• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권4호
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• pp.1904-1921
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• 2019

In this paper, we investigate the problem of secure communications in multiple-input-multiple-output interference networks from the perspective of physical layer security. Specifically, the legitimate transmitter-receiver pairs are divided into different categories of active and inactive. To enhance the security performances of active pairs, inactive pairs serve as cooperative jammers and broadcast artificial noises to interfere with the eavesdropper. Besides, active pairs improve their own security by using joint transceivers. The encoding of active pairs and inactive pairs are designed by maximizing the difference of mean-squared errors between active pairs and the eavesdropper. In detail, the transmit precoder matrices of active pairs and inactive pairs are solved according to game theory and linear programming respectively. Experimental results show that the proposed algorithm has fast convergence speed, and the security performances in different scenarios are effectively improved.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2022년도 추계학술대회
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• pp.600-602
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• 2022

본 논문은 드론 운항 거리를 20 km까지 확장할 수 있도록 과학기술정보통신부가 추진하고 있는 433 MHz 대역에서의 혼신과 간섭을 물리 계층 수준에서 제거하는 알고리즘을 제안한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2626-2646
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• 2014

This study presents a power and Physical Resource Blocks (PRBs) joint allocation algorithm to coordinate uplink (UL) interference in the device-to-device (D2D) underlaying Long Term Evolution-Advanced (LTE-A) networks. The objective is to find a mechanism to mitigate the UL interference between the two subsystems and maximize the weighted sum throughput as well. This optimization problem is formulated as a mixed integer nonlinear programming (MINLP) which is further decomposed into PRBs assignment and transmission power allocation. Specifically, the scenario of applying imperfect channel state information (CSI) is also taken into account in our study. Analysis reveals that the proposed PRBs allocation strategy is energy efficient and it suppresses the interference not only suffered by the LTE-A system but also to the D2D users. In another side, a low-complexity technique is proposed to obtain the optimal power allocation which resides in one of at most three feasible power vectors. Simulations show that the optimal power allocation combined with the proposed PRBs assignment achieves a higher weighted sum throughput as compared to traditional algorithms even when imperfect CSI is utilized.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.494-513
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• 2019

A multi-channel access problem based on hypergraph model in ultra-dense small cell networks is studied in this paper. Due to the hyper-dense deployment of samll cells and the low-powered equipment, cumulative interference becomes an important problem besides the direct interference. The traditional binary interference model cannot capture the complicated interference relationship. In order to overcome this shortcoming, we use the hypergraph model to describe the cumulative interference relation among small cells. We formulate the multi-channel access problem based on hypergraph as two local altruistic games. The first game aims at minimizing the protocol MAC layer interference, which requires less information exchange and can converge faster. The second game aims at minimizing the physical layer interference. It needs more information interaction and converges slower, obtaining better performance. The two modeled games are both proved to be exact potential games, which admit at least one pure Nash Equilibrium (NE). To provide information exchange and reduce convergecne time, a cloud-based centralized-distributed algorithm is designed. Simulation results show that the proposed hypergraph models are both superior to the existing binary models and show the pros and cons of the two methods in different aspects.

• ETRI Journal
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• 제39권2호
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• pp.255-263
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• 2017

This paper proposes a graph-theatrical approach to optimize spatial reuse by adopting a technique that quantizes the channel information into single bit sub-messages. First, we introduce an interference graph to model the network topology. Based on the interference graph, the computational requirements of the algorithm that computes the optimal spatial reuse factor of each user are reduced to quasilinear time complexity, ideal for practical implementation. We perform a resource allocation procedure that can maximize the efficiency of spatial reuse. The proposed spatial reuse scheme provides advantages in beamforming systems, where in the interference with neighbor nodes can be mitigated by using directional beams. Based on results of system level measurements performed to illustrate the physical interference from practical millimeter wave wireless links, we conclude that the potential of the proposed algorithm is both feasible and promising.

