• 한국조경학회지
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• 제31권4호
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• pp.57-66
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• 2003

The purpose of this study is to evaluate the resource value of existing mud flats in JANGWHARI, KANGWHADO, as strategies for ecotourism. The research methods used in this study are Limits of Acceptable Change(LAC), and Recreation Opportunity Spectrum(ROS). The LAC process draws attention to the existing area conditions that are judged to be acceptable. Managers must define desired area conditions and undertake actions to maintain or achieve these conditions. The ROS is within each of the recreation opportunity classes identified as being used at the regional level. The Results of this study are as follows: 1) The Opportunity Class of the ROS is ecological, physical, social, managerial setting as primitive, semi-primitive. non-motorized, semi-primitive$.$motorized, and roaded natural. 2) The indicator of the LAC is ecological, physical, social, and managerial setting; the indicator of ecological is wildlife populations, water quality, road paving; the indicator of physical is facilities; the indicator of social is visitor needs for knowledge, adventure, eco-experience, and environmental education programs; and, the indicator of managerial is limits of law, and degree of management. 3) Currently, the Opportunity Class of the ROS of JANGWHARI, KANGWHADO is levels II-III, and the Opportunity Class of the suggested ROS is levels I-II. 4) This paper describes strategies for mud flat area management: detection of water quality, resolving problems of equipment, supply of both environmental education programs and guide equipment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3237-3256
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• 2012

In the context of effective usage of a scarce spectrum resource, emerging wireless communication standards will demand spectrum sharing with existing systems as well as multiple access with higher spectral efficiency. We mathematically analyze the sum throughput of a spectrum sharing space-division multiple access (SDMA) system, which forms a transmit null in the direction of other coexisting systems while satisfying orthogonal beamforming constraints. For a large number of users N, the SDMA throughput scales as log N at high signal-to-noise ratio (SNR) ((J-1) loglog N at normal SNR), where J is the number of transmit antennas. This indicates that multiplexing gain of the spectrum sharing SDMA is $\frac{J-1}{J}$ times less than that of the non-spectrum sharing SDMA only using orthogonal beamforming, whereas no loss in multiuser diversity gain. Although the spectrum sharing SDMA always has lower throughput compared to the non-spectrum sharing SDMA in the non-coexistence scenario, it offers an intriguing opportunity to reuse spectrum already allocated to other coexisting systems.

• 천문학회지
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• 제37권5호
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• pp.543-546
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• 2004

The inverse Compton scattering of the cosmic microwave background (CMB) radiation with electrons in the intracluster medium which has a temperature gradient, was examined by the third-order perturbation theory of the Compton scattering. A new type of the spectrum distortion of the CMB was found and named as gradient T Sunyaev-Zel'dovich effect (gradT SZE). The spectrum has an universal shape. There is a zero distortion point, the cross over frequency, at 326GHz. When the hotter region locates closer to an observer, the intensity becomes brighter than the CMB in the frequency region lower than the cross over frequency and fainter than the CMB in the frequency region higher than the cross over frequency. When the cooler region locates closer to an observer, the distorted part of the spectrum has an opposite sign to the above case. The amplitude of the spectrum distortion does not de-pend on the electron density and depends on the heat conductivity and the total temperature variation along a line of sight. Therefore, the gradT SZE provides an unique opportunity to measure thermally nonequilibrium electron momentum distribution function in the ICM and combined with the X-ray measurements of the electron temperature distribution provides an opportunity of direct measurement of the heat conductivity in the ICM.

• Journal of Communications and Networks
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• 제8권2호
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• pp.151-157
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• 2006

In a continuously expanding wireless world, the number of radio systems increases every day and efficient spectrum usage becomes a more significant requirement. Ultra-wideband (UWB) and cognitive radio are two exciting technologies that offer new approaches to the spectrum usage. The main objective of this paper is to shed the first light on the marriage of these two important approaches. The strength of orthogonal frequency division multiplexing (OFDM) based UWB in co-existing with licensed systems is investigated. The opportunity concept is defined, and the requirements of the opportunistic spectrum usage are explained. It is proposed to take the UWB-OFDM from the current underlay implementation, and evolve it to a combined underlay and opportunistic spectrum usage technology, leading to cognitive UWB-OFDM. This way, we aim at making UWB more competitive in the wireless market with extended range, higher capacity, better performance, and a wide variety of applications.

• ETRI Journal
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• 제39권4호
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• pp.558-569
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• 2017

In this study, a non-preemptive M/G/1 queueing model of a spectrum handoff scheme for cognitive wireless networks is proposed. Because spectrum handoff gives secondary users an opportunity to carry on their transmissions, it is crucially important to determine the actions of primary users. In our queueing model, prioritized data traffic is utilized to meet the requirements of the secondary users. These users' packets are categorized into three different priority classes: urgent, real-time, and non-real time. Urgent data packets have the highest priority, while non-real time data packets have the lowest priority. Riverbed (OPNET) Modeler simulation software was used to simulate both reactive and proactive decision spectrum handoff schemes. The simulation results were consistent with the analytical results obtained under different load and traffic conditions. This study also revealed that the cumulative number of handoffs can be drastically decreased by exploiting priority classes and utilizing a decent spectrum handoff strategy, such as a reactive or proactive decision-based strategy.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권4호
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• pp.1192-1207
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• 2014

