• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.3
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• pp.137-141
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• 2015

Mobile cloud computing uses cloud service to solve the resource constraint problem of mobile devices. Offloading means that a task executed on the mobile device commits to cloud and many studies related to the energy consumption have been researched. In this paper, we designed a response time model considering sensing data synchronization to estimate the efficiency of the offloading scheme in terms of the response time. The proposed model considers synchronization of required sensing data to improve the accuracy of response time estimation when cloud processes the task requested from a mobile device. We found that the response time is effected by new sensing data generation rate and synchronization period through simulation results.

• IE interfaces
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• v.12 no.2
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• pp.305-311
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• 1999

Robot task program is needed to control and manage a Robot without explicitly describing the robot program by user which includes commands, procedures, geometric and signal data in the detail level. To use the Robot task program, a computer system is required to convert the Robot task into the Robot program, which can be understood by the Robot. In this paper, the systemic method for automatic generation of explicit Robot programs (ERP) from task-level commands is described. Specifically, a 3-step procedure including Robot task decomposition, task synchronization and ERP generation is presented.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.4
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• pp.291-303
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• 2009

Round robin based proportional share scheduling(RRPS) defines weight which determines share for each task and allocates CPU resource to each task in proportional to its respective weight. RRPS uses fairness as the measure of performance and aims at high fairness of scheduling. However, researches for scheduling fairness problem due to synchronization among tasks have been rarely investigated. In this paper, we discuss that scheduling delay due to synchronization may result high unfairness in RRPS. We explain such a situation as weight inversion. We then propose weight inheritance protocol(WIP), a synchronization mechanism, that prevents weight inversion. We also show that WIP can reduce unfairness using fairness analysis and simulation.

• Journal of information and communication convergence engineering
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• v.16 no.2
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• pp.84-92
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• 2018

For large wireless sensor networks running on battery power, the time synchronization of all sensor nodes is becoming a crucial task for waking up sensor nodes with exact timing and controlling transmission and reception timing. However, as network size increases, this synchronization process tends to require long processing time consume significant power. Furthermore, a naïve synchronization scheduler may leave some nodes unsynchronized. This paper proposes a power-efficient scheduling algorithm for time synchronization utilizing the notion of density, which is defined by the number of neighboring nodes within wireless range. The proposed scheduling algorithm elects a sequence of minimal reference nodes that can complete the synchronization with the smallest possible number of hops and lowest possible power consumption. Additionally, it ensures coverage of all sensor nodes utilizing a two-pass synchronization scheduling process. We implemented the proposed synchronization algorithm in a network simulator. Extensive simulation results demonstrate that the proposed algorithm can reduce the power consumption required for the periodic synchronization process by up to 40% for large sensor networks compared to a simplistic multi-hop synchronization method.

• Journal of KIISE:Computer Systems and Theory
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• v.35 no.6
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• pp.273-283
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• 2008

Many embedded real-time systems have adopted processors supported with dynamic voltage scaling(DVS) recently. Power is one of the important metrics for optimization in the design and operation of embedded real-time systems. We can save considerable energy by using slowdown of processor supported with DVS. In this paper, we propose heuristic algorithms to calculate task slowdown factors for an efficient energy consumption in embedded real-time systems with task synchronization. The previous algorithm has a following constraint : given the tasks are ordered in a nondecreasing order of their relative deadline, the task slowdown factors computed are in a nonincreasing order. In this paper, we relax the constraint and propose heuristic algorithms which have the same time complexity that previous algorithm has and can save more energy. Experimental results show that the proposed algorithms are energy efficient.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.10
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• pp.1264-1274
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• 1999

본 논문에서는 분산된 클록들을 주기적으로 동기화 시키는 분산 실시간 시스템에서 시간적 제약을 만족시키기 위한 정적/동적 시간 제약(timing constraint) 변환 기법을 제안한다. 전형적인 이산클록동기화(discrete clock synchronization) 알고리즘은 클록의 값을 순간적으로 조정하여 클록의 시간이 불연속적으로 진행한다. 이러한 시간상의 불연속성은 시간적 이벤트를 잃어버리거나 다시 발생시키는 오류를 범하게 한다.클록 시간의 불연속성을 피하기 위해 일반적으로 연속클록동기화(continuous clock synchronization) 기법이 제안되고 있지만 소프트웨어적으로 구현되면 많은 오버헤드를 유발시키는 문제점이 있다. 본 논문에서는 시간적 제약을 동적으로 변환시키는 DCT (Dynamic Constraint Transformation) 기법을 제안하였으며, 이를 통해 기존의 이산클록동기화 알고리즘을 수정하지 않고서도 클록 시간의 불연속성에 의한 문제점들을 해결할 수 있도록 하였다. 아울러 DCT에 의해 이산클록동기화 하에서 생성된 태스크 스케쥴이 연속클록동기화에 의해 생성된 스케쥴과 동일함을 증명하여 DCT의 동작이 이론적으로 정확함을 증명하였다.또한 분산 실시간 시스템에서 지역 클록(local clock)이 기준 클록과 완벽하게 일치하지 않아서 발생하는 스케쥴링상의 문제점을 다루었다. 이를 위해 먼저 두 가지의 스케쥴링 가능성, 지역적 스케쥴링 가능성(local schedulability)과 전역적 스케쥴링 가능성(global schedulability)을 정의하고, 이를 위해 시간적 제약을 정적으로 변환시키는 SCT (Static Constraint Transformation) 기법을 제안하였다. SCT를 통해 지역적으로 스케쥴링 가능한 태스크는 전역적으로 스케쥴링이 가능하므로, 단지 지역적 스케쥴링 가능성만을 검사하면 스케쥴링 문제를 해결할 수 있도록 하였고 이를 수학적으로 증명하였다.Abstract In this paper, we present static and dynamic constraint transformation techniques for ensuring timing requirements in a distributed real-time system possessing periodically synchronized distributed local clocks. Traditional discrete clock synchronization algorithms that adjust local clocks instantaneously yield time discontinuities. Such time discontinuities lead to the loss or the gain of events, thus raising serious run-time faults.While continuous clock synchronization is generally suggested to avoid the time discontinuity problem, it incurs too much run-time overhead to be implemented in software. We propose a dynamic constraint transformation (DCT) technique which can solve the problem without modifying discrete clock synchronization algorithms. We formally prove the correctness of the DCT by showing that the DCT with discrete clock synchronization generates the same task schedule as the continuous clock synchronization.We also investigate schedulability problems that arise when imperfect local clocks are used in distributed real-time systems. We first define two notions of schedulability, global schedulability and local schedulability, and then present a static constraint transformation (SCT) technique. The SCT ensures that it is sufficient to check the schedulability of a task locally in a node with a local clock, since the global schedulability of the task is derived from its local schedulability through SCT. We formally prove the correctness of SCT.

