the first time, a novel ‘Self-propelled Pre-biased Synchronous Charge Extraction (spSCE)’ EEC is presented with theoretical analysis as well as experimental results. The proposed EEC offers a universal plug-and-play solution for any TENG operating under any ambient vibration, owing to its self-propelled switching feature. In addition, its inbuilt pre-biasing (pre-charging of TENG capacitor at the operation extremes) action enhances the net transduced energy from the mechanical source beyond the per-cycle energy limit for any non-pre-biasing EEC set by the existing Synchronous Charge Extraction (SCE) circuit. Accounting for the energy costs of spSCE actions, our experiments validated 119.7% (respectively, 163.7%) energy gain over the SCE circuit at a load of 5V (respectively, 15V).

    • Pathak, Madhav, and Ratnesh Kumar. “Synchronous Inductor Switched Energy Extraction Circuits for Triboelectric Nanogenerator.” IEEE Access, vol. 9, 2021.
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    • Singh, Kanishka Aman, Madhav Pathak, Robert J. Weber, and Ratnesh Kumar. “A Self-Propelled Mechanism to Increase Range of Bistable Operation of a Piezoelectric Cantilever-Based Vibration Energy Harvester.” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 65, no. 11, November 2018.
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    • Singh, Kanishka Aman, Ratnesh Kumar, and Robert J. Weber. “A Broadband Bistable Piezoelectric Energy Harvester With Nonlinear High-Power Extraction.” IEEE Transactions on Power Electronics, vol. 30, no. 12, December 2015.
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Energy Systems

    • Hossain, Ramij Raja, and Ratnesh Kumar. “A Distributed-MPC Framework for Voltage Control Under Discrete Time-Wise Variable Generation/Load.” IEEE Transactions on Power Systems, 2023.
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    This article presents a distributed predictive design for real-time voltage control under changing load and generation profiles at discrete intervals. The existing control designs include centralized approach, providing an optimal solution but less scalable and susceptible to single-point failures/attacks, as well as decentralized or localized approach, having increased scalability and attack resilience but lacking optimality. The proposed distributed solution offers the attractive features of both approaches, where the neighboring nodes share their local information to attain an optimal solution while retaining scalability and resilience to single-point failures/attacks. We first introduce the centralized version of the voltage control problem assuming grid observability and then transfer it to the distributed versions based on both bus-wise and area-wise decompositions of the network. The distributed version is solved via alternating direction method of multipliers (ADMM) that, for bus-wise decomposition, needs a full set of local measurements, whereas only a partial set of local measurements (that guarantee area-wise grid observability for each area) is needed for area-wise decomposition, along with neighbor-to-neighbor communications. Additionally, leveraging the availability of measurement data, the framework includes a distributed method to estimate the admittance matrix \mathbf Y of the underlying network graph. The proposed framework is validated against IEEE-30, IEEE-57 bus transmission systems, and IEEE-123 bus distribution systems and can tolerate certain levels of generation/load prediction uncertainties, modeling errors, and communication failures; plus, its in-built redundancy supports attack detection.

    • Talukder, Soumyabrata, and Ratnesh Kumar. “Robust Stability of Neural-Network-Controlled Nonlinear Systems With Parametric Variability.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, 2023.
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    Stability certification and identification of a safe and stabilizing initial set are two important concerns in ensuring operational safety, stability, and robustness of dynamical systems. With the advent of machine-learning tools, these issues need to be addressed for the systems with machine-learned components in the feedback loop. To develop a general theory for stability and stabilizability of neural network (NN)-controlled nonlinear systems subject to bounded parametric variations, a Lyapunov-based stability certificate is proposed and is further used to devise a maximal Lipschitz bound for a class of stabilizing NN controllers, and also a corresponding maximal Region of Attraction (RoA) within a user-specified safety set. To compute a robustly stabilizing NN controller that also maximizes the system’s long-run utility, a stability-guaranteed training (SGT) algorithm is proposed. The effectiveness of the proposed framework is validated through an illustrative example.

    • Hossain, Ramij Raja, Rahmat Adesunkanmi, and Ratnesh Kumar. “Data-Driven Linear Koopman Embedding for Networked Systems: Model-Predictive Grid Control.” IEEE Systems Journal, 2023.
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    • Hossain, Ramij Raja, and Ratnesh Kumar. “Machine Learning Accelerated Real-Time Model Predictive Control for Power Systems.” IEEE/CAA Journal of Automatica Sinica, vol. 10, no. 4, 2023.
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    • Kumar, Ratnesh, Thomas I. Strasser, Geert Deconinck, Chun Sing Lai, and Loi Lei Lai. “Special Issue on Recent Advances for Intelligence in Power and Energy Systems.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 51, no. 4, April 2021.
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    • Talukder, Soumyabrata, Mariam Ibrahim, and Ratnesh Kumar. “Resilience Indices for Power/Cyberphysical Systems.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 51, no. 4, April 2021.
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    • Jin, Licheng, Ratnesh Kumar, and Nicola Elia. “Reachability Analysis Based Transient Stability Design in Power Systems.” International Journal of Electrical Power & Energy Systems, vol. 32, no. 7, September 2010.
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    • Jin, Licheng, Ratnesh Kumar, and Nicola Elia. “Model Predictive Control-Based Real-Time Power System Protection Schemes.” IEEE Transactions on Power Systems, vol. 25, no. 2, May 2010.
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    • Liu, Haifeng, Licheng Jin, J. D. McCalley, Ratnesh Kumar, V. Ajjarapu, and N. Elia. “Planning Reconfigurable Reactive Control for Voltage Stability Limited Power Systems.” IEEE Transactions on Power Systems, vol. 24, no. 2, May 2009.
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Embedded Software:

    • Li, Meng, and Ratnesh Kumar. “Reachability Resolution for Discrete-Time Hybrid Systems with Application to Automated Test Generation for Simulink/Stateflow.” IET Cyber-Physical Systems: Theory & Applications, vol. 2, no. 1, April 2017.
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    • Li, Meng, and Ratnesh Kumar. “Automated Test Generation and Error Localisation for Simulink/Stateflow Modelled Systems Using Extended Automata.” IET Cyber-Physical Systems: Theory & Applications, vol. 1, no. 1, December 2016.
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    • Zhou, Changyan, and Ratnesh Kumar. “Semantic Translation of Simulink Diagrams to Input/Output Extended Finite Automata.” Discrete Event Dyn Syst, vol. 22, no. 2, December 2010.
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Networks:

