• Journal of the Korea Society for Simulation
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• v.15 no.3
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• pp.87-91
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• 2006

With the growth of the internet, the number of wireless internet users has increased continuously up to date. However, mobile communications could not support high speed transmission rate with cheap communication fee and wireless LAN has problems in providing terminal mobility and wide area connectivity, respectively. So the WMAN standard has been newly designed to make up for these limits. The initial 802.16 specification effectively offers a solution for providing fixed users with high speed wireless communication but it does not offer terminal mobility. So the 802.16d and 802.16e have been developed as the next generation solution that can support various PHY layer (SC, SCa, OFDM, OFDMA) and offer the terminal mobility. In this paper, we propose an effective uplink scheduling algorithm for VoIP with using UGS, and we show that our proposed algorithm is superior in view of average delay and management of uplink bandwidth to conventional rtPS algorithm and the scheme in reference, with using NS-2 network simulator.

• Geophysics and Geophysical Exploration
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• v.5 no.1
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• pp.33-45
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• 2002

It was necessary to devise new techniques to overcome and enhance the resolution limits of traveltime tomography. Waveform inversion has been one of the methods for giving very high resolution result. High resolution image could be acquired because waveform inversion used not only phase but amplitude. But waveform inversion was much time consuming Job because forward and backward modeling was needed at each iteration step. Velocity-stress method was used for effective modeling. Resolution limits of imaging methods such as travel time inversion, acoustic and elastic waveform inversion were investigated with numerical models. it was investigated that Resolution limit of waveform inversion was similar tn resolution limit of migration derived by Schuster. Horizontal resolution limit could be improved with increased coverage by adding VSP data in cross hole that had insufficient coverage. Also, waveform inversion was applied to realistic models to evaluate applicability and using initial guess of travel time tomograms to reduce non-linearity of waveform inversion showed that the better reconstructed image could be acquired.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.6
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• pp.683-690
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• 2006

Reducing power consumption to extend network lifetime is one of the most important challenges in designing wireless sensor networks. One promising approach to conserving system energy is to keep only a minimal number of sensors active and put others into low-powered sleep mode, while the active sensors can maintain a connected covet set for the target area. The problem of computing such minimum working sensor set is NP-hard. In this paper, a centralized Voronoi tessellation (CVT) based approximate algorithm is proposed to construct the near optimal cover set. When sensor's communication radius is at least twice of its sensing radius, the covet set is connected at the same time; In case of sensor's communication radius is smaller than twice of its sensing radius, a connection scheme is proposed to calculate the assistant nodes needed for constructing the connectivity of the cover set. Finally, the performance of the proposed algorithm is evaluated through theoretical analysis and extensive numerical experiments. Experimental results show that the proposed algorithm outperforms the greedy algorithm in terms of the runtime and the size of the constructed connected cover set.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.119-124
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• 2010

디지털 제작, 압축 기술의 발전, 유무선 인터넷 보급 확산, 다양한 전송 및 서비스 플랫폼의 등장, 전송 기술의 광대역화, 단말 기술의 발전, 라이프스타일 변화와 킬러 서비스 등장으로 미디어 시장은 급속도로 발전하고 있다. 지상파 방송은 아날로그에서 디지털로 전환하고 있으며, 고화질, 다채널, 모바일, 3D 서비스를 제공하거나 제공할 예정에 있다. 현재 디지털 TV는 아날로그 TV와 동시 방송 형태로 제공되고 있지만 2012년말 디지털 TV로 완전한 전환을 앞두고 있으며, 모바일 TV인 DMB는 2005년말 본방송을 시작하여 전국 서비스를 제공하고 방송 커버리지를 확장하고 있다. FM과 AM의 디지털화를 위한 디지털 오디오 방송도 방식 선정을 위한 절차가 진행 중이다. 전파는 송신소에서 단말까지 전송되는 도중 신호레벨 감쇠, 페이딩, 왜곡, 잡음 유입 등을 겪게 된다. 양질의 지상파 방송을 제공하기 위해서는 전파가 수신 가능한 상태 이상의 양호한 상태로 시청자에게 전달되어야 한다. 이를 위해 방송사는 방송 수신 품질을 측정하고 수신이 불량한 지역에 대해서는 송신기 설치, 송신 출력 증강, 중계기 설치 등을 통해 양질의 서비스 제공이 가능한 방송 서비스 영역을 확대한다. 다양한 지상파 방송 매체에서 수신 품질 평가를 위해 가장 많이 측정하는 항목은 전계강도이다. 대부분의 경우 어떤 지역의 전계강도가 해당 매체가 요구하는 기준 레벨 이상이면 해당 지역을 양호 지역으로 평가한다. 본 논문에서는 다양한 지상파 방송 매체에 대한 전계강도를 측정하고 이를 분석할 수 있는 시스템을 제안하고자 한다. 제안 시스템을 이용하면 자동화된 절차에 의해 최단 시간에 다양한 지역에 대한 방송 수신 품질을 측정하고, 그 결과를 분석하여 방송 서비스 영역에 대한 평가를 내릴 수 있으며, 측정결과를 DB로 관리하여 동일 채널에 대한 이전 측정결과와 비교 분석, 다른 채널과 전계강도 비교 분석을 통해 특정 송신기 출력이 감소되거나 특정 안테나 출력에 문제가 발생한 경우에도 이를 쉽게 감지하여 최적의 방송망 구축 및 관리가 가능하다.

