• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권10호
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• pp.5168-5181
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• 2017

The popularity of augmented reality (AR) applications and games are in high demand. Currently, the best common platform to implement AR services is on a smartphone, as online games, navigators, personal assistants, travel guides are among the most popular applications of smartphones. However, the power consumption of an AR application is extremely high, and therefore, highly adaptable and dynamic low power control schemes must be used. Dynamic voltage and frequency scaling (DVFS) schemes are widely used in smartphones to minimize the energy consumption by controlling the device's operational frequency and voltage. DVFS schemes can sometimes lead to longer response times, which can result in a significant problem for AR applications. In this paper, an AR response time monitor is used to observe the time interval between the AR image input and device's reaction time, in order to enable improved operational frequency and AR application process priority control. Based on the proposed response time monitor and the characteristics of the Linux kernel's completely fair scheduler (CFS) (which is the default scheduler of Android based smartphones), a response time step control (RSC) scheme is proposed which adaptively adjusts the CPU frequency and interactive application's priority. The experimental results show that RSC can reduce the energy consumption up to 10.41% compared to the ondemand governor while reliably satisfying the response time performance limit of interactive applications on a smartphone.

• 대한전기학회논문지:전력기술부문A
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• 제49권2호
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• pp.62-69
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• 2000

In this paper, we design a GA-fuzzy precompensated PID controller for the load frequency control of two-area interconnected power system. Here, a fuzzy precompensated PID controller is designed as a fuzzy logic-based precompensation approach for PID controller. This scheme is easily implemented simply by adding a fuzzy precompensator to an existing PID controller. And we optimize the fuzzy precompensator with a genetic algorithm for complements the demerit such as the difficulty of the component selection of fuzzy controller, namely, scaling factor, membership function and control rules. Simulation results show that the proposed control technique is superior to a conventional PID control and a fuzzy precompensated PID control in dynamic responses about the load disturbances of power system and is convinced robustness reliableness in view of structure.

• 한국지진공학회논문집
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• 제24권5호
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• pp.219-232
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• 2020

The slip-weakening model developed by Ohnaka and Yamashita is extended over the breakdown zone by equating the scaling relationships for the breakdown zone and the whole rupture area. For the extension, the study uses the relationship between rupture velocity and radiation efficiency, which was derived in the theory of linear elastic fracture mechanics, and the definition of f_max given in the specific barrier model proposed by Papageorgiou and Aki. The results clearly show that the extended scaling relationship is governed by the ratio of rupture velocity to S wave velocity, and the velocity ratio can be determined by the ratio of characteristic frequencies of a Fourier amplitude spectrum, which are corner frequency, f_c, and source-controlled cut-off frequency, f_max, or vice versa. The derived relationship is tested by using the characteristic frequencies extracted from previous studies of more than 130 shallow crustal events (focal depth less than 25 km, M_W 3.0~7.5) that occurred in Japan. Under the assumption of a dynamic similarity, the rupture velocity estimated from f_max/f_c and the modified integral timescale give quite similar scale-dependence of the rupture area to that given by Kanamori and Anderson. Also, the results for large earthquakes show good agreement to the values from a kinematic inversion in previous studies. The test results also indicate the unavailability of the spectral self-similarity proposed by Aki because of the scale-dependent rupture velocity and the rupture velocity-dependent f_max/f_c; however, the results do support the local similarity asserted by Ohnaka. It is also remarkable that the relationship between the rupture velocity and f_max/f_c is quite similar to Kolmogorov's hypothesis on a similarity in the theory of isotropic turbulence.

• Journal of Communications and Networks
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• 제18권4호
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• pp.540-550
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• 2016

Since energy efficiency has become a significant concern for network infrastructure, next-generation network devices are expected to have embedded advanced power management capabilities. However, how to effectively exploit the green capabilities is still a big challenge, especially given the high heterogeneity of devices and their internal architectures. In this paper, we introduce a hierarchical power management architecture (HPMA) which represents physical components whose power can be monitored and controlled at various levels of a device as entities. We use energy aware state (EAS) as the power management setting mode of each device entity. The power policy controller is capable of getting information on how many EASes of the entity are manageable inside a device, and setting a certain EAS configuration for the entity. We propose the optimal local control policy which aims to minimize the router power consumption while meeting the performance constraints. A first-order Markov chain is used to model the statistical features of the network traffic load. The dynamic EAS configuration problem is formulated as a Markov decision process and solved using a dynamic programming algorithm. In addition, we demonstrate a reference implementation of the HPMA and EAS concept in a NetFPGA frequency scaled router which has the ability of toggling among five operating frequency options and/or turning off unused Ethernet ports.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(A)
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• pp.206-208
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• 2012

현재까지 DVFS(Dynamic Voltage and Frequency Scaling)를 효율적으로 사용하여 프로세서의 소모전력을 줄이는 것을 목표로 하는 많은 연구가 진행되어 왔다. 그 중에서 GPHT(Global Phase History Table)는 워크로드를 예측하여 최적의 DVFS를 설정하는 연구이다. 이 연구는 Last Value기법 보다 예측 적중률을 향상시켰지만 연속적인 워크로드 상황에서는 예측 적중률이 저하되는 한계점을 가지고 있다. 본 논문은 이 문제를 해결하기 위해 Run-Length Encoding기법을 도입한 새로운 GPHT모델을 소개하며, 시뮬레이션 결과 GPHT 대비 적중률을 최대 8.98%, 평균 3.28% 향상 시켰다.

