List of English Publication

@article{nokey,

title = {A Lyapunov Characterization of Prescribed Performance Control Systems},

author = {Yutian Wang and Tengfei Liu and Hyungbo Shim and George A. Rovithakis and Zhong-Ping Jiang},

doi = {10.1109/TAC.2024.3399090},

issn = {0018-9286},

year  = {2024},

date = {2024-11-01},

urldate = {2024-11-01},

journal = {IEEE Transactions on Automatic Control},

volume = {69},

issue = {11},

pages = {7917 - 7924},

abstract = {This paper contributes a Lyapunov formulation for prescribed performance controller designs. In particular, we first show that the closed-loop system of a typical class of prescribed performance control systems can be transformed into an interconnection of input-to-state practically stable (ISpS) subsystems characterized by ISpS-Lyapunov functions. Then, we take advantage of the gain-interconnections between the subsystems and construct a Lyapunov function for the closed-loop system. The proposed approach is validated through prescribed performance control for both SISO and MIMO plants, as well as systems not necessarily in the lower-triangular form and systems with dynamic uncertainty.},

keywords = {Input-to-state practical stability, Lyapunov function, Prescribed performance control},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Encrypted Dynamic Control Exploiting Limited Number of Multiplications and a Method Using RLWE-based Cryptosystem},

author = {Joowon Lee and Donggil Lee and Junsoo Kim and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10730788},

doi = {10.1109/TSMC.2024.3452007},

issn = {2168-2216},

year  = {2024},

date = {2024-10-23},

urldate = {2024-10-23},

journal = {IEEE Transactions on Systems, Man, and Cybernetics: Systems},

abstract = {In this article, we present a method to encrypt dynamic controllers that can be implemented through most homomorphic encryption schemes, including somewhat, leveled fully, and fully homomorphic encryption. To this end, we represent the output of the given controller as a linear combination of a fixed number of previous inputs and outputs. As a result, the encrypted controller involves only a limited number of homomorphic multiplications on every encrypted data, assuming that the output is re-encrypted and transmitted back from the actuator. A guidance for parameter choice is also provided, ensuring that the encrypted controller achieves predefined performance for an infinite time horizon. Furthermore, we propose a customization of the method for ring learning with errors (RLWE)-based cryptosystems, where a vector of messages can be encrypted into a single ciphertext and operated simultaneously, thus reducing computation and communication loads. Unlike previous results, the proposed customization does not require extra algorithms, such as rotation, other than basic addition and multiplication. Simulation results demonstrate the effectiveness of the proposed method.},

keywords = {Controller encryption, Homomorphic encryption},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{nokey,

title = {Evaluating MR-GPR and MR-NN: An Exploration of Data-driven Control Methods for Nonlinear Systems},

author = {Hyuntae Kim and Hamin Chang and Hyungbo Shim},

doi = {/10.1007/s12555-023-0695-x},

issn = {1598-6446},

year  = {2024},

date = {2024-08-01},

urldate = {2024-08-01},

journal = {International Journal of Control, Automation, and Systems},

abstract = {This paper addresses the challenge of data-driven control of nonlinear systems, focusing on the limi-tations and capabilities of model reference Gaussian process regression (MR-GPR) and its evolved counterpart,model reference neural networks (MR-NN). MR-GPR, based on Gaussian processes renowned for their adaptabil-ity to diverse data structures, encounters scalability issues especially when handling large datasets. To address theselimitations, this paper introduces MR-NN, an extension of MR-GPR, leveraging neural networks (NN) to managelarge datasets and capture complex nonlinear dynamics effectively. We present a comprehensive evaluation of bothmethods through a classical control problem of the inverted pendulum, a system well-recognized for its nonlinearbehavior. Numerical experiments are conducted to compare the methods in terms of control performance, compu-tational efficiency, and reliability.},

keywords = {Data-driven control, Gaussian process, Neural Network, nonlinear systems, Stability, System identification},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {On Existence of Uniformly Marginally Stable Zeros of Linear Sampled-data Systems and its Application to Stable Inversion-based Control},

author = {Gyunghoon Park and Hyungbo Shim and Tomomichi Hagiwara},

url = {https://ieeexplore.ieee.org/document/10488419},

doi = {10.1109/ACCESS.2024.3384396},

issn = {2169-3536},

year  = {2024},

date = {2024-07-01},

urldate = {2024-07-01},

booktitle = {IEEE Access},

journal = {IEEE Access},

volume = {12},

pages = {49826 - 49836},

publisher = {IEEE Access},

abstract = {This paper investigates a class of sampled-data systems in which at least one of the discretetime zeros remains on the unit circle regardless of the sampling period. This type of zero is referred to as an

