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Prof. Hwangnam Kim
Professor, Electrical Engineering, Korea University, Korea

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Research Keywords & Expertise

0 Internet of Things
0 Cyber physical system
0 UTM
0 wireless network
0 Unmanned Aircraft System

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Internet of Things
wireless network

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Journal article
Published: 16 August 2021 in ICT Express
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Blockchain technology innovatively removes the need for intermediaries and establishes a trust-less trust system by peer-to-peer networks and distributed ledger technology. It is still difficult to clarify the specific degree of decentralization of blockchain even though the decentralized characteristic of the system is derived from this system structure. Namely, the criteria for determining whether decentralized are not well established and do not reflect the real world well. So we propose two approaches to measure the degree of decentralization of blockchain system that currently exists: Censorship resistance and geographical diversity. This paper outlines the meaning of each decentralization quotient and explains how those indices can be applied in respect of the user protection.

ACS Style

Jaeseung Lee; Byungheon Lee; Jaeyoung Jung; Hojun Shim; Hwangnam Kim. DQ: Two approaches to measure the degree of decentralization of blockchain. ICT Express 2021, 1 .

AMA Style

Jaeseung Lee, Byungheon Lee, Jaeyoung Jung, Hojun Shim, Hwangnam Kim. DQ: Two approaches to measure the degree of decentralization of blockchain. ICT Express. 2021; ():1.

Chicago/Turabian Style

Jaeseung Lee; Byungheon Lee; Jaeyoung Jung; Hojun Shim; Hwangnam Kim. 2021. "DQ: Two approaches to measure the degree of decentralization of blockchain." ICT Express , no. : 1.

Journal article
Published: 15 April 2021 in Sensors
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Recently, unmanned aerial vehicles (UAVs) have been applied to various applications. In order to perform repetitive and accurate tasks with a UAV, it is more efficient for the operator to perform the tasks through an integrated management program rather than controlling the UAVs one by one through a controller. In this environment, control packets must be reliably delivered to the UAV to perform missions stably. However, wireless communication is at risk of packet loss or packet delay. Typical network communications can respond to situations in which packets are lost by retransmitting lost packets. However, in the case of UAV control, delay due to retransmission is fatal, so control packet loss and delay should not occur. As UAVs move quickly, there is a high risk of accidents if control packets are lost or delayed. In order to stably control a UAV by transmitting control messages, we propose a control packet transmission scheme, ConClone. ConClone replicates control packets and then transmits them over multiple network connections to increase the probability of successful control packet transmission. We implemented ConClone using real equipment, and we verified its performance through experiments and theoretical analysis.

ACS Style

Woonghee Lee; Joon Lee; Hyeontae Joo; Hwangnam Kim. An MPTCP-Based Transmission Scheme for Improving the Control Stability of Unmanned Aerial Vehicles. Sensors 2021, 21, 2791 .

AMA Style

Woonghee Lee, Joon Lee, Hyeontae Joo, Hwangnam Kim. An MPTCP-Based Transmission Scheme for Improving the Control Stability of Unmanned Aerial Vehicles. Sensors. 2021; 21 (8):2791.

Chicago/Turabian Style

Woonghee Lee; Joon Lee; Hyeontae Joo; Hwangnam Kim. 2021. "An MPTCP-Based Transmission Scheme for Improving the Control Stability of Unmanned Aerial Vehicles." Sensors 21, no. 8: 2791.

Journal article
Published: 15 March 2021 in IEEE Access
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This paper presents a comprehensive survey on anti-drone systems. After drones were released for non-military usages, drone incidents in the unarmed population are gradually increasing. However, it is unaffordable to construct a military grade anti-drone system for every private or public facility due to installation and operation costs, and regulatory restrictions. We focus on analyzing anti-drone system that does not use military weapons, investigating a wide range of anti-drone technologies, and deriving proper system models for reliable drone defense. We categorized anti-drone technologies into detection, identification, and neutralization, and reviewed numerous studies on each. Then, we propose a hypothetical anti-drone system that presents the guidelines for adaptable and effective drone defense operations. Further, we discuss drone-side safety and security schemes that could nullify current anti-drone methods, and propose future solutions to resolve these challenges.

ACS Style

Seongjoon Park; Hyeong Tae Kim; Sangmin Lee; Hyeontae Joo; Hwangnam Kim. Survey on Anti-Drone Systems: Components, Designs, and Challenges. IEEE Access 2021, 9, 42635 -42659.

