• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.12
• /
• pp.5249-5267
• /
• 2016

Cognitive radio is an efficient technique to improve spectrum efficiency and relieve the pressure of spectrum resources. In this paper, we investigate the spectrum sensing period in cooperative relay cognitive radio networks; analyze the relationship between the available capacity and the signal-to-noise ratio of the received signal of second users, the target probability of detection and the active probability of primary users. Finally, we derive the closed form expression of the optimal spectrum sensing period in terms of maximum throughput. We simulate the probability of false alarm and available capacity of cognitive radio networks and compare optimal spectrum sensing period scheme with fixed sensing period one in these performance. Simulation results show that the optimal sensing period makes the cognitive networks achieve the higher throughput and better spectrum sensing performance than the fixed sensing period does. Cooperative relay cognitive radio networks with optimal spectrum sensing period can achieve the high capacity and steady probability of false alarm in different target probability of detection. It provides a valuable reference for choosing the optimal spectrum sensing period in cooperative relay cognitive radio networks.

• Journal of Communications and Networks
• /
• v.16 no.2
• /
• pp.193-201
• /
• 2014

In cognitive radio networks, the packet transmissions of the secondary users (SUs) can be interrupted randomly by the primary users (PUs). That is to say, the PU packets have preemptive priority over the SU packets. In order to enhance the quality of service (QoS) for the SUs, we propose a spectrum access strategy with an ${\alpha}$-Retry policy. A buffer is deployed for the SU packets. An interrupted SU packet will return to the buffer with probability ${\alpha}$ for later retrial, or leave the system with probability (1-${\alpha}$). For mathematical analysis, we build a preemptive priority queue and model the spectrum access strategy with an ${\alpha}$-Retry policy as a two-dimensional discrete-time Markov chain (DTMC).We give the transition probability matrix of the Markov chain and obtain the steady-state distribution. Accordingly, we derive the formulas for the blocked rate, the forced dropping rate, the throughput and the average delay of the SU packets. With numerical results, we show the influence of the retrial probability for the strategy proposed in this paper on different performance measures. Finally, based on the trade-off between different performance measures, we construct a cost function and optimize the retrial probabilities with respect to different system parameters by employing an iterative algorithm.

• Journal of the Korea Safety Management & Science
• /
• v.14 no.2
• /
• pp.55-63
• /
• 2012

As of Dec. 31, 2011, the number of nation's escalators accounts for 24,248 units, 5.4% of total elevators in our country, safety accidents take up as many 539 case, 55.2% of total elevators' safety accidents. Escalator safety accidents show high incident ratio of primary safety accidents breaking out by users' careless and abnormal use type, taking up multi-caused accident, which mainly take place from vulnerable age groups such as children under 13, and elders above 65. The Government will have to devote itself for policy and support for the establishment of safety management system fit for current state, the revitalization of preventive education for safety accident, the enhancement of safety awareness to escalators' users in order to secure escalator safety environment on an international level and support domestic industrial development.

• ETRI Journal
• /
• v.38 no.6
• /
• pp.1153-1162
• /
• 2016

This paper addresses the resource allocation (RA) problem in multi-cell cognitive radio networks. Besides the interference power threshold to limit the interference on primary users PUs caused by cognitive users CUs, a proportional fairness constraint is used to guarantee fairness among multiple cognitive cells and the impact of imperfect spectrum sensing is taken into account. Additional constraints in typical real communication scenarios are also considered-such as a transmission power constraint of the cognitive base stations, unique subcarrier allocation to at most one CU, and others. The resulting RA problem belongs to the class of NP-hard problems. A computationally efficient optimal algorithm cannot therefore be found. Consequently, we propose a suboptimal RA algorithm composed of two modules: a subcarrier allocation module implemented by the immune algorithm, and a power control module using an improved sub-gradient method. To further enhance algorithm performance, these two modules are executed successively, and the sequence is repeated twice. We conduct extensive simulation experiments, which demonstrate that our proposed algorithm outperforms existing algorithms.