‘‘uniformly marginally stable’’ (UMS) zero. Utilizing this novel concept, we present necessary conditions

as well as sufficient conditions for the continuous-time plant whose sampled-data model has an UMS

zero. The significance of the symmetry regarding the zeros and the poles of the continuous-time plant is

highlighted as it plays a vital role in enforcing a discrete-time zero of the sampled-data system to be UMS,

for both discretization zeros and intrinsic zeros. We develop the theory for sampled-data systems employing

a conventional sampler and a zero-order hold together with a single-input single-output continuous-time

plant, and then observe that certain results can be extended to the generalized holds. As an application, we

establish a condition for sampled-data systems that allow for discrete-time stable inversion-based control

where the absence of such an UMS zero is crucial in the design of such control systems.},

keywords = {Linear Systems, marginal stability, Sampled data system},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Maintaining and steering a formation in an unknown dynamic environment via a consistent distributed dynamic map},

author = {Miao Guo and Bayu Jayawardhana and Jin Gyu Lee and Hyungbo Shim},

doi = {/10.1002/rnc.7414},

issn = { 1049-8923},

year  = {2024},

date = {2024-05-22},

urldate = {2024-05-22},

journal = {International Journal of Robust and Nonlinear Control},

volume = {34},

issue = {13},

pages = {8785-8801},

abstract = {In this paper, we study the problem of maintaining a stable mobile robot formation, steering and localizing all robots in an unknown dynamic environment consisting of multiple periodically moving objects, without the presence of a global positioning system or a robot tracking system. We propose a distributed observer such that each agent can estimate global positions of all mobile robots and that of moving landmarks in an unknown environment. By combining the proposed distributed observer with the distributed formation control and centroid tracking control law, we show that the formation shape can be maintained by utilizing its available relative measurements and the estimated relative measurements to its neighbors, and the group's centroid follows a desired trajectory. We present 

 stability analysis of the closed-loop system. Finally, we validate the proposed methods in a simulation result where a group of mobile robots can maintain a robust formation and maneuver in an unknown dynamic environment.},

keywords = {Formation control, Localization, simultaneous localization and mapping},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Path Generating Inverse Gaussian Process Regression for Data-Driven Ultimate Boundedness Control of Nonlinear Systems},

author = {Yeongjun Jang and Hamin Chang and Heein Park and Hyungbo Shim},

doi = {10.1109/LCSYS.2024.3403525},

issn = {2475-1456},

year  = {2024},

date = {2024-05-20},

urldate = {2024-05-20},

journal = {IEEE Control Systems Letters},

volume = {8},

pages = {748 - 753},

abstract = {A data-driven ultimate boundedness controller for a nonlinear system is proposed. The controller is designed based on the inverse model of the system identified by Gaussian process regression with state/input measurement data to track a reference trajectory suitable for achieving a desired ultimate bound. In particular, a suitable reference trajectory is actively generated based on the data that have been used for the identification. For this reason, the controller is named the path generating inverse Gaussian process regression (PGIGP) controller. We provide a sufficient condition on the data under which the PGIGP controller guarantees ultimate boundedness with a desired ultimate bound. It is shown that the condition can serve as a practical guideline for data acquisition and, conversely, be employed to determine the baseline of the control performance achievable from a given dataset. The effectiveness of the PGIGP controller is demonstrated through numerical simulations.},

keywords = {Data-driven control, Gaussian process, nonlinear systems},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Decentralized Design and Plug-and-Play Distributed Control for Linear Multi-Channel Systems},

author = {Taekyoo Kim and Donggil Lee and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10174243},

