• Journal of Communications and Networks
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• 제16권2호
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• pp.110-120
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• 2014

This article proposes a spectrum sharing method which can avoid the mutual interference in both primary and secondary systems. The two systems make them a priority to use two single-dimension orthogonal signals, the real and imaginary pulse amplitude modulation signals, if the primary system is not in outage with this use. A secondary transmitter is selected to be the primary relay and the active secondary source to perform this. This allows a simultaneous spectrum access without any mutual interference. Otherwise, the primary system attempts to use a full two-dimensional signal, the quadrature amplitude modulation signal. If there is no outage with respect to this use, the secondary spectrum access is not allowed. When both of the previous attempts fail, the secondary system is allowed to freely use the spectrum two whole time slots. The analysis and simulation are provided to analyze the outage performance and they validate the considerable improvement of the proposed method as compared to the conventional one.

• Journal of Communications and Networks
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• 제16권2호
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• pp.140-145
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• 2014

In this paper, we propose an anti-interference cooperative spectrum sharing strategy for cognitive system, in which a secondary system can operate on the same spectrum of a primary system. Specifically, the primary system leases a fraction of its transmission time to the secondary system in exchange for cooperation to achieve the target rate. To gain access to the spectrum of the primary system, the secondary system needs to allocate a fraction of bandwidth to help forward the primary signal. As a reward, the secondary system can use the remaining bandwidth to transmit its own signal. The secondary system uses different bandwidth to transmit the primary and its own signal. Thus, there will be no interference felt at primary and secondary systems. We study the joint optimization of time and bandwidth allocation such that the transmission rate of the secondary system is maximized, while guaranteeing the primary system, as a higher priority, to achieve its target transmission rate. Numerical results show that the secondary system can gain significant improvement with the proposed strategy.

• Journal of Communications and Networks
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• 제14권2호
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• pp.162-168
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• 2012

This paper considers the scenario in which a set of nodes share a common channel. Some nodes have a rechargeable battery and the others are plugged to a reliable power supply and, thus, have no energy limitations. We consider two source-destination pairs and apply the concept of cognitive radio communication in sharing the common channel. Specifically, we give high-priority to the energy-constrained source-destination pair, i.e., primary pair, and low-priority to the pair which is free from such constraint, i.e., secondary pair. In contrast to the traditional notion of cognitive radio, in which the secondary transmitter is required to relinquish the channel as soon as the primary is detected, the secondary transmitter not only utilizes the idle slots of primary pair but also transmits along with the primary transmitter with probability p. This is possible because we consider the general multi-packet reception model. Given the requirement on the primary pair's throughput, the probability p is chosen to maximize the secondary pair's throughput. To this end, we obtain two-dimensional maximum stable throughput region which describes the theoretical limit on rates that we can push into the network while maintaining the queues in the network to be stable. The result is obtained for both cases in which the capacity of the battery at the primary node is infinite and also finite.

• 한국항공우주학회지
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• 제43권10호
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• pp.936-942
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• 2015

국가위상 제고와 국내 발사체산업 발전에 따른 경제 발전을 위하여 우주발사서비스 시장진입은 필수적이다. 발사체 개발의 후발주자로써 시장에 효과적으로 진입하기 위해서는 시장의 트렌드를 정확하게 파악하고, 체계적인 시장진입전략을 수립하여야한다. 본 논문에서는 세계 우주발사서비스 시장의 3가지 핵심트렌드(고성능의 대형 우주발사체 수요 증가, 저가형 우주발사체 증가, Dual/Multi-Launch 증가)를 도출하고, 각 핵심트렌드에 대응하기 위한 전략의 우선순위를 쌍대비교분석법을 통해 평가하였다. 그 결과 모든 트렌드 하에서 발사체 신뢰성 확보 전략이 가장 중요하며, 고성능의 대형 우주발사체 수요 증가 트렌드 하에서는 정부 지원 전략이, 저가형 우주발사체 및 Dual/Multi-Launch 증가 트렌드 하에서는 가격 경쟁력 확보전략이 두 번째 우선순위를 보였다.