• Korean Journal of Health Education and Promotion
• /
• v.26 no.2
• /
• pp.63-73
• /
• 2009

Objectives: The purpose of this study was to identify the degree of internet addiction and factors affecting internet addiction in elementary school students. Methods: A cross-sectional survey design was employed in this study. The subjects were 378 students who were recruited from 5th and 6th grade in five elementary schools in J city, Korea. Data were collected through a structured questionnaire. The data were analyzed using the SPSS Win 10.1 program. Results: Of the children, 51.9% reported being average online users, 45.5%, heavy online users, and 2.6%, internet addicted. The level of internet addiction of subjects correlated significantly with the behavioral activation system, behavioral inhibition system, family cohesion, and learned self-concept, but not family adaptability. Significant predictors influencing internet addiction were the behavioral activation system, learned self-concept, and family cohesion. These predictors accounted for 22% of variance in internet addiction. Conclusion: This study found that the behavioral activation system in personality aspects, family cohesion in the family system, and learned self-concept are primary factors that explain internet addiction among elementary students. We suggest these results be used to develop an online addiction prevention or treatment program.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.7 no.6
• /
• pp.1471-1477
• /
• 2012

Social Network has common functions such as acting as primary platforms smoothing the sharing and distribution by combination with various contents. Hence, questionnaire has been conducted to users of all of Twitter, Facebook and KakaoStory, and the factors affected by each service are presented by statistical analyses of the survey and the results are resolved by dividing them into complete and instrumental social capital. This study will be able to provide a standard for users to select Social Network according to their purposes and contribute to development of new Social Network or improvement of existing ones.

• ETRI Journal
• /
• v.37 no.3
• /
• pp.460-470
• /
• 2015

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM-based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify-and-Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF-relay, and incremental relaying modes. The outage performance of the proposed AF relay-based CR network is proven to be better than that of direct mode.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.9 no.4
• /
• pp.123-127
• /
• 2009

Cognitive Radio rules provide that the user outside service region should not utilize communication system in Cognitive Radio environment. The reason why main user should use service without any loss and interference. If this rule is guaranteed, CR users are able to be offered enough services outside service region. In this paper, we target the issue which can operate practical cognitive systems even without causing excessive interference to legacy users. Also, we focus use on non-interference to the primary system rather than realizable benefits for the secondary systems, and using the proposed device. In this paper, we present the possible scheme using Bi-directional Beamforming Antenna.

• Perspectives in Nursing Science
• /
• v.8 no.2
• /
• pp.139-147
• /
• 2011

Purpose: An integrative literature review was done to identify the best interventions for older adults with dyslipidemia in an effort to promote nursing involvement in the prevention of statin-induced symptoms (SIS). Such awareness could increase the capacity of interventions by geriatric nurses using evidence-based practices in the reassessment of statin therapy. Methods: CINAHL, Pubmed, and ProQuest were searched using these terms: dyslipidemia in, elderly, statins, adverse effects, and quality of life. Eleven articles fitting the inclusion criteria were identified and analyzed. Results: The findings indicate no evidence for the benefit of statin therapy for morbidity/mortality in a high-risk primary prevention set-up, specifically in the elderly population. Although SIS prevails among older adults, there are limited data that confidently support this observation along with nursing interventions specifically for the geriatric nursing community. Conclusion: Future research is necessary to shift nursing intervention with statin users (specifically in older adults) from an illness-based intervention to a preventive care plan to provide optimal care based on evidence. It is essential to involve self-reporting, cooperation, and communication with health care professionals, specifically with geriatric nurses. Additional studies are needed to further direct practice interventions in elderly statin users.

• Journal of Satellite, Information and Communications
• /
• v.9 no.4
• /
• pp.20-25
• /
• 2014

In this paper, we provide efficient spectrum sensing technology for smooth use of frequency and energy charge of multi-copter. The proposed structures focus on improving performance of spectrum sensing that is based on Ad-hoc network. First, we explain basic principles and disadvantages of cooperative spectrum sensing and ad-hoc based spectrum sensing. To solve these problems, in this paper, we employ the beamforming technology that guarantees higher transmit primary users' signal power to secondary users in ad-hoc network. The performance of proposed algorithm is analyzed in terms of detection probabilities, and the results of this paper can be applied to the various ad-hoc based Cognitive Radio system.