• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5A
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• pp.450-456
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• 2011

In this paper, idle channel search schemes based on spectrum sensing are proposed for cognitive radio systems with multiple channels. Specifically, we propose a scheme for determining the order of sensing for multiple channels, for which the probability of each channel being idle is estimated every search interval. By performing sensing in the descending order of the probabilities, the time required for searching idle channels is expected to decrease. In addition, we combine the proposed scheme with a user grouping scheme to further improve the sensing performance. Simulation results show that the user grouping reduces the search time, although it degrades the reliability of detection. The proposed search scheme based on probability estimation of channel idleness is found to reduce the search time significantly as compared to the conventional random search scheme. We apply both the proposed search scheme and user grouping scheme to a cognitive radio system to validate the overall performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1C
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• pp.48-56
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• 2011

Cognitive radio (CR) systems have received significant interest as a promising solution to the spectral shortage problem through efficient use of the frequency spectrum by opportunistically exploiting unlicensed frequency bands. Orthogonal frequency division multiplexing (OFDM) is widely regarded as a highly promising candidate for CR systems. However, the frequency bands used by CR systems are expected to suffer from non-Gaussian noise, which considerably degrades the performance of the conventional OFDM carrier frequency offset (CFO) estimation schemes. In this paper, robust CFO estimation schemes for OFDM-based CR systems in non-Gaussian channels are proposed. Simulation results demonstrate that the proposed estimators offer robustness and substantial performance improvement over the conventional estimator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.391-400
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• 2009

Recently, cellular communication networks are migrating from 2G to 3G. Spectrum utilization tends to be inefficient during the transition. Cognitive radio (CR) technology can be a key solution to increase spectrum efficiency by allowing secondary networks to utilize frequency resource of primary networks. However, conventional CR approaches which do not utilize the frequency reuse factor of primary networks may incur degradation of whole network performance. In this paper, we propose a mechanism that a secondary network senses pilot signals of a primary network and select optimum frequency bands. In order to maximize whole network performance, we formulate an optimization problem subject to interference constraints for a primary network and present algorithms. Simulation results compare the proposed method with the conventional method. Our proposed method shows performance gain over the conventional method if channel variation of a primary network is dynamic and the frequency reuse factor of a primary network is high.

• Journal of Advanced Navigation Technology
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• v.16 no.5
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• pp.794-800
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• 2012

In this paper, we propose a scheme for improving not only the utilization of frequency bands in the guard channel scheme but also the dropping rate of cognitive radio user in the wireless cognitive radio-based cellular network. The proposed scheme enables cognitive radio users to utilize the guard channel for servicing only handoff calls in normal times, but cognitive radio users must vacate the frequency channel when handoff call appearing. At this time our scheme ensures their seamless services for cognitive radio users, by predicting handoff call's appearance by MMOSPRED (Multi-Media One Step Prediction) method and then reserving the demanded channels for spectrum handoff calls. Our simulations show that our scheme performs better than other schemes; GCS(Guard Channel Scheme) and a scheme without prediction in terms of cognitive users call's dropping rate and resource utilization efficiency.

• Journal of Internet Computing and Services
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• v.12 no.1
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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

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.3310-3316
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• 2011

Hematoxylin is the main component of Hematoxylon campechianum which has been utilized in the southern provinces of Korea as a folk remedy for diabetic complications. In the present study, to investigate the hypoglycemic mechanism of hematoxylin, the 2-deoxyglucose uptake and phospholipid metabolism were examined in sciatic nerves from three groups of rats : normal control, diabetic control, diabetic hematoxylin-treated group. Hematoxylin significantly reduced blood glucose levels in diabetic control rats. On a wet weight basis, the nerves from diabetic rats showed a 20% decrease in total phospholipid from that of controls and a relative decrease in phosphatidylinositide. Hematoxylin treatment increased the incorporation rate of 2-[3H] myo-inositol into total phosphoinositids in diabetic rat. The effectiveness were more potent in higher dose hematoxylin-treated rats than lower dose hematoxylin-treated rats. These results suggest that hematoxylin increases glucose transport and lipid metabolism by partially normalizing concerned with myo-inositol metabolism in diabetic rat. Therefore we propose that hematoxylin can be a promising candidate for diabetes medication.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.47-52
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• 2018

In this study, the effects of the heat treatment and multi-scale hierarchical structures on the durability of the nano-patterned functional PMMA(Poly(methyl-methacrylate)) film was evaluated. The heat treatments that consisted of high-pressure/high-temperature flat pressing and rapid cooling process were employed to improve mechanical property of the PMMA films. Multi-scale hierarchical structures were fabricated by thermal nanoimprint to protect nano-scale structures from the scratch. Examination on surface structures and functionalities such as wetting angle and transmittance revealed that the preopposed heat treatment and multi-scale hierarchical structures are effective to minimize surface damages.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.1
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• pp.77-82
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• 2020

As Korea enters an aging age, social efforts to improve the IADL of the elderly are increasing. In this study, to improve the performance of financial management activities that the elderly is particularly burdened, we aim to learn the elderly through ATM simulation education contents so that they can use ATM smoothly. To this end, interviews were conducted with seniors to derive four major financial activities (deposits, withdrawals, deposit inquiries and bank account arrangements), and developed tablet PC-based ATM education contents identical to the existing bank ATM interfaces. The experiment was conducted on 20 elderly people in the Elderly Day Care Center, and their satisfaction, fatigue and performance were measured before and after education. The results of this study can provide ATM design guidelines for the elderly who have difficulty using ATM.

• Journal of Digital Convergence
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• v.19 no.2
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• pp.143-150
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• 2021

Prior research on consumer psychology has primarily focused on when and why consumers exhibit impulsive behavior, such as impulse buying. This study focuses on physical stimulation during an impulse purchase as another meaningful factor. Specifically, this study examines whether thirst depletes cognitive resources. The results of two experiments show that impulse purchase tendency increases when consumers are thirsty (Exp. 1), and that the loss of self-control is based on the relationship between thirst and impulse purchase tendency (Exp. 2). These findings suggest that physical stimulation, such as thirst, may be a useful indicator of impulsive behavior in consumers.

• Journal of the Korea Society of Computer and Information
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• v.27 no.1
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• pp.83-89
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• 2022

As a representative technique of recommender systems, collaborative filtering has been successfully in service through many commercial and academic systems. This technique recommends items highly rated by similar neighbor users, based on similarity of ratings on common items rated by two users. Recently research on time-aware recommender systems has been conducted, which attempts to improve system performance by reflecting user rating time of items. However, the decay rate uniform to past ratings has a risk of lowering the rating prediction performance of the system. This study proposes a rating time-aware similarity measure between users, which is a novel approach different from previous ones. The proposed approach considers changes of similarity value over time, not item rating time. In order to evaluate performance of the proposed method, experiments using various parameter values and types of time change functions are conducted, resulting in improving prediction accuracy of existing traditional similarity measures significantly.