• Journal of Communications and Networks
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• 제16권2호
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• pp.193-201
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• 2014

In cognitive radio networks, the packet transmissions of the secondary users (SUs) can be interrupted randomly by the primary users (PUs). That is to say, the PU packets have preemptive priority over the SU packets. In order to enhance the quality of service (QoS) for the SUs, we propose a spectrum access strategy with an ${\alpha}$-Retry policy. A buffer is deployed for the SU packets. An interrupted SU packet will return to the buffer with probability ${\alpha}$ for later retrial, or leave the system with probability (1-${\alpha}$). For mathematical analysis, we build a preemptive priority queue and model the spectrum access strategy with an ${\alpha}$-Retry policy as a two-dimensional discrete-time Markov chain (DTMC).We give the transition probability matrix of the Markov chain and obtain the steady-state distribution. Accordingly, we derive the formulas for the blocked rate, the forced dropping rate, the throughput and the average delay of the SU packets. With numerical results, we show the influence of the retrial probability for the strategy proposed in this paper on different performance measures. Finally, based on the trade-off between different performance measures, we construct a cost function and optimize the retrial probabilities with respect to different system parameters by employing an iterative algorithm.

• 수산해양교육연구
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• 제25권1호
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• pp.139-151
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• 2013

Recently, in the context of increased interest for marine tourism, Jeju region of South Korea has attractive waterfront space and also has potential requirements for development. The objective of this paper was to analyze the priority for resource development of waterfront in Jeju region. In order to calculate the importance of factors related to the development of waterfront in Jeju area, this study conducted exploratory factor analysis to extract the factors and established the AHP model based on the factors name focusing on a total of 198 tourists. In this study, in accordance with the procedures of AHP analysis, pairwise comparisons were conducted focusing on a total of 15 experts. Especially, difference test between groups (academics and bureaucratic) was conducted. In the 1st criterion for evaluation, 'exploring experience' factor is most important thing and 'facilities & infrastructure' factors were in the following order. In the secondary criterion, AHP analysis showed that experience facilities, environmental management, and absence of residents consciousness were the important factors. In the future time, the results of this research can be utilized as basic data in the aspects of tourism development in Jeju waterfront region.

• 한국과학교육학회지
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• 제20권4호
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• pp.572-581
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• 2000

본 연구에서는 교육에서 가장 중요한 구성요소중의 하나인 교사가 과학교육목표에 대해 어떻게 인식하고 있는지, 과학교육목표가 학교 현장에서 실현되지 못하는 이유는 무엇인지를 조사하였다. 연구 대상은 대구시의 중고등학교 교사 217명과, 초등학교 교사 76명이었는데, 연구자들이 제작한 선택형 설문지에 이들이 직접 반응하는 방법을 채택하였다. 통계적인 분석은 종속변인이 서열이나 빈도인 관계로 비모수 통계법인 Friedman test, Kruskal-Wallis test, 카이자승법을 사용하였다. 본 연구 결과를 종합한 결론은 다음과 같다. 첫째, 교사들은 현재의 교육과정이 탐구, 지식, 과학적 태도, STS 순으로 중요시한다고 인식하고 있었다. 특히 초등학교 교사들은 탐구를 가장 중요하게 다룬다고 인식하고 있는데 반해, 중등학교 교사들은 지식을 더 중요하게 다룬다고 인식하고 있었다. 과학적 태도에 있어서도 초등교사가 중등교사들보다 더 중요하게 다루고 있다고 인식하고 있었다. 교사 자신들은 목표들 중에서 탐구를 가장 강조하고 있었고, 그 다음으로 과학적 태도, STS, 지식의 순으로 지적하였다. 근무학교별로는 초등학교 교사들과 연령이 높은 교사들이 탐구에 더 높은 우선 순위를 두었고, 중등학교 교사들은 과학적 태도를 더 중요하게 생각하고 있었다. 지식에 대해서는 유의미한 차이가 없었다. 한편, 실제 수업에서 교사들은 탐구를 가장 강조한다고 보고하였고, 그 다음으로 과학적 태도, 지식, STS의 순으로 나타났었다. 초등학교 교사들과 연령이 높은 교사들이 탐구를 더 중요시하고 있었고, 지식은 고 중 초등학교 순으로 중요하다고 인식했다. 또한 연령이 낮은 교사들이 지식을 더 중요하게 다루고 있었다. 둘째로, 목표달성에 대한 장애물에 관해서는 초등학교 교사들은 학급 인원수 과다로 인해서 탐구, 과학적 태도의 목표가 잘 실현되지 않는다고 응답한 반면, 중등학교 교사들은 입시제도의 중압감과 지식의 편중으로 인해서 학생들의 흥미가 떨어졌다고 응답했다. 특히 STS 목표의 경우는 교재 내용이 목표에 맞게 엮어져 있지 않기 때문이라고 응답하였다.