AMA Style

Seongjoon Park, Hyeong Tae Kim, Sangmin Lee, Hyeontae Joo, Hwangnam Kim. Survey on Anti-Drone Systems: Components, Designs, and Challenges. IEEE Access. 2021; 9 ():42635-42659.

Chicago/Turabian Style

Seongjoon Park; Hyeong Tae Kim; Sangmin Lee; Hyeontae Joo; Hwangnam Kim. 2021. "Survey on Anti-Drone Systems: Components, Designs, and Challenges." IEEE Access 9, no. : 42635-42659.

Journal article
Published: 11 December 2020 in IEEE Access
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This paper addresses a novel approach for multi-agent control systems including Unmanned Vehicles (UV). As UV technology advances, one or a group of UVs can be used in a wide range of industrial or military applications. Centralized monitoring has limitations on various resources (e.g. communication bandwidth, propagation delay, and computational power), but can lead to an optimal solution to the movement of the swarm. The artificial potential field (APF) method is well-known for modeling decentralized behavior, but most APF research only focuses on naive actions such as collision avoidance, flocking, or path planning. In our proposed design Versatile Multi-Vehicle Control System (VMCS), we defined high-level conditions as APF and let UVs perform swarm intelligence in various mission environments. Furthermore, we devised a novel algorithm that controls the UVs’ APF topology which can significantly enhance the mission efficiency. We simulated the VMCS in 3D space and showed our scheme can control the dynamic mission scenarios for multi-UV systems.

ACS Style

Seongjoon Park; Hyeong Tae Kim; Hwangnam Kim.. VMCS: Elaborating APF-Based Swarm Intelligence for Mission-Oriented Multi-UV Control. IEEE Access 2020, 8, 223101 -223113.

AMA Style

Seongjoon Park, Hyeong Tae Kim, Hwangnam Kim.. VMCS: Elaborating APF-Based Swarm Intelligence for Mission-Oriented Multi-UV Control. IEEE Access. 2020; 8 (99):223101-223113.

Chicago/Turabian Style

Seongjoon Park; Hyeong Tae Kim; Hwangnam Kim.. 2020. "VMCS: Elaborating APF-Based Swarm Intelligence for Mission-Oriented Multi-UV Control." IEEE Access 8, no. 99: 223101-223113.

Journal article
Published: 30 October 2020 in Sensors
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Practical evaluation of the Unmanned Aerial Vehicle (UAV) network requires a lot of money to build experiment environments, which includes UAVs, network devices, flight controllers, and so on. To investigate the time-sensitivity of the multi-UAV network, the influence of the UAVs’ mobility should be precisely evaluated in the long term. Although there are some simulators for UAVs’ physical flight, there is no explicit scheme for simulating both the network environment and the flight environments simultaneously. In this paper, we propose a novel co-simulation scheme for the multiple UAVs network, which performs the flight simulation and the network simulation simultaneously. By considering the dependency between the flight status and networking situations of UAV, our work focuses on the consistency of simulation state through synchronization among simulation components. Furthermore, we extend our simulator to perform multiple scenarios by exploiting distributed manner. We verify our system with respect to the robustness of time management and propose some use cases which can be solely simulated by this.

ACS Style

Seongjoon Park; Woong Gyu La; Woonghee Lee; Hwangnam Kim. Devising a Distributed Co-Simulator for a Multi-UAV Network. Sensors 2020, 20, 6196 .

AMA Style

Seongjoon Park, Woong Gyu La, Woonghee Lee, Hwangnam Kim. Devising a Distributed Co-Simulator for a Multi-UAV Network. Sensors. 2020; 20 (21):6196.

Chicago/Turabian Style

Seongjoon Park; Woong Gyu La; Woonghee Lee; Hwangnam Kim. 2020. "Devising a Distributed Co-Simulator for a Multi-UAV Network." Sensors 20, no. 21: 6196.

Journal article
Published: 21 April 2020 in IEEE Access
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The researches on Real Time Kinematic GPS (RTK-GPS) have been actively conducted to accurately estimate the location of drones, and there were many use cases applied to drones. However, such systems using RTK-GPS do not provide the protection against network instability, failure of the components that make up the RTK-GPS service. In other words, availability is not provided to ensure the stability of the RTK-GPS. In this paper, we propose an architecture enabling redundancy to improve the availability of RTK-GPS system by switching or parallelizing the GPS correction data sources. We also introduce how to propagate the correction messages through the drone network. After evaluating the system on empirical testbed, we validated that the correction messages propagated without delay, the message source was switched or multiplexed among several message sources through the proposed system when the network was unstable, and the switching time was short enough not to affect our propagation system. Consequently, we have confirmed availability through the proposed architecture of RTK-GPS redundancy.

