• Journal of KIISE:Information Networking
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• v.33 no.2
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• pp.165-174
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• 2006

Data dissemination using either flooding or legacy ad-hoc routing protocol is not realistic approach in the wireless sensor networks, which are composed of sensor nodes with very weak computing power, small memory and limited battery. In this paper, we propose the ELF(Energy-efficient Localized Flooding) protocol. The ELF is energy-efficient data dissemination protocol for wireless sensor networks. In the ELF protocol, there are two data delivery phases between fixed source and mobile sink node. The first phase, before the tracking zone, sensing data are forwarded by unicasting. After that, within the tracking zone, sensing data are delivered by localized flooding. Namely, the ELF Properly combines advantages from both unicasting and flooding. According to evaluation results by simulation, the proposed ELF protocol maintains very high data delivery ratio with using a little energy. Also, the property of average delay is better than others. From our research results, the ELF is very effective data dissemination protocol for wireless sensor networks.

• Journal of KIISE:Information Networking
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• v.41 no.4
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• pp.177-185
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• 2014

It has been occurred many times that wireless sensor networks (WSNs) had congested areas because all the sensing data collected by multiple sensor nodes are delivered to one sink node. Typically, in order to control congested areas, it used to reduce the traffic by increasing the sensing period or discarding packets. However, those schemes have a disadvantage that it loses the reliability when delivering sensing data. Moreover, there are no schemes considering case of having poor quality of links between nodes in practical terms. In this paper, we suggest a scheme not to reduce the traffic but to distribute the traffic by changing routing paths depends on the traffic and the quality of links. Also, it can be seen that the reliability of delivering of the sensing data is improved with the experiments improving collection rates and shortening end-to-end delay.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.4
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• pp.341-351
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• 2008

Communication in wireless sensor networks comprising a plurality of sensor nodes located in an ad hoc environment is unidirectional in that data gathered by sensor nodes are transmitted to a sink node and not vice versa. In those networks, it is not possible for a server or a gateway to send commands to the sensor nodes to determine whether some previously received data are valid when the data indicate unusual conditions, which makes it difficult to make appropriate reactions to the unusual situations. This paper proposes and implements a TDMA-based sensor network communication protocol named BiWSLP(Bidirectional Wireless Sensor Line Protocol) supporting bidirectional communication capability. The BiWSLP is an extension of the WSLP, a unidirectional sensor network communication protocol based on the TDMA protocol. To test the feasibility of the proposed BiWSLP, we construct a virtual bridge management system capable of sending commands to sensor nodes as well as collecting data from the sensor nodes. Based on the test results of the virtual bridge management system, we show the applicability and advantages of the BiWSLP in terms of energy efficiency and bidirectional communication capability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10C
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• pp.1011-1022
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• 2006

WSN(Wireless Sensor Network) performs to detect and collect environmental information for one purpose. The WSN is composed of a sink node and several sensor nodes and has a constraint in an aspect of energy consumption caused by limited battery resource. So many required mechanisms in WSN should consider the remaining energy condition. To deploy WSN, tile collected information is required to protect from an adversary over the network in many cases. The security mechanism should be provided for collecting the information over the network. we propose asynchronized key management considering energy efficiency over WSN. The proposed key management is focused on independence and difference of the keys used to deliver the information over several routes over the network, so disclosure of any key does not results in exposure of total key information over the overall WSN. Also, we use hash function to update key information for energy efficiency Periodically. We define the insecurity for requested security Properties and Proof that the security properties are guaranteed. Also, we evaluate and analyze the energy efficiency for the proposed mechanism.

• Journal of Korea Spatial Information System Society
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• v.12 no.1
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• pp.10-17
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• 2010

Sensor nodes used in Geosensor network are resource limited and power constrained. So it is necessary to research on routing protocols to gather data by using energy efficiently. Wireless sensor networks collect data gathered from sensor nodes by transfering it to the sink using multihop. However, it has two problems. First, the existing works require unnecessary data transmission for choosing a proper parent node to transfer data. Secondly, they have a large number of data transmission because each sensor node has a different path. To solves the problems, we, in this paper, propose a designated path based data aggregation scheme for efficient energy management in WSNs. The proposed scheme can reduce unnecessary data transmission by pre-determining a set of paths and can enable all the sensor nodes to participate in gathering data by running them in round-robin fashion. We show from performance analysis that the proposed scheme is more energy efficient than the existing directed diffusion(DD) and the hierarchical data aggregation(HDA).

