• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.2
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• pp.29-34
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• 2011

In this paper, we propose antenna and relay selection system by considering channel environment between nodes. Each node has multiple antennas in each hop. And, we analyze the performance of proposed system. A General MIMO system receives signals through multiple channels and obtains diversity gain. But MIMO system causes performance degradation due to poor received signals. The proposed system consider transmitters-relays channels, relays-receivers channels and select a best channel. This channel selection prevents performance degradation and increase total system's performance. Therefore, we must select best antennas and a best relay, simultaneously.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.2
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• pp.215-220
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• 2012

Recently, one of the research topics is wireless Ad-Hoc network minimizing power consumption because of limited power. We propose optimal power allocation scheme of each transmit node and derive performance analysis of system that recently designed Double opportunistic relay system which fixed branch receiver to use more than efficient power consumption. Optimal power location scheme is shown that outage probability has always better performance than equal power allocation. Furthermore, we are known that outage probability is minimized by increasing average transmit relays to obtain the diversity gain when average channel power gain is less.

• ETRI Journal
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• v.40 no.5
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• pp.613-623
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• 2018

The instability of operational channels on cognitive radio networks (CRNs), which is due to the stochastic behavior of primary users (PUs), has increased the complexity of the design of the optimal routing criterion (ORC) in CRNs. The exploitation of available opportunities in CRNs, such as the channel diversity, as well as alternative routes provided by the intermediate nodes belonging to routes (internal backup routes) in the route-cost (or weight) determination, complicate the ORC design. In this paper, to cover the channel diversity, the CRN is modeled as a multigraph in which the weight of each edge is determined according to the behavior of PU senders and the protection of PU receivers. Then, an ORC for CRNs, which is referred to as the stability probability of communication between the source node and the destination node (SPC_SD), is proposed. SPC_SD, which is based on the obtained model, internal backup routes, and probability theory, calculates the precise probability of communication stability between the source and destination. The performance evaluation is conducted using simulations, and the results show that the end-to-end performance improved significantly.

• Journal of Information Processing Systems
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• v.14 no.2
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• pp.286-308
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• 2018

The availability of powerful and sensor-enabled mobile and Internet-connected devices have enabled the advent of the ubiquitous sensor network (USN) paradigm. USN provides various types of solutions to the general public in multiple sectors, including environmental monitoring, entertainment, transportation, security, and healthcare. Here, we explore and compare the features of wireless sensor networks and USN. Based on our extensive study, we classify the security- and privacy-related challenges of USNs. We identify and discuss solutions available to address these challenges. Finally, we briefly discuss open challenges for designing more secure and privacy-preserving approaches in next-generation USNs.

• Journal of information and communication convergence engineering
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• v.15 no.1
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• pp.14-20
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• 2017

In this paper, we discuss physical layer security techniques in downlink networks, including eavesdroppers. The main objective of using physical layer security is delivering a perfectly secure message from a transmitter to an intended receiver in the presence of passive or active eavesdroppers who are trying to wiretap the information or disturb the network stability. In downlink networks, based on the random feature of channels to terminals, opportunistic user scheduling can be exploited as an additional tool for enhancing physical layer security. We introduce user scheduling strategies and discuss the corresponding performances according to different levels of channel state information (CSI) at the base station (BS). We show that the availability of CSI of eavesdroppers significantly affects not only the beamforming strategy but also the user scheduling. Eventually, we provide intuitive information on the effect of CSI on the secrecy performance by considering three scenarios: perfect, imperfect, and absence of eavesdropper's CSI at the BS.

• Journal of information and communication convergence engineering
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• v.13 no.4
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• pp.221-227
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• 2015

Spectrum sensing plays an essential role in a cognitive radio network, which enables opportunistic access to an underutilized licensed spectrum. In conventional cooperative spectrum sensing (CSS), all cognitive users (CUs) in the network spend the same amount of time on spectrum sensing and waste time in remaining silent when other CUs report their sensing results to the fusion center. This problem is solved by the superposition cooperative spectrum sensing (SPCSS) scheme, where the sensing time of a CU is extended to the reporting time of the other CUs. Subsequently, SPCSS assigns the CUs different sensing times and thus affects both the sensing performance and the throughput of the system. In this paper, we propose an algorithm to determine the optimal sensing time of each CU for SPCSS that maximizes the achieved system throughput. The simulation results prove that the proposed scheme can significantly improve the throughput of the cognitive radio network compared with the conventional CSS.

