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Dive into the research topics where Sookyoung Lee is active.

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Featured researches published by Sookyoung Lee.


Journal of Parallel and Distributed Computing | 2010

Recovery from multiple simultaneous failures in wireless sensor networks using minimum Steiner tree

Sookyoung Lee; Mohamed F. Younis

In some applications, wireless sensor networks (WSNs) operate in very harsh environments and nodes become subject to increased risk of damage. Sometimes a WSN suffers from the simultaneous failure of multiple sensors and gets partitioned into disjoint segments. Restoring network connectivity in such a case is crucial in order to avoid negative effects on the application. Given that WSNs often operate unattended in remote areas, the recovery should be autonomous. This paper promotes an effective strategy for restoring the connectivity among these segments by populating the least number of relay nodes. Finding the optimal count and position of relay nodes is NP-hard and heuristics are thus pursued. We propose a Distributed algorithm for Optimized Relay node placement using Minimum Steiner tree (DORMS). Since in autonomously operating WSNs it is infeasible to perform a network-wide analysis to diagnose where segments are located, DORMS moves relay nodes from each segment toward the center of the deployment area. As soon as those relays become in range of each other, the partitioned segments resume operation. DORMS further model such initial inter-segment topology as Steiner tree in order to minimize the count of required relays. Disengaged relays can return to their respective segments to resume their pre-failure duties. We analyze DORMS mathematically and explain the beneficial aspects of the resulting topology with respect to connectivity, and traffic balance. The performance of DORMS is validated through extensive simulation experiments.


IEEE Journal on Selected Areas in Communications | 2010

Optimized relay placement to federate segments in wireless sensor networks

Sookyoung Lee; Mohamed F. Younis

Federating disjoint segments may be necessary in some applications of wireless sensor networks (WSNs). The segments can be simply distinct WSNs that operate autonomously or partitions of a single WSN that has suffered a significant damage. Linking these segments is subject to varying distances among segments which may be longer than twice the communication range of a relay node. In this work, we focus on designing an effective approach for federating these segments by populating the least number of relay nodes. The deployment area is modeled as a grid with equal-sized cells. The optimization problem is then mapped to selecting the fewest count of cells to populate relay nodes such that all segments are connected. Finding the optimal number and positions of relay nodes with respect to length between segments is NP-hard and heuristics are thus pursued. We propose a distributed Cell-based Optimized Relay node Placement (CORP) algorithm and explain the beneficial aspects of the resulting topology with respect to connectivity, and traffic balance. The performance of CORP is validated through extensive simulation experiments.


global communications conference | 2008

A Localized Self-Healing Algorithm for Networks of Moveable Sensor Nodes

Mohamed F. Younis; Sookyoung Lee; Sheetal Gupta; Kevin Fisher

The effectiveness of wireless sensor networks (WSNs) deployed in search and rescue, battlefield reconnaissance, surveillance, and other applications depends on inter-node interaction and maintaining network connectivity. While connectivity can be provisioned at startup, then sustained through careful coordination when nodes move, the network can be partitioned if a node suddenly fails. This paper presents recovery through inward motion (RIM), a distributed algorithm to efficiently restore network connectivity after a node failure. Instead of performing a network-wide analysis to assess the impact of the node failure and set a course of action, RIM triggers a local recovery process by relocating the neighbors of the lost node. RIM minimizes messaging overhead and reduces the distance that individual nodes travel during the recovery. Simulations validate RIMs performance.


IEEE Transactions on Computers | 2010

A Localized Algorithm for Restoring Internode Connectivity in Networks of Moveable Sensors

Mohamed F. Younis; Sookyoung Lee; Ameer Ahmed Abbasi

Recent years have witnessed a growing interest in the applications of wireless sensor networks (WSNs). In some of these applications, such as search and rescue and battlefield reconnaissance, a set of mobile nodes is deployed in order to collectively survey an area of interest and/or perform specific surveillance tasks. Such collaboration among the sensors requires internode interaction and thus maintaining network connectivity is critical to the effectiveness of WSNs. While connectivity can be provisioned at startup time and then sustained through careful coordination when nodes move, a sudden failure of a node poses a challenge since the network may get partitioned. This paper presents RIM; a distributed algorithm for Recovery through Inward Motion. RIM strives to efficiently restore the network connectivity after a node failure. Instead of performing a networkwide analysis to assess the impact of the node failure and orchestrate a course of action, RIM triggers a local recovery process by relocating the neighbors of the lost node. In addition to minimizing the messaging overhead, RIM opts to reduce the distance that the individual nodes have to travel during the recovery. The correctness of the RIM algorithm is proven and the incurred overhead is analyzed. The performance of RIM is validated through simulation experiments.


Computer Networks | 2012

Optimized relay node placement for connecting disjoint wireless sensor networks

Sookyoung Lee; Mohamed F. Younis

Wireless sensor networks (WSNs) often operate in a harsh environment such as battlefield and may suffer simultaneous failure of multiple sensors that cause the network to become partitioned into disjoint segments. In order to prevent the application from being inoperative, restoring the overall network connectivity is crucial. In this paper, we propose an effective strategy for establishing connectivity among the partitioned segments by deploying the least count of relay nodes (RNs). Finding the optimal number and position of RNs is NP-hard and we thus pursue heuristics. We propose an Optimized Relay node placement algorithm using a minimum Steiner tree on the Convex hull (ORC). ORC strives to identify Steiner points (SPs) in which relays are populated such that the segments will be connected with the least number of relays. ORC deploys RNs inwards from the periphery of the area identified by the convex hull. We analyze ORC mathematically and explain the beneficial aspects of the resulting topology with respect to connectivity, and traffic balance. The performance of ORC is validated through extensive simulation experiments.


