• Journal of Communications and Networks
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• 제17권4호
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• pp.406-418
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• 2015

Cognitive radio networks (CRNs) have emerged as a promising solution to the problem of spectrum under utilization and artificial radio spectrum scarcity. The paradigm of dynamic spectrum access allows a secondary network comprising of secondary users (SUs) to coexist with a primary network comprising of licensed primary users (PUs) subject to the condition that SUs do not cause any interference to the primary network. Since it is necessary for SUs to avoid any interference to the primary network, PU activity precludes attempts of SUs to access the licensed spectrum and forces frequent channel switching for SUs. This dynamic nature of CRNs, coupled with the possibility that an SU may not share a common channel with all its neighbors, makes the task of multicast routing especially challenging. In this work, we have proposed a novel multipath on-demand multicast routing protocol for CRNs. The approach of multipath routing, although commonly used in unicast routing, has not been explored for multicasting earlier. Motivated by the fact that CRNs have highly dynamic conditions, whose parameters are often unknown, the multicast routing problem is modeled in the reinforcement learning based framework of learning automata. Simulation results demonstrate that the approach of multipath multicasting is feasible, with our proposed protocol showing a superior performance to a baseline state-of-the-art CRN multicasting protocol.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.123-145
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• 2017

Due to the increasing demand for spectrum resources, cognitive radio networks and dynamic spectrum access draw a lot of research into efficiently utilizing limited spectrum resources. To set up cluster-based CR ad-hoc common channels, conventional methods require a relatively long time to successfully exchange the initialization messages. In this paper, we propose a fast and reliable common channel initialization protocol for CR ad-hoc networks. In the proposed method, the cluster head sequentially broadcasts a system activation signal through its available channels with a predetermined correlation pattern. To detect the cluster head's broadcasting channels and to join the cluster, each member node implements fast Fourier transform (FFT) and computes autocorrelation of an FFT bin sequence for each available channel of the member node. This is compared to the predetermined reference pattern. The join request and channel decision procedures are also presented in this paper. In a simulation study, the performance of the proposed method is evaluated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권11호
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• pp.4367-4386
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• 2015

The concept of Internet of Things (IoT) has shed new light on WSN technologies. MAC protocol issues improving the network performance are important in WSNs because of the increase in demand for various applications to secure spectrum resources. Cognitive radio (CR) technology is regarded as a solution to the problems in this future wireless network. In recent years, energy efficiency has become an issue in CR networks. However, few relevant studies have been conducted. In this paper, an energy-efficient non-overlapping channel MAC (ENC-MAC) for CR-enabled sensor networks (CRSNs) is proposed. Applying the dedicated control channel approach, ENC-MAC allows the SUs to utilize channels in a non-overlapping manner, and thus spectrum efficiency is improved. Moreover, the cooperative spectrum sensing that allows an SU to use only two minislots in the sensing phase is addressed to en-hance energy efficiency. In addition, an analytical model for evaluating the performance, such as saturation throughput, average packet delay, and network lifetime, is developed. It is shown in our results that ENC-MAC remarkably outperforms existing MAC protocols.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권5호
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• pp.1532-1553
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• 2014

Radio spectrum is a precious resource and characterized by fixed allocation policy. However, a large portion of the allocated radio spectrum is underutilized. Conversely, the rapid development of ubiquitous wireless technologies increases the demand for radio spectrum. Cognitive Radio (CR) methodologies have been introduced as a promising approach in detecting the white spaces, allowing the unlicensed users to use the licensed spectrum thus realizing Dynamic Spectrum Access (DSA) in an effective manner. This paper proposes a generalized framework for DSA between the licensed (primary) and unlicensed (secondary) users based on Continuous Time Markov Chain (CTMC) model. We present a spectrum access scheme in the presence of sensing errors based on CTMC which aims to attain optimum spectrum access probabilities for the secondary users. The primary user occupancy is identified by spectrum sensing algorithms and the sensing errors are captured in the form of false alarm and mis-detection. Simulation results show the effectiveness of the proposed spectrum access scheme in terms of the throughput attained by the secondary users, throughput optimization using optimum access probabilities, probability of interference with increasing number of secondary users. The efficacy of the algorithm is analyzed for both imperfect spectrum sensing and perfect spectrum sensing.

• Industrial Engineering and Management Systems
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• 제13권2호
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• pp.185-192
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• 2014

This study stems from the work of Lehman et al. (Ergonomics, 2001) which concluded that standing yields better work performance, and from the growing health trend of recommending the reduction of the amount of time spent in sitting (Owen et al., Exercise and Sport Science Reviews, 2010). Lajoie et al. (Experimental Brain Research, 1993) provided an initial significant contribution to a theory that standing requires a person to control balance, equating to demand higher productive output from the cognitive system than when a person is sitting. An assumption was formulated that standing position during class is feasible and can be adopted on the belief that it might contribute positive results to students' performance. The purpose of this study is to identify whether a body position during exams tested along with exposure durations has a significant effect on college students' performance. Mathematical analysis and reading comprehension exam was used to measure the cognitive performance of the students. Two factors, position and duration, were tested for significance with two levels each subjected to six replicates. Twenty-four students from the College of Engineering and Agro-Industrial Technology, University of the Philippines Los Ba$\tilde{n}$os were randomly selected. The experiment showed that the body position during exams is a significant factor for the Math exam, but insignificant for the Reading Comprehension exam.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권10호
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• pp.3810-3830
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• 2015

