Chang-Gun Lee

Chang-Gun Lee
Seoul National University | SNU · School of Computer Science and Engineering

About

104
Publications
5,382
Reads
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2,922
Citations
Citations since 2016
22 Research Items
741 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120

Publications

Publications (104)
Article
Scheduling algorithms are called "global" if they can migrate tasks between cores. Global scheduling algorithms are the de-facto standard practice for general purpose Operating Systems, to balance the workload between cores. However, the exact schedulability analysis of real-time applications for these algorithms is proven to be weakly NP-hard. Des...
Article
Full-text available
Delivery of automatic electrical defibrillator (AED) by unmanned aerial vehicle (UAV) was suggested for out-of-hospital cardiac arrest (OHCA). The goal of this study is to assess the effect of topographic and weather conditions on call to AED attach time by UAV-AED. We included OHCA patients from 2013 to 2016 in Seoul, South Korea. We developed a U...
Preprint
Full-text available
Designing or learning an autonomous driving policy is undoubtedly a challenging task as the policy has to maintain its safety in all corner cases. In order to secure safety in autonomous driving, the ability to detect hazardous situations, which can be seen as an out-of-distribution (OOD) detection problem, becomes crucial. However, most convention...
Article
Targeting global EDF scheduling, this paper proposes an optimal algorithm for parallelizing tasks with parallelization freedom. For this, we extend the interference-based sufficient schedulability analysis and derive monotonic increasing properties of both tolerance and interference for the schedulability. Leveraging those properties, we propose a...
Preprint
Full-text available
Background Delivery of automatic electrical defibrillator (AED) by unmanned aerial vehicle like drones was suggested to improve early defibrillation for out-of-hospital cardiac arrest. We developed a drone-AED flight virtual simulator using 3-dimensional topographic and meteorological information. The goal of this study is to assess the effect of t...
Chapter
Existing simulation methods cannot provide functionally and temporally correct simulations for the cyber-side of automotive systems since they do not correctly model temporal behaviours such as varying execution times and task preemptions. To address such limitations, our previous work proposes a novel simulation technique that guarantees the funct...
Chapter
Mixed-criticality systems integrate tasks with various levels of criticality onto the same hardware platform. Critical tasks require tight bounding of worst case latency at any cost, yet for non-critical tasks it is important to provide high performance as much as possible. In this paper, we take workload-driven approach and propose a novel workloa...
Article
Full-text available
Existing multi-screening technologies have been limited to mirroring the current screen of the smartphone onto all the connected external display devices. In contrast, NANS (N-App N-Screen) technology is able to display different applications (N-App) on different multiple display devices (N-Screen) using only a smartphone. For such NANS services, t...
Article
Recent parallel programming frameworks such as OpenCL and OpenMP allow us to enjoy the parallelization freedom for real-time tasks. The parallelization freedom creates the time vs. density tradeoff problem in fluid scheduling, i.e., more parallelization reduces thread execution times but increases the density. By system-widely exercising this trade...
Article
TDoA (Time Difference of Arrivals) based location tracking systems using RF and ultrasonic signals often give unacceptable errors due to the line-of-sight limitation of the ultrasonic signal. To overcome this limitation, many researchers have devoted their efforts using various methods. To further enhance accuracy and improve performance, this pape...
Article
Cyber-physical systems (CPS) have emerged as a promising research paradigm, which is the convergence of control, communication, and computation. In CPS, real-time transactions visit multiple resources such as sensors, actuators, networks, and microprocessors. One fundamental issue, which is called control and real-time scheduling co-design, is how...
Article
IEEE 802.15.4 is a global standard designed for emerging applications in low-rate wireless personal area networks (LR-WPANs). The standard provides beneficial features, such as a beacon-enabled mode and guaranteed time slots for realtime data delivery. However, how to optimally operate those features is still an open issue. For the optimal operatio...
Article
When developing a vehicle control system, simulation methods are widely used to validate the whole system in theearly development phase. With this regard, the simulator should correctly behave just like the real parts that are not yetimplemented while interacting with already implemented parts in real-time. However, most simulators cannot provide f...
Article
Integrated vehicle safety system is a key issue when developing intelligent safety vehicles. In order to validate such complex systems before actual ECU implementation, ECU-in-the-Loop Simulation (EiLS) is widely used. However, current EiLS methods only simulate the functional behavior of the target system thus cannot validate the temporal behavior...
Article
Network control and management techniques (e.g., dynamic path switching and on-demand bandwidth provisioning) rely on active measurements of the end-to-end network status. The measurements are needed to meet network monitoring objectives such as network weather forecasting, anomaly detection, and fault-diagnosis. Recent widespread deployment of ope...
