• Journal of Communications and Networks
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• 제11권2호
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• pp.115-121
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• 2009

In cognitive radio (CR) systems, cognitive users can use the frequency bands when the primary users are not present. Hence, reliable detection of available spectrum is foundation of cognitive radio technology. To ensure unimpaired operation of primary users, cooperative spectrum sensing is needed. To reduce the network overhead of cooperative spectrum sensing, a novel cooperative spectrum sensing algorithm based on credibility is proposed. In particular, the close-form expressions for probability of detection and false-alarm are derived for the novel algorithm, and expression for the average overhead used for cooperation is given. The thresholds design method for the algorithm is also discussed. The conclusion is proved by computer simulations.

• Journal of Communications and Networks
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• 제13권5호
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• pp.463-471
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• 2011

Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to channel conditions. However throughput performance degradation is observed by low-rate stations in multi-rate circumstances resulting in so-called performance anomaly. In this paper, we propose active relay-based cooperative medium access control (AR-CMAC) protocol, in which active relays desiring to transmit their own data for cooperation participate in relaying, and it is designed to increase throughput as a solution to performance anomaly. We have analyzed the performance of the simplified AR-CMAC using an embedded Markov chain model to demonstrate the gain of AR-CMAC and to verify it with our simulations. Simulations in an infrastructure network with an IEEE 802.11b/g access point show noticeable improvement than the legacy schemes.

• Journal of information and communication convergence engineering
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• 제17권2호
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• pp.105-116
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• 2019

Recently, there has been an increase in research on wireless sensor networks (WSNs) because they are easy to deploy in applications such as internet-of-things (IoT) and body area networks. However, WSNs have constraints in terms of power, quality-of-service (QoS), computation, and others. To overcome the power constraint issues, wireless energy harvesting has been introduced into WSNs, the application of which has been the focus of many studies. Additionally, to improve system performance in terms of achievable rate, cooperative networks are also being explored in WSNs. We present a review on current research in the area of energy harvesting in WSNs, specifically on the application of simultaneous wireless information and power transfer (SWIPT) in a cooperative sensor network. In addition, we discuss possible future extensions of SWIPT and cooperative networks in WSNs.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권1호
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• pp.222-236
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• 2019

Wireless content caching in small cell networks has recently been considered as a promising way to alleviate the congestion of the backhaul in emerging heterogenous cellular network. However, how to select files which are cached in SBSs and how to make SBSs work together is an important issue for cooperative cache research for the propose of reducing file download time. In this paper, a Cooperative-Greedy strategy (CGS) among cache-enabled small base stations (SBSs) in small cell network is proposed, in order to minimize the download time of files. This problem is formulated as a Chinese restaurant game.Using this game model, we can configure file caching schemes based on file popularity and the spectrum resources allocated to several adjacent SBSs. Both the existence and uniquencess of a Nash equilibrium are proved. In the theoretical analysis section, SBSs cooperate with each other in order to cache popular files as many as possible near UEs. Simulation results show that the CGS scheme outperforms other schemes in terms of the file-download time.

• 경영과학
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• 제29권2호
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• pp.21-34
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• 2012

This paper addresses a network design problem in a supply chain system that involves locating both plants and distribution centers, and determining the best strategy for distributing products from the suppliers to the plants, from the plants to the distribution centers and from the distribution centers to the customers. This paper suggests a cooperative coevolutionary algorithm (CCEA) approach to solve the model. First, the problem is decomposed into three subproblems for each of which the chromosome population is created correspondingly. Each chromosome in each population is represented as a permutation denoting the priority. Then an algorithm generating a solution from the combined set of chromosomes from each population is suggested. Also an algorithm evaluating the performance of a solution is suggested. An experimental study is carried out. The results show that our CCEA tends to generate better solutions than the previous CCEA as the problem size gets larger and that the permutation representation for chromosome used here is better than other representation.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2007년도 하계종합학술대회 논문집
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• pp.195-196
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• 2007

The purpose of this paper is to analyze the resource allocation problem in a self organizing network from the viewpoint of game theory. The main focus is to suggest the model and analyze a power control algorithm in wireless ad-hoc networks using non cooperative games. Our approach is based on a model for the level of satisfaction and utility a wireless user in a self organizing network derives from using the system. Using this model, we show a distributed power control scheme that maximizes utility of each user in the network. Formulating this as a non-cooperative game we will show the feasibility of such power control as well as existence of the Nash Equilibrium achieved by the non-cooperative game.