ACS Style

Inseop Um; Seongjoon Park; Hyeong Tae Kim; Hwangnam Kim. Configuring RTK-GPS Architecture for System Redundancy in Multi-Drone Operations. IEEE Access 2020, 8, 76228 -76242.

AMA Style

Inseop Um, Seongjoon Park, Hyeong Tae Kim, Hwangnam Kim. Configuring RTK-GPS Architecture for System Redundancy in Multi-Drone Operations. IEEE Access. 2020; 8 (99):76228-76242.

Chicago/Turabian Style

Inseop Um; Seongjoon Park; Hyeong Tae Kim; Hwangnam Kim. 2020. "Configuring RTK-GPS Architecture for System Redundancy in Multi-Drone Operations." IEEE Access 8, no. 99: 76228-76242.

Journal article
Published: 03 March 2020 in IEEE Access
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Despite the increasing importance of network security, increasing Internet of Things (IoT) uptake and traffic tends to apply tighter resource constraints for cryptography. To cope with the constraints, security systems must choose between time cost and security. Cyber-attack model evolution and quantum computing technologies have severely limited current cryptography uptake and imposed too much overhead to operate effectively on lightweight communication environments. Therefore, we propose a new operation mode using multiple symmetric key ciphers alternately in a regularized order. The proposed design exploits lightweight cryptography methods, reducing encryption/decryption overhead compared to a single heavy cryptography approach, as well as avoiding exhaustive key extraction attack. Since sequences can change both time cost and security performance widely, the design can be applied to various situations, from the delay-constrained communications to highly secure networks. Our cryptography design incorporates patterned cipher block (PCB) operation, an integrity verification technique to identify if a ciphertext has been forged, handshaking protocol exchanging pattern information and a key using two-round communication, and pattern optimization to maximize the cryptographic performance. We confirmed the proposed operation mode numerically, and verified the outcomes experimentally, confirming that the proposed scheme outperformed current best practice cryptography.

ACS Style

Seounghwan Oh; Seongjoon Park; Hwangnam Kim. Patterned Cipher Block for Low-Latency Secure Communication. IEEE Access 2020, 8, 44632 -44642.

AMA Style

Seounghwan Oh, Seongjoon Park, Hwangnam Kim. Patterned Cipher Block for Low-Latency Secure Communication. IEEE Access. 2020; 8 (99):44632-44642.

Chicago/Turabian Style

Seounghwan Oh; Seongjoon Park; Hwangnam Kim. 2020. "Patterned Cipher Block for Low-Latency Secure Communication." IEEE Access 8, no. 99: 44632-44642.

Journal article
Published: 09 February 2020 in Applied Sciences
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A UAV network composed of multiple UAVs allows a wide operating radius and various tasks to be performed. However, a UAV network mostly suffers from high probability of transmission failure due to interference or mobility. Also, nodes connected to the network often experience connection loss and segment loss caused by frequent node mobility and routing update. Since congestion is not the only cause of data loss in UAV networks, the TCP congestion control should not be run if there is a possibility of transient link instability unless a reduction in transmission speed is required. For this reason, we propose an algorithm to improve the transmission performance of UAV network through TCP with Slow-Start threshold (Ssthresh) value adjusted. The adjustment algorithm is called Adaptive Ssthresh Reviser for flying Ad hoc Network (ASRAN) that quickly restores unnecessary decrease of transmission speed in UAV network.

ACS Style

Joon Yeop Lee; Woonghee Lee; HyunSoon Kim; Hwangnam Kim. Adaptive TCP Transmission Adjustment for UAV Network Infrastructure. Applied Sciences 2020, 10, 1161 .

AMA Style

Joon Yeop Lee, Woonghee Lee, HyunSoon Kim, Hwangnam Kim. Adaptive TCP Transmission Adjustment for UAV Network Infrastructure. Applied Sciences. 2020; 10 (3):1161.

Chicago/Turabian Style

Joon Yeop Lee; Woonghee Lee; HyunSoon Kim; Hwangnam Kim. 2020. "Adaptive TCP Transmission Adjustment for UAV Network Infrastructure." Applied Sciences 10, no. 3: 1161.

