• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.9
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• pp.1928-1934
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• 2009

This paper proposes a power management scheme for sensor nodes in wireless sensor networks based on sensor node operating system supporting the sensor transparency, which can turn off the sensors when the MCU is in sleep mode. We classify the sensors in two types, that is, event sensors and polling sensors, to be able to decide whether the sensor is a type of sensors whose power supply can be turned off or not, and we design a new scheduler to support recognition of those different types of sensors. Implementing and evaluation of the scheduler and the power manager supporting sensor transparency are shown based on Nano-Q+.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.457-466
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• 2019

This study develops a damage detection method based on neural networks. The performance of the method is numerically and experimentally verified using a three-story shear building model. The framework is mainly composed of two hierarchical stages to identify damage location and extent using artificial neural network (ANN). The normalized damage signature index, that is a normalized ratio of the changes in the natural frequency and mode shape caused by the damage, is used to identify the damage location. The modal parameters extracted from the numerically developed structure for multiple damage scenarios are used to train the ANN. The positive alarm from the first stage of damage detection activates the second stage of ANN to assess the damage extent. The difference in mode shape vectors between the intact and damaged structures is used to determine the extent of the related damage. The entire procedure is verified using laboratory experiments. The damage is artificially modeled by replacing the column element with a narrow section, and a stochastic subspace identification method is used to identify the modal parameters. The results verify that the proposed method can accurately detect the damage location and extent.

• Journal of Korean Society of Transportation
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• v.26 no.1
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• pp.127-135
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• 2008

Generally, optimum shortest path algorithms adopt single attribute objective among several attributes such as travel time, travel cost, travel fare and travel distance. On the other hand, multi-objective shortest path algorithms find the shortest paths in consideration with multi-objectives. Up to recently, the most of all researches about multi-objective shortest paths are proceeded only in single transportation mode networks. Although, there are some papers about multi-objective shortest paths with multi-modal transportation networks, they did not consider transfer problems in the optimal solution level. In particular, dynamic programming method was not dealt in multi-objective shortest path problems in multi-modal transportation networks. In this study, we propose a multi-objective shortest path algorithm including dynamic programming in order to find optimal solution in multi-modal transportation networks. That algorithm is based on two-objective node-based label correcting algorithm proposed by Skriver and Andersen in 2000 and transfer can be reflected without network expansion in this paper. In addition, we use non-dominated paths and tree sets as labels in order to improve effectiveness of searching non-dominated paths. We also classifies path finding attributes into transfer and link travel attribute in limited transit networks. Lastly, the calculation process of proposed algorithm is checked by computer programming in a small-scaled multi-modal transportation network.

• Journal of Korea Water Resources Association
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• v.33 no.5
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• pp.537-550
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• 2000

In this study, Neural Networks models were used to forecast daily streamflow at Jindong station of the Nakdong River basin. Neural Networks models consist of CASE 1(5-5-1) and CASE 2(5-5-5-1). The criteria which separates two models is the number of hidden layers. Each model has Fletcher-Reeves Conjugate Gradient BackPropagation(FR-CGBP) and Scaled Conjugate Gradient BackPropagation(SCGBP) algorithms, which are better than original BackPropagation(BP) in convergence of global error and training tolerance. The data which are available for model training and validation were composed of wet, average, dry, wet+average, wet+dry, average+dry and wet+average+dry year respectively. During model training, the optimal connection weights and biases were determined using each data set and the daily streamflow was calculated at the same time. Except for wet+dry year, the results of training were good conditions by statistical analysis of forecast errors. And, model validation was carried out using the connection weights and biases which were calculated from model training. The results of validation were satisfactory like those of training. Daily streamflow forecasting using Neural Networks models were compared with those forecasted by Multiple Regression Analysis Mode(MRAM). Neural Networks models were displayed slightly better results than MRAM in this study. Thus, Neural Networks models have much advantage to provide a more sysmatic approach, reduce model parameters, and shorten the time spent in the model development.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1318-1323
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• 2013

We consider the design of opportunistic spectrum access schemes where secondary users can opportunistically access unused spectrum in non-slotted primary systems. Two non-slotted spectrum sensing and access schemes for secondary users are considered. We present experimental results that demonstrate the performance of the considered schemes.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.163-174
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• 2008