    • Sahota, Herman, and Ratnesh Kumar. “Sensor Localization Using Time of Arrival Measurements in a Multi-Media and Multi-Path Application of In-Situ Wireless Soil Sensing.” Inventions, vol. 6, no. 1, February 2021.
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    • Sahota, Herman, and Ratnesh Kumar. “Maximum-Likelihood Sensor Node Localization Using Received Signal Strength in Multimedia With Multipath Characteristics.” IEEE Systems Journal, vol. 12, no. 1, March 2018.
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    • Ouedraogo, Lucien, and Ratnesh Kumar. “Computation of the Precise Worst-Case Response Time of FlexRay Dynamic Messages.” IEEE Transactions on Automation Science and Engineering, vol. 11, no. 2, April 2014.
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    • Xu, Songyan, Ratnesh Kumar, and Alessandro Pinto. “Correct-by-Construction and Optimal Synthesis of Beacon-Enabled ZigBee Network.” IEEE Transactions on Automation Science and Engineering, vol. 10, no. 1, January 2013.
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    • Sahota, Herman, Ratnesh Kumar, and Ahmed Kamal. “A Wireless Sensor Network for Precision Agriculture and Its Performance.” Wirel. Commun. Mob. Comput., vol. 11, no. 12, Wiley, 2011.
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    • Bhattacharyya, S., Ratnesh Kumar, and Z. Huang. “A Discrete Event Systems Approach to Network Fault Management: Detection and Diagnosis of Faults.” Asian Journal of Control, vol. 13, no. 4, February 2011.
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    • Kumar, Ratnesh, Sudhir Nelvagal, and Steven I. Marcus. “A Discrete Event Systems Approach for Protocol Conversion.” Discrete Event Dynamic Systems, vol. 7, no. 3, 1997.
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Cyber-Physical Systems:

Agriculture Systems

    • Bhar, Anupam, Benjamin Feddersen, Robert Malone, and Ratnesh Kumar. “Agriculture Model Comparison Framework and MyGeoHub Hosting: Case of Soil Nitrogen.” Inventions, vol. 6, no. 2, March 2021.
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    • Sahota, Herman, and Ratnesh Kumar. “Sensor Localization Using Time of Arrival Measurements in a Multi-Media and Multi-Path Application of In-Situ Wireless Soil Sensing.” Inventions, vol. 6, no. 1, February 2021.
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    • Bhar, Anupam, Ratnesh Kumar, Zhiming Qi, and Robert Malone. “Coordinate Descent Based Agricultural Model Calibration and Optimized Input Management.” Computers and Electronics in Agriculture, vol. 172, May 2020.
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    • Sahota, Herman, and Ratnesh Kumar. “Maximum-Likelihood Sensor Node Localization Using Received Signal Strength in Multimedia With Multipath Characteristics.” IEEE Systems Journal, vol. 12, no. 1, March 2018.
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Machine Learning

    • Wu, Gang, Viswanathan Swaminathan, and Ratnesh Kumar. “Matrix Completion under Gaussian Models Using MAP and EM Algorithms.” JCM, 2017.
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Resilience

    • Talukder, Soumyabrata, Mariam Ibrahim, and Ratnesh Kumar. “Resilience Indices for Power/Cyberphysical Systems.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 51, no. 4, April 2021.
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Security

    • Ghazo, Alaa T. Al, and Ratnesh Kumar. “Critical Attacks Set Identification in Attack Graphs for Computer and SCADA/ICS Networks.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, 2023.
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    Supervisory control and data acquisition/industrial control systems (SCADA/ICSs) networks are becoming more vulnerable to attacks that exploit the interdependence of security weaknesses at the atomic level to compromise system-level security. Attack graphs are an effective approach to depict these complex attack scenarios, assisting security administrators in determining how to best safeguard their systems. However, due to time and financial constraints, it is frequently not possible to address all atomic-level flaws at the same time. In this article, we propose a method for automatically detecting a minimal set of critical attacks that, when defended against, render the system secure. Finding a minimal label cut is typically an NP-complete problem. However, we propose a linear complexity approximation that uses the attack graph’s strongly connected components (SCCs) to create a simplified version of the graph in the form of a tree over the SCCs. Then, we perform an iterative backward search over this tree to find a set of backward-reachable SCCs, as well as their outward edges and labels, in order to find a cut of the tree with the fewest labels, which is a critical attack set. We put our proposed method to the test on real-world case studies, such as IT and SCADA networks for a cyber–physical system for water treatment, and outperformed previous state-of-the-art algorithms in terms of approximation accuracy and/or computational speed. Our solution provides security administrators with a practical and efficient method for prioritizing efforts to address vulnerabilities in SCADA/ICS networks.

    • Kumar, Ratnesh, Ramij Raja Hossain, Soumyabrata Talukder, Amit Jena, and Alaa T. Al Ghazo. “Recursive Histogram Tracking-Based Rapid Online Anomaly Detection in Cyber-Physical Systems.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, 2022.
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    Prompt online detection of anomalies induced by malicious attacks enhances the efficacy of real-time operation and mitigation of attack, an indispensable part of any cyber-physical system (CPS) management. This article proposes a novel online rapid detection scheme that continuously monitors the data packet stream and infers the sequence of probability distributions, estimated as histograms, and alerts when a change in the histogram is detected, reporting both the attack as well as an estimate of its instant of commencement. A statistical data-driven attack model is proposed and employed that is general enough to represent two ubiquitous types of attacks on CPS: 1) replay and 2) bias-injection. The proposed detection framework relies on the fact that CPSs possess well-defined dynamics that are affected by quasistationary noise, which allows the histogram sequences of the system data packets to converge (to different distributions under the presence of the attack versus the absence of attack). The proposed online scheme detects an attack, and estimates the attack commencement time by relying on the computed distance between real-time estimated histogram versus apriori learned nominal histogram. Our formulation further sheds light on two different attack initiation-time-based subcases, “early” (attack starts before sufficient data of nominal behavior was collected to allow its histogram sequence to be closer to its nominal value) versus “late.” The designed algorithm of our scheme has linear time complexities in the dimension of data packets and algorithm parameters, which makes it suited for rapid detection. The proposed algorithm is implemented and validated on two real supervisory control and data acquisition system datasets, where a low detection delay demonstrates the effectiveness of the scheme.

    • Ghazo, Alaa T. Al, Mariam Ibrahim, Hao Ren, and Ratnesh Kumar. “A2G2V: Automatic Attack Graph Generation and Visualization and Its Applications to Computer and SCADA Networks.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 50, no. 10, October 2020.
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    • Chen, Jun, Mariam Ibrahim, and Ratnesh Kumar. “Quantification of Secrecy in Partially Observed Stochastic Discrete Event Systems.” IEEE Transactions on Automation Science and Engineering, vol. 14, no. 1, January 2017.
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Testing

    • Li, Meng, and Ratnesh Kumar. “Reachability Resolution for Discrete-Time Hybrid Systems with Application to Automated Test Generation for Simulink/Stateflow.” IET Cyber-Physical Systems: Theory & Applications, vol. 2, no. 1, April 2017.
    • BibTeX
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    • Li, Meng, and Ratnesh Kumar. “Automated Test Generation and Error Localisation for Simulink/Stateflow Modelled Systems Using Extended Automata.” IET Cyber-Physical Systems: Theory & Applications, vol. 1, no. 1, December 2016.
    • BibTeX
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    • Zhou, Changyan, and Ratnesh Kumar. “Semantic Translation of Simulink Diagrams to Input/Output Extended Finite Automata.” Discrete Event Dyn Syst, vol. 22, no. 2, December 2010.
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Real Time

