Jai-Hoon Kim

Ajou University, Sŏul, Seoul, South Korea

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Publications (56)24.85 Total impact

  • Sanghyuk Park · Jai-Hoon Kim · Geoffrey Fox
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    ABSTRACT: CPS (Cyber Physical Systems) tightly couple their cyber factor and physical factor in distributed computing or Grids environments to provide real-time services such as avionics, transportation, manufacturing processes, energy, healthcare, etc. We need to consider not only the cyber space (CPU, network, storage systems, etc.) and the physical space (location, migration, etc.) but also the socio space and mental space for the precise analysis and useful services. In this paper, real-time scheduling algorithms, namely ELST (Effective Least Slack Time First) and H-ELST (Heuristic-Effective Least Slack Time First), are presented for CPS, where servicing node needs to move to serviced node for real-time services. We measure the real-time performance in terms of deadline meet ratio by mathematical analysis and simulations. The results show that our algorithms reduce a deadline miss ratio approximately up to 50% and 20% compared to the conventional real-time scheduling algorithm, FIFO (First In First Out) and LST (Least Slack Time First), respectively.
    No preview · Article · Mar 2014 · Future Generation Computer Systems
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    ABSTRACT: The recent increase in smartphone supply drives more users to utilize mobile financial services and it magnifies the importance of mobile security solutions. But it is not easy to defend cyber-attacks against financial services because the attacks get more diverse every year. The recent solution, OTP one time password, is the most commonly used financial security measure to defend session attacks, but the downside is that it is hard to implement differentiated OTP creation mechanism to it. This research intends to solve the problem by suggesting Two-Factor authentication mechanism that utilizes graphical OTP. It is an extension of OTP mechanism which implements the graphical one time password to mobile financial security to reinforce mobile's way of authenticating with only ID and Password or digital certificate from banks; and it will defend against more diverse mobile hackings.
    No preview · Article · Dec 2013 · International Journal of Computer Mathematics
  • Minkyung Kim · Dong-Wook Lee · Kangseok Kim · Jai-Hoon Kim
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    ABSTRACT: The researches for collecting personal daily behaviors and providing lifelog services with them have been recently increasing. Recent advances in mobile devices and sensor technologies have motivated to collect a huge amount of personal lifelog data in real time. With the rapid growth of the need for the research, there is a coming need for the effective lifelog management system which collects time-series big lifelog data sent from sensing devices and extracts major activities through processing them. For the effective lifelog management, the lifelog data can be processed in separated computing resources depending on the size and level of data. In this paper, we propose hierarchical structured data logging to support lifelog based personal services and to reduce the processing complexity and storage cost. First, we present the architecture of personal lifelog management system. With the system we present hierarchical lifelog data logging to optimally utilize computing and storage resources. Then we describe cost analysis and performance comparison for demonstrating the efficacy of our proposed system. Finally, as an initial step for experiments in our research, we describe experimental results of recognizing physical activities and extracting lifelog data which indicate major activities from them.
    No preview · Article · May 2013 · Multimedia Tools and Applications
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    ABSTRACT: Collaboration is about interactions among multiple users by sharing resources. With the advent of new generation of mobile access devices such as smartphone and tablet PC, we address this for ubiquitous collaboration—the capability of multiple users to link together with disparate access devices in anytime and in anywhere. The implementation and experiments of mobile applications for ubiquitous collaboration were challenge since cell phone (also referred to feature phone) prior to smartphone had high network latency and low computing performance. However, even though mobile device technologies and wireless networking are becoming more advanced with time, the research on the impact of ubiquitous collaboration is still immature. This paper extends our prior work with interactive multimedia services—whiteboard application on 3G and Wi-Fi Android platform based mobile devices, based on MVC (Model View Controller) architecture for ubiquitous collaboration. Then, we present interaction and usability study with multiple users using (wire, wireless) small-sized devices (smartphones), mid-sized devices (tablet PCs), and large-sized device (desktops) to show how disparate access devices and networking have an effect on software design of shared applications in ubiquitous collaboration system.
    No preview · Article · Mar 2013 · Multimedia Tools and Applications
  • Sung-Hwa Lim · Byoung-Hoon Lee · Jai-Hoon Kim
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    ABSTRACT: It is important to support disconnected operations in mobile computing, because wireless communication requires substantial power consumption by mobile devices. Suitable usage of voluntary disconnected operations with pre-fetching of data in mobile environments can effectively save energy and money for mobile devices in wireless pervasive computing. In this paper, we analyze energy expenditure, including voluntary disconnected operations, to evaluate the energy efficiency of mobile computing. We estimate the energy expenditure using various parameters. The results of our analysis will assist efficient employment of disconnected operations and performance prediction.