Journal article
Published: 27 November 2019 in Energies
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Following striking developments in Unmanned Aerial Vehicle (UAV) technology, the use of UAVs has been researched in various industrial fields. Furthermore, a number of studies on operating multiple autonomous networking UAVs suggest a potential to use UAVs in large-scale environments. To achieve efficiency of performance in multi-UAV operations, it is essential to consider a variety of factors in UAV network conditions, such as energy efficiency, network overhead, and so on. In this paper, we propose a novel scheme that improves the energy efficiency and network throughputs by controlling the topology of the network. Our proposed network topology control scheme functions between the data link layer (L3) and the network layer (L2). Accordingly, it can be considered to be layer 2.5 in the network hierarchy model. In addition, our methodology includes swarm intelligence, meaning that whole topology control can be generated with less cost and effort, and without a centralized controller. Our experimental results confirm the notable performance of our proposed method compared to previous approaches.

ACS Style

Seongjoon Park; Hyeong Tae Kim; Hwangnam Kim. Energy-Efficient Topology Control for UAV Networks. Energies 2019, 12, 4523 .

AMA Style

Seongjoon Park, Hyeong Tae Kim, Hwangnam Kim. Energy-Efficient Topology Control for UAV Networks. Energies. 2019; 12 (23):4523.

Chicago/Turabian Style

Seongjoon Park; Hyeong Tae Kim; Hwangnam Kim. 2019. "Energy-Efficient Topology Control for UAV Networks." Energies 12, no. 23: 4523.

Journal article
Published: 15 October 2019 in Sensors
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Unmanned aerial vehicles (UAVs) with high mobility can perform various roles such as delivering goods, collecting information, recording videos and more. However, there are many elements in the city that disturb the flight of the UAVs, such as various obstacles and urban canyons which can cause a multi-path effect of GPS signals, which degrades the accuracy of GPS-based localization. In order to empower the safety of the UAVs flying in urban areas, UAVs should be guided to a safe area even in a GPS-denied or network-disconnected environment. Also, UAVs must be able to avoid obstacles while landing in an urban area. For this purpose, we present the UAV detour system for operating UAV in an urban area. The UAV detour system includes a highly reliable laser guidance system to guide the UAVs to a point where they can land, and optical flow magnitude map to avoid obstacles for a safe landing.

ACS Style

Joon Yeop Lee; Albert Y. Chung; Hooyeop Shim; Changhwan Joe; Seongjoon Park; Hwangnam Kim. UAV Flight and Landing Guidance System for Emergency Situations †. Sensors 2019, 19, 4468 .

AMA Style

Joon Yeop Lee, Albert Y. Chung, Hooyeop Shim, Changhwan Joe, Seongjoon Park, Hwangnam Kim. UAV Flight and Landing Guidance System for Emergency Situations †. Sensors. 2019; 19 (20):4468.

Chicago/Turabian Style

Joon Yeop Lee; Albert Y. Chung; Hooyeop Shim; Changhwan Joe; Seongjoon Park; Hwangnam Kim. 2019. "UAV Flight and Landing Guidance System for Emergency Situations †." Sensors 19, no. 20: 4468.

Journal article
Published: 18 September 2019 in Energies
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In this paper, we propose a scheme that implements a Distributed Ledger Technology (DLT) based on Directed Acyclic Graph (DAG) to generate, validate, and confirm the electricity transaction in Smart Grid. The convergence of the Smart Grid and distributed ledger concept has recently been introduced. Since Smart Grids require a distributed network architecture for power distribution and trading, the Distributed Ledger-based Smart Grid design is a spotlighted research domain. However, only the Blockchain-based methods, which are a type of the distributed ledger scheme, are currently either being considered or adopted in the Smart Grid. Due to computation-intensive consensus schemes such as Proof-of-Work and discrete block generation, Blockchain-based distributed ledger systems suffer from efficiency and latency issues. We propose a DAG-based distributed ledger for Smart Grids, called PowerGraph, to resolve this problem. Since a DAG-based distributed ledger does not need to generate blocks for confirmation, each transaction of the PowerGraph undergoes the validation and confirmation process individually. In addition, transactions in PowerGraph are used to keep track of the energy trade and include various types of transactions so that they can fully encompass the events in the Smart Grid network. Finally, to ensure that PowerGraph maintains a high performance, we modeled the PowerGraph performance and proposed a novel consensus algorithm that would result in the rapid confirmation of transactions. We use numerical evaluations to show that PowerGraph can accelerate the transaction processing speed by over 5 times compared to existing DAG-based DLT system.

ACS Style

Seongjoon Park; Hwangnam Kim. DAG-Based Distributed Ledger for Low-Latency Smart Grid Network. Energies 2019, 12, 3570 .