• 공학교육연구
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• 제19권3호
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• pp.13-22
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• 2016

The purpose of this study is to analyze middle and high school technology teachers' recognition and educational need about engineering education. For this, we surveyed secondary school technology teachers. The result of this study is as follow. First, most technology teachers perceive that engineering contents are lack in technology education, therefore they recognize the needs of reinforcement of engineering contents. Second, most technology teachers perceive that present technology subject does not give positive affect to students for their own career selection on engineering field. Furthermore, they perceive that if it contained the contents of engineering in technology education, students would experience creative design and problem solving process. Third, most technology teachers perceive that they are able to teach engineering in technology education and they need the change of national curriculum and the development of engineering program contents. Fourth, they perceive that the 7~9 grade is the best grade to start to study engineering in elementary and secondary school. Fifth, they perceive that 'design', 'problem solving' and 'creative thinking' are the priority of educational needs of teaching ability and knowledge about engineering. Sixth, they perceive that the aerospace engineering, the electrical engineering, the electronic engineering, the mechanical engineering, the computer engineering and the environmental engineering are the priority of educational needs of teaching knowledge about engineering fields.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권7호
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• pp.1777-1791
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• 2012

This paper considers a downlink cognitive radio (CR) network where one secondary user (SU) and one primary user (PU) share the same base station (BS). The spectrum of interest is divided into a set of independent, orthogonal subchannels. The communication of the PU is of high priority and the quality of service (QoS) is guaranteed by the minimum rate constraint. On the other hand, the communication of the SU is of low priority and the SU opportunistically accesses the subchannels that were previously discarded by the PU during power allocation. The BS assigns fractions ?? and 1 ?? of the total available transmit power to the PU and the SU respectively. Two power allocation schemes with opportunistic subchannel access are proposed, in which the optimal values of ??'s are also obtained. The objective of one scheme is to maximize the rate of the SU, and the objective of the other scheme is to maximize the sum rate of the SU and the PU, both under the PU minimum rate constraint and the total transmit power constraint. Extensive simulation results are obtained to verify the effectiveness of the proposed schemes.

• Journal of Communications and Networks
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• 제18권4호
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• pp.610-618
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• 2016

A green cognitive radio network (CRN), characterized by base stations (BSs) that conserve energy during sleep periods, is a promising candidate for realizing more efficient spectrum allocation. To improve the spectrum efficiency and achieve greener communication in wireless applications, we consider CRNs with an long term evolution advanced (LTE-A) structure and propose a novel energy-saving strategy. By establishing a type of preemptive priority queueing model with a single vacation, we capture the stochastic behavior of the proposed strategy. Using the method of matrix geometric solutions, we derive the performance measures in terms of the average latency of secondary user (SU) packets and the energy-saving degree of BSs. Furthermore, we provide numerical results to demonstrate the influence of the sleeping parameter on the system performance. Finally, we compare the Nash equilibrium behavior and social optimization behavior of the proposed strategy to present a pricing policy for SU packets.