    • Xu, Songyan, Shengbing Jiang, and Ratnesh Kumar. “Diagnosis of Dense-Time Systems Under Event and Timing Masks.” IEEE Transactions on Automation Science and Engineering, vol. 7, no. 4, October 2010.
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    We study diagnosis of timed discrete-event systems (TDESs) modeled as timed-automata. Earlier works on diagnosis of TDESs assumed that a diagnoser has partial observation of events but can measure (or observe) time with arbitrary precision. In practice, however, time can only be measured with finite precision. We model the finite precision observability of time using a digital-clock that measures time discretely by executing ticks. For the diagnosis purposes, the set of nonfaulty timed-traces is specified as another timed-automaton that is deterministic, generalizing the forms of nonfaulty specifications considered in the earlier works. We show that the set of timed-traces observed using a digital-clock with finite precision is regular, i.e., can be represented using a finite (untimed) automaton. We show that the verification of diagnosability (ability to detect the execution of a faulty timed-trace within a bounded time delay) as well as the offline synthesis of a diagnoser are decidable by reducing these problems to the untimed setting. The reduction of the diagnosis problem to the untimed setting also suggests an effective method for the offline computation of a diagnoser as well as its online implementation for diagnosis.

    • Xu, Songyan, and Ratnesh Kumar. “Real-Time Control of Dense-Time Systems Using Digital-Clocks.” IEEE Transactions on Automatic Control, vol. 55, no. 9, September 2010.
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    We study the supervisory control of dense-time discrete event systems (DESs) in which the supervisors employ finite-precision digital-clocks to observe the event occurrence times, thereby relaxing the assumption of the prior works that time can be measured precisely. In our paper, the passing of time is measured using the number of ticks generated by a digital-clock and we allow the plant events and digital-clock ticks to occur concurrently. We formalize the notion of a control policy that issues the control actions based on the observations of events and their occurrence times as measured using a digital-clock, and show that such a control policy can be equivalently represented as a “digitalized”-automaton, namely, an untimed-automaton that evolves over events (of the plant) and ticks (of the digital-clock). We introduce the notion of observability with respect to the partial observation of time resulting from the use of a digital-clock, and show that this property together with controllability serves as a necessary and sufficient condition for the existence of a supervisor to enforce a real-time specification on a dense-time discrete event plant. The observability condition presented in the paper is very different from the one arising due to a partial observation of events since a partial observation of time is in general nondeterministic (the number of ticks generated in any time interval can vary from execution to execution of a digital-clock). We also present a method to verify the proposed observability and controllability conditions, and an algorithm to compute a supervisor when such conditions are satisfied.

Control

    • Kumar, Ratnesh, and Zhonghui Luo. “Optimizing the Operation Sequence of a Chip Placement Machine Using TSP Model.” IEEE Transactions on Electronics Packaging Manufacturing, vol. 26, no. 1, January 2003.
    • BibTeX
    • Link
    • Balduzzi, Fabio, Ratnesh Kumar, and Dip di Automatica. “Hybrid Automata Model of Manufacturing Systems and Its Optimal Control Subject to Logical Constraints.” International Journal of Hybrid Systems, vol. 3, no. 1, 2003.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and J. A. Stover. “A Behavior-Based Intelligent Control Architecture with Application to Coordination of Multiple Underwater Vehicles.” IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans, vol. 30, no. 6, 2000.
    • BibTeX
    • Link
    • Luo, Zhonghui, Ratnesh Kumar, Joseph Sottile, and Jon C. Yingling. “An MILP Formulation for Load-Side Demand Control.” Electric Machines & Power Systems, vol. 26, no. 9, 1998.
    • BibTeX
    • Abstract
    • Link

    This paper presents a mixed integer linear programming formulation for load-side control of electrical energy demand. The formulation utilizes demand prediction to determine if control actions are necessary, and it schedules both shedding and restoration times based on an optimization model that minimizes the net cost of load shedding. Operational constraints are satisfied through the use of minimum/maximum uptimes/downtimes, which depend upon the current state of the system. The algorithm is evaluated using a simulation model of an underground coal mining operation where, (i) its performance is compared with a traditional static, priority-based, load-shedding schedule, and, (ii) its potential is established for producing net savings through demand control.

Stochastics

    • Chen, Jun, and Ratnesh Kumar. “Stochastic Failure Prognosis of Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 67, no. 10, October 2022.
    • BibTeX
    • Abstract
    • Link

    This article studies the prognosis of failure, i.e., its prediction prior to its occurrence, in stochastic discrete event systems. Prior work has focused on the definition and offline verification of m-steps stochastic-prognosability, or S_m-prognosability, which allows the prediction of a fault at least m-steps in advance. This article complements the existing work by proposing an algorithm for the computation of online failure prognoser. The proposed algorithm reduces the condition for issuing an affirmative prognostic decision to verification condition of a safety property of a Markov chain. We discuss how such a verification condition can be computed using a finitely terminating algorithm.

    • Chen, Jun, and Ratnesh Kumar. “Stochastic Failure Prognosis of Discrete Event Systems.” IEEE Transactions on Automatic Control, 2021.
    • BibTeX
    • Abstract
    • Link

    This paper studies the prognosis of failure, i.e., its prediction prior to its occurrence, in stochastic discrete event systems. Prior work has focused on the definition and offline verification of m-steps Stochastic-Prognosability, or Sm-Prognosability, which allows the prediction of a fault at least m-steps in advance. This paper complements the existing work by proposing an algorithm for the computation of online failure prognoser. The proposed algorithm reduces the condition for issuing an affirmative prognostic decision to verification condition of a safety property of a Markov chain. We discuss how such a verification condition can be computed using a finitely terminating algorithm.

