• Journal of Korea Multimedia Society
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• v.13 no.10
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• pp.1423-1435
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• 2010

Building wireless sensor networks requires a constituting sensor node to consider the following limited hardware resources: a small battery lifetime limiting available power supply for the sensor node, a low-power microprocessor with a low-performance computing capability, and scarce memory resources. Despite such limited hardware resources of the sensor node, the sensor node platform needs to activate real-time sensing, guarantee the real-time processing of sensing data, and exchange data between individual sensor nodes concurrently. Therefore, in this paper, we propose an energy-efficient real-time task scheduling technique for battery-powered wireless sensor nodes. The proposed energy-efficient task scheduling technique controls the microprocessor's operating frequency and reduces the power consumption of a task by exploiting the slack time of the task when the actual execution time of the task can be less than its worst case execution time. The outcomes from experiments showed that the proposed scheduling technique yielded efficient performance in terms of guaranteeing the completion of real-time tasks within their deadlines and aiming to provide low power consumption.

• Journal of Internet Computing and Services
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• v.1 no.2
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• pp.61-67
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• 2000

In case of the remote controllable web-camera that was took notice especially in internet real-time broadcasting systems, a great many clients connect the server of web-camera to request the service. So, the scheduling methods are important. Web-camera systems have used to the traditional FIFO(First In First Out) or SDF(Shortest Distance First) scheduling method. But they does not satisfy both the minimization of moving distance on the web-camera and the fairness on the users. In this paper, We propose the 2D scheduling method, As a result, the moving distance of the web-camera decreases compared with FIFO scheduling method. And the starvation state on the user's request does not happen compared with SDF scheduling method. Thus, if the remote controllable web-camera systems use the 2D scheduling method, they are satisfied with the minimization of moving distance on the remote controllable web-camera and the fairness on the users simultaneously. Therefore the user's satisfaction and the performance of the systems are improved.

• Journal of KIISE:Information Networking
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• v.41 no.4
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• pp.192-201
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• 2014

User scheduling boosts the Multi-User Multi-Input Multi-Output (MU-MIMO) gain by selecting an optimal set of users to increase the 802.11 Wi-Fi system capacities. Many kinds of user scheduling algorithms, however, fail to realize the advantages of MU-MIMO due to formidable Channel State Information (CSI) overhead. In this paper, we propose a user scheduling method considering such CSI exchange overhead and its MAC protocol, called ACE (Active CSI Exchange based User Scheduling for MU-MIMO Transmission). Unlike most proposals, where user scheduling is performed after an Access Point (AP) receives CSI from all users, ACE determines the best user set during the CSI exchange phase. In particular, the AP broadcasts a channel hint about previously scheduled users, and the remaining users actively send CSI reports according to their Effective Channel Gains (ECGs) calculated from the hint. Through trace-driven MATLAB simulations, we prove that the proposed scheme improves the throughput gain significantly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.20-26
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• 2010

The downlink scheduling algorithm has a great impact on the performance of mobile telecommunication system. In proportional fairness (PF) scheduling algorithm, the resource is allocated proportionally to the quality of wireless channel. Thus, PF has difficulty in servicing the users having more downlink traffic. One can allocate the resource proportionally to the accumulated queue length. However, this leads to system throughput degradation since the users having low channel quality get more and more resource allocated due to accumulation property of queue. In this paper, we propose a new downlink scheduling algorithm, which extends PF algorithm by incorporating downlink traffic arrival rate. The proposed algorithm can effectively cope with users having more downlink traffic, and maintain high system throughput by eliminating accumulation effect in the algorithm. With computer simulations, it is verified that the proposed algorithm performs better than existing algorithms.

• Journal of the Korea Society of Computer and Information
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• v.29 no.1
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• pp.1-9
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• 2024

This paper proposes an integration of the ED-H scheduling algorithm, known for optimal real-time scheduling, with the LoRaEnergySim simulator. This integration facilitates the simulation of interactions between real-time scheduling algorithms for tasks with time constraints in Class-A LoRaWAN Class-A devices using a super-capacitor-based energy harvesting system. The time and energy characteristics of LoRaWAN status and state transitions are extracted in a log format, and the task model is structured to suit the time-slot-based ED-H scheduling algorithm. The algorithm is extended to perform tasks while satisfying time constraints based on CPU executions. To evaluate the proposed approach, the ED-H scheduling algorithm is executed on a set of tasks with varying time and energy characteristics and CPU occupancy rates ranging from 10% to 90%, under the same conditions as the LoRaEnergySim simulation results for packet transmission and reception. The experimental results confirmed the applicability of co-simulation by demonstrating that tasks are prioritized based on urgency without depleting the supercapacitor's energy to satisfy time constraints, depending on the scheduling algorithm.