Article
For advanced features of next generation vehicles, the real-time programs in automotive embedded systems are dramatically increasing. For such large volume program codes, this paper proposes a novel framework to use high-density and low-cost nonvolatile memory, i.e., NAND flash memory, as a low-cost means of storing and executing hard real-time pro...
Conference Paper
This paper introduces a global research collaboration project performed by a Korean-USA research group. The project aims at designing and implementing a run-time platform for reliable, safe, and secure cyber physical systems (CPS). The project consists of layered sub-projects including SoC design for reliable systems, virtualized software architect...
Conference Paper
We propose a new real-time simulation framework for cyber-physical systems (CPSs). It can efficiently dispatch simulation events for real-time simulation of complex events. It can also be easily reconfigured to adapt to various development steps.
Article
This paper proposes a novel technique called mRT-PLRU (Multitasking Real-Time constrained combination of Pinning and LRU), which forms a generic framework to use inexpensive nonvolatile NAND flash memory for storing and executing real-time programs in multitasking environments. In order to execute multiple real-time tasks stored in NAND flash memor...
Article
When developing a CPS, since it is nature of CPS to interact with a physical system, CPS should be verified during its development process by real-time simulation supporting timely interactions between the simulator and existing implemented hardwares. Furthermore, when a part of a simulated system is implemented to real hardwares, i.e., incremental...
Conference Paper
The TDoA (Time Difference of Arrivals) based location tracking systems using the RF and ultrasonic signals often give unacceptable errors due to the line-of-sight limitation of the ultrasonic signal. Overcoming this limitation, this paper proposes a novel TDoA based location tracking technique that explicitly exploits the ultrasonic reflection scen...
Conference Paper
In cyber-physical systems, it is required to provide an end-to-end delay guarantee for each chain of software tasks, called a transaction, running in the system in order to monitor and control the physical parts in real-time. This paper proposes a schedulability analysis of sporadic transactions on a real time pipeline, which relaxes the assumption...
Article
We propose a new simulation scheme for supporting smooth development of cyber-physical systems (CPSs) from all-simulated systems to all-real systems. For this, we introduce two functionalities which cyber physical simulation should provide.
Article
The automotive design paradigm is shifting from the "one-function on one ECU (Electronic Control Unit)" paradigm toward the "multi-function on one ECU" paradigm to reduce the ever increasing number of ECUs in a vehicle. In order to support such paradigm shift, this paper proposes a HW (hardware) resource componentizing technique that provides the i...
Article
Simulation methods are widely used when designing complex systems to reduce the development effort and cost. Especially when designing cyber-physical systems (CPSs), the importance of the simulation grows bigger and bigger. To simulate CPSs precisely, a holistic simulator is needed considering cyber and physical systems as a whole. In this paper, w...
Article
The localization systems using Time Difference of Arrival (TDoA) of ultrasonic and RF signals are hard to be used in practical settings because of line-of-sight limitation of the ultrasonic signal. Overcoming this limitation, novel multi-lateration method that explicitly exploiting the ultrasonic reflections was proposed. This paper verifies the pr...
Article
Fair queueing algorithms based on Generalized Processor Sharing (GPS) provide sessions with instantaneous fair sharing of server capacity, as well as guaranteed service rate and delay. The instantaneous fair sharing distributes server capacity to currently back-logged sessions in proportion to their weights regardless of the amount of service that...
Article
NAND flash memory has been widely used as a nonvolatile storage for storing data. However, it is challenging to execute program codes on NAND flash memory, since NAND flash memory only supports page-based reads, not byte-level random reads. This paper proposes an automated process to find the optimal paging strategy called RT-PLRU (Real-Time constr...
Article
Emerging cyber-physical systems (CPSs) demand a new computing abstraction since the traditional ones have fun- damental limitations in handling the para-functional also called physical requirements of CPSs such as timeliness, reliability, and evolvability. With the traditional computing abstractions such as processes, virtual memory, etc., multiple...
Conference Paper
Full-text available
In this paper, we propose an optimization approach for robust control design with end-to-end response time constraints in a multi-resource cyber-physical systems (CPS). We introduce a rigorous performance metric for robust system design from the control theoretic viewpoint. Then, we investigate the impact of end-to-end response time analysis techni...
Conference Paper
IEEE 802.15.4 is a global standard designed for emerging applications in low-rate wireless personal area networks (LR-WPANs). The standard provides nice features such as a beacon-enabled mode and guaranteed time slots for real-time data delivery. However, how to optimally operate those features is still an open issue. For the optimal operation of t...
Conference Paper
This paper presents a technique for an Android mobile device to best utilize its surrounding external display device such as high-definition TV, in order to overcome the size and resolution limitation of the small LCD in the mobile device. Unlike current techniques that simply expand the LCD screen image to an external large display, our technique...
Article
This paper proposes software bridge mechanism which supports the UPnP, discovery protocol of various wireless devices. Using the proposed bridge mechanism, the user would be able to use diverse contents through heterogeneous devices according to his or her choice. In this paper, porting was done to Android platform in order to verify the proposed m...