    • Chen, Jun, Christoforos Keroglou, Christoforos N. Hadjicostis, and Ratnesh Kumar. “Revised Test for Stochastic Diagnosability of Discrete-Event Systems.” IEEE Transactions on Automation Science and Engineering, vol. 15, no. 1, January 2018.
    • BibTeX
    • Link
    • Chen, Jun, Mariam Ibrahim, and Ratnesh Kumar. “Quantification of Secrecy in Partially Observed Stochastic Discrete Event Systems.” IEEE Transactions on Automation Science and Engineering, vol. 14, no. 1, January 2017.
    • BibTeX
    • Link
    • Wu, Gang, Viswanathan Swaminathan, and Ratnesh Kumar. “Matrix Completion under Gaussian Models Using MAP and EM Algorithms.” JCM, 2017.
    • BibTeX
    • Link
    • Chen, Jun, and Ratnesh Kumar. “Fault Detection of Discrete-Time Stochastic Systems Subject to Temporal Logic Correctness Requirements.” IEEE Transactions on Automation Science and Engineering, vol. 12, no. 4, October 2015.
    • BibTeX
    • Link
    • Chen, Jun, and Ratnesh Kumar. “Failure Detection Framework for Stochastic Discrete Event Systems With Guaranteed Error Bounds.” IEEE Transactions on Automatic Control, vol. 60, no. 6, June 2015.
    • BibTeX
    • Link
    • Hsu, Shun-Pin, Aristotle Arapostathis, and Ratnesh Kumar. “On Controlled Markov Chains with Optimality Requirement and Safety Constraint.” Int. J. Innovative Comput., Inform. and Control, vol. 6, no. 6, 2010.
    • BibTeX
    • Link
    • Arapostathis, A., Ratnesh Kumar, and S. P. Hsu. “Control of Markov Chains With Safety Bounds.” IEEE Transactions on Automation Science and Engineering, vol. 2, no. 4, October 2005.
    • BibTeX
    • Link
    • Arapostathis, A., Ratnesh Kumar, and S. Tangirala. “Controlled Markov Chains with Safety Upper Bound.” IEEE Transactions on Automatic Control, vol. 48, no. 7, July 2003.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and V. K. Garg. “Control of Stochastic Discrete Event Systems Modeled by Probabilistic Languages.” IEEE Transactions on Automatic Control, vol. 46, no. 4, April 2001.
    • BibTeX
    • Link
    • Garg, V. K., Ratnesh Kumar, and S. I. Marcus. “A Probabilistic Language Formalism for Stochastic Discrete-Event Systems.” IEEE Transactions on Automatic Control, vol. 44, no. 2, 1999.
    • BibTeX
    • Link

Temporal Logic

    • Basu, Samik, and Ratnesh Kumar. “Control of Non-Deterministic Systems With μ-Calculus Specifications Using Quotienting.” IEEE/CAA Journal of Automatica Sinica, vol. 8, no. 5, May 2021.
    • BibTeX
    • Link
    • Chen, Jun, and Ratnesh Kumar. “Fault Detection of Discrete-Time Stochastic Systems Subject to Temporal Logic Correctness Requirements.” IEEE Transactions on Automation Science and Engineering, vol. 12, no. 4, October 2015.
    • BibTeX
    • Link
    • Jiang, Shengbing, and Ratnesh Kumar. “Supervisory Control of Discrete Event Systems with CTL∗ Temporal Logic Specifications.” SIAM Journal on Control and Optimization, vol. 44, no. 6, January 2006.
    • BibTeX
    • Link
    • Jiang, S., and Ratnesh Kumar. “Failure Diagnosis of Discrete-Event Systems With Linear-Time Temporal Logic Specifications.” IEEE Transactions on Automatic Control, vol. 49, no. 6, June 2004.
    • BibTeX
    • Link
    • Jiang, Shengbing, and R. Kumar. “Diagnosis of Repeated Failures for Discrete Event Systems with Linear-Time Temporal Logic Specifications.” 42nd IEEE International Conference on Decision and Control (IEEE Cat. No.03CH37475), vol. 4, IEEE, 2003.
    • BibTeX
    • Abstract
    • Link

    In our earlier work, we introduced a state-based approach for the diagnosis of repeatedly occurring failures in discrete event systems (DESs). Since temporal logic provides a simpler way of specifying system properties, in this paper a temporal logic based approach for diagnosing the occurrence of a repeated number of failures is developed. Linear-time temporal logic (LTL) formulae are used to represent the specifications of DESs. Notions of pre-diagnosability for failures and diagnosability for repeated failures are introduced in the setting of temporal logic. A polynomial algorithm for the test of pre-diagnosability for failures is provided. The diagnosis problem for repeated failures in the temporal logic setting is reduced to one in a state-based setting, and so the prior results of state-based repeated failure diagnosis can be applied.

Bisimulation

    • Kumar, Ratnesh, Shengbing Jiang, and Changyan Zhou. “Comment on ‘Bisimilarity Control of Partially Observed Nondeterministic Discrete Event Systems and a Test Algorithm’ [Automatica 47 (2011) 782–788].” Automatica, vol. 50, no. 1, 2014.
    • BibTeX
    • Abstract
    • Link

    An article on bisimilarity enforcing supervisory control of discrete event systems was published recently in 2011, Issue 4, Volume 47, pages 782–788, of Automatica. The article introduced a certain definition of composition of plant and supervisor to define a controlled system, so as to come up with an existence condition of bisimilarity enforcing control. Such definition changes the semantics of event-based control to transition-based control, selectively disabling nondeterministic transitions. Any results reported in the paper thus raise question about value and applicability.

    • Zhou, Changyan, and Ratnesh Kumar. “Finite Bisimulation of Reactive Untimed Infinite State Systems Modeled as Automata With Variables.” IEEE Transactions on Automation Science and Engineering, vol. 10, no. 1, January 2013.
    • BibTeX
    • Link
    • Zhou, Changyan, and Ratnesh Kumar. “Bisimilarity Enforcement for Discrete Event Systems Using Deterministic Control.” IEEE Transactions on Automatic Control, vol. 56, no. 12, December 2011.
    • BibTeX
    • Link
    • Zhou, Changyan, and Ratnesh Kumar. “Bisimilarity Control of Partially Observed Deterministic Systems.” IEEE Transactions on Automatic Control, vol. 52, no. 9, September 2007.
    • BibTeX
    • Abstract
    • Link

    Control for safety and nonblockingness using a deterministic supervisor requires the specification language be controllable and observable (under the setting that marking is also decided by a supervisor). We argue that there exist cases where the above properties do not hold, yet a safe and nonblocking control can be synthesized by allowing the supervisor to be nondeterministic. Use of a nondeterministic supervisor yields a controlled system that is nondeterministic for which a language equivalence only preserve the safety but not the nonblocking property, and so instead we require the stronger equivalence of bisimilarity (which preserves "sequential" behavior such as safety as well as "branching" behavior such as nonblockingness). This motivates us to consider control of deterministic systems for achieving bisimulation equivalence to possibly nondeterministic specifications. We introduce the notions of state-achievability (SA) and state-achievability-bisimilar (SAB) as part of the existence condition, and develop effective algorithms for verify the existence conditions as well as for synthesizing a supervisor when the existence condition holds. We show that the complexity of verifying the existence of a controller is polynomial, whereas that of computing a controller (when one exists) is singly exponential. The proposed approach can be applied to enforce any property that depends on branching and sequential behavior.