AMA Style

Seongjoon Park, Hwangnam Kim. DAG-Based Distributed Ledger for Low-Latency Smart Grid Network. Energies. 2019; 12 (18):3570.

Chicago/Turabian Style

Seongjoon Park; Hwangnam Kim. 2019. "DAG-Based Distributed Ledger for Low-Latency Smart Grid Network." Energies 12, no. 18: 3570.

Journal article
Published: 10 September 2019 in Sensors
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The indoor pedestrian positioning methods are affected by substantial bias and errors because of the use of cheap microelectromechanical systems (MEMS) devices (e.g., gyroscope and accelerometer) and the users’ movements. Moreover, because radio-frequency (RF) signal values are changed drastically due to multipath fading and obstruction, the performance of RF-based localization systems may deteriorate in practice. To deal with this problem, various indoor localization methods that integrate the positional information gained from received signal strength (RSS) fingerprinting scheme and the motion of the user inferred by dead reckoning (DR) approach via Bayes filters have been suggested to accomplish more accurate localization results indoors. Among the Bayes filters, while the particle filter (PF) can offer the most accurate positioning performance, it may require substantial computation time due to use of many samples (particles) for high positioning accuracy. This paper introduces a pedestrian localization scheme performed on a mobile phone that leverages the RSS fingerprint-based method, dead reckoning (DR), and improved PF called a double-stacked particle filter (DSPF) in indoor environments. As a key element of our system, the DSPF algorithm is employed to correct the position of the user by fusing noisy location data gained by the RSS fingerprinting and DR schemes. By estimating the position of the user through the proposal distribution and target distribution obtained from multiple measurements, the DSPF method can offer better localization results compared to the Kalman filtering-based methods, and it can achieve competitive localization accuracy compared with PF while offering higher computational efficiency than PF. Experimental results demonstrate that the DSPF algorithm can achieve accurate and reliable localization with higher efficiency in computational cost compared with PF in indoor environments.

ACS Style

Kwangjae Sung; Hyung Kyu Lee; Hwangnam Kim. Pedestrian Positioning Using a Double-Stacked Particle Filter in Indoor Wireless Networks. Sensors 2019, 19, 3907 .

AMA Style

Kwangjae Sung, Hyung Kyu Lee, Hwangnam Kim. Pedestrian Positioning Using a Double-Stacked Particle Filter in Indoor Wireless Networks. Sensors. 2019; 19 (18):3907.

Chicago/Turabian Style

Kwangjae Sung; Hyung Kyu Lee; Hwangnam Kim. 2019. "Pedestrian Positioning Using a Double-Stacked Particle Filter in Indoor Wireless Networks." Sensors 19, no. 18: 3907.

Journal article
Published: 03 May 2019 in Sensors
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As the era of IoT comes, drones are in the spotlight as a mobile medium of Internet of Things (IoT) devices and services. However, drones appear to be vulnerable to physical capture attacks since they usually operate far from operators. If a drone is illegally captured, some important data will be exposed to the attacker. In this paper, we propose a saveless-based key management and delegation system for a multi-drone control system. The proposed system enables a multi-drone control system to highly resist physical capture by minimizing exposure of confidential data. In addition, when the drone leaves the formation for performing another mission or by a natural environment, the system can allow the drone to securely re-participate in the formation with the help of the ground control station (GCS) when it comes back. The analysis result shows that the proposed system can reduce storage space usage and require less computational overhead. From the result, we expect that the system can guarantee the resistance of physical capture and secure key management to the drones as well as many mobile IoT devices.

ACS Style

Mungyu Bae; Hwangnam Kim. Authentication and Delegation for Operating a Multi-Drone System. Sensors 2019, 19, 2066 .

AMA Style

Mungyu Bae, Hwangnam Kim. Authentication and Delegation for Operating a Multi-Drone System. Sensors. 2019; 19 (9):2066.

Chicago/Turabian Style

Mungyu Bae; Hwangnam Kim. 2019. "Authentication and Delegation for Operating a Multi-Drone System." Sensors 19, no. 9: 2066.