    No preview · Article · Feb 2013 · Intelligent Automation and Soft Computing
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    Sanghyuk Park · Jai-Hoon Kim · Chang-Hee Han · Kangseok Kim
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    ABSTRACT: Recently, NCO (Network Centric Operation) has been intensively studied. The new concept provides many benefits by sharing information among distributed militaries linked by network. Based on these, we propose a novel correspondence algorithm of O(N2Log(N)) complexity while maintaining comparable BE (Battle Effects) with the optimal algorithm. We verify the efficiency of our algorithm in terms of complexity and BE by simulation and experiment. The results show that our algorithm improves BE up to 40% comparing to conventional random correspondence methods. Also, our algorithm speeds up by several orders comparing to the optimal algorithm while sacrificing BE only 6%.
    Preview · Article · Apr 2012 · International Journal of Advanced Robotic Systems
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    ABSTRACT: OTP (One Time Password), a financial security authentication mechanism mainly used nowadays, is possible to cope with session attacks but has an weakness that it is difficult to apply differentiated mechanisms. This study intends to propose an extended OTP mechanism utilizing Graphical password method in order to solve such problem of the existing method. The proposed method is a Graphical password mechanism in story method based on user's memory and can cope with various financial hackings and attack techniques. The existing authentication mechanisms have also a weakness in reliability to be used in mobile devices. In order to complement such weakness, GOTP (Graphical One Time Password) method was introduced so that users may use it in the Smartphone environment more easily and safely. Lastly, the effectiveness and validity were confirmed through an user study.
    No preview · Chapter · Jan 2012
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    ABSTRACT: The research for monitoring and recognizing personal behaviors from various digital sensors has recently been doing in a variety of fields. We address this for “lifelog” - all of the digital information about personal daily life. The research typically focuses on collecting personal lifelog, managing huge amount of lifelog data, and recognizing activities and behavior patterns from them. The methods of extracting key features and characterizing patterns would be crucial for finding meaningful information from huge and complex lifelog data. The research is a significant challenge because individual's lifelog data would be useful to provide personal life services such as healthcare. In this paper, we propose the process for predicting personal future behavior by tracing back to the past experiences. The behavior prediction process is composed of five stages. Firstly, physical activities through various sensors are collected and then, major physical activities are extracted through feature selection. Secondly, behavioral context information such as location, time and object is annotated to each activity for recognizing the behavior states more exactly. Then all sequences of physical activities with contextual information are divided into each daily set. Thirdly, behavior patterns from them are extracted by analyzing key features. After that, all daily sequences are transferred as the set of semantic activities for presenting major behavior states. Fourthly, from the set of semantic activities, based on the behavior probability to be used for the behavior prediction in next step, a sequence tree is generated. Finally, the highest predicted activities can be shown in a user interface from the query based on 'Time' or 'Event'. In a user interface, the functions for retrieving past and current behaviors and searching the predicted behaviors will be provided by choosing specific point in time or the specific event. Currently we are building a system for - rocessing the proposed behavior prediction.
    No preview · Conference Paper · Jan 2012
  • Dong-Wook Lee · Jai-Hoon Kim
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    ABSTRACT: In order to provide efficient and suitable services for users in a ubiquitous computing environment, many kinds of context information technologies have been researched. Wireless sensor networks are among the most popular technologies providing such information. Therefore, it is very important to guarantee the reliability of sensor data gathered from wireless sensor networks. However, there are several factors associated with faulty sensor readings which make sensor readings unreliable. In this paper, we classify faulty sensor readings into sensor faults and measurement errors, then propose a novel in-network data verification algorithm which includes adaptive fault checking, measurement error elimination and data refinement. The proposed algorithm eliminates faulty readings as well as refines normal sensor readings, to increase reliability. Also, to achieve scalability of sensor networks and minimize network overhead, the proposed scheme involves a distributed implementation in a local area. The simulation study shows that the in-network data verification algorithm is highly reliable and its network overhead is very low compared to previous works. Reliability and overhead is improved by a maximum of 10–30% and 70%, respectively. KeywordsWireless sensor network-Reliability-Data verification-Refinement-Sensor fault
    No preview · Article · Aug 2010 · Wireless Personal Communications
  • Byoung-Hoon Lee · Sung-Hwa Lim · Jai-Hoon Kim
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    ABSTRACT: Scalable real-time monitoring is one of important requirements to supply smart services for customers, on time, in ubiquitous smart space. We propose a scalable real-time monitoring method to aggregate large amounts of data from various sensor devices distributed over different domain areas. The real-time monitoring scheme can process data from sensor devices within deadline and is scalable based on the number of sensor devices. The scalability of monitoring can be improved by employing a hierarchical monitoring agent for sensor devices while still satisfying the data deadlines. Simulation results show that our real-time monitoring scheme can improve the met deadline ratio up to 27% compared to the previous schemes.