doi = {10.1109/TAC.2023.3293036},

issn = {0018-9286},

year  = {2024},

date = {2024-05-01},

urldate = {2023-07-06},

journal = {IEEE Transactions on Automatic Control},

volume = {69},

issue = {5},

pages = {2807 - 2822},

abstract = {We propose a distributed control, in which many identical control agents are deployed for controlling a linear time-invariant plant that has multiple input-output channels. Each control agent can join or leave the control loop during the operation of stabilization without particular initialization over the whole networked agents. Once new control agents join the loop, they self-organize their control dynamics, which does not interfere the control by other active agents, which is achieved by local communication with the neighboring agents. The key idea enabling these features is the use of Bass' algorithm, which allows the distributed computation of stabilizing gains by solving a Lyapunov equation in a distributed manner.},

keywords = {Distributed algorithm, Multi-channel system, Plug-and-play},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {How Does a Swarm Exhibit Emergent Behavior Through Synchronization?},

author = {Hyungbo Shim},

url = {https://icros.org/publication/sub03_04.asp?sub_param=4},

doi = {https://doi.org/10.5302/J.ICROS.2024.24.0039},

issn = {1976-5622},

year  = {2024},

date = {2024-04-01},

urldate = {2024-04-01},

journal = {Journal of Institute of Control, Robotics and Systems},

volume = {30},

issue = {4},

pages = {352},

abstract = {A swarm of individuals often exhibits behaviors that are not possible for each individual. This phenomenon is called emergence, and this paper mathematically demonstrates that new dynamics can arise in swarm behavior that cannot be explained by the dynamics of individuals. In particular, we argue that emergence occurs when heterogeneity is coupled with synchronization.

These two concepts may seem conflicting, as heterogeneity is the tendency to differ whereas synchronization is the tendency toward sameness. However, we show that emergent behavior arises from the interplay between the two.},

keywords = {Blended dynamics, Multi-agent systems, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Node-Wise Monotone Barrier Coupling Law for Formation Control},

author = {Jin Gyu Lee and Cyrus Mostajeran and Graham Van Goffrier},

url = {https://www.mdpi.com/1099-4300/26/2/134},

doi = {https://doi.org/10.3390/e26020134},

issn = {1099-4300},

year  = {2024},

date = {2024-01-31},

urldate = {2024-01-31},

journal = {Entropy},

volume = {26},

issue = {2},

pages = {134},

abstract = {We study a node-wise monotone barrier coupling law, motivated by the synaptic coupling of neural central pattern generators. It is illustrated that this coupling imitates the desirable properties of neural central pattern generators. In particular, the coupling law (1) allows us to assign multiple central patterns on the circle and (2) allows for rapid switching between different patterns via simple ‘kicks’. In the end, we achieve full control by partitioning the state space by utilizing a barrier effect and assigning a unique steady-state behavior to each element of the resulting partition. We analyze the global behavior and study the viability of the design.},

keywords = {Consensus, Formation control, Nonlinear space, Positivity},

pubstate = {published},

tppubtype = {article}

}

@article{noneb,

title = {Asymptotic output tracking in a class of non-minimum phase nonlinear systems via learning-based inversion},

author = {Namguk Kim and Hyungbo Shim},

doi = {https://doi.org/10.1002/rnc.6969},

issn = {1049-8923},

year  = {2024},

date = {2024-01-10},

urldate = {2024-01-10},

journal = {International Journal of Robust and Nonlinear Control},

volume = {34},

issue = {1},

pages = {240-269},

abstract = {Asymptotic output tracking of non-minimum phase (NMP) nonlinear systems has been a popular topic in control theory and applications. Many approaches have focused on finding solutions under minimal assumptions either in the target system or desired trajectories, as there is no general solution available. In this article, we propose a practical and simple solution for cases where the reference trajectory is periodic in time. Our approach employs a learning-based scheme to iteratively determine the desired feedforward input. Unlike previous learning-based frameworks, our method only requires the output tracking error to update the feedforward input iteratively and can be applicable to NMP systems. Our method retains the key advantages of the learning-based framework, including robustness to parameter uncertainties and periodic disturbances. We evaluate the effectiveness of our algorithm using simulation results with an inverted pendulum on a cart, a typical NMP nonlinear system.},