Journal article
Published: 23 October 2018 in Applied Sciences
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Various unmanned aerial vehicles (UAVs), also called drones, have developed based on advances in hardware and software technologies. Thus, service providers in diverse areas have tried to utilize drones to create more effective solutions. In many cases, employing multiple drones is more effective to perform the given mission than using a single drone. To utilize multiple drones, the drones should be strongly connected, but it is not trivial to construct reliable and efficient networks for drones due to their high mobility. Therefore, we propose a ground control system (GCS) routing protocol (GCS-routing) to overcome this limitation and provide reliable and efficient multi-drone control system, where GCS-routing maximizes GCS utilization. GCS is the essential component of flying ad-hoc network (FANET) and can obtain information about drones. Using this information, GCS-routing can provide more effective routing, predict any topology changes, and react immediately. GCS-routing does not issue any periodic HELLO message for neighbor discovery or link cost estimation, which significantly enhances network performance. We implemented GCS-routing on real drones, and applied GCS-routing to actual drone fleets, as well as simulations to evaluate GCS-routing performance. The results clearly identify the advantages of the proposed routing protocol for drone networks compared with current routing protocols.

ACS Style

Woonghee Lee; Joon Yeop Lee; Jiyeon Lee; Kangho Kim; Seungho Yoo; Seongjoon Park; Hwangnam Kim. Ground Control System Based Routing for Reliable and Efficient Multi-Drone Control System. Applied Sciences 2018, 8, 2027 .

AMA Style

Woonghee Lee, Joon Yeop Lee, Jiyeon Lee, Kangho Kim, Seungho Yoo, Seongjoon Park, Hwangnam Kim. Ground Control System Based Routing for Reliable and Efficient Multi-Drone Control System. Applied Sciences. 2018; 8 (11):2027.

Chicago/Turabian Style

Woonghee Lee; Joon Yeop Lee; Jiyeon Lee; Kangho Kim; Seungho Yoo; Seongjoon Park; Hwangnam Kim. 2018. "Ground Control System Based Routing for Reliable and Efficient Multi-Drone Control System." Applied Sciences 8, no. 11: 2027.

Conference paper
Published: 01 October 2018 in 2018 14th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob)
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Over the past decade, techniques for remote control vehicles (RCVs) have progressed a lot, and RCVs are receiving huge attention in various fields. Since RCVs, such as drones, have high mobility, it is important for operators to control RCVs reliably. Thus, to keep monitoring and controlling RCVs, operators continuously exchange control packets with RCVs by wireless. However, control packets can be delayed or lost due to any communication or network problems, which may cause collisions or crashes. To overcome this limitation, in this paper, we propose DupCon, a new control packet transmission scheme. Considering characteristics of packets, DupCon duplicates only control packets, not data packets, and transmits the originals and their duplicates through different paths, respectively. We designed and implemented DupCon on real devices. Moreover, we conduct an analysis on DupCon to demonstrate the validity of DupCon theoretically. Furthermore, we conducted various experiments, and the results show that DupCon improves reliability and stability of real-time remote vehicle control.

ACS Style

Woonghee Lee; Joon Yeop Lee; Hwangnam Kim. Improving Reliability of Real-Time Remote Vehicle Control through Duplicating Control Packets. 2018 14th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob) 2018, 1 -8.

AMA Style

Woonghee Lee, Joon Yeop Lee, Hwangnam Kim. Improving Reliability of Real-Time Remote Vehicle Control through Duplicating Control Packets. 2018 14th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob). 2018; ():1-8.

Chicago/Turabian Style

Woonghee Lee; Joon Yeop Lee; Hwangnam Kim. 2018. "Improving Reliability of Real-Time Remote Vehicle Control through Duplicating Control Packets." 2018 14th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob) , no. : 1-8.

Journal article
Published: 27 September 2018 in Applied Sciences
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This paper addresses the analysis and the deployment of the network infrastructure based on multiple Unmanned Air Vehicles (UAVs). Despite the unprecedented potential to the mobility of the network infrastructure, there has been no effort to establish a mathematical model of the infrastructure and formation control strategies. We model the generic dynamics of the network infrastructure and derive the network throughput of the infrastructure. Through the parametrization of the model, we extract the generic factors of the network protocols and verify our model through the Network Simulator 3 (ns-3). By exploiting our network analysis model, we propose a novel formation control algorithm that determines the location of the UAVs to maximize the efficiency of the network. To achieve the objectives of the infrastructure, we define the formation-shaping effect as forces and elaborately design them using the generic factors. The formation algorithm continuously approaches to the optimized formation of a fleet of UAVs to enhance the overall throughput of the terrestrial devices. Our evaluations show that the algorithm guarantees remarkably higher throughput than the static formations. Through the dynamic transformation of the UAV formation, we believe that the multi-UAV-based network infrastructure could expand the boundary of the existing infrastructure while reducing the network traffic.

ACS Style

Seongjoon Park; Kangho Kim; HyunSoon Kim; Hwangnam Kim. Formation Control Algorithm of Multi-UAV-Based Network Infrastructure. Applied Sciences 2018, 8, 1740 .