• Journal of Korea Multimedia Society
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• v.15 no.1
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• pp.93-100
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• 2012

Recently, the security monitoring and control systems based on spatial information in various field are operated and being developed according to evolve the spatial information technology. Especially, the CCTV monitoring and control system can be used in various field as a typical system. However, the security vulnerability problems have become an issue because the system connected by computer network and getting bigger than before. Therefore we studied security vulnerabilities of CCTV monitoring and control system which is being developed and operated. In addition, it is important to consider disaster and terrorism with unauthorized changes on location information. Therefore we analyzed the performance of observation when the cameras are break down as a result by hacking to CCTV monitoring and control system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12C
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• pp.1020-1028
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• 2010

Relay has attracted great attention due to its inherent capability to extend the service coverage and combat shadowing in next generation mobile communication systems. So far, most relay technologies have been developed under the half-duplex (HD) constraint that prevents relays from transmitting and receiving at the same time. Although half-duplex relay (HDR) is easy to implement, it requires partitioning of resource for transmission and reception, reducing the whole system capacity. In this paper, we propose a multinser precoding and power control scheme with sum rate matching for a full-duplex (FD) multiple-input multiple-output (MIMO) relay. Full-duplex relay (FDR) can overcome the drawback of HDR by transmitting and receiving on the same frequency at the same time, while it is crucial to reduce the effect of self-interference that is caused by its own transmitter to its own receiver. The proposed precoding scheme cancels the self-interference of the FDR as well as to support multiuser MIMO. Moreover, we suggest a power allocation scheme for FD MIMO relay with the constraint that the sum rate of the relay's received data streams is equal to that of the relay's transmit data streams.

• Journal of KIISE
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• v.44 no.8
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• pp.854-859
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• 2017

Caching popular videos in the storage of base stations is an efficient method to reduce the transmission latency. This paper proposes an incentive proactive cache mechanism in the wireless network to motivate the content providers (CPs) to participate in the caching procedure. The system consists of one/many Infrastructure Provider (InP) and many CPs. The InP aims to define the price it charges the CPs to maximize its revenue while the CPs compete to determine the number of files they cache at the InP's base stations (BSs). We conceive this system within the framework of Stackelberg game where InP is considered as the leader and CPs are the followers. By using backward induction, we show closed form of the amount of cache space that each CP renting on each base station and then solve the optimization problem to calculate the price that InP leases each CP. This is different from the existing works in that we consider the non-uniform pricing scheme. The numerical results show that InP's profit in the proposed scheme is higher than in the uniform pricing.

• Journal of Korea Multimedia Society
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• v.11 no.11
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• pp.1525-1535
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• 2008

High Altitude Platform (HAP) based networks deploy network infrastructures of Mobile Base Station (MBS) in a form of Unmanned Aerial Vehicle (UAV) at stratosphere in order to build network configuration. The ultimate goal of HAP based network is a wireless network service for wide area by deploying multiple MBS for such area. In this paper we assume multiple UAVs over designated area and solve the MBS placement and coverage problem by clustering the mobile ground nodes. For this study we assumed area around Cheju island and nearby naval area where multiple mobile and fixed nodes are deployed and requires HAP based networking service. By simulation, visual results of stratospheric MBS placement have been presented. These results include clustering, MBS placement and coverage as well as dynamic reclustering according to the movement of mobile ground nodes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.3
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• pp.543-548
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• 2017

In the conventional algorithm, the D2D message dissemination algorithm based on the Epidemic routing protocol frequently causes a problem of duplication of the received messages due to the overlaps of D2D transmission coverages. It is because all D2D devices that receive the messages perform relaying the message replicas to other D2D devices within their transmission range. Therefore, we herein propose the farthest-k relay selection algorithm to mitigate this message duplication problem. In the farthest-k relay selection algorithm, less than k devices within the D2D transmission range perform message relay. Furthermore, we perform comparative performance analysis between the conventional D2D data dissemination algorithm and our farthest-k relay selection algorithm. By using intensive MATLAB simulations we prove the performance excellency of our farthest-k relay algorithm compared with the conventional algorithm with respect to coverage probability, the total number of initially and duplicately received messages, and transmission efficiency.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.46-51
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• 2012

In this paper, we investigate the power allocation for cognitive relay networks. Cognitive relay networks offer not only increasing spectral efficiency by spectrum sharing but also extending the coverage through the use of relays. For spectrum sharing, conventional works have assumed that secondary users know perfect channel information between the secondary and primary users. However, this channel information may be outdated at the secondary user because of the time-varying properties or feedback latency from the primary user. This causes the violation for interference constraint, and the secondary user cannot share the spectrum of the primary after all. To overcome this problem, we propose the power allocation scheme for the secondary user under the allowable primary user's outage probability constraint. Since the proposed power allocation scheme does not use the instantaneous channel information, the secondary users have lower feedback burden. In addition, the proposed scheme is also robust to the outdated channel environment.