• 기술혁신연구
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• 제29권1호
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• pp.39-73
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• 2021

연구기관의 협력 네트워크 구조 및 특징은 기관의 학문적 성과에 영향을 미친다. 특히 한국의 정부출연연구기관은 선도적인 국가 연구개발 수행 주체로서 효율적인 협력 체제를 구축해야 할 필요가 있다. 본 연구는 효율적인 네트워크 구조로 논의되어 온 좁은 세상 구조와 노드 간 특징을 나타내는 중심성을 한국 과학기술계 정부출연연구기관 협력 네트워크에 적용하였다. 2010년~2019년 과학기술계 정부출연연구기관의 논문 데이터를 바탕으로 좁은 세상 구조적 특징 및 중심성과 논문 성과 간 관계를 네트워크 분석과 Feasible GLS 회귀모형을 이용하여 분석하였다. 그 결과, 정부출연연구기관 협력 네트워크는 좁은 세상 구조를 취할수록 학문적 성과에 유의미한 양의 성과를 거둘 수 있는 것으로 나타났다. 또한, 직접적인 연결 정도를 나타내는 중심성은 양의 유의성을 보였으나, 중개자 정도를 나타내는 중심성은 유의하지 않거나 음으로 유의했다. 교류 협력하는 기관의 수가 많을수록 논문 성과가 높았으며, 협력의 중심지 역할을 하는 기관과 협력 관계인 기관의 성과가 높다. 또한, 정부출연연구기관의 협력 네트워크가 좁은 세상의 특성을 강하게 가질수록 연구 성과 창출에 효과적이라는 것을 규명하였다. 본 연구는 기존에 효율적인 네트워크 구조로서 논의되던 좁은 세상 구조와 중심성을 정부출연연구기관 협력 네트워크에 적용하고 성과와의 관계를 실증 분석할 뿐 아니라 정부출연연구기관 간 연구개발 협력관련 정책 및 전략 수립에 시사점을 제시한다.

• 한국문헌정보학회지
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• 제42권3호
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• pp.233-257
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• 2008

다양한 해외 디지털 지식정보의 통합 및 협력 네트워크를 구축하기 위해서 디지털 정보자원의 통합 개방, 참여, 기술이 핵심적인 부분이라고 할 수 있다. 해외 협력망인 WDL, IPL, TEL의 사례를 첫째 장서의 규모, 협력, 주제화범위의 내용적인 측면, 둘째 협력의 목적 등의 정책적인 측면, 셋째 표준화, 수집 및 선정, 검색, 메타데이터 관리의 기술적인 측면, 넷째 운영 조직 및 자금 수준의 운영적인 측면으로 분석하였다 분석된 내용 및 결과는 다양한 장서분석 기준과 접목하여 해외 협력을 위한 장서 분석 기준을 도출에 활용하였다. 분석된 기준은 디지털 정보자원의 핵심 부분인 디지털 정보자원에 대한 통함 체계를 지원하는 통합 모델, 협력 및 공유를 위한 자원 및 시스템 공유의 개방 모델 이용자 참여를 통한 지식정보의 창출, 지식정보자원의 공유할 수 있는 기술 모델 등 네 가지 모델로 구분하여 각 세부 평가 기준을 노출하는 데 활용하였다. 도출된 기준은 실제 장서분석 평가를 통하여 해외 협력망 구축을 위한 발전 전략 및 방향을 설정하기 위한 현재 장서에 대한 평가와 장서 관리를 위한 원칙과 모델을 제안하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3447-3469
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• 2019

It is well-known that the cooperative communication and error control technology can improve the network performance, but most existing cooperative MAC protocols have not focused on how to cope with the contention process caused by cooperation and how to reduce the bad influence of channel packet error rate on the system performance. Inspired by this, this paper first modifies and improves the basic rules of the IEEE 802.11 Medium Access Control (MAC) protocol to optimize the contention among the multi-relay in a cooperative ARQ scheme. Secondly, a hybrid ARQ protocol with soft combining is adopted to make full use of the effective information in the error data packet and hence improve the ability of the receiver to decode the data packet correctly. The closed expressions of network performance including throughput and average packet transmission delay in a saturated network are then analyzed and derived by establishing a dedicated two-dimensional Markov model and solving its steady-state distribution. Finally, the performance evaluation and superiority of the proposed protocol are validated in different representative study cases through MATLAB simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권3호
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• pp.273-288
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• 2010

In this paper, we propose a cooperative multi-relay scheme for a secondary system to achieve spectrum access along with a primary system. In the primary network, a primary transmitter (PT) transmits the primary signal to a primary receiver (PR). In the secondary network, N secondary transmitter-receiver pairs (ST-SR) selected by a centralized control unit (CCU) are ready to assist the primary network. In particular, in the first time slot, PT broadcasts the primary signal to PR, which is also received by STs and SRs. At STs, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions of the available power to the primary and secondary signals respectively. The combined signal is then broadcasted by STs in a predetermined order. In order to achieve diversity gain, STs, SRs and PT will combine received replicas of the primary signal, using selection combining technique (SC). We derive the exact outage probability for the primary network as well as the secondary network. The simulation results are presented to verify the theoretical analyses.