• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.826-834
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• 2002

Asynchronous third generation mobile communication system is able to service Packet Switching through adding GPRS Network to the second generation system GSM. Therefore, it is necessary to study packet traffic service of GGSN node which is due to perform gateway role that GPRS Network is enable to inter-connect with Internet in order to optimize the capability and performance of GGSN. In this paper, the Internet packet traffic model that it is arrived to GGSN node from the Internet is studied and In order to process the Inter traffic efficiently, performance analysis model in GGSN is proposed to optimize packet processing capability of each processor. In order to guarantee QoS requirement of the real time traffic Speech and Video, several scheduling algorithm is applied to performance model and each mechanism is compared with several performance parameters.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.205-213
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• 2011

The Long Term Evolution (LTE) system is designed to provide a high quality data service for fast moving mobile users. It is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the training samples which are systematically built within the transmitting data. Either a preamble or a lattice type is used for the distribution of training samples and the latter suits better for the multipath fading channel environment whose channel frequency response (CFR) fluctuates rapidly with time. In the lattice-type structure, the estimation of the CFR makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in time-and in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. All interpolation schemes should rely on the pilot estimates only, and thus, their performances are bounded by the quality of pilot estimates. However, the additive noise give rise to high fluctuation on the pilot estimates, especially in a communication environment with low signal-to-noise ratio. These high fluctuations could be monitored in the alternating high values of the first forward differences (FFD) between pilot estimates. In this paper, we analyzed statistically those FFD values and propose a postprocessing algorithm to suppress high fluctuations in the noisy pilot estimates. The proposed method is based on a localized adaptive moving-average filtering. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification. It is shown that the mean-squared error (MSE) between the actual CFR and pilot estimates could be reduced up to 68% from the noisy pilot estimates.

• ETRI Journal
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• v.37 no.5
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• pp.877-887
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• 2015

This paper is a first-hand summary on our comprehensive live trial of cellular-assisted device-to-device (D2D) communications currently being ratified by the standards community for next-generation mobile broadband networks. In our test implementation, we employ a full-featured 3GPP LTE network deployment and augment it with all necessary support to provide realtime D2D connectivity over emerging Wi-Fi-Direct (WFD) technology. As a result, our LTE-assisted WFD D2D system enjoys the required flexibility while meeting the existing standards in every feasible detail. Further, this paper provides an account on the extensive measurement campaign conducted with our implementation. The resulting real-world measurements from this campaign quantify the numerical effects of D2D functionality on the resultant system performance. Consequently, they shed light on the general applicability of LTE-assisted WFD solutions and associated operational ranges.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.5
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• pp.101-110
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• 2009

The unconscious and non-intrusive measurements of activity signals or physiological signals represent important enabling technologies for realizing a ubiquitous healthcare environment as well as a related UI. Particularly, non-intrusive measurements should be used in activity monitoring system for long-term monitoring. This paper is based on activity estimation by measuring the activity signals of a user using a handhold device with an accelerometer. The user activity estimation system (UAES) presented in this paper makes non-intrusive measurements of activity signals to minimize inconveniencing a user and to create a more practical implementation in real life. Thus, a variety of positions in which the handhold device can be carried by a user for daily use is considered, such as in the front/hip/shirt pockets, a backpack, on the waist, and in the hand.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.1-8
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• 2000

This paper presents a simulation model of the Quadrature detector to demodulate FSK signal, which is widely used in wireless paging system for its simple hardware implementation and economics of It fabrication. Quadrature detecter has nonlinear phase characteristic for changes linear changes of input signal frequency. So until now Quadrature detector system analysis remained a difficult problem and performance analysis has not been carried out adequately On these backgrounds, this paper presents the FSK signal demodulation process using Quadrature detector and optimal performance derived from digital simulation technique. First, PSN(Phase Shift Network) which is composed of analog RLC tank circuit is transformed into its equivalent digital transfer function using First-order-hold theorem. Though the demodulated outputs of the Quadrature detector for 4FSK are 4-level signals, only 2 comparators are used and it is shown that optimal performance can be obtained by choosing operation parameter Q value and threshold level decision which are proposed herein.

• International Journal of Knowledge Content Development & Technology
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• v.7 no.3
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• pp.67-86
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• 2017

The emergence of smart devices such as smartphones (e.g., iPhone) and tablets (e.g., iPad) may enhance e-learning by increasing communication and collaborative learning outside the classroom. These devices also facilitate the use of online technologies such as Facebook. However, the adaptation of Learning Management System (LMS) services to mobile devices took longer than social networks or online tools such as Facebook and Twitter have already been long used via smartphone. The main purposes of this study are to explore students' skill levels of LMS (Moodle) and their knowledge of online tools or technologies and then examine if there is a correlation between smartphone use and using of online tools and Moodle in learning. The study conducted among 173 students in the Department of Information Studies (DIS) in Oman, using online survey. The study found that most students demonstrated high levels of accessing course/subject materials and regularly engaging with studies of using LMSs. YouTube, Wikipedia and Facebook were clearly recorded as the most popular sites among students while LinkedIn and Academia.edu were two online tools that had never been heard of by over half of the 142 participants. Emailing and searching are recorded the most popular online learning activities among students. The study concluded that students prefer to use smartphone for accessing these tools rather than using it to access LMSs, while a positive correlation was found between the use of these tools and smartphones, but there was no correlation between smartphones and using LMSs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1085-1094
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• 1999

In the global system for the mobile communication (GSM) system, the class of training sequences used in a TDMA frame is a preamble sequence with a period of 16 bits for the channel impulse response measurement and the start up equalization during the training period. If the transmitted preamble sequence and the binary sequence in the receiver properly satisfy a condition, this training sequences used for fastly adjusting the tap coefficients and impulse response can be measured by calculating the crosscorrelation function. In this paper, it is used that training sequences have zero values of the autocorrelation at all delays except zero and middle shifts. A comparison of convergence rate, a mathematical approach for fast start-up equalization and correctly channel impulse response measurement are proposed.

• 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 Korea Contents Association Conference
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• 2008.05a
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• pp.902-905
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• 2008

With development of internet, location-based service (LBS) is getting more interest in wire and wireless network, and many studies are in progress to provide various services such as GIS and GPS technique related to this. Today positioning and information providing service is accomplished by mobile communication companies' chasing the cell or building unique GIS system, but there is a lot of building-cost that must be endured to define boundary of collecting precise location information from chasing Cell and provide unique location information service. In this paper, it desires to make the database of location information with using GPS, relatively precise satellite positioning system, to cut the cost of building location information service, and to present service models such as children's positioning service that is to reduce the cost of building GIS by using Web Open API and provide location information of discrete object in real-time.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.632-636
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• 2006

It is needed to use the beam scanning to control the cell coverage of the base station considering operation conditions, season, time period, radiation character and mobility of customers and vehicles for varied wireless communication service and quality improvement. This paper proposes a mobile antenna system which can obtain the characteristics of the beam scanning by controlling the directivity depending on the operation condition. Radiation block is made of 2 sub-array of $1\times3$ patched antennas for ITS of 5.8GHZ bandwidth with the gain of 13dBi, and of 2 sub-array of single patched antenna for WiBro of 2.3GHZ bandwidth with the gain of 12dBi. RF module is made of a switch, an amplifier, a PAD, a 3-Bit phase shifter, and a power divider. The system is able to control the beam tilting with electronic methode by using 3-bit phase shifter$(45^{\circ},\;90^{\circ},\;180^{\circ})$.