• Journal of Internet Computing and Services
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• v.17 no.5
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• pp.17-23
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• 2016

Wireless sensor-actuator networks (WSANs) enhance the existing wireless sensor networks (WSNs) by equipping sensor nodes with an actuator. The actuators work with the sensor nodes and perform application-specific operations. The WSAN systems have several applications such as disaster relief, intelligent building, military surveillance, health monitoring, and infrastructure security. These applications require capability of reliable data transfer to act responsively and accurately. Biologically inspired modeling techniques have received considerable attention for achieving robustness, scalability, and adaptability, while retaining individual simplicity. In this paper, an epidemic-inspired algorithm for data dissemination with delay constraints while minimizing energy consumption in WSAN is proposed. The steady states and system stability are analyzed using control theory. Also, simulation results indicate that the proposed scheme provides desirable dissemination delay and energy saving.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.265-267
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• 2012

최근 들어, 하드웨어 플랫폼은 다수의 코어 아키텍처의 메모리 대역폭을 유지하기 위해 NUMA 구조로 설계되고 있다. 이러한 NUMA 시스템 구조에서 다른 노드의 메모리에 접근할 경우, 더 많은 시간과 비용이 소모된다. 따라서 이를 고려한 스케줄링 기법들이 가상화 혹은 가상화되지 않은 시스템 환경에서 연구되고 있다. 하지만, 아직까지 NUMA 시스템 가상화 환경에서 리모트 접근을 제거함과 동시에 이에 따른 오버헤드를 최소화하는 연구는 없었다. 따라서 본 논문에서는 이러한 환경에서 메모리 접근 지연을 줄이기 위한 VCPU 스케줄링 기법을 제안한다. 본 기법은 노드별 페이지 테이블 관리, LRU 기반 게스트 스케줄러, 캐시 오염 태스크 전용 버퍼 관리 기술을 이용한다. 다른 기법들과의 비교 및 분석 결과에서 알 수 있듯이, 본 기법을 적용할 경우 NUMA 시스템 노드 간 리모트 접근을 없애고, 이에 따른 오버헤드를 최소화하며, 주어진 하드웨어 캐시를 효율적으로 사용할 수 있다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.12
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• pp.539-546
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• 2002

In this paper, we consider a wireless multimedia environment to service both real-time video traffic and non-real-time WWW-application traffic In our suggested new packet scheduling algorithm, we consider both the accumulation counter and SIR to reduce delay in real-time traffic. In addition, our packet scheduling algorithm gives priority first to real-time video traffic service and then to non-real-time internet Packet service when real-time traffic service is absent. From the simulation results, we find that the AC (Accumulation Counter) scheme has much smaller delay than the conversional M-LWDF scheme for real-time video data users, which has a special quality sensitive to its own delay. We also consider the transmission structure of using both the frame period in the time-axis and the OVSF codes in the code-axis at the same time, which is similar to the structure of HSDPA system.

• The Journal of the Korea Contents Association
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• v.8 no.2
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• pp.57-66
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• 2008

Most concurrency control protocols have been devised for resolving data conflicts among real-time transactions of a single type. Recent real-time database systems should support various types of real-time transactions due to needs of many different types of applications and steady improvement of hardware. In this paper, we propose integrated concurrency control protocol to resolve data conflicts among hard and soft real-time transactions. Our proposed protocol, based on PCP(Priority Ceiling Protocol) for a hard real-time transactions and MVPR(Multiversion with Precedence Relationship), guarantees that hard real-time transactions meet their deadline, and decreases the deadline miss ratio of soft real-time transactions. We also proved that the proposed protocol guarantees serializable schedules and no deadlocks. The performance of the proposed protocol has been compared with other real-time concurrency protocols.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.403-405
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• 2005

무선 센서 네트워크에서 이동하는 물체를 에너지 효율적으로 추적하기 위하여 많은 연구가 진행되고 있다. 그 중 대표적인 것은 물체의 이동에 따라 동적으로 클러스터링을 구성해 나가는 방법이다. 물체의 이동에 따라 클러스터를 구성한 후 클러스터 내부에서는 모든 센서 노드들이 연속적으로 물체를 모니터링하거나 혹은 일반적인 스케줄링 기법을 사용하여 에너지 소모를 분산시킨다. 이런 스케줄링 기법들은 환경 모니터링 등 일반적인 센서 네트워크를 대상으로 개발되고 있기 때문에 이동하는 물체를 추적하는 응용에서는 적합하지 않다. 본 논문에서는 물체의 이동경로를 따른 동적 클러스터링 환경에서 물체의 이동 정보를 고려한 클러스터 내부에서의 스케줄링 기법을 제안함으로써 이동하는 물체에 대한 missing-rate를 최소화하는 동시에 에너지 소모를 최대한 줄임으로써 전체 센서 네트워크의 생명주기를 연장시키고자 한다. 시뮬레이션 결과가 증명하는 바와 같이 제안한 방안은 보다 낮은 에너지 소모와 missing-rate를 달성하였다.