• Journal of Advanced Navigation Technology
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• v.16 no.5
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• pp.801-809
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• 2012

Dispersion management (DM) is the typical technique compensating for the distorted signals due to interaction of group velocity dispersion (GVD) and optical nonlinear effects for transmitting wavelength division multiplexed (WDM) channel with the excellent performance. Optimal net residual dispersion (NRD) and effective launching power range of optical transmission links with random distribution and artificial distribution of single mode fiber (SMF) length and residual dispersion per span (RDPS) required to flexibly design of optical links in DM. It is confirmed that optimal net residual dispersion (NRD) are +10 ps/nm and -10 ps/nm controlled by precompensation and postcompensation, respectively, in both of the considered distribution patterns of SMF length and RDPS. And, in optimal NRD, system performance in optical links with the descending distribution of SMF length and the ascending distribution of RDPS among the artificial distribution patterns are more improved, consequently, effective launching power range is expanded by almost 2 dB than those in optical links with the uniform distribution.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.347-352
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• 2014

In this paper, we propose a Markovian queueing model(M/M/1)-based call admission control to reduce forced terminating rate of non-real secondary user's call for Multi-services Cognitive Radio Networks. A existing control has a problem that the forced terminating rate increases because of adopting a policy of spectrum priority allocation to real calls. In our scheme the rate can be reduced as the call that has no useful spectrum waits in a queue until getting an available spectrum. Our scheme use a neural-net based prediction of primary user's reappearance. Through the simulation, we analysis the call forced terminating rate, access delay and spectrum utilization efficiency, and then show that our scheme can more reduce the forced terminating rate of the call, compared to that of the existing algorithm.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.214-217
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• 2001

This paper presents an implementation methodology of common Rf- integrated PCS base station system which, is capable of providing PCS services for 3 PCS carriers concurrently and wireless system performance evaluation data is shown. We have built up a common PCS base station system using a commonization module, which is consisted of a multi-channel combiner, duplexer, LNA, power divider, feeder line, and a common set of antennas. It was shown that the performance of the system within the total 30MHz PCS frequency range is uniformly acceptable and measured signal quality and coverage are equivalent to that of the individual PCS base station. It is expected that PCS carriers are able to save a huge amount of installation and maintenance expenses by installing and sharing this base station system. This paper forms a groundwork for deploying efficient and economical IMT-2000 network.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1773-1779
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• 2015

Shore-to-sea visible light communication using color clustered multiple-input and multiple-output (MIMO) is presented. The proposed maritime visible light communication (MVLC) offers a low-cost, high-speed wireless link for shore-to-sea maritime communications. Each color cluster is comprised of 50 red, green and blue (RGB) light emitting diodes (LEDs) and is modulated using on-off-keying (OOK). Selection combining is performed at the receiver, producing diversity effect within that color cluster. In this paper, we employ sea states (wave height, wind speed, etc.) data from both Pierson-Moskowitz and JONSWAP spectrum models under atmospheric turbulence conditions. Based on the simulation model, the maritime link quality is analysed in terms of coverage distance and bit error rate performance. The results show that the proposed system provides an efficient MVLC, while satisfying International Association of Lighthouse Authorities (IALA) requirements for maritime buoyage system and also offering sufficient illumination from high power LEDs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.867-869
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• 2012

FRUC(Frame Rate Up Conversion) is core techniques for higher quality terminals or low channel rate. For these applications, in this paper, we propose a block-based reliability evaluation method for FRUC techniques using bi-lateral symmetrical motion estimation. First, in order to measure the reliability, by introducing cost evaluation tools such as motion vector consistency as well as temporal matching and spatial matching characteristics and then by combining these tools, we propose an efficient method which arrange the blocks according to distortion size. Through several simulations, it is shown that the proposed method is very effective in finding the high distortion blocks. Furthermore, it is expected that the proposed method can be effectively utilized in FRUC techniques and Distributed Video Coding technologies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11B
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• pp.968-980
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• 2008

Providing handover with guaranteed QoS for real-time multimedia service such as VoIP, video/audio streaming, and video conferencing in wireless LAN is a challenging task. In this paper, we present efficient layer 2 handover mechanism in wireless LAN, which can provide fast handover with guaranteed QoS for real-time multimedia service. To this end, the scanning period and the number of channels per scanning for handover are dynamically adapted to the type of applications and wireless networking environment, so that both the degradation of application service quality and signaling overhead are minimized simultaneously. The performance of the proposed mechanism is verified by the simulation. The simulation results show that the proposed mechanism guarantess QoS of each multimedia application with minimal power consumption.