Performance of downlink transmission strategies exploiting cooperative transmit diversity is investigated for distributed multiple-input single-output (MISO) systems, for which geographically distributed remote antennas (RA) in a cell can either communicate with distinct mobile stations (MS) or cooperate for a common MS. Statistical characteristics in terms of the signal-to-interference-plus-noise ratio (SINR) and the achievable capacity are analyzed for both cooperative and non-cooperative transmission schemes, and the preferred mode of operation for given channel conditions is presented using the analysis result. In particular, we determine an exact amount of the maximum achievable gain in capacity when RAs for signal transmission are selected based on the instantaneous channel condition, by deriving a general expression for the SINR of such antenna selection based transmission. For important special cases of selecting a single RA for non-cooperative transmission and selecting two RAs for cooperative transmission among three RAs surrounding the MS, closed-form formulas are presented for the SINR and capacity distributions.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1752-1755
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• 2002

The world wide web (WWW) already accounts f3r more Internee network traffic than any other application, including il and simple file transfer. It is also a collaborative technology in a weak sense of the word - it allows people to share information. Synchronous collaboration is where an interactive activity is simultaneous and in teal-time. Computer based real time collaborative systems like shared whiteboards. collaborative editor etc. are only beginning to emerge recently. These applications invoking more than two users exchanging information, require Multicast communication. Multicast communication is a transmission mode that is now supported by a variety of local and wide area networks. Multicasting enables multiparty communication across a wide area to sparsely distributed groups by minimizing the network load. Multicasting itself is one of the key technologies in the nut generation of the Internet This paper describes the technical issues from the aspect of multicast communication and its reliability in synchronous collaborative application.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.335-343
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• 2014

This paper considers the crucial problem of deploying wireless relays for achieving a connected wireless sensor network in indoor environments, an important aspect related to the management of the sensor network. Several algorithms have been proposed for ensuring full sensing coverage and network connectivity. These algorithms are not applicable to indoor environments because of the complexity of indoor environments, in which a radio signal can be dramatically degraded by obstacles such as walls. We first prove theoretically that the indoor relay placement problem is NP-hard. We then predict the radio coverage of a given relay deployment in indoor environments. We consider two practical scenarios; wire-connected relays and radio-connected relays. For the network with wire-connected relays, we propose an efficient greedy algorithm to compute the deployment locations of relays for achieving the required coverage percentage. This algorithm is proved to provide a $H_n$ factor approximation to the theoretical optimum, where $H_n=1+{\frac{1}{2}}+{\cdots}+{\frac{1}{n}}={\ln}(n)+1$, and n is the number of all grid points. In the network with radio-connected relays, relays have to be connected in an ad hoc mode. We then propose an algorithm based on the previous algorithm for ensuring the connectivity of relays. Experimental results demonstrate that the proposed algorithms achieve better performance than baseline algorithms.

• Journal of Korea Multimedia Society
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• v.10 no.3
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• pp.348-357
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• 2007

One of the major issues in recent researches on wireless sensor networks is to reduce energy consumption of sensor nodes operating with limited battery power, in order to lengthen their lifespan. Among the researches, we are interested in the schemes in which a sensor node periodically turns on and off its radio and requires information on the time when its neighbors will wake up (or turn on). Clock synchronization is essential for wakeup scheduling in such schemes. This paper proposes three methods based on the asynchronous averaging algorithm for clock synchronization in sensor nodes which periodically wake up: (1) a fast clock synchronization method during an initial network construction period, (2) a periodic clock synchronization method for saving energy consumption, and (3) a decision method for switching the operation mode of sensor nodes between the two clock synchronization methods. Through simulation, we analyze maximum clock difference and the number of messages required for clock synchronization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.153-164
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• 2010

In this paper, we propose a multi-channel MAC protocol to improve the channel efficiency and network performance in wireless ad hoc networks. There are two main problems encountered in designing multi-channel MAC protocols. The first problem is the rendezvous problem and the second is multi-channel hidden node problem. In order to solve these problems, most of previous researches that have considered multi-channel MAC protocols use a common control channel to exchange control packets. However, they have a bottleneck problem at common control channel as increasing the number of data channels. The proposed MAC protocol solves the multi-channel hidden node problem using a TDMA scheme and increases the network throughput because transmitting and receiving data at the same time is possible. Also, since there is no common control channel, the network does not suffer from the common control channel saturation problem. Moreover, it achieves energy savings by allowing nodes that are not involved in communication to go into sleep mode. Simulation results show that the proposed MAC protocol improves the network throughput and channel efficiency and provides energy savings.