Wontaek Lim

A Novel Reference Node Selection Algorithm Based on Trilateration for Indoor Sensor Networks

The key problem of location service in indoor sensor networks is to quickly and precisely acquire the position information of mobile nodes. Traditional positioning algorithms, such as two-phase positioning (TPP) algorithm, are too complicated to be used in a mobile node and they cannot satisfy the time constraints. We analyze the localization error and draw the conclusion that the localization error is the least when three reference nodes form an equilateral triangle. We also proof three basic positioning theorem of reference node. Therefore, we propose a novel reference node selection algorithm based on trilateration (RNST), which can effective meet realtime localization requirement of the mobile nodes in indoor environment, and guarantee less localization error.

A Reliable Approach of Establishing Trust for Wireless Sensor Networks

Wireless sensor networks (WSNs), which consist of spatially distributed autonomous sensing and computing devices to monitor physical conditions such as temperature and motion. Under a hostile military environment, sensor networks can be easily attacked by malicious nodes and hostile nodes using the natural cooperation of WSNs. In this paper, we introduce the trust mechanism in the human society into WSNs and propose a more overall trust model without a central trust authority, which provides a reliable approach to establish trust for WSNs. The approach combines all kinds of trust values together, including the direct trust and indirect trust value of nodes. The simulation results show that our trust model can efficiently defend against the attacks of the malicious nodes.

A Novel Sensor Node Selection Method Based on Trust for Wireless Sensor Networks

Wireless sensor networks (WSNs) is drawing a lot of attention as a method for realizing a ubiquitous society, which needs more than one sensor to accomplish the task together. Malicious nodes are well disguised in a hostile military environment, so they can attack the whole network using the natural cooperations of WSNs. Therefore, how to choose one or more suitable sensor nodes to cooperate in a hostile environment and guarantee better system performance in the meantime is a difficult problem. To overcome this, we study trust mechanism in the human society and introduce it into a WSN. We also construct a trust model in accordance with the characteristics of a WSN. Based on trust model, we propose a novel sensor node selection algorithm. The simulation results show that our algorithm can improve the system stability of sensor networks, and efficiently defend against the attacks of malicious nodes and also prolong the lifetime of sensor networks.

Instruction Cache Design for Energy-Aware Embedded Processors by Using Backward Branch Information

Continuing advances in semiconductor technology and demand for higher performance will lead to more powerful embedded processors. Unfortunately, as the computing power of a processor increases, energy consumption in the processor dramatically increases. For this reason, energy efficiency should be considered together with performance when designing embedded processors. This paper proposes a new energy-aware instruction cache design using backward branch information to reduce the energy consumption in a embedded processor, since instruction caches consume a significant fraction of the on-chip energy. Proposed instruction cache is composed of two caches: a large main instruction cache and a small loop instruction cache. Proposed technique enables the selective access between the main instruction cache and the loop instruction cache to reduce the number of accesses to the main instruction cache, leading to good energy efficiency. We evaluated the energy efficiency by running cycle accurate simulator, SimpleScalar, with power parameters obtained from CACTI. Analysis results show that the proposed cache reduces the energy consumption by 20% on the average, compared to the traditional cache.

An Efficient and Lightweight EWS for non-Internet Devices in Ubiquitous Computing Environment

The greatest benefit of embedded Web server (EWS) is without a doubt the availability of a standard connection to non-Internet devices using the Internet. Since the use of Web server in ubiquitous computing opens new method for maintaining and supervising non-Internet devices, Web server has become a helpful tool for users to control and manage these non-Internet devices remotely. In this paper, we propose an efficient and lightweight EWS - Webit and evaluate how far it can be said to give the users fast and user-friendly ways to access, monitor, control and configure non-Internet devices with standard Web browsers in real-time. We also describe the architecture of Webit in detail and present how to design and implement it. Finally we compare the results of Webits performance with those of other similar EWS products.