• ETRI Journal
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• v.28 no.5
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• pp.660-663
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• 2006

In this letter, we propose a frame-size adaptive MAC protocol for high rate wireless personal area networks (WPANs). In the proposed scheme, during communication, frame error rate is periodically reported to a transmitting device and the frame size is changed according to the measured results. Thus, the channel can be more effectively utilized by adapting to variable radio conditions. Analytical results show that this scheme achieves a much higher throughput than a non-frame-size adaptive media access control protocol in high-rate WPANs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.320-322
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• 2002

A new simple spatial scheme for base station with adaptive antenna in Code Division Multiplexing Access (CDMA) systems is presented. In the proposed scheme, by applying the new spatial structure lot the receiver, the system can debate the problem of which the number of users exceeds the number of adaptive antenna elements existing in the conventional spatial scheme. An adaptive algorithm based on the Mean Square Error (MSE) criterion is also derived to update the weight matrix of the proposed scheme. The results of the system capacity enhancement can be achieved by using the proposed approach. Numerical simulations are included fer illustration and verification.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.721-725
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• 2014

In this paper, we propose a fast adaptive power allocation method for an orthogonal frequency division multiple access (OFDMA) system that employs an adaptive modulation and coding (AMC) scheme. The proposed scheme aims to reduce the calculation complexity of greedy adaptive power allocation (APA), which is known as the optimal algorithm for maximizing the utility argument of power. Unlike greedy APA, which starts power allocation from "0", the proposed algorithm initially allocates a certain level of power determined by the water-filling scheme. We theoretically demonstrate that the proposed algorithm has almost the same capability of maximizing the utility argument as the greedy APA while reducing the number of operations by 2M, where M is the number of AMC levels.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.2 s.25
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• pp.96-102
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• 2006

In this paper, the design, construction and basic characteristics of an electronically adaptive array antenna for the GPS receiver is described. The susceptibility of the GPS signals to the interference is of concern to the GPS user community. Because of the low received power of the GPS signals, outages can easily occur due to the unintentional interference and the easily obtainable low cost GPS jammer denying access to the GPS signals. We propose a technique of the adaptive array antenna that detects the GPS interference sources and controls the null beam pattern only toward the jamming sources to acquire GPS navigation data after acquisition and tracking of the GPS signals.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.201-204
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• 1998

This paper study on blind adaptive interference suppression algorithm without training sequence to solve Near-Far problem due to multi access interference. And the performance of each algorithm in the presence of the multipath fading channels over DS-CDMA is evaluated. Simulation results showed that Modified LMS-CMA algorithm has a higher capacity than MOE in SIR/SNR.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.581-584
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• 2003

본 논문에서는 링크 상황에 따라서 변복조 방식과 코딩 방식을 달리하는 기술인 AMC(Adaptive Modulation and Coding)기능과 연동하는 2 단계 ARQ(Automatic Repeat Request)방식을 제안하여 한정된 무선채널을 여러 종류의 서비스와 여러 가입자가 동시에 공유하는 경우에 발생되는 QoS(Quality of Service) 문제를 해결하고자 한다. 제안한 2 단계 ARQ 방식은 MAC(Medium Access Control) 계층에 위치하여 상위 계층으로부터 IP(Internet Protocol) packet 를 수신한 후 2 단계의 ARQ 동작을 수행함으로써 물리 채널에서 전송 중에 발생되는 오류 확률을 감소시킨다. 따라서 TCP(Transmission Control Protocol)단에서의 재전송 감소에 의한 향상된 성능도 기대할 수가 있겠다.

• Journal of Broadcast Engineering
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• v.16 no.6
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• pp.1073-1076
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• 2011

In this paper, we propose a scalable random access scheme in SVC based DASH service that enables random access support not only for base layer of SVC but also for enhancement layers. The proposed method includes extension of segment index box ('sidx') from DASH standard, as well as new RAP Synchronization Box ('raps'). Since the proposed scheme provides random access service for movie fragments with SVC encoded video layers, adaptive scalable random access service is possible.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.5
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• pp.211-219
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• 2008

This paper is proposed context-aware based access control, model by extending original access control model. In this paper, we survey the recent researches about security model based context-aware such as xoRBAC and CAAC. For exactly policy evaluation, we make an addition Context Broker and Finder in existing CAAC security model. By this security model, Context information and context decision information is able to be collected easily for more correct policy decision. This paper controlled access of possible every resources that is able to access by user's event and constraint from primitive access resources. In this paper proposed security model can be offer dynamically various security level and access authority method alone with specified policy and constraint adjustment at user's role.

• Journal of Communications and Networks
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• v.6 no.4
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• pp.307-316
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• 2004

Wireless local area networks have known an increasing popularity during the past few years. However, as new user applications diverge from the traditional data-centric model, the introduction of efficient, QoS aware medium access methods becomes of utmost importance. EY-NPMA is a medium access protocol belonging to the contention paradigm that provides support for service differentiation and low collision rates. In this paper, we address a shortcoming of EY-NPMA as indicated by previous studies, namely the insensitivity of the protocol to different working conditions. In this work, we study and evaluate a mechanism that allows a network employing EY-NPMA to adapt its operating parameters according to the offered load. Simulation studies further document and confirm the positive characteristics of the proposed mechanism.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1107-1109
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• 2007

Context-based access control is an emerging approach for modeling adaptive solution, making access control management more flexible and powerful. However, these strategies are inadequate for the increased flexibility and performance that ubiquitous computing environment requires because such systems can not utilize effectively all benefit from this environment. In this paper, we propose a solution based on risk to make use of many context parameters in order to provide good decisions for a safety environment. We design a new model for risk assessment in ubiquitous computing environment and use risk as a key component in decision-making process in our access control model.