• Journal of KIISE:Computer Systems and Theory
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• v.31 no.10
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• pp.562-574
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• 2004

We address the problem of energy-optimal voltage scheduling for fixed-priority hard real-time systems. First, we prove that the problem is NP-hard. Then, we present a fully polynomial time approximation scheme (FPTAS) for the problem. for any $\varepsilon$>0, the proposed approximation scheme computes a voltage schedule whose energy consumption is at most (1+$\varepsilon$) times that of the optimal voltage schedule. Furthermore, the running time of the proposed approximation scheme is bounded by a polynomial function of the number of input jobs and 1/$\varepsilon$. Experimental results show that the approximation scheme finds more efficient voltage schedules faster than the best existing heuristic.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.298-300
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• 2003

최근의 임베디드 시스템 분야에서 실시간 운영체제를 탑재하여 개발 된 제품들이 점차 늘어 증가하는 추세이다. 실시간 운영체제는 다른 범용 운영체제와는 달리 시간 결정성을 보장하는 운영체제이다. 그리고 실시간 운영체제를 포함하는 임베디드 시스템은 특정 목적을 위해 간결하게 만들어지기 때문에 한정된 자원을 효율적으로 사용해야 한다. 본 논문에서는 실시간 운영체제 iRTOS$^{TM}$에서 태스크의 우선순위를 64 에서 256 으로 확장하면서 발생하는 메모리의 낭비를 줄이는 스케줄링 방법을 설계하고 구현한 내용을 설명한다.

• The Journal of the Korea Contents Association
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• v.21 no.6
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• pp.12-18
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• 2021

A proportional share scheduler allocates CPU time to tasks and determines which task will be dispatched according to their priorities. In this paper, we investigate the correlation between the characteristics of applications and task priorities in the Linux Completely Fair Scheduler(CFS), which is one of the representative proportional share schedulers. We also propose a method of controlling the granularity of priority assignments according to the characteristics of applications. We implemented the proposed technique in a Linux system and confirmed the meaningful experimental results.

• Annual Conference of KIPS
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• 2009.04a
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• pp.670-673
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• 2009

TinyOS는 현재 가장 널리 사용되는 센서 노드용 운영체제이지만, 태스크의 실시간성을 지원하지 않는다는 단점이 있다. 이에 TinyOS에 실시간성을 부여하기 위한 다양한 연구가 진행되었다. 그러나 이들 연구는 TinyOS의 사용자 태스크에 대한 실시간성만을 고려하여, TinyOS 플랫폼이 제공하는 태스크가 포함된 실제의 센서 노드 작업에 대해서는 실시간성을 만족시키지 못한다는 문제점이 있다. 따라서 본 논문에서는 TinyOS에서 센서 노드 작업의 실시간성을 지원하는 새로운 스케줄링 기법을 제안하고자 한다. 이를 위해 기존 연구의 스케줄링 기법을 센서 노드 작업에 적용했을 때 나타나는 작업 중첩 현상과 우선순위 조정 현상을 분석하고, 이를 효율적으로 해결하는 비선점형 EDF(Earliest Deadline First) 작업 스케줄링 기법을 구현하였다. 그리고 제안한 스케줄링 기법은 TinyOS의 이벤트 기반 비선점형 속성을 유지하여 제한된 하드웨어 자원을 가지는 센서 노드에 적합하다는 것을 확인하였다.

• Journal of Korea Multimedia Society
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• v.13 no.9
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• pp.1285-1298
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• 2010

Since the TinyOS incorporating a non-preemptive task scheduling policy uses a FIFO (First-In First-Out) queue, a task with the highest priority cannot preempt a task with lower priority before the task with lower priority must run to completion. Therefore, the non-preemptive TinyOS cannot guarantee the completion of real-time user tasks within their deadlines. Additionally, the non-preemptive TinyOS needs to meet the deadlines of user tasks as well as those of TinyOS platform tasks called by user tasks in order to guarantee the deadlines of the real-time services requested by user tasks. In this paper, we present a group-based real-time scheduling technique that makes it possible to guarantee the deadlines of real-time user tasks in the TinyOS incorporating a non-preemptive task scheduling policy. The proposed technique groups together a given user task and TinyOS platform tasks called and activated by the user task, and then schedule them as a virtual big task. A case study shows that the proposed technique yields efficient performance in terms of guaranteeing the completion of user tasks within their deadlines and aiming to provide them with good average response time, while maintaining the compatibility of the existing non-preemptive TinyOS platform.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.1
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• pp.103-109
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• 2019

