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In the last ten years, supported by the advances in technologies for unmanned aerial vehicles (UAVs), UAVs have developed rapidly and are utilized for a wide range of applications. To operate UAVs safely, by exchanging control packets continuously, operators should be able to monitor UAVs in real-time and deal with any problems immediately. However, due to any networking problems or unstable wireless communications, control packets can be lost or transmissions can be delayed, which causes the unstable drone control. To overcome this limitation, in this paper, we propose MuTran for enabling reliable UAV control. MuTran considers the packet type and duplicates only control packets, not data packets. After that, MuTran transmits the original and duplicate packets through multiple protocols and paths to improve the reliability of control packet transmissions. We designed MuTran and conducted a lot of theoretical analyses to demonstrate the validity of MuTran and analyze it from various aspects. We implemented MuTran on real devices and evaluated MuTran using the devices. We conducted experiments to verify the limitations of the existing systems and demonstrate that control packets can be transmitted more stably by using MuTran. Through the analysis and experimental results, we confirmed that MuTran reduces the control packet transfer delay, which improves the reliability and stability of controlling UAVs.
Woonghee Lee. Enabling Reliable UAV Control by Utilizing Multiple Protocols and Paths for Transmitting Duplicated Control Packets. Sensors 2021, 21, 3295 .
AMA StyleWoonghee Lee. Enabling Reliable UAV Control by Utilizing Multiple Protocols and Paths for Transmitting Duplicated Control Packets. Sensors. 2021; 21 (9):3295.
Chicago/Turabian StyleWoonghee Lee. 2021. "Enabling Reliable UAV Control by Utilizing Multiple Protocols and Paths for Transmitting Duplicated Control Packets." Sensors 21, no. 9: 3295.
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.
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 StyleWoonghee 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 StyleWoonghee 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.
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.
Seongjoon Park; Woong Gyu La; Woonghee Lee; Hwangnam Kim. Devising a Distributed Co-Simulator for a Multi-UAV Network. Sensors 2020, 20, 6196 .
AMA StyleSeongjoon 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 StyleSeongjoon Park; Woong Gyu La; Woonghee Lee; Hwangnam Kim. 2020. "Devising a Distributed Co-Simulator for a Multi-UAV Network." Sensors 20, no. 21: 6196.
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.
Joon Yeop Lee; Woonghee Lee; HyunSoon Kim; Hwangnam Kim. Adaptive TCP Transmission Adjustment for UAV Network Infrastructure. Applied Sciences 2020, 10, 1161 .
AMA StyleJoon Yeop Lee, Woonghee Lee, HyunSoon Kim, Hwangnam Kim. Adaptive TCP Transmission Adjustment for UAV Network Infrastructure. Applied Sciences. 2020; 10 (3):1161.
Chicago/Turabian StyleJoon Yeop Lee; Woonghee Lee; HyunSoon Kim; Hwangnam Kim. 2020. "Adaptive TCP Transmission Adjustment for UAV Network Infrastructure." Applied Sciences 10, no. 3: 1161.
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.
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 StyleWoonghee 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 StyleWoonghee 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.
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.
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 StyleHwangnam 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 StyleHwangnam 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.
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.
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 StyleHyunSoon 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 StyleHyunSoon 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.
Over the past decades, hardware and software technologies for wireless sensor networks (WSNs) have significantly progressed, and WSNs are widely used in various areas including Internet of Things (IoT). In general, existing WSNs are mainly used for applications that require delay-tolerance and low-computation due to the poor resources of traditional sensor nodes in WSNs. However, compared to the traditional sensor nodes, today’s devices for WSNs have more powerful resource. Thus, sensor nodes these days not only conduct sensing and transmitting data to servers but also are able to process many operations, so more diverse applications can be applied to WSNs. Especially, many applications using audio data have been proposed because audio is one of the most widely used data types, and many mobile devices already have a built-in microphone. However, many of the applications have a requirement that heavy-operations should be done by a tight deadline, so it is difficult for a single node in WSNs to run relatively heavy applications by itself. In this paper, to overcome this limitation of WSNs, we propose a new emerging system, HeaLow, a cooperative computing system for heavy-computation and low-latency processing in WSNs. We designed HeaLow and carried out the practical implementation on real devices. We confirmed the effectiveness of HeaLow through various experiments using the real devices and simulations. Using HeaLow, nodes in WSNs are able to perform heavy-computation processes while satisfying a completion time requirement.