IEEE Transactions on Computers | 2011

EQAR: Effective QoS-Aware Relay Node Placement Algorithm for Connecting Disjoint Wireless Sensor Subnetworks

Sookyoung Lee; Mohamed F. Younis

In some applications of wireless sensor networks (WSNs), it may be necessary to link a number of disjoint segments in order to form a federated system. The segments can be simply distinct WSNs that operate autonomously or partitions of a single WSN that has suffered significant damage. Linking these segments may be subject to different intersegment quality of service (QoS) requirements. This paper presents an effective approach for federating these segments by populating the least number of relay nodes (RNs) such that the connectivity and QoS requirements are satisfied. Finding the optimal number and position of RNs is NP-hard and heuristics are thus pursued. The deployment area is modeled as a grid with equal-sized cells. A cost is assigned to each cell based on the residual capabilities of relays populated in it. The optimization problem is then mapped to finding the cell-based least-cost paths that collectively meet the QoS requirements. The performance of our approach is validated through extensive simulation experiments. We further demonstrate the beneficial aspects of the resulting topology with respect to degree of connectivity and fault resilience.


International Journal of Security and Networks | 2009

An efficient One-Time Password authentication scheme using a smart card

Sookyoung Lee; Krishna M. Sivalingam

This paper presents a One-Time Password (OTP) mechanism to provide authentication, with particular application to thin clients in wireless networks. Many of the current OTP mechanisms have high client side computation costs, high communication costs, or limited login times. To cope with these problems, this paper proposes a new one-time password scheme using a smart card. In the scheme, we present a novel modification to the Depth-First Search (DFS) based on a unique tree structure to generate a private key. We present a detailed analysis of the proposed scheme using an OpenSSL based implementation.


international conference on communications | 2009

QoS-Aware Relay Node Placement in a Segmented Wireless Sensor Network

Sookyoung Lee; Mohamed F. Younis

In some applications of wireless sensor networks (WSNs) it may be necessary to federate a number of disjoint segments. Linking these segments may be subject to varying inter-segment quality of service (QoS) requirements. This paper presents an effective approach for federating these segments. The main idea is to place relay nodes (RNs) in order to establish inter-segment connectivity with the least number of RNs while meeting the desired QoS requirements. Finding the optimal number and position of RNs is shown to be NP-hard and heuristics are thus pursued. The deployment area is modeled as a grid with equal-sized cells. Each cell is evaluated based on the residual capabilities of RNs populated in the cell. The optimization problem is then mapped to finding the cell-based least cost paths that collectively meet the QoS requirements. The performance of the proposed approach is validated through simulation


Archive | 2014

Topology Management Techniques for Tolerating Node Failure

Mohamed F. Younis; Sookyoung Lee; Izzet F. Senturk; Kemal Akkaya

In Wireless Sensor Networks (WSNs) sensor nodes often operate unattended in a collaborative manner to perform some tasks. In many applications, the network is deployed in harsh environments such as battlefield where the nodes are susceptible to damage. In addition, nodes may fail due to energy depletion and breakdown in the onboard electronics. The failure of nodes may have major consequences. First, some areas may be left uncovered. Second, the fidelity of the collected data gets degraded. And finally, the network may get partitioned into disjoint segments. In particular, losing network connectivity has a very negative effect on the applications since it prevents data exchange and hinders coordination among some nodes. Therefore, restoring the overall network connectivity with the least resource overhead and performance impact is very crucial. This chapter focuses on network topology management techniques for tolerating node failures. It analyzes the effects of node failure on network connectivity in WSNs, categorizes recently published recovery schemes, and outlines related open issues.


military communications conference | 2006

Routing for Data Delivery in Dynamic Networks

Padma Mundur; Sookyoung Lee; Matthew Seligman

In this paper, we present a routing algorithm for a class of dynamic networks called the delay tolerant networks (DTNs). The proposed algorithm takes into account the quintessential DTN characteristic namely, intermittent link connectivity. Assuming a store and forward type of network transfers, our main objective in designing routing algorithms for such an environment is to maximize the number of delivered messages subject to storage constraints on intermediate nodes. We modify the simple breadth first search (BFS) algorithm to take into account link activation/deactivation and find the quickest route possible between source and destination nodes. We adopt a message drop policy at intermediate nodes to incorporate storage constraint into data delivery. We also introduce the idea of storage domain where a few connected nodes act as a single storage unit by sharing the aggregated storage capacity of the nodes in the domain. We evaluate the routing algorithm with and without storage domain in an extensive simulation for two types of network topologies-flat and layered. We implement the proposed routing algorithm in ns2 and present an extensive performance analysis using metrics such as delivery ratio, incomplete transfers with no routes and dropped messages. The most significant simulation result shows that routing with storage domain mitigates the storage bottleneck at a gateway node for a layered network topology. For instance, the delivery ratio for storage capacity of 10 with storage domain surpasses the delivery ratio for storage capacity of 20 without storage domain

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Osama Farrag

Johns Hopkins University

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Izzet F. Senturk

Southern Illinois University Carbondale

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Jaewook Kim

University of Maryland

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Kemal Akkaya

Southern Illinois University Carbondale

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Yun Peng

University of Maryland

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