• 한국전문물리치료학회지
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• 제21권4호
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• pp.34-39
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• 2014

The purpose of this study was to examine the effect of three cognitive tasks on gait at a preferred walking speed, and at a fast speed, using dual-task methodology. A total of 29 stroke patients participated in the study. All 29 subjects performed 2 motor tasks (10-meter walk task and timed up and go task each at a preferred and a fast speed) and three cognitive tasks [Stroop, word list generation (WLG), serial subtraction (SS)] under dual-task conditions [cognitive-motor interference (CMI)] in a randomized order. Gait speeds were measured in six different conditions. A repeated-measure analysis of variance was employed to compare the results of the Stroop training, WLG, and SS tasks during preferred and fast walking. A Bonferroni adjustment use for post hoc analysis. The level of statistical significance was set at ${\alpha}=.05$. A CMI effect occurred for performance of a 10-meter walking task at two different speed and a cognitive task (p<.05). Stroop had a significantly greater effect than SS and WLG (p<.05). The timed up and go task was affected when performed with fast walking speed during Stroop cognitive task (p<.05), but was not affected if performed with preferred walking speed during a cognitive task (p>.05). This study showed that CMI of Stroop can be used as a rehabilitation program for stroke patients.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.28-38
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• 2001

A numerical method for the assessment and correction of tunnel wall interference effects on forced-oscillation testing is presented. The method is based on the wall pressure signature method using computed wall pressure distributions. The wall pressure field is computed using unsteady three-dimensional full Navier-Stokes solver for a 70-degree pitching delta wing in a wind tunnel. Approximately-factorized alternate direction implicit (AF-ADI) scheme is advanced in time by solving block tri-diagonal matrices. The algebraic Baldwin-Lomax turbulence, model is included to simulate the turbulent flow effect. Also, dual time sub-iteration with, local, time stepping is implemented to improve the convergence. The computed wall pressure field is then imposed as boundary conditions for Euler re-simulation to obtain the interference flow field. The static computation shows good agreement with experiments. The dynamic computation demonstrates reasonable physical phenomena with a good convergence history. The effects of the tunnel wall in upwash and blockage are analyzed using the computed interference flow field for several reduced frequencies and amplitudes. The corrected results by pressure signature method agree well with the results of free air conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권4호
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• pp.1679-1691
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• 2016

Successive interference cancellation (SIC) is an effective means of multi-packet reception to combat interference at the physical layer. We investigate the joint optimization issue of channel access and power control for capacity maximization in SIC-enabled wireless networks. We propose a new interference model to characterize the sequential detection nature of SIC. Afterward, we formulize the joint optimization problem, prove it to be a nondeterministic polynomial-time-hard problem, and propose a novel approximation approach based on the genetic algorithm (GA). Finally, we discuss the design and parameter setting of the GA approach and validate its performance through extensive simulations.

• Journal of Communications and Networks
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• 제14권5호
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• pp.487-494
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• 2012

A standard paradigm for the allocation of wireless resources in communication demands symmetry, that is, all users are assumed to be on equal footing and hence get equal shares of the system's communication capabilities. However, there are situations in which "prime users" should be given priority, as for example in the transmission of emergency messages. We examine prioritization policies that could be implemented at the physical layer and propose a new one, termed interference priority (IP), which is shown to have excellent performance. We evaluate the performance of these prioritization techniques both in controlled settings and within the context of a full cellular system and discuss the impact of prioritized use of resources on the unprioritized users.

• Perspectives in Nursing Science
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• 제15권1호
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• pp.18-28
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• 2018

Purpose: This study was designed to explore the levels of physical activity and fatigue among nurses and to identify the relationship between these variables. Methods: Participants were 89 nurses working at an intensive care unit and an operating room in a children's hospital. Data were collected using self-reported questionnaires including the International Physical Activity Questionnaire and Brief Fatigue Inventory. Results: Most of the nurses' physical activity was work related, and there was a significant difference according to the working unit. Nurses with higher work stress and lower job satisfaction showed higher levels of fatigue than their counterparts did. Work-related physical activity and the interference of fatigue with relationships were related positively, whereas transport and leisure time physical activity were negatively related to usual fatigue and the interference of fatigue with life enjoyment. Conclusion: The levels of physical activity and fatigue of nurses were higher than those observed among other populations. The appropriate level of physical activity for these nurses needs to be investigated carefully. Also, in the intervention for nurses' fatigue, their level of work-related and leisure-time physical activity should be considered separately, and their work environment and psychological satisfaction level should be included.