Jongtack Jung; Woonghee Lee; Hwangnam Kim. Cooperative Computing System for Heavy-Computation and Low-Latency Processing in Wireless Sensor Networks. Sensors 2018, 18, 1686 .
AMA StyleJongtack Jung, Woonghee Lee, Hwangnam Kim. Cooperative Computing System for Heavy-Computation and Low-Latency Processing in Wireless Sensor Networks. Sensors. 2018; 18 (6):1686.
Chicago/Turabian StyleJongtack Jung; Woonghee Lee; Hwangnam Kim. 2018. "Cooperative Computing System for Heavy-Computation and Low-Latency Processing in Wireless Sensor Networks." Sensors 18, no. 6: 1686.
Supported by the technological advancements in wireless communication systems, current mobile devices are capable of utilizing diverse radio interfaces. Furthermore, there are various networks around the mobile devices in heterogeneous networks. If the mobile devices are aware of the status of channels used by different communications, the devices can utilize a wide range of network options intelligently in heterogeneous networks. However, it is not easy for mobile devices to estimate the quality of channels used by different networks because of differences among communication standards. To overcome this limitation, we view the channel map used for Bluetooth communications from a new angle. In this paper, we propose a new scheme which utilizes the channel map to estimate channels qualities of other standards, not of Bluetooth. Using the proposed scheme named BluS, mobile devices can estimate channels qualities of standards using the 2.4 GHz ISM band. Therefore, the devices with BluS are able to make decisions more intelligently and properly in heterogeneous networks. We implemented BluS on off-the-shelf smartphones and conducted extensive experiments and analysis to verify the performance of BluS.
Woonghee Lee; Hwangnam Kim. Channel Quality Estimation for Improving Awareness of Communication Situation in the 2.4 GHz ISM Band. IEEE Transactions on Mobile Computing 2018, 17, 2002 -2013.
AMA StyleWoonghee Lee, Hwangnam Kim. Channel Quality Estimation for Improving Awareness of Communication Situation in the 2.4 GHz ISM Band. IEEE Transactions on Mobile Computing. 2018; 17 (9):2002-2013.
Chicago/Turabian StyleWoonghee Lee; Hwangnam Kim. 2018. "Channel Quality Estimation for Improving Awareness of Communication Situation in the 2.4 GHz ISM Band." IEEE Transactions on Mobile Computing 17, no. 9: 2002-2013.
Much research has been conducted in the area of face and gesture recognition in order to classify one’s emotional state. Surprisingly, utilizing computerized algorithms which recognize emotional conditions based on body postures has not yet been systematically developed. In this paper, we propose a novel method, Computerized Emotion Perception based on Posture (CEPP), to determine the emotional state of the user. This method extracts features from body postures and estimates the emotional state by computing a similarity distance. With the proposed algorithm, we will provide new insights into automatically recognizing one’s emotional state.
Suk Kyu Lee; Mungyu Bae; Woonghee Lee; Hwangnam Kim. CEPP: Perceiving the Emotional State of the User Based on Body Posture. Applied Sciences 2017, 7, 978 .
AMA StyleSuk Kyu Lee, Mungyu Bae, Woonghee Lee, Hwangnam Kim. CEPP: Perceiving the Emotional State of the User Based on Body Posture. Applied Sciences. 2017; 7 (10):978.
Chicago/Turabian StyleSuk Kyu Lee; Mungyu Bae; Woonghee Lee; Hwangnam Kim. 2017. "CEPP: Perceiving the Emotional State of the User Based on Body Posture." Applied Sciences 7, no. 10: 978.