• 대한임베디드공학회논문지
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• 제11권1호
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• pp.1-8
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• 2016

We proposed a load unbalancing scheduling method for energy-efficient multi-core embedded systems considering DVFS (Dynamic Voltage/Frequency Scaling) power consumption and task characteristics. It is a new kind of scheduler which combines load balancing and load unbalancing technique. The purpose of the method is to effectively utilize energy without much effect in performance. In this paper, we conduct experiments on energy consumption and performance using the previous load balancing and unbalancing techniques and our proposed technique. The proposed technique reduced energy consumption more than 13.7% when compared to other algorithms. As a result, the proposed technique shows low energy consumption without much decline in the performance and is adequate for energy-efficient multi-core embedded systems.

• ETRI Journal
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• 제37권1호
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• pp.157-164
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• 2015

As GPU power consumption in smartphones increases with more advanced graphic performance, it becomes essential to estimate GPU power consumption accurately. The conventional GPU power model assumes, simply, that a GPU consumes constant power when turned on; however, this is no longer true for recent smartphone GPUs. In this paper, we propose an accurate GPU power model for smartphones, considering newly adopted dynamic voltage and frequency scaling. For the proposed GPU power model, our evaluation results show that the error rate for system power estimation is as low as 2.9%, on average, and 4.6% in the worst case.

• 반도체디스플레이기술학회지
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• 제18권1호
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• pp.123-128
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• 2019

Currently mobile services are on the verge of full commercialization ahead of 5G mobile communication (5G). The first goal could be to preempt the 5G market through realistic media services utilizing VR (Virtual Reality) and AR (Augmented Reality) technologies that users can most easily experience. Basically this movement is based on the advanced development of smart devices and high quality graphics processing computing power of mobile application processors. Accordingly, the importance of mobile GPUs is emerging and the most concern issue becomes a model for predicting the power and performance for smooth operation of high quality mobile contents. In many cases, the performance of mobile GPUs has been introduced in terms of power consumption of mobile GPUs using dynamic voltage and frequency scaling and throttling functions for power consumption and heat management. This paper introduces several studies of mobile GPU performance prediction model with user-friendly methods not like conventional power centric performance prediction models.

• 한국지반공학회논문집
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• 제25권11호
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• pp.27-38
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• 2009

본 연구에서는 조밀한 포화 사질토 지반과 느슨한 포화 사질토 지반에 근입된 모형말뚝을 대상으로 다양한 말뚝휨 강성과 입력 가속도 진폭, 그리고 입력 가속도 진동수 조건에서 1g 진동대 실험을 수행하였다. 그 결과로, 조밀한 포화 사질토 지반조건에 대해, 각 실험 p-y 곡선 상 최대 지반 반력이 나타나는 꼭지점들을 연결하여 등가정적해석에 적용할 수 있는 동적 p-y 중추곡선을 쌍곡선 함수로 나타내었으며, 중추곡선을 쌍곡선 함수로 나타내는데 필요한 초기 기울기($k_{ini}$)와 극한 저항력($p_u$)을 결정하기 위한 경험식을 마찰각과 구속압의 함수로 제안하였다. 제안한 동적 p-y 중추곡선의 적용성을 기존 문헌에 발표된 원심모형실험 결과와 비교하여 검증하였으며, 실제 설계에 적용되고 있는 기존의 p-y 곡선들과도 비교, 분석하였다. 또한 느슨한 포화 사질토 지반조건에서, 진동 중 발생하는 과잉간극수압에 따라 지반 저항이 감소하는 정도를 나타내는 동적 지반 저항 감소 계수($S_F$)를 제안하였다.

• 한국멀티미디어학회논문지
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• 제11권5호
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• pp.641-650
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• 2008

휴대 기기의 보급 확대에 따라 작은 배터리의 사용 시간 연장을 위해 배터리의 전력 관리 기법이 필요하다. 기존의 전력 관리 기법들은 전압 변경에 따른 오버헤드를 고려하지 않거나 부분적으로 고려하였다. 따라서 전압 변경 오버헤드는 개인용 멀티미디어 시스템의 실시간 태스크의 스케줄을 보장 못하는 경우가 발생할 수 있다. 본 논문은 전압 변경 오버헤드를 고려하면서 시스템의 이용률 정보를 바탕으로 사용 가능한 주파수의 개수와 연속된 주파수 사이의 간격을 조절하여 소비 전력을 줄이는 전력 관리 알고리즘을 제안한다. 본 알고리즘은 주파수 변경 회수를 줄여 기존의 CC RT-DVS 방법과 smoothing 방법에 비해 10에서 25%정도 소비 전력을 절감할 수 있다.