    • Zhou, Changyan, and Ratnesh Kumar. “A Small Model Theorem for Bisimilarity Control Under Partial Observation.” IEEE Transactions on Automation Science and Engineering, vol. 4, no. 1, January 2007.
    • BibTeX
    • Link
    • Zhou, C., Ratnesh Kumar, and S. Jiang. “Control of Nondeterministic Discrete-Event Systems for Bisimulation Equivalence.” IEEE Transactions on Automatic Control, vol. 51, no. 5, May 2006.
    • BibTeX
    • Link
    • Zhou, Changyan, and Ratnesh Kumar. “A Small Model Theorem for Bisimilarity Control under Partial Observation.” Proceedings of the 2005, American Control Conference, 2005., IEEE, 2005.
    • BibTeX
    • Link

Discrete Event Systems

Discrete Event Systems: Modeling
    • Takai, Shigemasa, and Ratnesh Kumar. “A Generalized Inference-Based Prognosis Framework for Discrete Event Systems.” IFAC-PapersOnLine, vol. 50, no. 1, July 2017.
    • BibTeX
    • Abstract
    • Link

    We previously introduced an inference-based framework for decentralized prognosis of discrete event systems, and formulated the notion of N-inference V-prognosability to characterize the existence of a disjunctive decentralized prognosis scheme such that any fault can be predicted prior to its occurrence by at least one of the prognosers, using at most N-levels of inferencing. While the disjunctive scheme relies on one of the prognosers making a positive decision, the dual conjunctive scheme relies on none of the prognosers making a negative decision. It is known that the two schemes are incomparable, and in this paper we extend our earlier work to provide a more general framework, by introducing a notion of N-inference prognosability, that captures both disjunctive and conjunctive schemes. We also develop a method for verifying N-inference prognosability.

    • Huang, Z., V. Chandra, S. Jiang, and Ratnesh Kumar. “Modeling Discrete Event Systems With Faults Using a Rules-Based Modeling Formalism.” Mathematical and Computer Modelling of Dynamical Systems, vol. 9, no. 3, September 2003.
    • BibTeX
    • Link
    • CHANDRA, V., and Ratnesh Kumar. “A Event Occurrence Rules Based Compact Modeling Formalism for a Class of Discrete Event Systems.” Mathematical and Computer Modelling of Dynamical Systems, vol. 8, no. 1, March 2002.
    • BibTeX
    • Link
    • Chandra, V., and R. Kumar. “A Discrete Event Systems Modeling Formalism Based on Event Occurrence Rules and Precedences.” IEEE Transactions on Robotics and Automation, vol. 17, no. 6, December 2001.
    • BibTeX
    • Abstract
    • Link

    The analysis (verification, diagnosis, control, etc.) of discrete event systems requires a correct model of the system and of its specifications. In this paper, we present a new modeling formalism for generating valid models of complex systems. The class of systems this applies to is one which consists of signals that take binary values. The technique presented here makes the task of modeling considerably less cumbersome and less error-prone and is user-friendly. Another advantage of using this modeling formalism is that the size of the system model is polynomial in the number of signals, whereas the number of states in the automata models is exponential in the number of signals. We present automated techniques for deriving an automaton-based model from the model in the proposed formalism. We illustrate the modeling formalism using examples drawn from manufacturing systems and process control.

    • Shayman, M. A., and Ratnesh Kumar. “Process Objects/Masked Composition: an Object-Oriented Approach for Modeling and Control of Discrete-Event Systems.” IEEE Transactions on Automatic Control, vol. 44, no. 10, 1999.
    • BibTeX
    • Link
    • Kumar, Ratnesh, V. K. Garg, and S. I. Marcus. “Corrections to ‘Finite Buffer Realization of Input-Output Discrete Event Systems.’” IEEE Transactions on Automatic Control, vol. 41, no. 4, April 1996.
    • BibTeX
    • Link
    • Kumar, Ratnesh, V. K. Garg, and S. I. Marcus. “Finite Buffer Realization of Input-Output Discrete-Event Systems.” IEEE Transactions on Automatic Control, vol. 40, no. 6, June 1995.
    • BibTeX
    • Link
Discrete Event Systems: Stability
    • Kumar, Ratnesh, Vijay Garg, and Steven I. Marcus. Language Stability and Stabilizability of Discrete Event Dynamical Systems. Defense Technical Information Center, July 1992.
    • BibTeX
    • Link
Discrete Event Systems: Control
    • Ouedraogo, L., Ratnesh Kumar, R. Malik, and K. Akesson. “Nonblocking and Safe Control of Discrete-Event Systems Modeled as Extended Finite Automata.” IEEE Transactions on Automation Science and Engineering, vol. 8, no. 3, July 2011.
    • BibTeX
    • Link
    • Takai, Shigemasa, and Ratnesh Kumar. “Synthesis of Over-Approximating Inference-Based Decentralized Supervisors for Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 55, no. 8, August 2010.
    • BibTeX
    • Abstract
    • Link

    In our past work, we presented a framework for the decentralized control of discrete event systems involving inferencing over ambiguities about the system state of various local decision-makers, and introduced the notion of N-inference-observability as an existence condition of a certain decentralized supervisor. When a given specification fails to satisfy the N-inference-observability property, a supervisor achieving the given specification does not exist, and a technique for synthesizing a decentralized supervisor that achieves an N-inference-observable superlanguage is presented here (a dual problem of computing an N-inference-observable sublanguage was studied in our past work).

    • Jiang, Shengbing, Ratnesh Kumar, Shigemasa Takai, and Wenbin Qiu. “Decentralized Control of Discrete-Event Systems With Multiple Local Specifications.” IEEE Transactions on Automation Science and Engineering, vol. 7, no. 3, July 2010.
    • BibTeX
    • Link
    • Huang, Jing, and Ratnesh Kumar. “Directed Control of Discrete Event Systems for Safety and Nonblocking.” IEEE Transactions on Automation Science and Engineering, vol. 5, no. 4, October 2008.
    • BibTeX
    • Link
    • Takai, Shigemasa, and Ratnesh Kumar. “Synthesis of Inference-Based Decentralized Control for Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 53, no. 2, March 2008.
    • BibTeX
    • Link
    • Huang, Jing, and Ratnesh Kumar. “Optimal Nonblocking Directed Control of Discrete Event Systems.” 2007 American Control Conference, IEEE, 2007.
    • BibTeX
    • Link
    • Kumar, Ratnesh, Shigemasa Takai, Martin Fabian, and Toshimitsu Ushio. “Maximally Permissive Mutually and Globally Nonblocking Supervision with Application to Switching Control.” Automatica, vol. 41, no. 8, August 2005.
    • BibTeX
    • Link
    • Takai, S., Ratnesh Kumar, and T. Ushio. “Characterization of Co-Observable Languages and Formulas for Their Super/Sublanguages.” IEEE Transactions on Automatic Control, vol. 50, no. 4, April 2005.
    • BibTeX
    • Link
    • Chandra, V., Zhongdong Huang, and R. Kumar. “Automated Control Synthesis for an Assembly Line Using Discrete Event System Control Theory.” IEEE Transactions on Systems, Man, and Cybernetics, Part C (Applications and Reviews), vol. 33, no. 2, May 2003.
    • BibTeX
    • Abstract
    • Link

    The design of logic controllers for event-driven systems continue to rely largely on intuitive methods rather than on formal techniques. This approach results in a control code that requires extensive verification, is hard to maintain and modify, and may even fail at times. Supervisory control theory (SCT) provides a formal approach to logic control synthesis. In order to demonstrate the usefulness of the supervisory control theory in manufacturing systems, an educational test-bed that simulates an automated car assembly line has been built using LEGO/spl reg/ blocks. Finite state machines (FSMs) are used for modeling operations of the assembly line, and for the specifications that accomplish the task of successfully completing the assembly repeatedly. Using the technique of SCT, we derive a supervisor that enforces the specifications while offering the maximum flexibility of assembly. Subsequently a controller is extracted from the maximally permissive supervisor for the purpose of implementing the control by selecting, when possible, at most one controllable event from among the ones allowed by the supervisor. Testing to check the correctness of the control code is reduced, since the controller is guaranteed to enforce the specifications.