keywords = {asymptotic output tracking, iterative learning, Non-minimum phase, stable inversion},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Spectral Trade-off for Measurement Sparsification of Pose-graph SLAM},

author = {Jiyeon Nam and Soojeong Hyeon and Youngjun Joo and DongKi Noh and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10333265},

doi = {10.1109/LRA.2023.3337590},

issn = {2377-3766},

year  = {2024},

date = {2024-01-02},

urldate = {2024-01-02},

journal = {IEEE Robotics and Automation Letters},

volume = {9},

issue = {1},

pages = {723 - 730},

abstract = {In this paper, we propose a trade-off optimization algorithm to compute an appropriate number of edges for measurement (edge) sparsification in pose-graph SLAM. The greater the amount of measurement data, the larger is the computational burden. To reduce computational burden, one can remove a portion of measurements. However, reliable data, such as odometric measurements, can be lost if measurements are removed without any principle. To remove measurements which is redundant, we propose a trade-off optimization algorithm between maximization of the Fiedler value and minimization of the largest eigenvalue of adjacency matrix for measurement graph. This problem formulation gives virtues twofold. First, it is scalable. For any dataset, when a weight for trade-off is given, this algorithm determines the appropriate number of edges since this is a trade-off optimization problem. Second, the edges of the measurement graph can be distributed evenly. The algorithm considers the minimization of the largest eigenvalue of the adjacency matrix, so it suppresses the upper bound of the maximum degree of the measurement graph. It removes the redundant information concentrated on a few nodes, and improves the estimation accuracy of the sparsified graph. To validate the performance of the proposed trade-off optimization algorithm, we apply our approach to CSAIL, Intel, and Manhattan datasets.},

keywords = {optimal control, simultaneous localization and mapping},

pubstate = {published},

tppubtype = {article}

}

@article{Discrete-timeheterogeneousmulti-agentsystemMulti-stepcouplingBlendeddynamics,

title = {A design method of distributed algorithms via discrete-time blended dynamics theorem},

author = {Jeong Woo Kim and Jin Gyu Lee and Donggil Lee and Hyungbo Shim},

editor = {Automatica},

doi = {https://doi.org/10.1016/j.automatica.2023.111371},

issn = {0005-1098},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

booktitle = {Automatica},

journal = {Automatica},

volume = {159},

pages = {111371},

abstract = {We develop a discrete-time version of the blended dynamics theorem for the use of designing distributed computation algorithms. The blended dynamics theorem enables to predict the behavior of heterogeneous multi-agent systems. Therefore, once we get a blended dynamics for a particular computational task, design idea of node dynamics for individual heterogeneous agents can easily occur. In the continuous-time case, prediction by blended dynamics was enabled by high coupling gain among neighboring agents. In the discrete-time case, we propose an equivalent action, which we call multi-step coupling in this paper. Compared to the continuous-time case, the blended dynamics can have more variety depending on the coupling matrix. This benefit is demonstrated with three applications; distributed estimation of network size, distributed computation of the PageRank, and distributed computation of the degree sequence of a graph, which correspond to the coupling by doubly-stochastic, column-stochastic, and row-stochastic matrices, respectively.},

key = {Discrete-time heterogeneous multi-agent systemMulti-step couplingBlended dynamics},

keywords = {Blended dynamics, Discrete-time blended dynamics, Discrete-time heterogeneous multi-agent system, Multi-step coupling},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Model Reference Gaussian Process Regression: Data-Driven State Feedback Controller},

author = {Hyuntae Kim and Hamin Chang},

doi = {10.1109/ACCESS.2023.3336421},

issn = {2169-3536},

year  = {2023},

date = {2023-11-01},

journal = {IEEE Access},

volume = {11},

pages = {134374},

abstract = {This paper proposes a data-driven state feedback controller that enables reference tracking for nonlinear discrete-time systems. The controller is designed based on the identified inverse model of the system and a given reference model, assuming that the identification of the inverse model is carried out using only the system’s state/input measurements. When its results are provided, we present conditions that guarantee a certain level of reference tracking performance, regardless of the identification method employed for the inverse model. Specifically, when Gaussian process regression (GPR) is used as the identification method, we propose sufficient conditions for the required data by applying some lemmas related to identification errors to the aforementioned conditions, ensuring that the Model Reference-GPR (MR-GPR) controller can guarantee a certain level of reference tracking performance. Finally, an example is provided to demonstrate the effectiveness of the MR-GPR controller.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Edge-wise funnel output synchronization of heterogeneous agents with relative degree one},

