Saewoom Lee

HydroCast: Pressure Routing for Underwater Sensor Networks

A Sensor Equipped Aquatic (SEA) swarm is a sensor cloud that drifts with water currents and enables 4-D (space and time) monitoring of local underwater events such as contaminants, marine life, and intruders. The swarm is escorted on the surface by drifting sonobuoys that collect data from the underwater sensors via acoustic modems and report it in real time via radio to a monitoring center. The goal of this study is to design an efficient anycast routing algorithm for reliable underwater sensor event reporting to any surface sonobuoy. Major challenges are the ocean current and limited resources (bandwidth and energy). In this paper, these challenges are addressed, and HydroCast, which is a hydraulic-pressure-based anycast routing protocol that exploits the measured pressure levels to route data to the surface sonobuoys, is proposed. This paper makes the following contributions: a novel opportunistic routing mechanism to select the subset of forwarders that maximizes the greedy progress yet limits cochannel interference and an efficient underwater dead end recovery method that outperforms the recently proposed approaches. The proposed routing protocols are validated through extensive simulations.

Key Schemes for Security Enhanced TEEN Routing Protocol in Wireless Sensor Networks

In wireless sensor networks (WSNs), hierarchical routing protocol is commonly used for energy efficiency. In particular, the TEEN (Threshold sensitive Energy Efficient sensor Network) protocol is used widely as a basic clustered multihop routing protocol. However, energy efficient routing protocols without proper security suffer from many security vulnerabilities. Hence, in this paper, we propose a hybrid key scheme specially for the TEEN protocol: a symmetric key scheme for the intracluster and a public key scheme for the intercluster. The simulation results show that network lifetime of the proposed hybrid key scheme decreases about 8% than the TEEN protocol and about 4% compared with the TEEN protocol with symmetric key scheme. On the other hand, a hybrid key scheme provides better probability of successful transmission than that of the symmetric key scheme.

Basestation-Aided Coverage-Aware Energy-Efficient Routing Protocol for Wireless Sensor Networks

In wireless sensor networks, an energy-efficient routing protocol is a key design factor to prolong network lifetime. Recently, Optimal Coverage-Preserving Scheme (OCoPS) is proposed in [11] as an extension of the Low Energy Adaptive Clustering Hierarchy (LEACH) routing protocol with the coverage-preserving scheme which saves energy consumption through excluding redundant nodes of which sensing ranges are fully overlapped by their on-duty neighbors. In this paper, we propose a basestation-aided clustering-based routing protocol, namely, the Basestation-aided clustering routing protocol with the Coverage-Preserving Scheme (BCoPS). In BCoPS, the base station substitutes energy intensive tasks for deployed sensor nodes to prolong network lifetime. The performance of BCoPS is compared with the LEACH and OCoPS. The extensive simulation results show that BCoPS outperforms OCoPS by more than 20% on network lifetime and by more than 30% network lifetime until the coverage rate is higher than 80%.

Central Angle Decision Algorithm in Coverage-Preserving Scheme for Wireless Sensor Networks

In wireless sensor networks, energy efficiency is a key design factor to prolong the network lifetime. Recently, optimal coverage-preserving scheme (OCoPS) is proposed in the work of Boukerche et al., (2005) as an extension of the low energy adaptive clustering hierarchy (LEACH) protocol with the coverage-preserving scheme which saves energy consumption through excluding redundant nodes of which sensing ranges are fully overlapped by their on-duty neighbors. Nevertheless, in some stringent applications such as battlefield surveillance, fire detection, and toxic liquid leaking detection, the higher network coverage quality is also strictly required. In this paper, we propose the central angle decision algorithm (CADA) which guarantees no coverage-hole during the coverage-preserving scheme. To evaluate applicability of our proposed algorithm to routing protocols and its performance, we extend the OCoPS routing protocol with CADA, namely, the optimal coverage-preserving scheme with the central angel decision algorithm (OCoPS_CADA). Extensive simulations show that the OCoPS_CADA outperforms the OCoPS by initially guaranteeing 100% of the network coverage.

Sensor authentication scheme for clustering routing protocols in wireless sensor networks

In wireless sensor networks (WSNs), hierarchical routing protocol is commonly used for energy efficiency. However, routing protocols without proper security suffer from many security vulnerabilities. Hence, in this paper, we propose a sensor authentication scheme during key establishment procedure based on clustering routing protocol. It authenticates lower level nodes by using temporal keys which are generated from higher level nodes. The simulation result shows that an authentication probability of member nodes maintains about 99.62% during the whole network lifetime.

Study on Tactical Target Tracking Performance Using Unscented Transform-based Filtering

ABSTRACT Tracking the tactical object is a fundamental affair in network-equipped modern warfare. Geodetic coordinate system based on longitude, latitude, and height is suitable to represent the location of tactical objects considering multi platform data fusion. The motion of tactical object described as a dynamic model requires an appropriate filtering to overcome the system and measurement noise in acquiring information from multiple sensors. This paper introduces the filter suitable for multi-sensor data fusion and tactical object tracking, particularly the unscented transform(UT) and its detail. The UT in Unscented Kalman Filter(UKF) uses a few samples to estimate nonlinear- propagated statistic parameters, and UT has better performance and complexity than the conventional linearization method. We show the effects of UT-based filtering via simulation considering practical tactical object tracking scenario.Key Words : Communication, Network Centric Operational Environment, Tracking, Geodetic Coordinate System, Kalman Filter, Unscented Transform

Key renewal scheme for clustering routing protocols in wireless sensor networks

In wireless sensor networks (WSNs), hierarchical routing protocol is commonly used for energy efficiency. However, routing protocols without proper security suffer from many security vulnerabilities. Hence, in this paper, we propose a key renewal scheme based on clustering routing protocol. Especially, this scheme updates the key considering the amount of communication. The simulation result shows that the transmission probability goes up normally after renewal the key when network lifetime is decreased only 9% compared with the case of symmetric key without key renewal scheme.

SAMOP: Synchronization avoiding modification of outgoing packets in wireless sensor networks

In wireless sensor networks (WSNs), time synchronization is basically required to provide time-stamp for the reported events, active-sleep MAC protocols to extend network lifetime, etc. Most synchronization schemes assume that the send time of a packet is captured when packet transmission is just started, and the packet is modified to save the send time before packet transmission is not complete. However, it is difficult for system-performance limited sensor nodes to complete the packet modification in time. In this paper, we propose a synchronization scheme avoiding modification of the outgoing packet (SAMOP) based on the CSMA-CA protocol, where a transmitter and a receiver measure only time instance for the packet with their own local clocks and then a transmitter transfers the time measurements with a subsequent packet. Based on multiple time measurements, SAMOP synchronizes local clocks of both nodes. Simulation results show our SAMOP provides improved accuracy with respect to a synchronizing period.