• Composites Research
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• v.20 no.5
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• pp.64-69
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• 2007

Matrix dominant properties of composites are largely degraded under harmful environments such as temperature and humidity. Therefore we should consider the harmful environmental factors in the design of an UAV integral fuel tank subjected to high temperature and high humidity. The harmful environment experiment was performed for carbon/epoxy composites made of a unidirectional prepreg USN175B, and a plain woven fabric prepreg WSN3. The immersion experiment was performed under $90^{\circ}C$. The specimens were tested when the weight gam of specimen was saturated. The specimens were tested under $74^{\circ}C$ to obtain tensile and inplane shear properties. The results showed that the matrix dominant properties were extremely degraded by hygrothermal environment. To consider the variability of load, the anti-optimization method was applied. By using this method, the worst load case was found by comparing the load convex model and stability boundary. The stability boundary was obtained by analysis of the integral wing fuel tank of UAV using degraded properties. To do this, it was known that the worst load case of the integral wing fuel tank was the hovering mode load case.

• Smart Structures and Systems
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• v.12 no.1
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• pp.23-39
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• 2013

In this article, a smart multifunctional optical system-on-a-chip (SOC) sensor platform is presented and its application for fiber Bragg grating (FBG) sensor interrogation in optical sensor networks is investigated. The smart SOC sensor platform consists of a superluminescent diode as a broadband source, a tunable microelectromechanical system (MEMS) based Fabry-P$\acute{e}$rot filter, photodetectors, and an integrated microcontroller for data acquisition, processing, and communication. Integrated with a wireless sensor network (WSN) module in a compact package, a smart optical sensor node is developed. The smart multifunctional sensor platform has the capability of interrogating different types of optical fiber sensors, including Fabry-P$\acute{e}$rot sensors and Bragg grating sensors. As a case study, the smart optical sensor platform is demonstrated to interrogate multiplexed FBG strain sensors. A time domain signal processing method is used to obtain the Bragg wavelength shift of two FBG strain sensors through sweeping the MEMS tunable Fabry-P$\acute{e}$rot filter. A tuning range of 46 nm and a tuning speed of 10 Hz are achieved. The smart optical sensor platform will open doors to many applications that require high performance optical WSNs.

• IEMEK Journal of Embedded Systems and Applications
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• v.7 no.2
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• pp.71-78
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• 2012

Based on the Zigbee-based wireless sensor network, I suggest the way to reduce errors between the short distance, improving the accuracy of the presumed distance by revising the deviation of RSSI(Received Signal Strength Indication) values is to estimate the distance using only the RF signal power without the additional hardware. In general, the graph measured by RSSI values shows the proximity values which are ideally reduced in proportion to the distance under the free outdoor space in which LOS(Line-Of-Sight) is guaranteed. However, if the result of the received RSSI values are each substituted to the formula, it can produce a larger margin of error and less accurate measurement since it is based upon the premise that this free space is not affected by reflected waves or obstacles caused by the ground and electronic jamming engendered by the environment. Therefore, the purpose of this study is to reduce the margin of errors between the distances and to measure the proximity values with the ideal type of graph by suggesting the way to revise the received RSSI values in the light of these reflected waves or obstacles and the electronic jamming. In conclusion, this study proves that errors are reduced by comparing the proposed deviation correction method to the revised RSSI value.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.5
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• pp.1166-1179
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• 2013

In wireless sensor network (WSN) environments, environmental noises are generated by, for example, small passing animals, crickets chirping or foliage blowing and will interfere target detection if the noises are higher than the sensor threshold value. For accurate tracking by acoustic WSNs, these environmental noises should be filtered out before initiating track. This paper presents the effect of environmental noises on target tracking and proposes a new algorithm for the noise mitigation in acoustic WSNs. We find that our noise mitigation algorithm works well even for targets with sensing range shorter than the sensor separation as well as with longer sensing ranges. It is also found that noise duration at each sensor affects the performance of the algorithm. A detection algorithm is also presented to account for the Doppler effect which is an important consideration for tracking higher-speed ground targets. For tracking, we use the weighted sensor position centroid to represent the target position measurement and use the Kalman filter (KF) for tracking.

• Journal of the Korea Society of Computer and Information
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• v.22 no.9
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• pp.33-40
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• 2017

In this paper, we propose a sink-location management and data-routing scheme to effectively support the mobile sink in solar-powered WSN. Battery-based wireless sensor networks (WSNs) have a limited lifetime due to their limited energy, but solar energy-based WSNs can be supplied with energy periodically and can operate forever. On the other hand, introduction of mobile sink in WSNs can solve some energy unbalance problem between sink-neighboring nodes and outer nodes which is one of the major challenges in WSNs. However, there is a problem that additional energy should be consumed to notify each sensor node of the location of the randomly moving mobile sink. In the proposed scheme, one of the nodes that harvests enough energy in each cluster are selected as the cluster head, and the location information of the mobile sink is shared only among the cluster heads, thereby reducing the location management overhead. In addition, the overhead for setting the routing path can be removed by transferring data in the opposite direction to the path where the sink-position information is transferred among the heads. Lastly, the access node is introduced to transmit data to the sink more reliably when the sink moves frequently.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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• pp.1618-1637
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• 2018