author = {Jin Gyu Lee and Thomas Berger and Stephan Trenn and Hyungbo Shim},

url = {https://www.sciencedirect.com/science/article/pii/S0005109823003655},

doi = {https://doi.org/10.1016/j.automatica.2023.111204},

issn = {0005-1098},

year  = {2023},

date = {2023-10-01},

urldate = {2023-10-01},

journal = {Automatica},

volume = {156},

pages = {111204},

abstract = {When a group of heterogeneous node dynamics are diffusively coupled with a high coupling gain, the

group exhibits a collective emergent behavior which is governed by a simple algebraic average of the

node dynamics called the blended dynamics. This finding has been utilized for designing heterogeneous

multi-agent systems by building the desired blended dynamics first and then splitting it into the node

dynamics. However, to compute the magnitude of the coupling gain, each agent needs to know global

information such as the number of participating nodes, the graph structure, and so on, which prevents

a fully decentralized design of the node dynamics in conjunction with the coupling laws. To resolve this

issue, the idea of funnel control, which is a method for adaptive gain selection, can be exploited for a

node-wise coupling, but the price to pay is that the collective emergent behavior is no longer governed

by a simple average of the node dynamics. Our analysis reveals that this drawback can be avoided by an

edge-wise design premise, which is the idea that we present in this paper. After all, we gain benefits

such as a fully decentralized design without global information, collective emergent behavior being

governed by the blended dynamics, and the plug-and-play operation based on edge-wise handshaking

between two nodes},

keywords = {Blended dynamics, Funnel control, Heterogeneous multi-agents, output synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {A Toolkit for Globally Robust Observer-Based Feedback with Relaxed Characterization of iISS/ISS},

author = {Hiroshi Ito and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/abstract/document/9837417},

doi = {10.1109/TAC.2022.3193270},

issn = {0018-9286},

year  = {2023},

date = {2023-07-01},

urldate = {2022-07-22},

journal = {IEEE Transactions on Automatic Control},

volume = {68},

issue = {7},

pages = {3858-3871},

abstract = {This paper elaborates on flexibility in dealing with the interconnection of integral input-to-state stable (iISS) and input-to-state stable (ISS) systems. The undecoupled characterizations introduced separately for iISS and ISS in the literature are linked to build a framework enabling global analysis without settling for local and semi-global properties. Feedback control design in the presence of measurement noise can benefit from the framework immediately if plants are nonlinear, irrespective of application areas. This paper proposes a toolkit for providing robustness guarantees in observer-based output feedback control subject to measurement noise. For a nonlinear plant, the couplings among the plant state, the estimation error, and the measurement noise arising in the closed-loop equations often hinder global analysis such as ISS with respect to the measurement noise. In the formalism of iISS, this paper demonstrates that the flexibility in dealing with the couplings allows one to establish the robustness globally. Moreover, it gives a condition under which the closed-loop system can possess ISS and strong iISS which are stronger than iISS.},

keywords = {Integral input-to-state stability, Lyapunov function, Output feedback, Small gain theorem},

pubstate = {published},

tppubtype = {article}

}

@article{nokeyp,

title = {Distributed Resilient Observer: Blended Dynamics Theory Meets ℓ1-Minimization Approach},

author = {Donggil Lee and Junsoo Kim and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/10147254/},

doi = {10.1109/LCSYS.2023.3284592},

issn = {2475-1456},

year  = {2023},

date = {2023-06-09},

urldate = {2023-06-09},

journal = {IEEE Control Systems Letters},

volume = {7},

pages = {2083 - 2088},

abstract = {This paper presents a distributed resilient observer for continuous-time linear time-invariant plants that remains functional even under sensor attacks. The proposed method aims to determine the estimation outcome that matches the majority of sensor measurements, which is formulated as an ℓ1-minimization problem considering all the observable components of each sensor measurement. A distributed observer based on the blended dynamics theory is then proposed to solve the ℓ1-minimization problem in a distributed manner. As a result, the distributed resilient estimation is enabled for a broader class of systems compared to previous works. The design procedure is constructive with parameters obtained from a specified condition that is equivalent to the well-known null-space property.},

