• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5C
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• pp.479-486
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• 2010

In this paper, we propose a novel low-complexity Alamouti coded orthogonal frequency division multiplexing (OFDM) scheme for asynchronous cooperative communications. Exploiting the combination of OFDM symbols at the source node and simple operations including sign change and complex product at the relay node, the proposed scheme can achieve cooperative diversity gain without use of time-reversion and shifting operations that the conventional scheme proposed by Li and Xia needs. In addition, by using the cyclic prefix (CP) removal and insertion operations at the relay node, the proposed scheme does not suffer from a considerable degradation of bit-error-rate (BER) performance even though perfect timing synchronization is not achieved at the relay node. From the simulation results, it is demonstrated that the BER performance of the proposed scheme is much superior to that of the conventional scheme in the presence of timing synchronization error at the relay node. It is also shown that the proposed scheme obtains two times higher diversity gain compared with the conventional scheme at the cost of half reduction in transmission efficiency.

• Journal of KIISE:Information Networking
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• v.35 no.2
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• pp.166-172
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• 2008

This paper proposes an autonomous decentralized frame synchronization system for Ad-hoc Inter-Vehicle Communication Network (IVCN). We have to consider the feature of Ad-hoc IVCN: "time variant" about the number and the location of vehicles and receive power in IVCN, frame timing, and fading. Proposed scheme is different from other decentralized synchronization systems that have association with a fixed base station, and from centralized Personal Communication Systems. This system includes an autonomous decentralized frame synchronization scheme for Ad-hoc IVCN, a high-speed algorithm, a protocol for a newly joining subscriber in IVCN, and a utilization of spread spectrum ranging for frame timing error of the system under highway conditions. Performance evaluation of proposed scheme is validated through simulation. It is shown that Ad-hoc IVCN can be carried out among one and surrounding vehicles in such environment.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.655-657
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• 2001

일반적으로 위성에 장착된 GPS 수신기는 GPS 위성으로부터 창법 신호를 받아서 위성의 위치, 시간 및 속도 정보를 제공하는 것을 주요 목적으로 하고 있다. 또한 GPS 수신기에서 나오는 1pps 신호를 이용하여 위성체 각 프로세서의 기준시간으로 사용되어진다. 아리랑 위성2호에서는 3개의 프로세서가 탑재되며, 각 프로세서는 원격 측정 명령계. 자세 제어계 그리고 전력계 기능을 담당한다. 3개의 프로세서간의 내부 및 GPS에 동기 시키기 위하여 FEP와 DPLL을 통한 동기화 방식을 사용하며, 위성탑재 소프트웨어에 의한 제어를 필요로 한다. 본 논문에서는 아리랑 위성2호에 동기화 방식과 향상된 1Hz Sync 구조에 대하여 설명한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.11a
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• pp.396-399
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• 2013

TDMA(Time-Division Multiple Access)는 한정된 채널을 시간상에서 여러 개의 구간으로 분할하고, 자신에게 할당된 시간 구간에서 정보를 전송하는 기법이다. 본 논문은 TDMA 알고리즘의 한 종류인 DESYNC 알고리즘을 소규모 네트워크에 적용하여 별도의 동기화 작업 없이 간단한 규칙으로 동기화를 유지하는 기법을 소개 한다. 기존의 DESYNC 알고리즘은 모든 노드들이 전송 영역 안에 있어야 하고, 전부 연결되어있어야 한다는 단점이 있다. 이 문제점을 해결하고자 중앙제어장치인 CU(Central Unit)을 네트워크에 배치하여 2-홉 형태의 중앙 집중방식 네트워크가 운영되도록 하였다. 제시하는 알고리즘은 기존의 DESYNC 알고리즘과 마찬가지로 복잡한 동기화 과정 없이 단순한 방식으로 TDMA가 동작할 수 있도록 하면서, 전송 범위는 기존의 DESYNC 알고리즘의 성능에 비해 우수하다.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.524-529
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• 2006