• Journal of Internet Computing and Services
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• v.16 no.2
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• pp.7-17
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• 2015

To provide scalability, wireless sensor network has cluster-based architecture. Wireless sensor network can be implemented based on the IEEE 802.15.4 which is exploited in 2.4GHz ISM frequency band. Since this frequency band is used for various data communication, network status of wireless sensor networks frequently changes according to wireless environment. Thus, wireless channel selection to avoid reduction of transmission efficiency is required. This paper estimates network status using the information that a cluster-head collects in a cluster. Through objective function with throughput, RSSI level and reliability as input parameters, this paper proposes proper wireless channel selection. Simulation results show that the proposed method maintains transmission efficiency even though network status changes.

• Journal of the Korean GEO-environmental Society
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• v.16 no.9
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• pp.13-21
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• 2015

Recently, land subsidence and sinkhole are generated due to a change in the groundwater level in the city. For this reason, the necessity for management of stable underground water level is on the rise. In this study, it was conducted for the underground structure that passes through the lower of bus transfer center construction site to examine the influence on the stability for underground structures to changes in the groundwater level and effective stress, the coupled finite element analysis and structural analyses were performed to evaluate stability for underground structure. It is to secure stability for underground structures according to underground water level declines. In this way, effective construction management will be made by previewing and forecasting the influence on the ground behavior and adjacent structures due to changes in the groundwater level.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.50-63
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• 2017

In the wireless sensor networks, a sensor node has limited resources such as battery or memory. Hence, the routing protocol used in the wireless sensor networks is required efficient use of resources. In this paper, the VAP(Virtual Address Protocol), ensures the shortest transmission path for data transmission between the sink node and sensor node, is proposed. The VAP is assigned each node virtual address and sub address related with its neighboring nodes. The shortest transmission path to the destination node will be choose by comparing to each other address of its neighboring node. The comparison with other existing routing protocol shows that transmission path and usage of memory resource are minimized. Also transmission delay time of data was reduced.

• Journal of the Korean Magnetics Society
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• v.20 no.2
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• pp.52-60
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• 2010

The changes of magnetic flux density distribution and the degree of magnetic anomaly on the ground surface by underground fracture zones and empty spaces had been investigated through the variations of the measuring heights. The magnetic flux density distributions were monitored for the ground surfaces of fracture zones, empty spaces and tunnels by fluxgate-type magnetometer. The fracture zones showed the magnetic anomaly with (+) and (-) peak-pairs in the magnetic flux distribution measured at 0.15 m height from the ground surface, and this anomaly disappeared at the height of 1.15 m. The underground empty spaces and tunnels showed the decrease of magnetic flux densities, where the degree of this density decrease diminished with the increase of the underground depth. And, the existence and size of underground empty spaces, such as tunnels and sink holes, could be monitored by the phenomena of this decreasing flux density.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.12
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• pp.1007-1016
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• 2006

Although the advance in electronic technology enables a large number of circuity to be packed in a small volume, it is simultaneously required to remove the high heat load produced by them. In this study, the heat transfer and pressure drop characteristics of a mini-channel heat exchanger, which is designed for liquid cooling of electronic components, are investigated by varying operating conditions. Water and FC-72 were used as working fluids. The mini-channel heat exchanger was made with circular shape channels having din-meters of 2, 3, and 4 mm in regular intervals, and the channel length was 100 mm. The header and inlet guide pathway to provide uniform inflow were attached at the inlet of the test section. Copper block including the heaters was attached at the sidewall of the test section as a heat source, which provided the heat flux from 5 to $15W/cm^2$. The entrance effects enhanced the heat transfer coefficient in the mini-channel significantly. In addition, the single-phase pressure drop in the mini-channel was very similar to that predicted by the laminar flow correlation except that the transition Re decreased due to flow instability in the entrance region.