• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.5
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• pp.675-684
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• 1993

In this paper, we analyze a traffic control schemes at the interworking unit(IWU) of the IEEE 802.6 DQDB MAN and the B-ISDN, and estimate its performance via computer simulation. We also study traffic management, relaying sublayers for the cases of four service classes defined in the B-ISDN. As for performance criteria, we consider slot waiting time, slot loss rate, and the fairness between DQDB nodes in access networks. We propose a simple control algorithm that decreases the waitint delay at the OWU. With the buffer size of 40 [slots] at the IWU, we have found that the slot loss rate was nearly zero at traffic load below 0.9, and the slot waiting time became less than 15 slot times.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.10
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• pp.45-49
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• 2014

In this paper, the performance of the interference cancellation using multiple receive antennas is evaluated for heterogeneous cellular systems when user association and load balancing problems are optimized for cell edge users. The simulation results show that the interference cancellation method remarkably improves the rate performance of load-balanced cells.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2
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• pp.55-60
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• 1996

This paper describes the subjective assessment of the multi-channel audio quality according to the bitrate changing and evaluates the predistortion effect to avoid the unmasked noise after matrixing/dematrxing process in transmission and regeneration of the multi-channel audio. The simulation is processed by the perceptual coding that is MPEG-2 Audio layer II algorithm. We evaluate the quality improvement about predistortion using or not by 384, 320, 256, 128kbps. As the result of the double blind subjective assessment, 5 Grade-Impairment Scale is scored under minus one to 320kbps and so audio quality is evaluated to be perceptible, but not annoying in 3/2 channel. The effect of the predistortion is improved one level in 128kbps and especially speech test material I better improved than music test materials.

• Journal of Satellite, Information and Communications
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• v.3 no.2
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• pp.38-42
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• 2008

In 2005, DVB-S2 spec. was finalized. But with a large number of DVB-S receivers already installed, backwards compatibility may be required for a period of time, where old receivers continue to receive the same capacity as before, while the new DVB-S2 receivers could receive additional capacity broadcasts. To facilitate the reception of DVB-S serviced by DVB-S2 receivers, implementation of DVB-S in DVB-S2 chips is highly recommended. For the backward compatibility the system adapt the hierarchical modulation scheme. And the system has to meet system margin, so in this paper analyzes the effect according to the deviation angle and shows the BER performance. And finally this paper shows the result of the system implement using FPGA chip.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.8
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• pp.1928-1936
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• 1996

In this paper, we propose an adaptive bandwidth allocation algorithm for the transmission of VBR video through ATM Networks. In order to evaluate the required bandwidth for the VBR video, the characteristics of the compressed VBR video generated by the two-layered coder are analyzed with variations in the number of GOP(N), quantizer scale(q), and the number of low-frequency DCT coefficients(.betha.). The two-layer coder which is used to separate from the number of DCT coefficients is designed to transmit the VBR video efficiently. The compressed data generated by the two-layer coder are splitted into the high priority and low priority cells. If congestion is occurred in ATM networks, the minimum image quality is maintained by the high priority cells. The required bandwidth for VBR video is estimated with a prediction algorithm using the scene anframe correlations as well as the statistical properties of the VBR video sources. Strong correlation among the adjacent slices in a frame represents by the scene correlation andstrong correlation among the frames is represented by the frame correlation. The performance of the bandwidth allocation scheme proposed is evaluated in terms of the bandwith utilization, cell loss rate, and SNR with variations in q, n, .betha.. Simulation rewsults shown that the proposed scheme is superior to the conventional methods.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10d
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• pp.148-150
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• 2002

본 논문은 모바일 핸드셋이라는 제한적인 디스플레이 환경과 입력환경에서 필요한 라우트맵의 시각화에 따른 문제점과 그 해결방안을 제시한 논문이다. 자동차 네비게이션 시스템에서 널리 사용되는 경로표시 방법은 일반적으로 노트북이나, PDA, 전용 디스플레이 시스템등에서 구현되어 있으나, 모바일 핸드셋과 같이 제한된 디스플레이 환경에서의 경로표시 방법은 현재까지 많은 연구가 이루어지지 않고 있다. 본 논문은 인간의 인식능력이 임의의 경로를 회전방향점(turning point)의 연속으로 인식한다는 점에 착안하여 원래의 경로가 가진 축적을 변형하여 선분과 회전방향점으로 경로를 표시하는 라인 드라이브 시스템을 모바일 환경의 경로표시 방법으로 사용하였다. 본 논문에서 구현한 시스템은 GIS의 벡터 정보를 가지고 있는 서버와 Brew 플랫폼을 지원하는 모바일 핸드셋으로 구성된다. GIS 서버는 프로토타입 정보를 추출하여 모바일 핸드셋으로 전송하고, 이러한 정보는 모바일 핸드셋의 Brew 플랫폼에서 간략화, 도식화 과정을 거쳐서 시각화된다. 본 논문은 제한된 디스플레이 환경의 경로 확대표시를 위하여 계층별 경로 시각화 방법을 사용하여 가독성을 높이고 사용상의 편리함을 추구한다.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.5-8
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• 2001

Wideband code division multiple access (WCDMA) is the most widely adopted third generation air interface. The physical layer of the air interrace is the main discussion topic during standardization processes. This paper aims to investigate the performance of uplink WCDMA over many conceivable transmission scenarios in realistic operating conditions. The focus of the study is placed on the performance under frequency selective fading channel conditions with multiple access interference (MAI) in mixed services environments. For the investigation, a simulator has been developed and it encompasses a variety of WCDMA air interface features. The results show that the performance is greatly affected by MAI and is further aggravated with the presence of frequency selective fading, thereby necessitating a suitable compensation measure.

• Journal of Internet Computing and Services
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• v.4 no.1
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• pp.19-25
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• 2003

Mobile IPv6 services exposes its vulnerability when a mobile node is roaming across the subnets which belongs to the different domains. The AAA Infrastructure Is strongly recommended when the ISPs need to authenticate the mobile user come from the different domains. In addition to the basic requirements for AAA service, the authentication latency and AAA message overhead should be minimized for contiguity of the service. This paper considers the roaming service with AAA infra structure in Mobile IPv6 and proposes the key distribution method to authenticate the mobile node with secure manner by reducing and optimizing the exchanged messages for AAA entities.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.1
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• pp.55-68
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• 2010

IEEE WAVE is going through the final standardization process as the wireless access technology which provides drivers in high-speed vehicles with safety-related information and commercial services This paper presents an application-layer protocol for safe driving assistant service and a service system emulator based on this protocol. The safe driving assistant system includes a construction zone information service and a vehicle crash notification service, an emergency vehicle notification service, a probing service and a dilemma zone decision assistant service. Emulator System design for verifying functions of system, The emulator consists of an emulator server that models the movement of all vehicles and road states and a number of clients that models functional units for OBUs, RSUs, and a traffic control center).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3C
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• pp.271-278
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• 2003

In this paper, we propose a new MLP based detector which has low circuit complexity and fast adaptation capability for CDMA downlink in frequency selective fading, and is easy for parameter optimization. The simplified structure of the proposed MLP is designed by making use of transmission characteristics of downlinks such that all users signals transmitted over same propagation paths and the number of channelization codes are limited. Significant performance improvement over Rake receiver can be obtained with the proposed MLP and the efficiency of the proposed MLP was compared with that of conventional MLP.