keywords = {Blended dynamics, Blended Dynamics Approach, Distributed state estimation, Resilient state estimation},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Dynamic Controller that Operates over Homomorphically Encrypted Data for Infinite Time Horizon},

author = {Junsoo Kim and Hyungbo Shim and Kyoohyung Han},

url = {https://ieeexplore.ieee.org/abstract/document/9678042},

doi = {10.1109/TAC.2022.3142124},

issn = {1558-2523},

year  = {2023},

date = {2023-02-01},

urldate = {2023-02-01},

journal = {IEEE Transactions on Automatic Control},

volume = {68},

number = {2},

pages = {660-672},

publisher = {IEEE},

abstract = {In this paper, we present dynamic systems over encrypted data that compute the next state and the output using homomorphic properties of the cryptosystem, which has equivalent performance to the linear dynamic controllers over real-valued signals. Assuming that the input as well as the output of the plant is encrypted and transmitted to the system, the state matrix of the system is designed to consist of integers. This allows the proposed dynamic system to operate for infinite time horizon, without decryption or reset of the state. For implementation in practice, the use of cryptosystems based on Learning With Errors problem is considered, which allows both multiplication and addition over encrypted data. The effect of injecting errors during encryption is in turn controlled under closed-loop stability.},

keywords = {Controller encryption, Homomorphic encryption},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Development and evaluation of haltere-mimicking gyroscope for three-axis angular velocity sensing using a haltere-mimicking structure pair},

author = {Chulhong Kim and Junghyun Park and Taeyup Kim and Jee-Seong Kim and Jeongmo Seong and Hyungbo Shim and Hyoungho Ko and Dong-Il (Dan) Cho},

url = {https://iopscience.iop.org/article/10.1088/1748-3190/ac9c7d/meta},

doi = {10.1088/1748-3190/ac9c7d},

issn = {1748-3182},

year  = {2022},

date = {2022-11-15},

urldate = {2022-11-15},

journal = {Bioinspiration & Biomimetics},

volume = {18},

number = {1},

pages = {016003},

abstract = {This paper presents a three-axis biomimetic gyroscope, mimicking the haltere of Diptera. Diptera use a club-shaped mechanosensory organ called the haltere to get the three-axis angular velocity information, namely roll, pitch and yaw axes, for flight control. One pair of halteres is physically connected to the wings of Diptera that vibrate in antiphase to the flapping wings in ambient air. They sense the Coriolis force and relay angular velocity information to the Diptera. As an alternative to the conventional micro-electro-mechanical system gyroscopes which are widely used in robotics, many research groups have attempted to mimic the haltere. However, no previous study succeeded in measuring all three-axis components of angular velocity, due to various shortcomings. In this paper, we developed the first three-axis haltere-mimicking gyroscope. Two perpendicularly positioned haltere-mimicking structures that can vibrate at a 180° amplitude were mechanically integrated into a robot actuator. Two accelerometers, placed at the tip of each structure, were employed to measure the Coriolis force. The performance of the novel biomimetic gyroscope was measured in all rotational directions, using a motion capture system as the ground truth. One-axis input experiments were performed 240 times at different input magnitudes and directions, and the measured orientation error was less than ±2.0% in all experiments. In 80 three-axis input experiments, the orientation error was less than ±3.5%.},

keywords = {Biomimetic sensor, Gyroscope, Haltere},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Comparison of encrypted control approaches and tutorial on dynamic systems using Learning With Errors-based homomorphic encryption},

author = {Junsoo Kim and Dongwoo Kim and Yongsoo Song and Hyungbo Shim and Henrik Sandberg and Karl H. Johansson},