    • Fabian, M., and R. Kumar. “Mutually Nonblocking Supervisory Control of Discrete Event Systems.” Automatica, vol. 36, no. 12, 2000.
    • BibTeX
    • Abstract
    • Link

    A single maximally permissive and nonblocking supervisor to simultaneously fulfill several marked specifications pertaining to a single plant is investigated. Given a plant G and two marked specification languages K1 and K2, a supervisor S is said to be (K1,K2)-mutually nonblocking if (for i,j=1,2) Lm(G||S)∩Ki⊆Lm(G||S)∩Kj. This means that when the closed-loop system marks a trace of Ki, then it is always able to continue to a trace of Kj, also marked in the closed-loop system. Thus, the controlled system can execute traces within one specification while always being able to continue a trace of the other and hence not blocking the other specification. A complete, globally nonblocking and (K1,K2)-mutually nonblocking supervisor such that Lm(G||S)⊆K1∪K2 exists if and only if there exists a controllable mutually nonblocking sublanguage of the union of the specifications. There does exist a supremal such language. Furthermore, in the case that each specification is nonconflicting with respect to the prefix-closure of the other, this supremal language can be calculated by expressing it as the union of the supremal prefix-bounded sublanguages of the respective specifications. Finally, we show that the multiply nonblocking supervision of Thistle, Malhame, Hoang and Lafortune ((1997). Internal Report, Dept. de genie electrique et de genie informatique, Ecole Polytechnique de Montreal, Canada) is equivalent to globally and mutually nonblocking supervision.

    • Jiang, S., and Ratnesh Kumar. “Decentralized Control of Discrete Event Systems with Specializations to Local Control and Concurrent Systems.” IEEE Transactions on Systems, Man and Cybernetics, Part B (Cybernetics), vol. 30, no. 5, 2000.
    • BibTeX
    • Link
    • Kumar, R., H. M. Cheung, and S. I. Marcus. “Extension Based Limited Lookahead Supervision of Discrete Event Systems.” Automatica, vol. 34, no. 11, November 1998.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and Mark A. Shayman. “Formulae Relating Controllability, Observability, and Co-Observability.” Automatica, vol. 34, no. 2, February 1998.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and Vijay K. Garg. “Optimal Supervisory Control of Discrete Event Dynamical Systems.” SIAM Journal on Control and Optimization, vol. 33, no. 2, March 1995.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and Haomin Li. “Integer Programming Approach to Printed Circuit Board Assembly Time Optimization.” IEEE Transactions on Components, Packaging, and Manufacturing Technology: Part B, vol. 18, no. 4, 1995.
    • BibTeX
    • Link
    • Kumar, R., and V. K. Garg. “Extremal Solutions of Inequations over Lattices with Applications to Supervisory Control.” Proceedings of 1994 33rd IEEE Conference on Decision and Control, vol. 4, IEEE, 1994.
    • BibTeX
    • Abstract
    • Link

    We study the existence and computation of extremal solutions of a system of inequations defined over lattices. Using the Knaster-Tarski fixed point theorem, we obtain sufficient conditions for the existence of supremal as well as infimal solution of a given system of inequations. Iterative techniques are presented for the computation of the extremal solutions whenever they exist, and conditions under which the termination occurs in a single iteration are provided. These results are then applied for obtaining extremal solutions of various inequations that arise in computation of maximally permissive supervisors in control of logical discrete event systems (DESs). Thus our work presents a unifying approach for computation of supervisors in a variety of situations.

    • Brandt, R. D., V. Garg, Ratnesh Kumar, F. Lin, S. I. Marcus, and W. M. Wonham. “Formulas for Calculating Supremal Controllable and Normal Sublanguages.” Systems & Control Letters, vol. 15, no. 2, August 1990.
    • BibTeX
    • Link
Discrete Event Systems: Optimal Control
    • Huang, Jing, and Ratnesh Kumar. “Optimal Nonblocking Directed Control of Discrete Event Systems.” 2007 American Control Conference, IEEE, 2007.
    • BibTeX
    • Link
    • Takai, S., Ratnesh Kumar, and T. Ushio. “Characterization of Co-Observable Languages and Formulas for Their Super/Sublanguages.” IEEE Transactions on Automatic Control, vol. 50, no. 4, April 2005.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and Mark A. Shayman. “Formulae Relating Controllability, Observability, and Co-Observability.” Automatica, vol. 34, no. 2, February 1998.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and Vijay K. Garg. “Optimal Supervisory Control of Discrete Event Dynamical Systems.” SIAM Journal on Control and Optimization, vol. 33, no. 2, March 1995.
    • BibTeX
    • Link
    • Kumar, R., and V. K. Garg. “Extremal Solutions of Inequations over Lattices with Applications to Supervisory Control.” Proceedings of 1994 33rd IEEE Conference on Decision and Control, vol. 4, IEEE, 1994.
    • BibTeX
    • Abstract
    • Link

    We study the existence and computation of extremal solutions of a system of inequations defined over lattices. Using the Knaster-Tarski fixed point theorem, we obtain sufficient conditions for the existence of supremal as well as infimal solution of a given system of inequations. Iterative techniques are presented for the computation of the extremal solutions whenever they exist, and conditions under which the termination occurs in a single iteration are provided. These results are then applied for obtaining extremal solutions of various inequations that arise in computation of maximally permissive supervisors in control of logical discrete event systems (DESs). Thus our work presents a unifying approach for computation of supervisors in a variety of situations.