AMA Style

Seongjoon Park, Kangho Kim, HyunSoon Kim, Hwangnam Kim. Formation Control Algorithm of Multi-UAV-Based Network Infrastructure. Applied Sciences. 2018; 8 (10):1740.

Chicago/Turabian Style

Seongjoon Park; Kangho Kim; HyunSoon Kim; Hwangnam Kim. 2018. "Formation Control Algorithm of Multi-UAV-Based Network Infrastructure." Applied Sciences 8, no. 10: 1740.

Research article
Published: 12 July 2018 in Wireless Communications and Mobile Computing
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Many varied mobile device networks have been developed with the advancement of communication and network technologies. Cellular data networks are currently the most widely used, and the number of cellular network subscriptions has increased steadily. Most recent wireless access technologies employ asymmetric uplinks and downlinks because mobile subscribers usually download contents from the Internet. Therefore, most cellular network service providers allocate more bandwidth to downlinks than uplinks for mobile subscribers. However, this asymmetry can have unexpected influence on network performance, particularly TCP performance. When the uplink interface is congested, TCP ACK packets are delayed by TCP data packets on the uplink, causing considerable TCP retransmissions on the downlink channel. Thus, downlink bandwidth cannot be fully utilized, which results in significantly degraded downlink throughput. To resolve this problem, this paper proposes a feedback scheme, network traffic chunk regulator (NCR). We analyzed the aforementioned problem through the empirical study, and we designed and implemented NCR based on the analysis. NCR adaptively controls TCP according to the degree of link usage asymmetry. We evaluate NCR performance through simulations and experiments with real devices. We verify that the proposed scheme allows the downlink traffic to not interfere with the aggressive uplink traffic. Thus, NCR increases total link utilization and aggregated throughput significantly, without imposing additional overhead on base or mobile stations.

ACS Style

Hwangnam Kim; Woonghee Lee; HyunSoon Kim; Hwantae Kim; Jaehyeuk Michael Yang. Protecting Download Traffic from Upload Traffic over Asymmetric Wireless Links. Wireless Communications and Mobile Computing 2018, 2018, 1 -15.

AMA Style

Hwangnam Kim, Woonghee Lee, HyunSoon Kim, Hwantae Kim, Jaehyeuk Michael Yang. Protecting Download Traffic from Upload Traffic over Asymmetric Wireless Links. Wireless Communications and Mobile Computing. 2018; 2018 ():1-15.

Chicago/Turabian Style

Hwangnam Kim; Woonghee Lee; HyunSoon Kim; Hwantae Kim; Jaehyeuk Michael Yang. 2018. "Protecting Download Traffic from Upload Traffic over Asymmetric Wireless Links." Wireless Communications and Mobile Computing 2018, no. : 1-15.

Research article
Published: 10 July 2018 in Wireless Communications and Mobile Computing
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Today’s mobile devices mostly contain more than one wireless interface for Internet connection. Smartphones mostly have both LTE and Wi-Fi for data communication through Internet. Although the availability of Wi-Fi is incomparable to that of cellular network, its strength lies in the low cost and high data rate due to continuous PHY and MAC advancement of 802.11 protocol extensions. In this paper, we propose a device-centric system that performs cost-effective network connectivity to the mobile device by selectively activating Wi-Fi communication according to the device mobility and corresponding history of Wi-Fi usage. By analyzing the device mobility using attached sensors, the system selects appropriate Wi-Fi that has been often used in that mobility state. The system was implemented in actual mobile devices that were used to several experiments we designed to prove high performance of the system.

ACS Style

HyunSoon Kim; Mungyu Bae; Woonghee Lee; Hwangnam Kim. Adaptive Decision of Wireless Access Network for Higher User Satisfaction. Wireless Communications and Mobile Computing 2018, 2018, 1 -19.

AMA Style

HyunSoon Kim, Mungyu Bae, Woonghee Lee, Hwangnam Kim. Adaptive Decision of Wireless Access Network for Higher User Satisfaction. Wireless Communications and Mobile Computing. 2018; 2018 ():1-19.

Chicago/Turabian Style

HyunSoon Kim; Mungyu Bae; Woonghee Lee; Hwangnam Kim. 2018. "Adaptive Decision of Wireless Access Network for Higher User Satisfaction." Wireless Communications and Mobile Computing 2018, no. : 1-19.