In this paper, we investigate the differential game theoretic approach for distributed dynamic cooperative power control in cognitive radio ad hoc networks (CRANETs). First, a payoff function is defined by taking into consideration the tradeoff between the stock of accumulated power interference to the primary networks and the dynamic regulation of the transmit power of secondary users (SUs). Specifically, the payoff function not only reflects the tradeoff between the requirement for quickly finding the stable available spectrum opportunities and the need for better channel conditions, but also reveals the impact of the differentiated types of data traffic on the demand of transmission quality. Then the dynamic power control problem is modeled as a differential game model. Moreover, we convert the differential game model into a dynamic programming problem to obtain a set of optimal strategies of SUs under the condition of the grand coalition. A distributed dynamic cooperative power control algorithm is developed to dynamically adjust the transmit power of SUs under grand coalition. Finally, numerical results are presented to demonstrate the effectiveness of the proposed algorithm for efficient power control in CRANETs.

• 한국인지과학회:학술대회논문집
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• 한국인지과학회 2006년도 춘계학술대회
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• pp.59-60
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• 2006

To date, there has been minimal researchregarding the cerebral activation of Korean language. There need the database for Korean language that is quite different from alphabetic system. This study examined the brain activation of picture naming, word reading, picture-word matching, and semantic categorization in Korean language. Moreover, we investigated the cortical activation pattern according to semantic demand for the above tasks.

• 한국수학교육학회지시리즈C:초등수학교육
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• 제27권3호
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• pp.227-246
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• 2024

이 연구에서는 한국, 미국, 호주 초등 수학 교과서의 자료와 가능성 영역에 제시된 과제의 인지적 요구 수준과 발문 유형을 비교·분석하였다. 과제의 인지적 요구 수준은 과제에서 요구하는 지식과 과정 및 사고 유형을 구분하여 분석하였고, 과제의 발문 유형과 더불어 과제의 정답 유형과 응답 유형을 분석하였다. 과제의 인지적 요구수준을 분석한 결과, 세 나라 모두 과제의 지식과 과정의 측면에서는 '표현'이, 사고 유형의 측면에서는 '개념/기능적용'의 비율이 가장 높게 나타난다는 공통점이 있었다. 이 외에도 사고 유형의 측면에서 그래프 학습과 가능성 학습에 있어 세 나라 교과서 과제의 차이점을 발견하였다. 발문 유형을 분석한 결과, 세 나라 모두 '관찰 추론 발문'의 비율이 가장 높았고, 다음으로 '사실 발문'의 비율이 높게 나타난다는 공통점이 있었다. '구성 발문'의 경우, 미국과 호주 교과서 과제와 우리나라 교과서 과제에 제시된 특징이 다르게 나타났다. 분석 결과에 비추어 초등학교 자료와 가능성 영역에서의 교과서 과제 구성에 대한 시사점을 제시하였다.

• 한국과학교육학회지
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• 제27권1호
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• pp.18-27
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• 2007

이 연구에서는 변칙사례에 의해 유발된 인지갈등과 비인지적 변인이 개념변화 과정에 미치는 영향과 변칙사례가 상황 흥미를 유발하는 과정을 조사하였다. 중학교 1학년 학생들이 연구에 참여하였다. 밀도 개념에 대해 오개념을 지닌 학생들을 선별하기 위해 선개념 검사를 실시하였다. 변칙사례에 대한 인지적 반응검사와 상황 흥미 검사를 실시하였다. CAl 프로그램을 통해 학습하게 한 후, 주의집중 검사, 노력 검사, 개념 검사를 실시하였다. 경로 분석 결과, 변칙사례에 의해 유발된 인지갈등이 상황 흥미를 유발하고 이것이 개념학습 과정에서의 학생들의 주의집중과 노력에 영향을 미쳐 개념변화를 일으키는 것으로 나타났다. 변칙사례에 의해 처음으로 유발되는 것은 새로움이며, 새로움은 직접적으로 또는 주의집중 요구, 탐구 의도, 순간적 즐거움을 경유하여 상황 흥미를 불러일으키는 것으로 나타났다. 새로움은 도전에 직접적인 영향을 주고, 도전은 직접적으로 또는 인지갈등을 통해 순간적 즐거움에 부정적인 영향을 줌으로써 전체 흥미를 감소시키기도 하였다. 그러나 이 경로의 계수는 전자의 경로의 계수보다 상대적으로 작았다. 이에 대한 교육적 함의를 논의하였다.

• 보건의료산업학회지
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• 제12권1호
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• pp.81-93
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• 2018

Objectives : This cross-sectional study aims to investigate the differences in general health status (GHS) and physical care burdens (PCB) of inpatient groups in long-term care hospitals (LTCH). Methods : The data of 228 patients were analyzed by integrating the electronic medical record (EMR) data of 2016, recorded by the nurses of hospitalized patients in the hospital. Results : There was a statistically significant difference in the GHS between the high-medical demand group and the other groups, but there was no difference in the GHS among other groups. The overall PCB was higher in the high-medical demand group than in the middle-medical demand, and cognitive impairment groups, but not in the problem behavioral group. Conclusions : The current classification of patient groups has shown limitations in terms of the basis of differential benefits of the groups. In particular, the PCB of the problem behavior group was not different from that of any group; hence, it should be adjusted through further study. To control the surge of medical care costs, it is necessary to improve the irrationality of the LTCH pay system in terms of the integration and continuity for elderly care.