    • Brandt, R. D., V. Garg, Ratnesh Kumar, F. Lin, S. I. Marcus, and W. M. Wonham. “Formulas for Calculating Supremal Controllable and Normal Sublanguages.” Systems & Control Letters, vol. 15, no. 2, August 1990.
    • BibTeX
    • Link
Discrete Event Systems: Diagnosis
    • Takai, Shigemasa, and Ratnesh Kumar. “Implementation of Inference-Based Diagnosis: Computing Delay Bound and Ambiguity Levels.” Discrete Event Dyn Syst, vol. 28, no. 2, July 2017.
    • BibTeX
    • Link
    • Takai, Shigemasa, and Ratnesh Kumar. “A Generalized Framework for Inference-Based Diagnosis of Discrete Event Systems Capturing Both Disjunctive and Conjunctive Decision-Making.” IEEE Transactions on Automatic Control, vol. 62, no. 6, June 2017.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and Shigemasa Takai. “Comments on ‘Polynomial Time Verification of Decentralized Diagnosability of Discrete Event Systems’ versus ‘Decentralized Failure Diagnosis of Discrete Event Systems’: Complexity Clarification.” IEEE Transactions on Automatic Control, vol. 59, no. 5, May 2014.
    • BibTeX
    • Link
    • Bhattacharyya, S., Ratnesh Kumar, and Z. Huang. “A Discrete Event Systems Approach to Network Fault Management: Detection and Diagnosis of Faults.” Asian Journal of Control, vol. 13, no. 4, February 2011.
    • BibTeX
    • Link
    • Kumar, Ratnesh, and S. Takai. “Inference-Based Ambiguity Management in Decentralized Decision-Making: Decentralized Diagnosis of Discrete-Event Systems.” IEEE Transactions on Automation Science and Engineering, vol. 6, no. 3, July 2009.
    • BibTeX
    • Link
    • Zhou, Changyan, and Ratnesh Kumar. “Computation of Diagnosable Fault-Occurrence Indices for Systems With Repeatable Faults.” IEEE Transactions on Automatic Control, vol. 54, no. 7, July 2009.
    • BibTeX
    • Abstract
    • Link

    Certain faults, such as intermittent or non-persistent faults, may occur repeatedly. For discrete-event systems prone to repeated faults, Jiang, Kumar, and Garcia in 2003 introduced the notion of l-diagnosability requiring the diagnosis of the l th occurrence of a fault within a bounded delay. The present paper studies the identification of the set of all indices l for which the system is not l-diagnosable. (These are precisely the occurrence indices for which a repeatable-fault cannot be diagnosed.) We present an algorithm of cubic complexity to determine whether a system is diagnosable for every fault-occurrence index. For those systems for which the answer is negative, we show that the set of indices for which the system is non-diagnosable possesses the property that it is either finite or consists of a finite number of eventually periodic sets.

    • Qiu, Wenbin, Qin Wen, and Ratnesh Kumar. “Decentralized Diagnosis of Event-Driven Systems for Safely Reacting to Failures.” IEEE Transactions on Automation Science and Engineering, vol. 6, no. 2, April 2009.
    • BibTeX
    • Link
    • Qiu, Wenbin, and Ratnesh Kumar. “Distributed Diagnosis Under Bounded-Delay Communication of Immediately Forwarded Local Observations.” IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans, vol. 38, no. 3, May 2008.
    • BibTeX
    • Link
    • Qiu, Wenbin, Ratnesh Kumar, and Shengbing Jiang. “On Decidability of Distributed Diagnosis Under Unbounded-Delay Communication.” IEEE Transactions on Automatic Control, vol. 52, no. 1, January 2007.
    • BibTeX
    • Link
    • Qiu, Wenbin, and Ratnesh Kumar. “Decentralized Diagnosis of Event-Driven Systems for Safely Reacting to Failures.” IFAC Proceedings Volumes, vol. 38, no. 1, 2005.
    • BibTeX
    • Link
    • Jiang, Shengbing, Ratnesh Kumar, and H. E. Garcia. “Diagnosis of Repeated/Intermittent Failures in Discrete Event Systems.” IEEE Transactions on Robotics and Automation, vol. 19, no. 2, April 2003.
    • BibTeX
    • Link
    • Jiang, Shengbing, Ratnesh Kumar, and H. E. Garcia. “Optimal Sensor Selection for Discrete-Event Systems with Partial Observation.” IEEE Transactions on Automatic Control, vol. 48, no. 3, March 2003.
    • BibTeX
    • Link
    • Jiang, Shengbing, Zhongdong Huang, V. Chandra, and Ratnesh Kumar. “A Polynomial Algorithm for Testing Diagnosability of Discrete-Event Systems.” IEEE Transactions on Automatic Control, vol. 46, no. 8, 2001.
    • BibTeX
    • Link
Discrete Event Systems: Prognosis
    • Chen, Jun, and Ratnesh Kumar. “Stochastic Failure Prognosis of Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 67, no. 10, October 2022.
    • BibTeX
    • Abstract
    • Link

    This article studies the prognosis of failure, i.e., its prediction prior to its occurrence, in stochastic discrete event systems. Prior work has focused on the definition and offline verification of m-steps stochastic-prognosability, or S_m-prognosability, which allows the prediction of a fault at least m-steps in advance. This article complements the existing work by proposing an algorithm for the computation of online failure prognoser. The proposed algorithm reduces the condition for issuing an affirmative prognostic decision to verification condition of a safety property of a Markov chain. We discuss how such a verification condition can be computed using a finitely terminating algorithm.

    • Chen, Jun, and Ratnesh Kumar. “Stochastic Failure Prognosis of Discrete Event Systems.” IEEE Transactions on Automatic Control, 2021.
    • BibTeX
    • Abstract
    • Link

    This paper studies the prognosis of failure, i.e., its prediction prior to its occurrence, in stochastic discrete event systems. Prior work has focused on the definition and offline verification of m-steps Stochastic-Prognosability, or Sm-Prognosability, which allows the prediction of a fault at least m-steps in advance. This paper complements the existing work by proposing an algorithm for the computation of online failure prognoser. The proposed algorithm reduces the condition for issuing an affirmative prognostic decision to verification condition of a safety property of a Markov chain. We discuss how such a verification condition can be computed using a finitely terminating algorithm.

    • Kumar, Ratnesh, and Shigemasa Takai. “Comments on ‘Predictability of Failure Event Occurrences in Decentralized Discrete-Event Systems and Polynomial-Time Verification.’” IEEE Transactions on Automation Science and Engineering, vol. 16, no. 4, October 2019.
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    • Chen, Jun, and Ratnesh Kumar. “Stochastic Failure Prognosability of Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 60, no. 6, June 2015.
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    • Takai, Shigemasa, and Ratnesh Kumar. “Distributed Failure Prognosis of Discrete Event Systems With Bounded-Delay Communications.” IEEE Transactions on Automatic Control, vol. 57, no. 5, May 2012.
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    The task of failure prognosis requires the prediction of impending failures. This technical note formulates and studies the problem of distributed prognosis of discrete event systems, where the local prognosers exchange their observations for the sake of arriving at a prognostic decision. The observations are exchanged over communication channels that introduce bounded delays. A property of joint-prognosability is introduced to capture the condition under which any failure can be predicted by some local prognoser prior to its occurrence. We provide an algorithm to check the joint-prognosability property.