Article
As the software complexity drastically increases for multiresource real-time systems, industries have great needs for analytically validating real-time behaviors of their complex software systems. Possible candidates for such analytic validations are the end-to-end response time analysis techniques that can analytically find the worst-case response...
Conference Paper
For advanced features of next generation vehicles, the real-time programs in automotive embedded systems are dramatically increasing. For such large volume program codes, this paper proposes a novel framework to use high-density and low-cost nonvolatile memory, i.e., NAND flash memory, as a low-cost mean of storing and executing hard real-time prog...
Chapter
The decay usage scheduler pursues long-term fairness in terms of both service bandwidth and service delay, in contrast to GPS (generalized processor sharing)-based schedulers pursuing short-term fairness only in terms of service bandwidth. Due to this bandwidth-delay-balancing characteristic of the decay usage scheduler, I/O-bound interactive proce...
Conference Paper
This paper proposes a novel technique called mRT-PLRU (multi-tasking real-time constrained combination of pinning and LRU), which forms a generic framework to use inexpensive nonvolatile NAND flash memory for storing and executing real-time programs in multi-tasking environments. In order to execute multiple real-time tasks stored in NAND flash mem...
Article
Full-text available
Wireless sensor networks have great potentials to be applied to mission critical real-time applications such as target tracking, emergency detection, and disaster management. For such real-time applications, sensory data should be delivered within the end-to-end deadlines; otherwise, the data may become useless or misleading. In order to provide su...
Article
Sensors have been increasingly used for many ubiquitous computing applications such as asset location monitoring, visual surveillance, and human motion tracking. In such applications, it is important to place sensors such that every point of the target area can be sensed by more than one sensor. Especially, many practical applications require 3-cov...
Article
This paper presents novel techniques for scheduling radar dwells in phased array radar systems. In order to handle complex physical characteristics such as dwell interleaving, transmitting duty cycle constraint, and energy constraint, we propose a notion of schedulability envelope. The schedulability envelope designed offline hides the details of c...
Article
This paper proposes a safe stochastic analysis for fixed-priority scheduling, which is applicable to a broader spectrum of periodic tasks than the ones analyzable by any of the existing techniques. The proposed analysis can find a safe upper-bound of deadline miss probability for periodic tasks with (1) arbitrary execution time distributions, (2) v...
Conference Paper
NAND flash memory has been widely used as a non-volatile storage for storing data. However, it requires a large amount of SRAM for executing program codes stored in it since it only supports page-based reads, not byte-level random reads. This paper proposes a new paging mechanism called RT-PLRU (real-time constrained combination of pinning and LRU)...
Article
As the elderly population increases, elderly care using inexpensive technological means is becoming critical. This paper presents our prototype system that provides real-time indoor tracking of elderly residents and their belongings, which is essential to assisting and securing their independent living. For high-fidelity real-time tracking, we prop...
Conference Paper
Sensors have been increasingly used for many ubiquitous computing applications such as asset location monitoring, visual surveillance, and human motion tracking. In such applications, it is important to place sensors such that every point of the target area can be sensed by more than one sensor. Especially, many practical applications require 3-cov...
Article
Recent computing applications such as videoconferencing and grid computing run their tasks on distributed computing resources connected through networks. For such applications, knowledge of the network status such as delay, jitter, and available bandwidth can help them select proper network resources to meet the Quality-of-Service (QoS) requirement...
Article
Increased access to broadband networks has led to a fast-growing demand for Voice and Video over IP (VVoIP) appli-cations such as Internet telephony (VoIP), videoconferencing, and IP television (IPTV). For pro-active troubleshooting of VVoIP per-formance bottlenecks that manifest to end-users as performance impairments such as video frame freezing...
Conference Paper
Internet videoconferencing has emerged as a viable medium for communication and entertainment. However, its widespread use is being challenged. This is because videoconference end-users frequently experience perceptual quality impairments such as video frame freezing and voice dropouts due to changes in network conditions on the Inter- net. These i...
Conference Paper
Reducing energy consumption is important for mobile embedded systems and one of its solutions is dynamic voltage scaling (DVS). In this paper, we examine how to achieve further energy saving for periodic real-time tasks with non-preemptible sections on EDF algorithm by using DVS. Previous algorithms use two speed levels to deal with run-time blocki...
Article
Full-text available
Advances in networking, sensors, and embedded devices have made it feasible to monitor and provide medical and other assistance to people in their homes. Aging populations will benefit from reduced costs and improved healthcare through assisted living based on these technologies. However, these systems challenge current state-of-the-art techniques...
Article
This paper addresses the search and track coordination problems of multiple shipboard radars. The proposed approach first exploits the physical characteristics of a single phased array radar to improve its effective capacity. Its effective capacity is abstracted by a closed-form equation called a schedulability envelope. Using the schedulability en...