url = {https://www.sciencedirect.com/science/article/pii/S1367578822001031},

doi = {https://doi.org/10.1016/j.arcontrol.2022.10.002},

issn = {1367-5788},

year  = {2022},

date = {2022-10-28},

urldate = {2022-10-28},

journal = {Annual Reviews in Control},

volume = {54},

pages = {200-218},

abstract = {Encrypted control has been introduced to protect controller data by encryption at the stage of computation and communication, by performing the computation directly on encrypted data. In this article, we first review and categorize recent relevant studies on encrypted control. Approaches based on homomorphic encryption, multi-party computation, and secret sharing are introduced, compared, and then discussed with respect to computational complexity, communication load, enabled operations, security, and research directions. We proceed to discuss a current challenge in the application of homomorphic encryption to dynamic systems, where arithmetic operations other than integer addition and multiplication are limited. We also introduce a Learning With Errors based homomorphic cryptosystem called ‘‘Gentry-Sahai-Waters’’ scheme and discuss its benefits that allow for recursive multiplication of encrypted dynamic systems, without use of computationally expensive bootstrapping techniques.},

keywords = {Controller encryption, Homomorphic encryption},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Synchronization with prescribed transient behavior: Heterogeneous multi-agent systems under funnel coupling},

author = {Jin Gyu Lee and Stephan Trenn and Hyungbo Shim},

url = {https://www.sciencedirect.com/science/article/pii/S0005109822001224},

doi = {https://doi.org/10.1016/j.automatica.2022.110276},

issn = {0005-1098},

year  = {2022},

date = {2022-07-01},

urldate = {2022-07-01},

journal = {Automatica},

volume = {141},

pages = {110276},

abstract = {In this paper, we introduce a nonlinear time-varying coupling law, which can be designed in a fully decentralized manner and achieves approximate synchronization with arbitrary precision, under only mild assumptions on the individual vector fields and the underlying (undirected) graph structure. The proposed coupling law is motivated by the so-called funnel control method studied in adaptive control under the observation that arbitrary precision synchronization can be achieved for heterogeneous multi-agent systems by a high-gain coupling; consequently we call our novel synchronization method ‘(node-wise) funnel coupling.’ By adjusting the conventional proof technique in the funnel control study, we are even able to obtain asymptotic synchronization with the same funnel coupling law. Moreover, the emergent collective behavior that arises for a heterogeneous multi-agent system when enforcing arbitrary precision synchronization by the proposed funnel coupling law, is analyzed in this paper. In particular, we introduce a single scalar dynamics called ‘emergent dynamics’ which describes the emergent synchronized behavior of the multi-agent system under funnel coupling. Characterization of the emergent dynamics is important because, for instance, one can design the emergent dynamics first such that the solution trajectory behaves as desired, and then, provide a design guideline to each agent so that the constructed vector fields yield the desired emergent dynamics. We illustrate this idea via the example of a distributed median solver based on funnel coupling.},

keywords = {Funnel control, Heterogeneous multi-agents, Multi-agent systems, Synchronization},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Blended dynamics approach to distributed optimization: Sum convexity and convergence rate},

author = {Seungjoon Lee and Hyungbo Shim},

url = {https://www.sciencedirect.com/science/article/pii/S0005109822001364},

doi = {https://doi.org/10.1016/j.automatica.2022.110290.},

issn = {0005-1098},

year  = {2022},

date = {2022-04-26},

urldate = {2022-07-01},

journal = {Automatica},

volume = {141},

pages = {110290},

abstract = {In this paper, we introduce the concept of the blended dynamics of the multi-agent system, which is constructed using dynamics of individual agents. The blended dynamics approach is applied to the distributed optimization problem where the global cost function is given by a sum of local cost functions. The benefits include (i) individual cost function need not be convex as long as the global cost function is strongly convex and (ii) the convergence rate of the distributed algorithm is arbitrarily close to the convergence rate of the centralized one. Two particular continuous-time algorithms are presented using the proportional–integral-type couplings. One has benefit of ‘initialization-free’, so that agents can join or leave the network during the operation. The other one has the minimal amount of communication information. After presenting a general theorem that can be used for designing distributed algorithms, we particularly present a distributed heavy-ball method and discuss its strength over other methods.},

keywords = {Blended Dynamics Approach, Distributed optimization},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Distributed Dynamic Quantile Solver With Plug-and-Play Operation},