    • Takai, Shigemasa, and Ratnesh Kumar. “Inference-Based Decentralized Prognosis in Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 56, no. 1, January 2011.
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    • Kumar, Ratnesh, and S. Takai. “Decentralized Prognosis of Failures in Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 55, no. 1, January 2010.
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Discrete Event Systems: Fault Tolerance
    • Wen, Qin, Ratnesh Kumar, and Jing Huang. “Framework for Optimal Fault-Tolerant Control Synthesis: Maximize Prefault While Minimize Post-Fault Behaviors.” IEEE Transactions on Systems, Man, and Cybernetics: Systems, vol. 44, no. 8, August 2014.
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    • Wen, Qin, Ratnesh Kumar, Jing Huang, and Haifeng Liu. “A Framework for Fault-Tolerant Control of Discrete Event Systems.” IEEE Transactions on Automatic Control, vol. 53, no. 8, September 2008.
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Discrete Event Systems: Composition
    • Li, Meng, and Ratnesh Kumar. “Recursive Modeling of Stateflow as Input/Output-Extended Automaton.” IEEE Transactions on Automation Science and Engineering, vol. 11, no. 4, October 2014.
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    • Qiu, Wenbin, Ratnesh Kumar, and Vigyan Chandra. “Decentralized Control of Discrete Event Systems Using Prioritized Composition With Exclusion.” IEEE Transactions on Automatic Control, vol. 53, no. 10, November 2008.
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    • Zhou, Changyan, and Ratnesh Kumar. “Prioritized Synchronization Under Mask for Control and Interaction of Partially Observed Event-Driven Systems.” IEEE Transactions on Automation Science and Engineering, vol. 5, no. 1, January 2008.
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    • Chandra, V., Z. Huang, W. Qiu, and Ratnesh Kumar. “Prioritized Composition With Exclusion and Generation for the Interaction and Control of Discrete Event Systems.” Mathematical and Computer Modelling of Dynamical Systems, vol. 9, no. 3, September 2003.
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    • Jiang, Shengbing, and R. Kumar. “Supervisory Control of Nondeterministic Discrete-Event Systems with Driven Events via Masked Prioritized Synchronization.” IEEE Transactions on Automatic Control, vol. 47, no. 9, September 2002.
    • BibTeX
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    Studies the supervisory control problem of nondeterministic discrete event systems with driven events in the setting of masked prioritized synchronous composition (MPSC). MPSC was extended from prioritized synchronous composition (PSC) by Kumar and Heymann (2000) in order to permit systems interaction with their environment via interface masks. They also studied the supervisory control problem under the assumption that the set of driven events was empty. In this paper, the aforementioned assumption is relaxed. We first derive relations among behaviors at different levels of the system. Next, we solve the supervisor synthesis problem for controlling the plant behavior as observed at the interface level. Finally, we give a necessary and sufficient condition for the existence of the supervisor for controlling the plant behavior as observed at the plant level. We establish a link between MPSC and PSC by showing that a supervisory control problem in the setting of MPSC can be transferred to a supervisory control problem in the setting of PSC under certain conditions.

Discrete Event Systems: Infinite-behaviors
    • Kumar, Ratnesh, and V. K. Garg. “On Computation of State Avoidance Control for Infinite State Systems in Assignment Program Framework.” IEEE Transactions on Automation Science and Engineering, vol. 2, no. 1, January 2005.
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    • Kumar, R., and L. E. Holloway. “Supervisory Control of Deterministic Petri Nets with Regular Specification Languages.” IEEE Transactions on Automatic Control, vol. 41, no. 2, February 1996.
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    Algorithms for computing a minimally restrictive control in the context of supervisory control of discrete-event systems have been well developed when both the plant and the desired behaviour are given as regular languages. In this paper the authors extend such prior results by presenting an algorithm for computing a minimally restrictive control when the plant behaviour is a deterministic Petri net language and the desired behaviour is a regular language. As part of the development of the algorithm, the authors establish the following results that are of independent interest: i) the problem of determining whether a given deterministic Petri net language is controllable with respect to another deterministic Petri net language is reducible to a reachability problem of Petri nets and ii) the problem of synthesizing the minimally restrictive supervisor so that the controlled system generates the supremal controllable sublanguage is reducible to a forbidden marking problem. In particular, the authors can directly identify the set of forbidden markings without having to construct any reachability tree.

    • Kumar, Ratnesh, Vijay Garg, and Steven I. Marcus. Predicates and Predicate Transformers for Supervisory Control of Discrete Event Dynamical Systems. Defense Technical Information Center, July 1992.
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    • Kumar, Ratnesh, V. Garg, and S. I. Marcus. “On Supervisory Control of Sequential Behaviors.” IEEE Transactions on Automatic Control, vol. 37, no. 12, 1992.
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    • Kumar, Ratnesh, Vijay Garg, and Steven I. Marcus. “On ω-Controllability and ω-Normality of Deds.” 1991 American Control Conference, IEEE, 1991.
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Discrete Event Systems: Nondeterminism
    • Kumar, Ratnesh, Shengbing Jiang, Changyan Zhou, and Wenbin Qiu. “Polynomial Synthesis of Supervisor for Partially Observed Discrete-Event Systems by Allowing Nondeterminism in Control.” IEEE Transactions on Automatic Control, vol. 50, no. 4, April 2005.
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    • Kumar, Ratnesh, and Mark A. Shayman. “Centralized and Decentralized Supervisory Control of Nondeterministic Systems Under Partial Observation.” SIAM Journal on Control and Optimization, vol. 35, no. 2, March 1997.
    • BibTeX
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    • Kumar, Ratnesh, and M. A. Shayman. “Nonblocking Supervisory Control of Nondeterministic Systems via Prioritized Synchronization.” IEEE Transactions on Automatic Control, vol. 41, no. 8, 1996.
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    • Shayman, Mark A., and Ratnesh Kumar. “Supervisory Control of Nondeterministic Systems with Driven Events via Prioritized Synchronization and Trajectory Models.” SIAM Journal on Control and Optimization, vol. 33, no. 2, March 1995.
    • BibTeX
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    • Shayman, Mark A., and Ratnesh Kumar. “Supervisory Control of Nondeterministic Systems with Driven Events via Prioritized Synchronization and Trajectory Models.” SIAM Journal on Control and Optimization, vol. 33, no. 2, 1995.
    • BibTeX
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    The supervisory control of nondeterministic discrete event dynamical systems (DEDSs) with driven events in the setting of prioritized synchronization and trajectory models introduced by Heymann are studied. Prioritized synchronization captures the notions of controllable, uncontrollable, and driven events in a natural way, and the authors use it for constructing supervisory controllers. The trajectory model is used for characterizing the behavior of nondeterministic DEDSs since it is a sufficiently detailed model (in contrast to the less detailed language or failures models), and serves as a language congruence with respect to the operation of prioritized synchronization. Results concerning controllability and observability in this general setting are obtained.

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