• Journal of Distribution Research
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• v.15 no.5
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• pp.273-285
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• 2010

This paper analyzes retailers' purchasing patterns of fruits and vegetables and the problems with purchasing from agricultural product wholesale markets. While large-scale retailers purchase fruits and vegetables from various sources, medium and small-scale retailers and food service companies buy them mostly from agricultural product wholesale markets. The retailers point out the problems with purchasing from agricultural product wholesale markets as a lack of quality uniformity, not sufficient cooling storage facilities, not sufficient space for shipping area, high distribution cost, unnecessary price fluctuation, and etc. In order to enhance the linkage with retailers, agricultural product wholesale markets, first of all, have to adopt more flexible trading methods such as private treaty besides auctions which are exclusively legitimate trading methods in the market. Necessary are enlargement of jobbers' operating scale, securing shipping space for retailers, adoption of inspection service, introduction of methods to stabilize auction prices, saving of loading and unloading costs, implementation of marketing strategies.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.357-357
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• 2012

박막트랜지스터의 전극으로 Au, Ag, Mo, ITO와 같은 물질들이 이미 많이 연구되어 왔으며, 투명 Source/Drain 전극을 활용한 물질로는 ITO에 초점이 맞춰져 왔다. 하지만 ITO의 높은 가격과 Indium의 인체 유해한 독성 때문에 ITO를 대체하는 물질에 대해 많은 연구가 진행되고 있다. 그 중 Al이 도핑된 ZnO (AZO) 는 가시광 영역에서 85% 이상의 높은 투과율과 높은 전도성, 낮은 비저항으로 다양한 광전소자의 전극과 윈도우 물질로 많은 응용 가능성을 보여주고 있다. 본 실험에서는 고 품질의 박막성장이 가능하고, 박막의 두께를 세밀하게 조절할 수 있는 Pulsed Laser Deposition (PLD) 을 이용하여 온도변화에 따라 AZO 박막을 성장시키고 구조적, 전기적, 광학적 특성을 조사하였다. 또한 온도변화가 AZO 박막 특성에 미치는 영향을 분석하여 Source/Drain 전극으로 사용하기 위한 조건을 최적화하였고, 실제 투명박막트랜지스터 제작을 통해 소자의 I-V Curve 와 Transfer 특성을 확인하고, Transfer Length Method 방법을 이용하여 투명박막트랜지스터의 접촉저항, 채널 비저항 등을 확인해 보았다. 소결된 타겟으로는 99.99%의 순도를 갖는 ZnO-$Al_2O_3$ (98:2 wt%) 타겟을 이용하였으며, 장비조건으로는 355 nm의 파장대역을 갖는 Nd:YAG 레이저를 사용하였고, 실험변수로는 온도범위 RT, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$에서 실험을 진행하였다. AZO 박막의 구조적, 전기적 특성을 분석하기 위해 각각 X-Ray Diffraction (XRD), Hall measurement 장비를 사용하였으며, 광학적 특성을 분석하기 위한 투과도의 측정은 UV-Visible spectrophotometer 장비를 사용하였다.

• Journal of Broadcast Engineering
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• v.8 no.1
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• pp.72-79
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• 2003

The Eureka-147 Digital Audio Broadcasting(DAB) system is the new international standard for mobile broadcasting services including high-quality audio, program associated data and other multimedia data. In this paper, we design the transport frame structures for the mobile multimedia services by using the configuration of the Eureka-147 DAB multiplex and MPEG system specifications, and then compare their performances in terms of functionality and overhead. Especially, we suggest and analyze the effective transport structures, which are improved in the efficiency of media multiplexing architecture, by removing the functionally overlapped parts between DAB and MPEG systems. In addition, we evaluate the transmission environments of various DAB data channels and demonstrate the transmission error effects on the low bit rate video stream.

• Journal of KIISE:Information Networking
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• v.32 no.6
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• pp.723-731
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• 2005

Wide spread deployment of infrastructure WLANs has made Wi Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end to end performance, past research has focused on MAC protocol enhancement, analysis and simulation based performance evaluation without sufficient consideration for modeling inaccuracies stemming from inter layer dependencies, including physical layer diversity, that significantly impact performance. We take a fresh look at IEEE 802.11 WLANs, and using experiment, simulation, and analysis demonstrate its surprisingly agile performance traits. Contention based MAC throughput degrades gracefully under congested conditions, enabled by physical layer channel diversity that reduces the effective level of MAC contention. In contrast, fairness and jitter significantly degrade at a critical offered load. This duality obviates the need for link layer flow control for throughput improvement but necessitates traffic control for fairness and QoS. We use experimentation and simulation in a complementary fashion, pointing out performance characteristics where they agree and differ.