• Journal of Distribution Research
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• v.4 no.1
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• pp.93-122
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• 1999

Long-term relationship in distribution channels has been emphasized in the former researches. But many researches and literatures have not focused on how to achieve and maintain long-term relationship. To achieve and maintain long-term relationship, this study pays attention to the role of trust and commitment. The purpose of this study is explaining the relation between trust and commitment with the mutual perspectives of retailer and supplier. Research results indicate that trust has an effect on commitment, trust has two levels of firm and a responsible person, and perception of partners commitment has an effect on trust in two levels. And it shows that to increase perception of commitment, increasing commitment, quality of communication, satisfaction, reputation, and decreasing opportunistic behavior should be considered.

• Journal of Communications and Networks
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• v.14 no.5
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• pp.554-565
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• 2012

In this paper, we study a cross-layer and end-to-end optimization problem for the integrated wireless and wireline network that consists of one wireline core network and multiple wireless access networks. We consider joint end-to-end flow control/distribution at the transport and network layers and opportunistic scheduling at the data link and physical layers. We formulate a single stochastic optimization problem and solve it by using a dual approach and a stochastic sub-gradient algorithm. The developed algorithm can be implemented in a distributed way, vertically among communication layers and horizontally among all entities in the network, clearly showing what should be done at each layer and each entity and what parameters should be exchanged between layers and between entities. Numerical results show that our cross-layer and end-to-end optimization approach provides more efficient resource allocation than the conventional layered and separated optimization approach.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.8
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• pp.1770-1785
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• 2013

In this paper, a multi-hop transmission protocol based on parallel communication of secondary users (SUs) is proposed. The primary multi-hop network coexists with a set of SUs by cooperative spectrum sharing. The main optimization target of our protocol is the overall performance of the secondary system with the guarantee of the primary outage performance. The energy consumption of the primary system is reduced by the cooperation of SUs. The aim of the primary source is to communicate with the primary destination via a number of primary relays. SUs may serve as extra decode-and-forward relays for the primary network. When an SU acts as a relay for a primary user (PU), some other SUs that satisfy the condition for parallel communication are selected to simultaneously access the primary spectrum for secondary transmissions. For the proposed protocol, two opportunistic routing strategies are proposed, and a search algorithm to select the SUs for parallel communication is described. The throughput of the SUs and the PU is illustrated. Numerical results demonstrate that the average throughput of the SUs is greatly improved, and the end-to-end throughput of the PU is slightly increased in the proposed protocol when there are more than seven SUs.

• CRM연구
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• v.3 no.2
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• pp.21-41
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• 2010

The current research was conducted to examine the factors that affect outsourcing performances, and further investigate whether a discrepancy in performance exists between the medical institutions and hotel service institutions. The study surveyed both medical and hotel administrators for approximately two months, who managed outsourcing tasks. Total of 325 responses out of 350 distributed were collected. However, due to inadequate responses, six responses were excluded, amounting to total of 319 (155 medical institutions, 164 hotels) valid responses included in the final analysis. First, the informal outsourcing relationships between representatives of outsourcing service seekers and providers did not appear to have significant effects in terms of the levels of trust in neither medical institutions nor hotel industries. However, the relationships affected outsourcing degrees exclusively in medical institutions, showing the disparity between the two service institutions. This was explained due to the continuing long term efforts required to establish an informal relationship in medical institutions. Second, communication was shown to have positive effects on levels of trust in both medical institutions and hotel industries. This indicates a prominent outsourcing trait that emphasizes the significance of mutual cordial communication that contributes to establishing positive relationships. Third, opportunistic behavior of the outsourcing service providers appeared to negatively affect the levels of trust as well as outsourcing degrees for both medical and hotel industries. Therefore, opportunistic behaviors were found to have more tendencies to causing tension and discomfort rather than creating a relationship based on mutual credibility or conviviality. Fourth, the effect of service infrastructures on the level of trust did not appear to be significant on medical institutions, while showing positive influence on hotel industries. Additionally, service infrastructures were found to positively influence the outsourcing performance levels for both sectors. Fifth, trust between outsourcing service seekers and providers did not appear to have noticeable impact on the outsourcing degrees for either institution. On the contrary, trust appeared to have positive impacts on performance for both institutions. This further indicates that, when engaging in outsourcing, strengthening relationships through mutual partnership with outsourcing entities rather than establishing contractual relationships leads to improving the reciprocal trust, which in turn improves work results. Lastly the outsourcing degree of service seekers appeared to have positive impact on the outsourcing performance for both medical institutions and hotel industries, indicating the causal relationship between the affectability of outsourcing degrees and the following performance results.