author = {Jeong Mo Seong and Jeong Woo Kim and Seungjoon Lee and Hyungbo Shim},

url = {https://ieeexplore.ieee.org/document/9646895},

doi = {10.1109/ACCESS.2021.3134655},

issn = {2169-3536},

year  = {2021},

date = {2021-12-01},

urldate = {2021-12-01},

journal = {IEEE Access},

volume = {9},

pages = {165517-165525},

abstract = {In this paper, we propose a continuous-time distributed algorithm for the dynamic quantile problem. The problem is to find the quantile of time-varying signals in a network of agents, each of which having the signal of its own. For example, this problem includes finding the median, maximum, or the second largest value of the signals. The proposed algorithm guarantees convergence from arbitrary initial conditions and does not use the decaying gains. Hence our algorithm is suitable for plug-and-play operation, where agents may freely join or leave the network during the operation. An application to a simplified electricity market problem is presented to show the effectiveness of the design.},

keywords = {Blended Dynamics Approach, Distributed algorithm, Multi-agent system},

pubstate = {published},

tppubtype = {article}

}

@article{Kim21,

title = {Model Predictive Control Method for Autonomous Vehicles Using Time-Varying and Non-Uniformly Spaced Horizon},

author = {Minsung Kim and Donggil Lee and Joonwoo Ahn and Minsoo Kim and Jaeheung Park},

doi = {https://doi.org/10.1109/ACCESS.2021.3088937},

issn = {2169-3536},

year  = {2021},

date = {2021-06-01},

journal = {IEEE Access},

volume = {9},

pages = {86475-86487},

abstract = {This paper proposes an algorithm for path-following and collision avoidance of an autonomous vehicle based on model predictive control (MPC) using time-varying and non-uniformly spaced horizon. The MPC based on non-uniformly spaced horizon approach uses the time intervals that are small for the near future, and time intervals that are large for the distant future, to extend the length of the whole prediction horizon with a fixed number of prediction steps. This MPC has the advantage of being able to detect obstacles in advance because it can see the distant future. However, the presence of longer time interval samples may lead to poor path-following performance, especially for paths with high curvature. The proposed algorithm performs proper adjustment of the prediction interval according to a given situation. For sections with large curvature, it uses the short prediction intervals to increase the path-following performance; further, to consider obstacles over a wider range, it uses the long prediction intervals. This technique allows simultaneous improvement of the path-following performance and the range of obstacle avoidance with fixed computational complexity. The effectiveness of the proposed method is verified through an open-source simulator, CARLA and real-time experiments.},

keywords = {Autonomous vehicle, Collision avoiadance, Model predictive control, Path following},

pubstate = {published},

tppubtype = {article}

}

@article{Kim2020,

title = {Completely Decentralized Design of Distributed Observer for Linear Systems},

author = {Taekyoo Kim and Chanhwa Lee and Hyungbo Shim},

doi = {https://doi.org/10.1109/TAC.2019.2962360},

issn = {1558-2523},

year  = {2020},

date = {2020-11-01},

journal = {IEEE Transactions on Automatic Control},

volume = {65},

number = {11},

pages = {4664-4678},

abstract = {This article presents a decentralized design of a distributed state observer for a continuous-time linear time-invariant plant. The plant is monitored by a group of agents and each agent‘s measurement of the plant’s state suffers from lack of detectability with the plant dynamics. Then the missing information (i.e., the undetectable portion) is compensated by a local communication with the neighboring agents. In particular, when the local observer for each agent is designed, no global information such as the structure of network and the number of agents is needed, and so, the decentralized design is achieved. Therefore, the plug-and-play operation is enabled; that is, during the operation, a new agent can design a local observer for itself without any global information and join the network, and any agent may leave the network without hampering the operation as long as the rest of the agents remain detectable. The main idea is to let each agent recover its own detectable part while the undetectable part is compensated by a projection of the neighbors‘ estimates into the receiver’s undetectable subspace. An adaptive algorithm for individual agent is designed in order to find suitable gains for compensating the undetectable portion. Simulation results confirm the effectiveness of the proposed design.},

keywords = {Decentralized design, Distributed state estimation, Linear time-invariant system, Plug-and-play},

pubstate = {published},

tppubtype = {article}

}