    No preview · Article · Apr 2010 · Information Processing Letters
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    Sangyoon Oh · Jai-Hoon Kim · Geoffrey Fox
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    ABSTRACT: The publish/subscribe communication system have been popular communication model in many area. Especially, it is well suited for distributed real-time system in many ways. However, the research of cost model and anal- ysis for publish/subscribe system in distributed real-time system has not been announced yet. In this paper, we present our cost model for publish/subscribe system in real-time domain, analyze its performance, and compare to other communication models such as request/reply and polling models. Our empirical result on mobile embedded device shows accordance with cost analysis, which verifies correctness and usefulness of our cost model.
    Full-text · Article · Mar 2010 · Future Generation Computer Systems
  • Hyo-nam Lee · Sung-hwa Lim · Jai-hoon Kim
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    ABSTRACT: Ubiquitous smart space consists of various ubiquitous objects (devices and applications) and their collaborations that provide convenient and intelligent services for users. Many studies have focused on developing convenient ubiquitous systems and their applications. However, to provide smooth and satisfactory services to users, a ubiquitous system must be aware of the real-time context of its ubiquitous objects and their collaborations during execution. Therefore, monitoring and analyzing must be provided, not only for the status of the functions and performance of individual ubiquitous objects, but also for their collaborative status. This paper discusses the challenges of monitoring systems for ubiquitous smart space, and proposes seven prerequisites for a monitoring system that examines and diagnoses ubiquitous smart space. We also developed a monitoring system for a ubiquitous smart space scenario, to verify our proposal.
    No preview · Article · Sep 2009 · IEEE Transactions on Consumer Electronics
  • Dong-Wook Lee · Jai-Hoon Kim
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    ABSTRACT: In a wireless sensor network (WSN) each sensor node deals with numerous sensing data elements. For the sake of energy efficiency and network lifetime, sensing data must be handled effectively. A technique used for this is data aggregation. Sending/receiving data involves numerous steps such as MAC layer control packet handshakes and route path setup, and these steps consume energy. Because these steps are involved in all data communication, the total cost increases are related to the counts of data sent/received. Therefore, many studies have proposed sending combined data, which is known as data aggregation. Very effective methods to aggregate sensing data have been suggested, but there is no means of deciding how long the sensor node should wait for aggregation. This is a very important issue, because the wait time affects the total communication cost and data reliability. There are two types of data aggregation; the data counting method and the time waiting method. However, each has weaknesses in terms of the delay. A hybrid method can be adopted to alleviate these problems. But, it cannot provide an optimal point of aggregation. In this paper, we suggest a stochastic-based data aggregation scheme, which provides the cost (in terms of communication and delay) optimal aggregation point. We present numerical analysis and results.
    No preview · Article · Apr 2009 · KSII Transactions on Internet and Information Systems
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    ABSTRACT: There are many methods to maintain consistency in the distributed computing environment. Ideally, efficient schemes for maintaining consistency should take into account the following factors: lease duration of replicated data, data access pattern and system parameters. One method used to supply strong consistency in the web environment is the lease method. During the proxy’s lease time from a web server, the web server can notify the modification to the proxy by invalidation or update. In this paper, we analyze lease protocol performance by the varying update/invalidation scheme, lease duration and read rates. By using these analyses, we can choose the adaptive lease time and proper protocol (invalidation or update scheme of the modification for each proxy in the web environment). As the number of proxies for web caching increases exponentially, a more efficient method for maintaining consistency needs to be designed. We also present three-tier hierarchies on which each group and node independently and adaptively choose the proper lease time and protocol for each proxy cache. These classifications of the scheme make proxy caching adaptive to client access pattern and system parameters.
    Full-text · Article · Jan 2009 · Future Generation Computer Systems
  • Byoung-Hoon Lee · Sung-Hwa Lim · Jai-Hoon Kim · We-Duke Cho
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    ABSTRACT: In a ubiquitous environment, there are many applications where a server disseminates information of common interest to pervasive clients and devices. For an example, an advertisement server sends information from a broadcast server to display devices. We propose an efficient information scheduling scheme for information broadcast systems to reduce average waiting time for information access while maintaining fairness between information items. Our scheme allocates information items adaptively according to relative popularity for each local server. Simulation results show that our scheme can reduce the waiting time up to 30%; compared with the round robin scheme while maintaining cost-effective fairness. Copyright © 2008 John Wiley & Sons, Ltd.
