• Journal of Communications and Networks
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• v.11 no.2
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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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• v.13 no.5
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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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• v.17 no.2
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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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• v.13 no.1
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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.

• Korean Management Science Review
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• v.29 no.2
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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.

• Proceedings of the IEEK Conference
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• 2007.07a
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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.

• Journal of Technology Innovation
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• v.29 no.1
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• pp.39-73
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• 2021

The cooperative network structure influences the academic performance of the research institute. In particular, South Korea's Government-Funded Research Institutes(GRI) need to establish an efficient cooperative system as a leading national R&D implementer. This study applied the Small World structure, which has been discussed as an efficient network structure, and the centrality of representing the characteristics of nodes to the cooperative network of GRI in Korea. Based on the SCIE published data from 2010 to 2019, we analyze how the Small World characteristics and centrality of GRI contribute to academic performance using a network analysis and Feasible GLS regression. The GRI cooperative network has shown that the Small World network structure facilitates the academic performance. In addition, centrality indicating the degree of direct connection showed positive significance, but centrality indicating the degree of intermediary was not significant or negative. The results of this study explain that the higher the number of institutions that exchange and cooperate, the higher the academic performance, and the higher the performance of the institutions that serve as the center of cooperation. In addition, it was established that the stronger the cooperative network of GRIs have the characteristics of Small World, the more effective it is to create research results. This study applies centrality and Small World previously discussed as an efficient network structure to the GRI cooperation network and provide implications for establishing policies and strategies related to R&D cooperation among GRIs.

• Journal of the Korean Society for Library and Information Science
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• v.42 no.3
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• pp.233-257
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• 2008

The integration, openness, participation, and technology are essential elements of digital information resources in order to establish an unified and cooperative network of various digital knowledge-information abroad. This study analyzes policies, technologies and administrative aspects of international cooperative networks such as WDL, IPL, TEL. Based on the analysis, a number of collection standards for international cooperation are drawn. Analyzed standards are divided into four different aspects and applied to produce detailed appraisal standards for digital knowledge-information. In conclusion, in order to map out strategies and policies for developing an international cooperative network, the study proposes a number of principles and models for making an appraisal of collections.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.7
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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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• v.4 no.3
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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.