• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1743-1750
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• 2003

DC motor requires a rotor speed sensor for accurate speed control. The speed sensors such as resolvers and encoders are used as a speed detector, but they increase cost and size of the motor and restrict the industrial drive applications. So in these days, many papers have reported in the sensorless operation of DC motor〔3­5〕. This paper presents a new sensorless strategy using neural networks〔6­8〕. Neural network has three layers which are input layer, hidden layer and output layer. The optimal neural network structure was tracked down by trial and error, and it was found that 4­16­1 neural network structure has given suitable results for the instantaneous rotor speed. Also, learning method is very important in neural network. Supervised learning methods〔8〕 are typically used to train the neural network for learning the input/output pattern presented. The back­propagation technique adjusts the neural network weights during training. The rotor speed is gained by weights and four inputs to the neural network. The experimental results were found satisfactory in both the independency on machine parameters and the insensitivity to the load condition.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.1
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• pp.163-173
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• 1999

The CORBA provides a object-oriented middleware that lets applications extend their range across networks, languages, component boundaries, and operating systems. Java can provide a potable object that works in any operating system. Mapping Java into CORBA helps large scale information system operate through the Web by using the mobile code property of Java and object component technique of CORBA. This development environment is called the Object Web. This paper proposes an architecture of OSI network management with a CORBA manager using Object Web and an CORBA/CMIS gateway which apply a CMIS-level gateway model to gateway. In this architecture, CORBA manager is based on Object Web and can manage MOs in the OSI domain. The gateway has a role to translate CORBA IDLs into CMIS services and vice versa. In addition, an OSI agent is abstracted into a CORBA agent.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.421-425
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• 2005

The increasing number of wireless subscribers who can use internet service any time and any place have caused wireless communications networks to flourish. However, since total communication channel bandwidth for wireless communications is limited, it is very important to find the solution for maximizing the channel utilization. Thus, in this work we propose a QoS packet scheduler for IEEE 802.11e EDCA scheme which is able to maximize the channel throughput with changing the CW value considering wireless channel condition. This proposed scheme is evaluated with NS-2 network simulator under various environments and it is easily shown from the numerical results that the proposed scheme provides better performance than that of the original IEEE 802.11e scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.4
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• pp.761-766
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• 2004

Rayleigh fading due to multi-path degrades the mobile service quality, especially high data rate mobile services such as 1xEVDO and W-CDMA. The field test showed that down load date rate of 1xEVDO is seriously affected by Rayleigh fading. To reduce the effect of Rayleigh fading, transmit diversity was implemented in RF repeater. In field test, transmit diversity function increased the data rate about twice comparing with no transmit diversity repeater. Recently high data rate service is getting more important, so transmit diverstiy function will be an important function in repeater.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1105-1110
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• 2011

It is possible to synchronize the spatio-temporal data with a server using a wireless network. These data has the benefit to be up-to-date and able to service to the user efficiently. However, the mobile devices or the wireless network are very vulnerable to various hard or soft failures. If an failure occurs during a synchronization process, the spatio-temporal data which is synchronizing could be inconsistent state. In this paper, we propose the recovery scheme to solve the problem caused by the errors which occur during the synchronization on mobile environments. The proposed scheme writes the log records for the synchronization process into the both local storages of the server and the mobile client. When the errors arise, the data which are synchronizing are recovered using the written log records. Also, we design and implement the proposed recovery scheme on the synchronization system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1053-1059
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• 2011

DMX512 protocol is a typical protocol which controls LED lighting system. It has a strong feature and can be used to a lot of lighting system. But LED control system with cable has a few problem because they have a lot of control cables. It is very difficult to set up the complex lighting. Furthermore if it is set up it is not easy to keep and recover the system from the out of order. So it is required Wireless Lighting Control System. This paper describes the proposal, design, and implementation of a novel method which can provide versatile light effects with the increased capability of the mobility and the number of universes for Wireless Lighting system. And then we implement experiment environment to control indoor lighting system controled by ZigBee and WLAN converter not having complicating control line. Data frames are transferred to DMX512 device by encapsulation and decapsulation to control color LED. In the same time give the method to solve the data bottleneck problem which can be comes out because of speed difference between Heterogeneous network and measure performance of control system.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.217-222
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• 2006

To find a location, GPS has been wildly used. But, it is hard to use in indoor because of very weak signal level. To meet indoor requirements, there have been many studies applying wireless communication networks such as WLAN, UWB and ZigBee. Among these, ZigBee is widely adopted in many WSN applications because it has an advantage of low-power and low-cost. In ZigBee, the RSSI is used as range measurement for ad-hoc network. The RSSI are converted to ranges using the signal attenuation model and these ranges become inputs of positioning methods. The obtained position with RSSI has large error because of its poor accuracy. To overcome this problem, ultrasonic sensors are added in many researches. By measuring the arrival time difference of ZigBee and ultrasound as a range measurement, the precise position can be found. However, there are still many problems: scheduling of beacons to transmit signals in a correct order, addition and synchronization of beacons and low-rate positioning rate. At this paper, an efficient method to solve these problems is proposed. In the proposed method, a node transmits ZigBee and ultrasound signal simultaneously. And beacons find the range with the received signals and send it back to a node with ZigBee. The position is computed in a node with the received ranges. In addition, a new positioning algorithm to solve the risk of the divergence in the linearization method and the singularity problem in the Savarese method is presented. Both static and dynamic experimental results show 0.02m RMS errors with high output rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.5
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• pp.1284-1294
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• 2010

The ZigBee is one of the most important technologies for composing USN. It is one of the IEEE 802.15.4 standards to support personal area networks. It uses a hierarchical routing or an on-demand route discovery strategy as an address allocation method. A hierarchical routing doesn't use a routing table but only uses a child node or a parent node as an intermediate node for data delivery. Therefore, the ZigBee network's topology greatly affects the overall network performance. In this paper, we propose a more trustworthy algorithm than only using the depth and widely variable LQI during network formation, and moreover we propose an algorithm to measure network's trustworthiness. We simulate our algorithm using the NS-2 and implement our network using the MG2400 ZigBee module for verifying performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.5
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• pp.1185-1192
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• 2010

Recently, the demand for various contents and mobile web service has been rising due to the improvement of the techniques of wireless networks. In mobile web service, it is essential to exchange the device informations and contents using specific information which are standardized for users, operators and contents providers. This is based on the existing service providers based on the existing terminal, which provides information to help plan and operate independently of the mobile Web services and content services for various users needs. In this paper, the interoperable DDL is proposed for providing contents to fit with each different mobile device, which contributes toward the optimized mobile web service and guarantee the interoperability of device information. and we implemented the device information processing system, which has the purpose of servicing the device information and verifying the result to the interoperability of mobile web service on proposed DDL and the description language of the device information.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.11
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• pp.2664-2669
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• 2014

Recently, many research efforts have paid attention to spectrum pooling meshanism that provides efficient way to manage transient spectrum requests of secondary users in cognitive radio networks. Spectrum pooling is maintained by WSP (wireless service provider). WSP leases the spectrums stored in her spectrum pool to secondary users with being paid for it. It is natural that WSP tries to get profits as much as possible, which implies the WSP tries to minimize the cost required for maintaining her spectrum pool. In this paper, we model the spectrum pool into a probabilistic inventory model. Assuming secondary users' spectrum requests follow normal distribution, we give a strategic way that minimizes the maintenance cost of the spectrum pool. By a series of simulations, we show that WSP can reduce the total maintenance cost through our inventory model-based spectrum pooling than maintaining fixed inventory level.