By means of compressive sensing (CS) technique, this paper considers the collection of sensor data with spatiotemporal correlations in wireless sensor networks (WSNs). In energy-constrained WSNs, one-dimensional CS methods need a lot of data transmissions since they are less applicable in fully exploiting the spatiotemporal correlations, while the Kronecker CS (KCS) methods suffer performance degradations when the signal dimension increases. In this paper, an appropriate sensing matrix as well as an efficient sensing method is proposed to further reduce the data transmissions without the loss of the recovery performance. Different matrices for the temporal signal of each sensor node are separately designed. The corresponding energy-efficient data gathering method is presented, which only transmitting a subset of sensor readings to recover data of the entire WSN. Theoretical analysis indicates that the sensing structure could have the relatively small mutual coherence according to the selection of matrix. Compared with the existing spatiotemporal CS (CS-ST) method, the simulation results show that the proposed efficient measurement method could reduce data transmissions by about 25% with the similar recovery performance. In addition, compared with the conventional KCS method, for 95% successful recovery, the proposed sensing structure could improve the recovery performance by about 20%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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• pp.1779-1798
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• 2018

Heterogeneous wireless sensor networks (HEWSN) is a kind of wireless sensor networks (WSN), each sensor may has different attributes, HEWSN has been widely used in many aspects. Due to sensors are deployed in unattended environments and its resource constrained feature, the design of security and efficiency balanced authentication scheme for HEWSN becomes a vital challenge. In this paper, we propose a secure and lightweight user authentication and key agreement scheme based on biometric for HEWSN. Firstly, fuzzy extractor is adopted to handle the user's biometric information. Secondly, we achieve mutual authentication and key agreement among three entities, which are user, gateway and cluster head in the four phases. Finally, formal security analysis shows that the proposed scheme defends against various security pitfalls. Additionally, comparison results with other surviving relevant schemes show that our scheme is more efficient in term of computational cost, communication cost and estimated time. Therefore, the proposed scheme is well suitable for practical application in HEWSN.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.2848-2869
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• 2017

Mobile Wireless Sensor Networks (MWSN) are usually constrained in energy supply, which makes energy efficiency a key factor to extend the network lifetime. The management of the network topology has been widely used as a mechanism to enhance the lifetime of wireless sensor networks (WSN), and this work presents an alternative to this. Software Defined Networking (SDN) is a well-known technology in data center applications that separates the data and control planes during the network management. This paper proposes a solution based on SDN that optimizes the energy use in MWSN. The network intelligence is placed in a controller that can be accessed through different controller gateways within a MWSN. This network intelligence runs a Topology Control (TC) mechanism to build a backbone of coordinator nodes. Therefore, nodes only need to perform forwarding tasks, they reduce message retransmissions and CPU usage. This results in an improvement of the network lifetime. The performance of the proposed solution is evaluated and compared with a distributed approach using the OMNeT++ simulation framework. Results show that the network lifetime increases when 2 or more controller gateways are used.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.3
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• pp.1014-1034
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• 2015

Location information of sensor nodes plays a critical role in many wireless sensor network (WSN) applications and protocols. Although many localization algorithms have been proposed in recent years, they usually target at dense networks and perform poorly in sparse networks. In this paper, we propose two component-based localization algorithms that can localize many more nodes in sparse networks than the state-of-the-art solution. We first develop the Basic Common nodes-based Localization Algorithm, namely BCLA, which uses both common nodes and measured distances between adjacent components to merge components. BCLA outperforms CALL, the state-of-the-art component-based localization algorithm that uses only distance measurements to merge components. In order to further improve the performance of BCLA, we further exploit the angular information among nodes to merge components, and propose the Component-based Localization with Angle and Distance information algorithm, namely CLAD. We prove the merging conditions for BCLA and CLAD, and evaluate their performance through extensive simulations. Simulations results show that, CLAD can locate more than 90 percent of nodes in a sparse network with average node degree 7.5, while CALL can locate only 78 percent of nodes in the same scenario.

• IEIE Transactions on Smart Processing and Computing
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• v.1 no.1
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• pp.34-49
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• 2012

Recently, the smart grid (SG) has been introduced to solve the serious network issues caused by the increasing electrical demand and the complex nonlinear nature of the electric power distribution network. The SG, regarded as the next generation power grid, can transmit power in more efficient ways by building an automatic and distributed energy delivery network. In this paper, we first assess how various existing networking technologies, such as IEEE 802.11 (WiFi) and IEEE 802.15.4 (ZigBee), meet the requirements of the SG communication protocols. Specifically, we classify the existing network protocols into three categories: WSN-based networking, WiFi-based networking, and wireline-based networking. We then survey the security issues regarding the SG. Finally, we propose an agile SG networking architecture and show the effectiveness of different adopted networking technologies and, as a result, present a candidate solution to implement agile networking in SGs.