이더넷 환경에서 시간에 민감한 데이터를 전송하기 위해 각 장치들은 시간 동기를 맞출 필요가 있다. 동기식 이더넷에서는 정확한 시간 동기를 위해 IEEE 1588의 서브넷 개념을 이용한다. 현재 연구되고 있는 동기 방법은 LAN상의 장치 중 하나의 기준 되는 동기 정보를 제공하는 장치를 선정하고 이 장치에 의해 다른 모든 장치가 동기를 맞추는 방법을 이용한다. 본 논문은 이러한 동기 정보를 제공하는 장치를 선정하는 알고리즘을 제안한다. 제안된 방법은 기존의 동기 방법과는 달리 동기 정보를 제공하는 장치를 선정하는 동시에 통신하는 장치와 동기를 맞추게 된다. 제안된 방법으로 기존 이더넷에서 시간에 민감한 데이터 전송을 동기화하여 전송 할 수 있고 나아가 무선 통신 및 IEEE 1394와의 연계를 통한 네트워크 전반적인 백본망으로 구성 될 수 있다.

• Journal of Internet Computing and Services
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• v.14 no.1
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• pp.53-62
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• 2013

It is common among users to have multiple computing devices as well as to access their files or do work at different locations. To achieve file consistency as well as mobility in this scenario, an efficient approach for workspace synchronization should be used. However, file synchronization alone cannot guarantee the mobility of work environment which allows activities to be resumed at any place and time. This paper proposes a ubiquitous synchronization approach which provides cloud-based access to a user's workspace. Efficient synchronization is achieved by combining session monitoring with file system management. Experimental results show that the proposed mechanism outperforms Cloud Master-replica Synchronization in terms of number of I/O operations, CPU utilization, as well as the average and maximum latencies in responding to client requests.

• Journal of the Korean Society for Computer Game
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• v.31 no.4
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• pp.61-70
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• 2018

In this paper, we propose a synchronized playback method of 3D reference model and video by extracting golf swing information from learner's golf video to precisely compare and analyze each motion in each position and time in the golf swing, and present the implementation result. In order to synchronize the 3D model with the learner's swing video, the learner's golf swing movie is first photographed and relative time information is extracted from the photographed video according to the position of the golf club from the address posture to the finishing posture. Through applying time information from learners' swing video to a 3D reference model that rigs the motion information of a pro-golfer's captured swing motion at 120 frames per second through high-quality motion capture equipment into a 3D model and by synchronizing the 3D reference model with the learner's swing video, the learner can correct or learn his / her posture by precisely comparing his or her posture with the reference model at each position of the golf swing. Synchronized playback can be used to improve the functionality of manually adjusting system for comparing and analyzing the reference model and learner's golf swing. Except for the part where the image processing technology that detects each position of the golf posture is applied, It is expected that the method of automatically extracting the time information of each location from the video and of synchronized playback can be extended to general life sports field.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5512-5517
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• 2012

In this paper we suggest multimedia synchronization model that is based on the Petri-net and services desirable quality of service requirement. Proposed model applies variable buffer which can be allowed, and then it presents high quality of service and real time characteristics. This paper decreases the data loss resulted from variation of delay time and from loss time of media-data by means of applying delay jitter in order to deal with synchronization interval adjustment. Plus, the mechanism adaptively manages the waiting time of smoothing buffer, which leads to minimize the gap from the variation of delay time. The proposed paper is suitable to the system which requires the guarantee of high quality of service and mechanism improves quality of services such as decrease of loss rate, increase of playout rate.

• Journal of Korea Game Society
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• v.5 no.4
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• pp.33-38
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• 2005

In the online game that thousands of participants connect to a game world by using Internet simultaneously, participants of the game world may have different hardwares and network environments, and messages of participants should be synchronization. A solution for the synchronization problem is to wait for a certain amount of time until the server processes the message. It is not easy to determine a suitable waiting period because of the trade-off between the fairness and the responsiveness. In this paper we propose a method to decide a waiting period by considering features of the MMOFPS game and the probability of interaction among participants. We implement the proposed method and perform experiments for the performance evaluation.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.9
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• pp.461-468
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• 2001

Though shared virtual memory (SVM) system promise low cost solutions for high performance computing they suffer from long memory latencies. These latencies are usually caused by repetitive invalidations on shared data. Since shared data are accessed through synchronization and the patterns by which threads synchronizes are repetitive, a prefetching scheme bases on such repetitiveness would reduce memory latencies. Based on this observation, we propose a prefetching technique which predicts future access behavior by analyzing access history per synchronization variable. Our technique was evaluated on an 8-node SVM system using the SPLASH-2 benchmark. The results show the our technique could achieve 34%~45% reduction in memory access latencies.