Conference Paper
As the elderly population increases, the elderly care using inexpensive technological means becomes critical. This paper proposes novel scheduling algorithms for real-time indoor tracking of elderly residents, which is essential to assist and secure their independent living. Our scheduling algorithms are designed by harmonizing both sensing and com...
Article
Timing constraints for radar tasks are usually specified in terms of the minimum and maximum temporal distance between successive radar dwells. We utilize the idea of feasible intervals for dealing with the temporal distance constraints. In order to increase the freedom that the scheduler can offer a high-level resource manager, we introduce a tech...
Article
Full-text available
In this paper, we present a novel packet delivery mechanism called Multi-Path and Multi-SPEED Routing Protocol (MMSPEED) for probabilistic QoS guarantee in wireless sensor networks. The QoS provisioning is performed in two quality domains, namely, timeliness and reliability. Multiple QoS levels are provided in the timeliness domain by guaranteeing...
Conference Paper
Full-text available
This paper proposes a novel task model in which its physical and temporal parameters are specified as time-parameterized functions and their values are finally determined at the actual dispatch time. This model is clearly differentiated from the classical task model where parameters are fixed at the job release time. The new model better suits sens...
Conference Paper
Monitoring network status such as end-to-end delay, jitter, and available bandwidth is important to support QoS-sensitive applications and timely detection of network anomalies like denial of service attacks. For this purpose, Internet service providers (ISPs) have started to instrument their networks with network measurement infrastructures (NMIs)...
Article
Generalised Rate Monotonic Scheduling (GRMS) theory has now been widely adopted in practice and supported by open standards. In recent years, Ada runtime and COTS RTOSs supporting GRMS have met the DO 178B flight control standard (http://www.ddci.com/products_darts.shtml; http://ic.arc.nasa.gov/publications/pdf/2000-0213.pdf). This creates strong i...
Article
Full-text available
This paper describes a stochastic analysis framework which computes the response time distribution and the deadline miss probability of individual tasks, even for systems with a maximum utilization greater than one. The framework is uniformly applied to fixed-priority and dynamic-priority systems and can handle, tasks with arbitrary relative deadli...
Conference Paper
In recent studies, using mobile elements (MEs) as mechanical carriers of data has been shown to be an effective way of prolonging sensor network life time and relaying information in partitioned networks. As the data generation rates of sensors may vary, some sensors need to be visited more frequently than others. In this paper, a partitioning-base...
Conference Paper
Building real-time applications on 802.11 wireless networks is challenging because the medium access protocol is distributed and nodes contend for the channel nondeterministically. So far all attempts at providing real-time services in 802.11 require restrictive traffic assumptions such as periodicity. In this paper we describe distributed admissio...
Article
In this paper, we present our research on characterizing voice and video traffic behavior in large-scale Internet Videoconferencing sys-tems. We built a voice and video traffic quality measurement testbed to collect Videoconferencing traffic traces from several sites all over the world that were connected to our testbed via disparate network paths...
Conference Paper
Scheduling periodic tasks that allow some instances to be skipped produces spare capacity in the schedule. Only a fraction of this spare capacity is uniformly distributed and can easily be reclaimed for servicing aperiodic requests. The remaining fraction of the spare capacity is non-uniformly distributed, and no existing technique has been able to...
Conference Paper
In order to satisfy and maintain service level agreements (SLAs), which demand high network availability and good network health, ISPs have started instrumenting their networks with network measurement infrastructures (NMIs) that are composed of dedicated measurement servers. Active measurements are frequently used in NMIs to regularly monitor netw...
Conference Paper
Full-text available
In this paper, we present a novel packet delivery mechanism called multi-path and multi-speed routing protocol (MMSPEED) for probabilistic QoS guarantee in wireless sensor networks. The QoS provisioning is performed in two quality domains, namely, timeliness and reliability. Multiple QoS levels are provided in the timeliness domain by guaranteeing...
Conference Paper
This paper addresses the problem of operating parameter assignment to multiple real-time tasks in a phased array radar system. The objective is to maximize the resulting system utility while ensuring the schedulability of all tasks with the assigned operating parameters. For this, we propose a novel framework by integrating the existing resource ma...
Conference Paper
Timing constraints for radar tasks are usually specified in terms of the minimum and maximum temporal distance between successive radar dwells. We utilize the idea of feasible intervals for dealing with the temporal distance constraints. In order to increase the freedom that the scheduler can offer a high-level resource manager, we introduce a tech...
Article
Full-text available
This paper describes a stochastic analysis framework for general priority-driven periodic real-time systems. The proposed framework accurately computes the response time distribution of each task in the system, thus making it possible to determine the deadline miss probability of individual tasks, even for systems with a maximum utilization factor...