Journal article
Published: 14 June 2018 in Sensors
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Most surveillance systems only contain CCTVs. CCTVs, however, provide only limited maneuverability against dynamic targets and are inefficient for short term surveillance. Such limitations do not raise much concern in some cases, but for the scenario in which traditional surveillance systems do not suffice, adopting a fleet of UAVs can help overcoming the limitations. In this paper, we present a surveillance system implemented with a fleet of unmanned aerial vehicles (UAVs). A surveillance system implemented with a fleet of UAVs is easy to deploy and maintain. A UAV fleet requires little time to deploy and set up, and removing the surveillance is also virtually instant. The system we propose deploys UAVs to the target area for installation and perform surveillance operations. The camera mounted UAVs act as surveillance probes, the server provides overall control of the surveillance system, and the fleet platform provides fleet-wise control of the UAVs. In the proposed system, the UAVs establish a network and enable multi-hop communication, which allows the system to widen its coverage area. The operator of the system can control the fleet of UAVs via the fleet platform and receive surveillance information gathered by the UAVs. The proposed system is described in detail along with the algorithm for effective placement of the UAVs. The prototype of the system is presented, and the experiment carried out shows that the system can successfully perform surveillance over an area set by the system.

ACS Style

Jongtack Jung; Seungho Yoo; Woong Gyu La; Dongkyu Roy Lee; Mungyu Bae; Hwangnam Kim. AVSS: Airborne Video Surveillance System. Sensors 2018, 18, 1939 .

AMA Style

Jongtack Jung, Seungho Yoo, Woong Gyu La, Dongkyu Roy Lee, Mungyu Bae, Hwangnam Kim. AVSS: Airborne Video Surveillance System. Sensors. 2018; 18 (6):1939.

Chicago/Turabian Style

Jongtack Jung; Seungho Yoo; Woong Gyu La; Dongkyu Roy Lee; Mungyu Bae; Hwangnam Kim. 2018. "AVSS: Airborne Video Surveillance System." Sensors 18, no. 6: 1939.

Journal article
Published: 26 May 2018 in Sensors
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The reliable and accurate indoor pedestrian positioning is one of the biggest challenges for location-based systems and applications. Most pedestrian positioning systems have drift error and large bias due to low-cost inertial sensors and random motions of human being, as well as unpredictable and time-varying radio-frequency (RF) signals used for position determination. To solve this problem, many indoor positioning approaches that integrate the user’s motion estimated by dead reckoning (DR) method and the location data obtained by RSS fingerprinting through Bayesian filter, such as the Kalman filter (KF), unscented Kalman filter (UKF), and particle filter (PF), have recently been proposed to achieve higher positioning accuracy in indoor environments. Among Bayesian filtering methods, PF is the most popular integrating approach and can provide the best localization performance. However, since PF uses a large number of particles for the high performance, it can lead to considerable computational cost. This paper presents an indoor positioning system implemented on a smartphone, which uses simple dead reckoning (DR), RSS fingerprinting using iBeacon and machine learning scheme, and improved KF. The core of the system is the enhanced KF called a sigma-point Kalman particle filter (SKPF), which localize the user leveraging both the unscented transform of UKF and the weighting method of PF. The SKPF algorithm proposed in this study is used to provide the enhanced positioning accuracy by fusing positional data obtained from both DR and fingerprinting with uncertainty. The SKPF algorithm can achieve better positioning accuracy than KF and UKF and comparable performance compared to PF, and it can provide higher computational efficiency compared with PF. iBeacon in our positioning system is used for energy-efficient localization and RSS fingerprinting. We aim to design the localization scheme that can realize the high positioning accuracy, computational efficiency, and energy efficiency through the SKPF and iBeacon indoors. Empirical experiments in real environments show that the use of the SKPF algorithm and iBeacon in our indoor localization scheme can achieve very satisfactory performance in terms of localization accuracy, computational cost, and energy efficiency.

ACS Style

Kwangjae Sung; Dong Kyu ‘Roy’ Lee; Hwangnam Kim. Indoor Pedestrian Localization Using iBeacon and Improved Kalman Filter. Sensors 2018, 18, 1722 .

AMA Style

Kwangjae Sung, Dong Kyu ‘Roy’ Lee, Hwangnam Kim. Indoor Pedestrian Localization Using iBeacon and Improved Kalman Filter. Sensors. 2018; 18 (6):1722.

Chicago/Turabian Style

Kwangjae Sung; Dong Kyu ‘Roy’ Lee; Hwangnam Kim. 2018. "Indoor Pedestrian Localization Using iBeacon and Improved Kalman Filter." Sensors 18, no. 6: 1722.