Seungjae Han

Yonsei University, Sŏul, Seoul, South Korea

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Publications (7)4.43 Total impact

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    ABSTRACT: Generally, the lifetime of a wireless sensor network (WSN) is defined as the duration until any sensor node dies due to battery exhaustion. If the traffic load is not properly balanced, the batteries of some sensor nodes may be depleted quickly, and the lifetime of the WSN will be shortened. While many energy-efficient routing schemes have been proposed for WSNs, they focus on maximizing the WSN lifetime. In this paper, we propose a scheme that satisfies a given ‘target’ lifetime. Because energy consumption depends on traffic volume, the target lifetime cannot be guaranteed through energy-efficient routing alone. We take an approach that jointly optimizes the sensing rate (i.e., controlling the sensor-traffic generation or duty cycle) and route selection. Satisfying the target lifetime while maximizing the sensing rate is a NP-hard problem. Our scheme is based on a simple Linear Programming (LP) model and clever heuristics are applied to compute a near-optimal result from the LP solution. We prove that the proposed scheme guarantees a 1/2-approximation to the optimal solution in the worst case. The simulation results indicate that the proposed scheme achieves near-optimality in various network configurations.
    Computer Networks 06/2014; · 1.23 Impact Factor
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    ABSTRACT: Network lifetime maximization is challenging particularly for large-scale wireless sensor networks. The sensor nodes near the sink node tend to suffer high energy consumption due to heavy traffic relay operations, becoming vulnerable to energy depletion. The rationale of the sink mobility approach is that as the sink node moves around, such risk of energy depletion at some nodes can be alleviated. In this paper, we first obtain the optimal mobile sink sojourning pattern by solving a linear programming model and then we mathematically analyze why the optimal solution exhibits such sojourning pattern. We use the insights from this analysis to design a simple practical heuristic algorithm for sink mobility, which utilizes only local information. Our heuristic is very different from the existing algorithms which often use the traffic volume as the main decision factor, in that we consider the variance of residual energy of neighboring sensor nodes. The simulation results show that our scheme achieves near-optimal network lifetime even with the relatively low moving speed of the mobile sink.
    Wireless Networks 02/2014; · 0.74 Impact Factor
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    ABSTRACT: Sensor networks have become increasingly important in various areas, and most current applications require connectivity between sensor networks and the Internet. By being seamlessly integrated into IP network infrastructure, sensor network applications would benefit from standardized and established technology, as well as from the plethora of readily available applications. Preparing sensor networks for IP communication and integrating them into the IP network, however, present new challenges on the architecture and its functional blocks, e.g., the adaptation of the respective link technology for IP support, development of security mechanisms, and autoconfiguration to support ad hoc deployment. In this paper, we focus on the IPv6 address autoconfiguration issue and propose a proxy-based autoconfiguration protocol. The proposed protocol guarantees the assignment of a unique address to each node in the network. The protocol is simulated and implemented on off-the-shelf sensor network platforms. The experiment results show that our mechanism outperforms similar network address configuring mechanisms in terms of latency and overhead.
    Wireless Networks 01/2011; 17:183-197. · 0.74 Impact Factor
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    ABSTRACT: Network reprogramming is a process used to update program codes of sensor nodes that are already deployed. To deal with potentially unstable link conditions of wireless sensor networks, the epidemic approach based on 3-way advertise-request-data handshaking is preferred for network reprogramming. Existing epidemic protocols, however, require a long completion period and high traffic overhead in high-density networks, mainly due to the hidden terminal problem. In this paper, we address this problem by dynamically adjusting the frequency of advertisement messages in terms of the density of sensor nodes, which is the number of sensor nodes in a certain area. We compare the performance of the proposed scheme, called DANP (Density-Adaptive Network Reprogramming Protocol), with a well-known epidemic protocol, Deluge. Simulations indicate that, in the grid topologies, DANP outperforms Deluge by about 30% in terms of the completion time and about 50% in terms of the traffic overhead. Significant performance gain is observed in random topologies as well. The performance of DANP is further confirmed via measurements in an experimental test bed. Copyright © 2009 John Wiley & Sons, Ltd.
    Wireless Communications and Mobile Computing 01/2010; 10:857-874. · 0.86 Impact Factor
  • S. Sim, Sunju Park, Seongmoon Kim, SeungJae Han
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    ABSTRACT: Traditional simulation studies often assume that there exists a complete set of data ready for analysis. Such an assumption may be justified in cases where data requirement for simulation is precisely defined and all necessary data have been collected according to such requirement. In many cases, however, existing data is incomplete, and it may not be economically feasible nor time-wise plausible to begin an extensive data collection process. Aiming at the healthcare management systems that maintain the log of operation activities using timestamps, we propose a general method to process incomplete timestamp data and obtain necessary information for simulation analysis. The proposed method is successfully applied to a case study of a mid-size hospital in Korea.
    System Sciences, 2009. HICSS '09. 42nd Hawaii International Conference on; 02/2009
  • Sunju Park, SeungJae Han, Sung-woo Cho
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    ABSTRACT: While equilibrium analysis has been commonly used for network pricing under the assumption that user utility functions are precisely known, many researchers have criticized the validity of the assumption. In this paper, we propose a solution for bridging the gap between the existing theoretical work on optimal pricing and the unavailability of precise user utility information in real networks. In the proposed method, the service provider obtains increasingly more accurate estimates of user utility functions by iteratively changing the prices of service levels and observing the users’ service-level choices under various prices. Our study’s contribution is twofold. First, we have developed a general principle for estimating user utility functions. Especially, we present the utility estimation for dynamic user population. Second, we have developed a method for setting prices that can optimize the extraction of information about user utility functions. The extensive simulation results demonstrate the effectiveness of our method.
    Computers & Industrial Engineering. 01/2009; 56:1357-1368.
  • Dukju Ko, Seungjae Han, Hojung Cha, Rhan Ha
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    ABSTRACT: To support Quality of service (QoS)-sensitive applications like real-time video streaming in IEEE 802.11 networks, a MAC layer extension for QoS, IEEE 802.11e, has been recently ratified as a standard. This MAC layer solution, however, addresses only the issue of prioritized access to the wireless medium and leaves such issues as QoS guarantee and admission control to the traffic control systems at the higher layers. This paper presents an IP-layer traffic control system for IEEE 802.11 networks based on available bandwidth estimation. We build an analytical model for estimating the available bandwidth by extending an existing throughput computation model, and implement a traffic control system that provides QoS guarantees and admission control by utilizing the estimated available bandwidth information. We have conducted extensive performance evaluation of the proposed scheme via both simulations and measurements in the real test-bed. The experiment results show that our estimation model and traffic control system work accurately and effectively in various network load conditions without IEEE 802.11e. The presence of IEEE 802.11e will allow even more efficient QoS provision, as the proposed scheme and the MAC layer QoS support will complement each other. Copyright © 2006 John Wiley & Sons, Ltd.
    Wireless Communications and Mobile Computing 01/2008; 8:407-419. · 0.86 Impact Factor