The automotive electronic system should provide a method that can be safely performed by loading a number of application programs having time constraints in several electronic control devices. In this paper, we propose a timing protection mechanism for AUTOSAR, which is a real - time operating system specification for automotive field, in order to observe the deadline of each task when scheduling real - time tasks. We propose a dynamic non-preemption algorithm to guarantee a flexible deadline for fixed priority or dynamic priority tasks, and a location where execution time can be monitored for errors, and suggest ways to implement the AUTOSAR time protection mechanism.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.325-336
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• 2013

FlashLinQ, one of the typical D2D communication systems developed by Qualcomm, considers a single-tone communication based distributed channel-aware link scheduling method to realize the link scheduling process with low control overheads. However, considering the frequency selective fading effect of practical multi-path channel, the single-tone based SIR estimation causes a critical scheduling error problem because the received single-tone signal has quite different channel gain at each sub-carrier location. In order to overcome this problem, we propose a novel link scheduling method based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence for D2D communication system. In the proposed method, each link has a unique offset value set for the generation of CAZAC sequences. CAZAC sequences with the cyclic offsets are transmitted using multiple sub-blocks in the entire bandwidth, and then each device can obtain nearly full-band SIR using a good cyclic cross-correlation property of CAZAC sequence.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.1 no.2
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• pp.159-168
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• 1997

This paper presents a mechanism which supplies tasks with fast turn-around time on real-time multimedia environments. Tasks are classified into periodic and aperiodic tasks according to their executing period, and the types of them are classified into three groups : critical tasks, essential tasks and common tasks by the degree of its urgency. In the case of periodic tasks, we defer the execution of it within the extent to keep the deadline as long as possible and serve the aperiodic tasks, and provide aperiodic tasks with fast turn-around time. Changing the priority of each task is allowed within the same type and it is scheduled by using the dynamic priority. The emergency tasks are executed within deadline in any circumstances, and the least laxity one is served first when many real-time tasks are waiting for execution. The result of simulation shows that the proposed mechanism is better than the EDZL, known as suboptimal in multiprocessor systems, in the point of rum-around time.

• The KIPS Transactions:PartA
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• v.11A no.3
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• pp.213-216
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• 2004

Proirity queues(PQ) can be used in applications such as scheduling or sorting. The data structures for PQ can be constructed with or without pointers. The implicit representation without pointers uses less memory space than pointer-based representation. It if shown that a 2-heap, a traditional Implicit PQ based on a binary tree, is slower than an f-heap based on a 8-ary tree. This is because 8-heap utilizes cache memory more efficiently This paper presents a novel fast implicit heap called 8-heap＊ which is easier to implement. Experimental results show that the 8-heap＊ is faster than 8-heap as well as 2-heap.

• Annual Conference of KIPS
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• 2000.10b
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• pp.1243-1246
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• 2000

응용프로그램을 실행시키는 것은 많은 디스크 대역폭을 필요로 하고 있다. 데이터를 조회하는데 걸리는 시간을 최소로 하는 것이 성능을 향상시키는 가장 큰 문제이다. 디스크 기술은 속도와 용량면에서 많은 발전이 있었음에도 불구하고, 프로그램에서 요구하는 요구사항이 증가함하고 있다. 멀티미디어 서버는 여러 종류의 텍스트나 이미지, 비디오 등의 다양한 데이터 타입을 지원한다. 따라서 다른 데이터 타입들은 다른 마감시간의 요구와 우선 순위를 가지고 있다. 연속적인 오디오나 비디오 같은 것들 은 마감시간 제약을 가지고 있다. 이 논문에서 제한한 알고리즘은 모든 요청들을 두 개의 큐로 유지하고 탐색 시간을 최소화함으로써 디스크 대역폭의 처리율을 극대화시킨다. 즉 다양한 우선 순위의 요청들을 해당 클래스로 나누고 주기적인 요청을 위한 큐와 비 주기적인 요청이나 대화형 요청들을 위한 또 하나의 큐로 나누고 요청의 마감시간과 디스크 헤드의 움직임을 고려하여 스케줄링한다.