• Journal of Korea Society of Digital Industry and Information Management
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• 제14권3호
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• pp.77-85
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• 2018

Multi-User Multiple-Input Multiple-Output (MU-MIMO) is the core technology for improving the channel capacity compared to Single-User MIMO (SU-MIMO) by using multiuser gain and spatial diversity. Key problem for the MU-MIMO is the user selection which is the grouping the users optimally. To solve this problem, we adopt Extreme Value Theory (EVT) at the beginning of the proposed algorithm, which defines a primary user set instead of a single user that has maximum channel power according to a predetermined threshold. Each user in the primary set is then paired with all of the users in the system to define user groups. By comparing these user groups, the group that produces a maximum sum rate can be determined. Through computer simulations, we have found that the proposed method outperforms the conventional technique yielding a sum rate that is 0.81 bps/Hz higher when the transmit signal to noise ratio (SNR) is 30 dB and the total number of users is 100.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 한국해양정보통신학회 2010년도 추계학술대회
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• pp.141-144
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• 2010

OSA(Opportunistic Spectrum Access) allows secondary users not having a license for spectrum usage to opportunistically occupy an idle spectrum owned by a licensee named primary users. We propose two OSA schemes for un-slotted secondary users exploiting spectrum opportunities in un-slotted primary networks. We provide mathematical analysis and simulation results to reveal the impact of various system parameters.

• ETRI Journal
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• 제42권6호
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• pp.846-858
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• 2020

The non-orthogonal multiple access (NOMA) technique offers throughput improvement to meet the demands of the future generation of wireless communication networks. The objective of this work is to further improve the throughput by including an underlay cognitive radio network with an existing multi-carrier NOMA network, using cooperative communication. The throughput is maximized by optimal resource allocation, namely, power allocation, subcarrier assignment, relay selection, user pairing, and subcarrier pairing. Optimal power allocation to the primary and secondary users is accomplished in a way that target rate constraints of the primary users are not affected. The throughput maximization is a combinatorial optimization problem, and the computational complexity increases as the number of users and/or subcarriers in the network increases. To this end, to reduce the computational complexity, a dynamic network resource allocation algorithm is proposed for combinatorial optimization. The simulation results show that the proposed network improves the throughput.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제49권8호
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• pp.46-51
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• 2012

In this paper, we investigate the power allocation for cognitive relay networks. Cognitive relay networks offer not only increasing spectral efficiency by spectrum sharing but also extending the coverage through the use of relays. For spectrum sharing, conventional works have assumed that secondary users know perfect channel information between the secondary and primary users. However, this channel information may be outdated at the secondary user because of the time-varying properties or feedback latency from the primary user. This causes the violation for interference constraint, and the secondary user cannot share the spectrum of the primary after all. To overcome this problem, we propose the power allocation scheme for the secondary user under the allowable primary user's outage probability constraint. Since the proposed power allocation scheme does not use the instantaneous channel information, the secondary users have lower feedback burden. In addition, the proposed scheme is also robust to the outdated channel environment.

• Journal of Internet Computing and Services
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• 제12권1호
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• pp.1-10
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• 2011

The spectrum sensing is one of the fundamental functions to realize the cognitive radios. One of problems in the spectrum sensing is that the performance of spectrum sensing can be degraded due to fading and shadowing. In order to overcome the problem, cooperative spectrum sensing method is proposed, which uses a distributed detection model and can increase sensing performance. However, the performance of cooperative spectrum sensing can be still affected by the interference factors such as obstacle and malicious user. Especially, most of cooperative spectrum sensing methods only considered the stationary primary user. In the ubiquitous environment, however the mobile primary users should be considered. In order to overcome the aforementioned problem, in this paper we propose a robust spectrum detection method based on localization where we estimate the location of the mobile primary user, and then based on the location and transmission range of primary user we detect interference users if there are, and then the local sensing reporting from detected interference users are excluded in the decision fusion process. Through simulation, it is shown that the sensing performance of the proposed scheme is more accurate than that of conventional other schemes

• The Journal of Korean Institute of Communications and Information Sciences
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• 제34권9A호
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• pp.697-703
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• 2009

Cognitive radios are typically known to exploit vacant spectrum resources in order not to interfere with primary communication systems. However, cognitive radios may not be able to secure a clear spectrum band in a bustling spectrum band. Underlay spectrum sharing provides a way to cope with such a spectrum sharing problem. Cognitive radios share the same spectrum band with the spectrum licensees, i.e., primary users, by adjusting signal transmission power so as not to severely deteriorate the performance of the primary users. We propose an underlay spectrum sharing policy leveraging uplink spectrum resource to be used in a cellular network. A pair of end terminals attempts to establish a direct point-to-point link, and perform as cognitive radios in the sense that they share the uplink radio resource of other primary users. We formulate the transmit power constraints of the cognitive radios and propose a practical uplink band sharing framework. Our simulation results demonstrate that such an uplink sharing underlay direct link can enhance the throughput performance of point-to-point link with low overhead.

• Journal of information and communication convergence engineering
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• 제12권2호
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• pp.97-103
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• 2014

In spectrum sensing, there is a tradeoff between the probability of missed detection and the probability of a false alarm according to the value of the sensing threshold. Therefore, it is important to determine the sensing threshold suitable to the environment of cognitive radio networks. In this study, we consider a cognitive radio-based ad hoc network where secondary users directly communicate by using the same frequency band as the primary system and control their transmit power on the basis of the distance between them. First, we investigate a condition in which the primary and the secondary users can share the same frequency band without harmful interference from each other, and then, propose an algorithm that controls the sensing threshold dynamically on the basis of the transmit power of the secondary user. The analysis and simulation results show that the proposed sensing threshold control algorithm has low probabilities of both missed detection and a false alarm and thus, enables optimized spectrum sharing between the primary and the secondary systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권1호
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• pp.287-304
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• 2012

Spectrum sensing is an important functionality for cognitive users to look for spectrum holes before taking transmission in dynamic spectrum access model. Unlike previous works that assume perfect knowledge of the SNR of the signal received from the primary user, in this paper we consider a realistic case where the SNR of the primary user's signal is unknown to both fusion center and cognitive radio terminals. A Kalman filter based adaptive Takagi and Sugeno's fuzzy system is designed to make the global spectrum sensing decision based on the observed energies from cognitive users. With the capacity of adapting system parameters, the fusion center can make a global sensing decision reliably without any requirement of channel state information, prior knowledge and prior probabilities of the primary user's signal. Numerical results prove that the sensing performance of the proposed scheme outperforms the performance of the equal gain combination based scheme, and matches the performance of the optimal soft combination scheme.

• International journal of advanced smart convergence
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• 제13권2호
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• pp.258-266
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• 2024

E-learning systems have proliferated in recent years, particularly in the wake of the global COVID-19 pandemic. For kids, there isn't a specific online learning platform available, though. To do this, new conceptual models of training and learning software that are adapted to the abilities and preferences of end users must be created. Young pupils: those in kindergarten, preschool, and elementary school are unique subjects with little research history. From the standpoint of software technology, young students who have never had access to a computer system are regarded as specific users with high expectations for the functionality and interface of the software, social network connectivity, and instantaneous Internet communication. In this study, we suggested creating an electronic learning management system that is web-based and appropriate for primary school pupils. User-centered design is the fundamental technique that was applied in the development of the system that we are proposing. Test findings have demonstrated that students who are using the digital environment for the first time are studying more effectively thanks to the online learning management system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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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.