• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.35-38
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• 2006

Using the repeaters is indispensable to WiBro services. Repeater types are distinguished by usage, output power and required performance. In the paper, we have studied on the WiBro digital optic repeater design which has excellent performance characteristic than any other repeaters. WiBro has specific characteristic on modulation method TDD(Time Division Duplex)/OFDMA(Orthogonal Frequency Division Multiple Access) so that it demands specified H/W to design WiBro repeater. Switching technique has been introduced because of TDD characteristic in each amplifier on the repeater. Time Advance technique has been considered because of OFDM characteristic among RAS(Radio Access Station) and repeater. In this paper, we have studied on these techniques to increase repeater cell coverage and distance between RAS and repeater.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.3
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• pp.1-11
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• 1997

Since the radio spectrum is limited, future wireless system will have micro cellular architecture in order to provide multimedia traffic services on personal communicatons network. The small coverage area of micro cellular systems results in frequent hadnoffs and location updates. We focuse on network load and terminal power due to frequent location updates and propose a location tracking scheme using embedded-pager PCS terminals. The proposed scheme is expected to minimize theconsumption of PCS terminal powr and improve the receiving rate of callee because of the power saving mechanism and the embedded-pager PCS terminal. This paper proposes signaling flows among the network elements for the proposed location tracking scheme. The signaling flows are accomodated to not only the existed network architectures but alsothe ATM backbone network arcitecture. To verify the signaling flows, we used petri-Net model. The resutls show that the signaling flows are suitable to our proposed location tracking scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.304-310
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• 2008

In a wireless mesh network, there are two types of nodes: mesh routers and mesh clients. These two contradistinct network entities will be characterized and modeled depending on their role in the network. Mesh routers are essentially not mobile unlike the mesh clients. The differences on these nodes should be noted in any protocol design. In this paper, we present a mobility management for wireless mesh network (WMN). This mobility management handles movement of wireless mesh clients as it leaves from a coverage area of a wireless mesh router to another. We consider signaling overhead and mobility as performance metrics.

• Journal of the Korean Institute of Navigation
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• v.12 no.3
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• pp.1-21
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• 1988

A Satellite -aided search and rescue system is expected for its many advantage of global coverage, instantaneousness and low cost. In this paper, a calculation method is proposed , by which a position of distress can be determined with doppler frequency received through an orbital satellite. First, an algorithm and program is developed for calculating the position of distress with the received doppler frequency of EPIRB(Emergency Position Indicating Radio Beacon) with the least square method. Then, position error caused by the drift of the transmitting frequency is evaluated. The evaluation is made by the simulation using NNSS satellite orbital elements and varying position of EPIRB, numbers of Doppler data and magnitudes of various errors. As the result, the availability of this program for a satellite-aided search and rescue system is confirmed and the bounds of expected positioning accuracy is clarified.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2003.11a
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• pp.175-179
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• 2003

In this paper, we developed a DTV RF (Radio frequency) capture, analysis, and regeneration system adapting digital signal processing and high speed hard disk interfacing techniques and analyzed characteristics of captured RF signal. This system can be used in the various field of DTV transmission because this system can capture the receiving real DTV signals and analyze captured RF signals that contain the complex characteristics of the real-world RF environments and regenerate it in a laboratory without the performance degradation. The system can capture and replay the DTV RF signals in real-time on hard disk. Therefore, there is no limit for the amount of captured data with in the installed storage capacity. We can expect various possible applications for this system such as a tool for the development of the receiver performance analysis, design, and analysis for the DTV coverage areas, etc. This system can also be used as RF signal analyzer.

• Journal of information and communication convergence engineering
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• v.19 no.3
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• pp.131-135
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• 2021

The interference between closely placed co-coverage satellites was analyzed. In general, a satellite network may use different orthogonal polarizations and frequencies to increase the throughput of a satellite. However, when orthogonal linear polarization (horizontal polarization and vertical polarization) or orthogonal circular polarization (left-handed circular polarization and right-handed circular polarization) is used, the signal from one polarization sense to another may be coupled, resulting in cross-polarization interference. This signal-coupling arises due to the finite value of the cross-polarization discrimination of the earth station. In this study, field equations were used to analyze the interference between adjacent satellites using co-frequency. The level of interference was compared to that when two adjacent satellites used the same polarization. The simulation results show that the interference mainly depends on the off-axis co-polar pattern and the cross-polar pattern of the earth station antenna.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.139-141
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• 2019

This paper proposes the application of LoRa network, which has been under various research recently, to use control system for the transfer of Unmanned Vehicle. LoRa( Long Range) has a wide coverage of up to30 km, and is characterized by large-scale low-power long-distance radio communication. LoRa has already been studied in various industries. It is also proposed to study various functions by utilizing LoRa network and applying it to the control system of the uninhabited entity.

• International Journal of Computer Science & Network Security
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• v.22 no.4
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• pp.139-146
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• 2022

Wireless access technologies are emerging to enable high data rates for mobile users and novel applications that encompass both human and machine-type interactions. An essential approach to meet the rising demands on network capacity and offer high coverage for wireless users on upcoming fifth generation (5G) networks is heterogeneous networks (HetNets), which are generated by combining the installation of macro cells with a large number of densely distributed small cells Deployment in 5G architecture has several issues because to the rising complexity of network topology in 5G HetNets with many distinct base station types. Aside from the numerous benefits that dense small cell deployment delivers, it also introduces key mobility management issues such as frequent handover (HO), failures, delays and pingpong HO. This article investigates 5G HetNet mobility management in terms of radio resource control. This article also discusses the key challenges for 5G mobility management.

• Proceedings of the Korean Society of Computer Information Conference
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• 2020.07a
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• pp.139-142
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• 2020

NB-IoT(Narrow Band Internet of Things) is an emerging LPWAN(Low Power Wide Area Network) radio technology. NB-IoT has many advantages like low power, low cost, and high coverage. However low bandwidth and low sampling rates also lead to poor positioning accuracy. This paper proposed a solution to optimize positioning accuracy under the OTDOA(Observed Time Difference of Arrival) approach by utilizing MLR(Multiple Linear Regression) models. Through the MLR model to predict the influence degree of weather(temperature, humidity, light intensity and air pressure) on the arrival time of signal transmission to improve the measurement accuracy. The improvement of measurement accuracy can greatly improve IoT applications based on NB-IoT.

• International Journal of Computer Science & Network Security
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• v.24 no.3
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• pp.71-82
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• 2024

This paper proposes a new communication system for e-learning applications to mitigate the negative impacts of COVID-19 where the online massive demands impact the current commu-nications systems infrastructures and capabilities. The proposed system utilizes high-altitude platforms (HAPs) for fast and efficient connectivity provision to bridge the communication in-frastructure gap in the current pandemic. The system model is investigated, and its performance is analyzed using adaptive antenna arrays to achieve high quality and high transmission data rates at the student premises. In addition, the single beam and multibeam HAP radio coverage scenarios are examined using tapered uniform concentric circular arrays to achieve feasible communication link requirements.