• Journal of Korea Multimedia Society
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• v.13 no.1
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• pp.30-37
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• 2010

Many embedded real - lime systems have adopted processors supported with dynamic voltage scal-ing(DVS) recently. Power is one of the important metrics for Optimization in the design and operation of embedded real-time systems. We can save considerable energy by using slowdown of processor sup-ported with DVS. In this paper, we improved the previous algorithm at a point of view of time complexity to calculate task slowdown factors for an efficient energy consumption in embedded real-time systems with task synchronization. We grasped the properties of the previous algorithm having $O(n^{2})$ time complexity through mathematical analysis and s simulation. Using its properties we proposed the improved algorithms with O(nlogn) and O(n) time complexity which have the same performance as the previous algorithm has.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1C
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• pp.103-111
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• 2002

In RNC of IMT-2000, main control processors such as ASP, ACP and OMP are responsible for call control function, and the high reliability and real-time property should be provided for it. So, the study of real-time fault-tolerant for it is needed. In this paper, we proposes an Task based duplication method, in which Tasks in active side operated on message unit and send the updated data to standby side after operation, log in the message to standby side for recovery during take-over. This scheme decreases the dual down and the complexity of synchronization procedure, and performs the synchronization more exactly because Tasks control the synchronization of system. This paper also proposes the fault detection and the fault handing method for effective implementation of Task based duplication. This scheme focus on increasing the fault detection rate and intercepting originally that fault data is send to standby side.

• Proceedings of the Korean Society for Cognitive Science Conference
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• 2010.05a
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• pp.37-41
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• 2010

The previous investigations of electroencephalogram (EEG) activity in the memory retrieval tasks demonstrated that event-related potentials (ERP) during recollection showed different durations and the peak levels from those without recollection. However, it has been unknown that recollection in memory retrieval also modulates high-frequency brain rhythms as well as establishes large-scale synchronization across different cortical areas. In this study, we examined the spectral components of the EEG signals, especially the gamma bands (20-80Hz), measured during the memory retrieval tasks. Specifically, we focused on two major spectral components: first, we evaluated the temporal patterns of the power spectral density before and after the onset of the memory retrieval task; second, we estimated phase synchrony between all possible pairs of EEG channels to evaluate large-scale synchronization. Fourteen healthy subjects performed the memory retrieval task in the virtual reality environment where they selected whether or not t he present item was seen in the previous training period. When the subjects viewed the unseen items, the middle gamma power (40-60Hz) appeared to increase 200-500ms after stimulus onset while the low gamma power (20Hz) was suppressed all the way through the post-stimulus period 150ms after onset. The degree of phase synchronization in this low gamma level, however, increased when the subjects fetched the item from memory. This suggests that phase synchrony analysis might reveal different aspects of the memory retrieval process than the gamma power, providing additional information to the inference on the brain dynamics during memory retrieval.

• Journal of Music and Human Behavior
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• v.16 no.1
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• pp.47-72
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• 2019

This study reviewed and analyzed English-written studies using a rhythmic tapping task for motor control of children with autism spectrum disorder (ASD). Inclusion criteria for the participants were children with ASD and typically developing (TD) children. The keywords used for the outcome variables included rhythmic tapping, timed movement, and synchronization. Ten studies were included in the final analysis. The included studies were analyzed in terms of target variables, auditory stimuli, and measurements. A meta-analysis was also conducted to examine how children with ASD performed rhythmic tapping tasks compared to children with TD. In the identified studies, five variables were used: timed movement control, timing reproduction, bimanual coordination, synchronization, and interpersonal synchronization. It was found that rhythmic tapping performance was analyzed in terms of accuracy and precision of the movement and reported as significantly correlated to social skills measures. The meta-analysis results showed that there were no significant differences between the ASD and TD groups in continuing rhythmic movements when the presented auditory stimuli ended, whereas there were significant group differences in their ability to maintain their motor performance consistently and to synchronize with auditory cue or with others. These results support the rhythmic tapping task as an effective measure for not only motor control but also social skills development in children with ASD.