Dynamic spectrum sharing is a key technology to improve spectrum utilization in wireless networks. The elastic spectrum management provides a new opportunity for licensed primary users and unlicensed secondary users to efficiently utilize the scarce wireless resource. In this paper, we present a game-theoretic framework for dynamic spectrum allocation where the primary users rent the unutilized spectrum to the secondary users for a monetary profit. In reality, due to the ON-OFF behavior of the primary user, the quantity of spectrum that can be opportunistically shared by the secondary users is limited. We model this situation with the renewal theory and formulate the spectrum pricing scheme with the Bertrand game, taking into account the scarcity of the spectrum. By the Nash-equilibrium pricing scheme, each player in the game continually converges to a strategy that maximizes its own profit. We also investigate the impact of several properties, including channel quality and spectrum substitutability. Based on the equilibrium analysis, we finally propose a decentralized algorithm that leads the primary users to the Nash-equilibrium, called DST. The stability of the proposed algorithm in terms of convergence to the Nash equilibrium is also studied.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권5호
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• pp.1514-1531
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• 2014

Femtocell provides better coverage and higher spectrum efficiency in areas rarely covered by macrocells. However, serious two-tier interference emerging from randomly deploying femtocells may create dead zones where the service is unavailable for macro-users. In this paper, we present adopting cognitive radio spectrum overlay to avoid intra-tier interference and incorporating spectrum underlay and overlay to coordinate cross-tier interference. It is a novel centralized control strategy appropriate for both uplink and downlink transmission. We introduce the application of proper spectrum sharing strategy plus optimal power allocation to address the issue of OFDM-based femtocells interference-limited downlink transmission, along with, a low-complexity suboptimal solution proposed. Simulation results illustrate the proposed optimal scheme achieves the highest transmission rate on successfully avoiding two-tier interference, and outperforms the traditional spectrum underlay or spectrum overlay, via maximizing the opportunity to transmit. Moreover, the strength of our proposed schemes is further demonstrated by comparison with previous classic power allocation methods, in terms of transmission rate, computational complexity and signal peak-to-average power ratio.

• ETRI Journal
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• 제36권3호
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• pp.502-505
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• 2014

Polarized spectrum sharing (PSS) exploits the spectrum opportunities in a polarized domain. However, when it comes to wideband environments PSS is impaired by the frequency-dependent polarization mode dispersion (PMD); thus, the effective throughput of PSS drops. To combat the PMD effect, this work proposes a cluster-based PSS approach to enable PSS on a narrower frequency span. Simulation results show that the effective throughput of PSS on cluster basis outperforms that of PSS on bandwidth and subcarrier basis.

• 대한전자공학회논문지TC
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• 제47권11호
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• pp.59-68
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• 2010

본 논문은 보상함수 수정을 통해 보다 완벽한 DSA(Dynamic Spectrum Access)를 수행하는 새로운 방법을 제시하였다. POMDP(Partially Observable Markov Decision Process)는 미래의 스펙트럼 상태를 예측하는데 사용되는 알고리즘으로서, 그 중 보상함수는 스펙트럼을 예측하는데 있어 가장 중요한 부분이다. 그러나 보상함수는 Busy 및 Idle의 두 가지 상태만 갖고 있기 때문에 채널에서 충돌이 발생하게 되면 보상함수는 Busy를 반환함으로써 2차 사용자의 성능을 감소시키게 된다. 따라서 본 논문에서는 기존의 Busy를 Busy 및 Collision 의 두 상태로 구분하였고, 이렇게 추가된 Collision 상태를 통해 2차 사용자의 채널 접근 기회를 보다 향상시킴으로서 데이터 전송율을 증대시킬 수 있도록 하였다. 또한 본 논문은 새로운 알고리즘의 신뢰도 벡터를 수학적으로 분석하였다. 마지막으로 시뮬레이션 결과를 통해 개선된 보상함수의 성능을 검증하고, 이를 통해 새로운 알고리즘이 CR 네트워크에서 2차 사용자의 성능을 향상시킬 수 있음을 보인다.

• 한국전자파학회논문지
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• 제24권8호
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• pp.849-859
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• 2013

최근 각국은 무선 광대역 서비스용 주파수 확보를 위하여 공공주파수와 방송용 주파수의 효율적 이용을 도모하고 있다. 본 연구는 해외의 공공주파수 및 방송용 주파수 관리 정책 동향을 살펴보고, 이를 참고하여 우리나라의 관련 현안에 대한 정책 방안을 제시하고자 한다. 공공주파수의 효율적 활용을 위한 정책 방안으로, 공공주파수에 대한 이용실태 조사, 공공주파수에 대한 기회비용 부과, 주파수 효율성 기금의 설치, 군주파수의 효율적 이용을 위한 유인 제공, 공공주파수에 대한 공유정책 도입 등을 제안하였다. 그리고 방송용 주파수의 효율적 활용을 위하여는 단기적으로는 방송통신발전기금의 부과기준 변경, 중장기적으로 상업용 방송주파수에 대한 할당방식 변경과 행정가격 부과를 제안하였다.