    No preview · Article · Dec 2008 · Concurrency and Computation Practice and Experience
  • Sung-Hwa Lim · Byoung-Hoon Lee · Jai-Hoon Kim
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    ABSTRACT: In the hot-standby replication system, the system cannot process its tasks anymore when all replicated nodes have failed. Thus, the remaining living nodes should be well-protected against failure when parts of replicated nodes have failed. Design faults and system-specific weaknesses may cause chain reactions of common faults on identical replicated nodes in replication systems. These can be alleviated by replicating diverse hardware and software. Going one-step forward, failures on the remaining nodes can be suppressed by predicting and preventing the same fault when it has occurred on a replicated node. In this paper, we propose a fault avoidance scheme which increases system dependability by avoiding common faults on remaining nodes when parts of nodes fail, and analyze the system dependability.
    No preview · Article · Sep 2008 · Information Processing Letters
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    ABSTRACT: Many studies have been focused on the construction of convenient ubiquitous systems and their applications. Ubiquitous smart space consists of a ubiquitous environment to provide more convenient and intelligent service for users using the cooperation of diverse ubiquitous objects. In the ubiquitous smart space, it is necessary to monitor and analyze not only the individual function, performance and status of the ubiquitous objects but also the cooperative status. This paper discusses the problems of the existing monitoring systems to adopt in ubiquitous smart space, and proposes the 7 requisites of a monitoring system to manage and monitor the ubiquitous smart space. We developed a monitoring system and applied to a ubiquitous smart space scenario to verify our proposal.
    Preview · Article · Jan 2008
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    Jeong-Ah Lee · Dong-Wook Lee · Jai-Hoon Kim · We-Duke Cho · Jan Pajak
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    ABSTRACT: There are many schemes to increase energy efficiency in wireless sensor network as energy is a precious resource. We focus on improving energy efficiency in sensing module while most of the previous works focus on the energy saving in communication module. When a sensor network continuously senses wide area, energy consumption is needed largely in the sensing module. We consider a change rate of sensed data and adjust sensing period to reduce energy consumption while minimizing average delay between change of field and detection. Additionally, cooperation among neighbor nodes is essential to reduce energy consumption and the delay. Our dynamic sensing algorithm reduces the energy consumption and delay between change of field and detection. Our scheme controls sensing cycle based on change of sensing data and information of neighbor nodes such as sensing cycle and number of cooperative nodes. It improves energy efficiency up to 90% comparing with the static sensing method, and reduces the delay up to 84% comparing to the previous works.
    Preview · Article · Sep 2007 · International Journal of Information Acquisition
  • Jeong-Ah Lee · Dong-Wook Lee · Jai-Hoon Kim · We-Duke Cho · Jan Pajak
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    ABSTRACT: There are many schemes to increase energy efficiency in wireless sensor network as energy is precious resource. We focus on improving energy efficiency in sensing module while most of the previous works focus on the energy saving in communication module. When a sensor network continuously senses wide area, energy consumption is needed largely in sensing module. We consider a change rate of sensed data and adjust sensing period to reduce energy consumption while minimizing average delay between change of field and detection. Additionally, cooperation among neighbor nodes is essential to reduce energy consumption and the delay. Our dynamic sensing algorithm reduces the energy consumption and delay between change of field and detection. Our scheme controls sensing cycle based on change of sensing data and sensing cycle of neighbor nodes. It improves energy efficiency up to 90%, and reduces the delay up to 84%, comparing to the previous works.
    No preview · Conference Paper · Jan 2007
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    ABSTRACT: Wireless sensor network consists of sensor nodes having limited resources. Energy saving is very important to increase the life time of these networks. In this paper, we propose Minimum Energy and Latency MAC (MELM) protocol for wireless sensor networks. MELM uses dual frequency radio setup inspired by STEM and LEEM to minimize the energy consumption and the latency in a multi-hop environment. Both LEEM and STEM protocols squander energy and increase latency because of overhearing, over-transmission and packet collisions. MELM eliminates these problems by maintaining a scheduling table in all nodes having logical 2-hop distance from the receiver node and by using advance channel reservation mechanism. MELM eradicates the hidden terminal and the exposed terminal problems, which is a key advantage, by maintaining a 2-hop receiver centric scheduling table.
    No preview · Conference Paper · Jan 2007