• The Journal of Korean Institute of Communications and Information Sciences
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• 제30권11A호
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• pp.1081-1091
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• 2005

Unlike conventional DVB-T transmission with the streaming method, DVB-H system based on the IPDC(IP Data Casting) method uses Time-slicing scheme to achieve the maximization of portability by reducing the power consumption of a receiver. To enhance the power efficiency of the receiver, Time-slicing scheme controls the receiver operation to perform only for corresponding burst in specific time slot. The additional power saving can also be achieved by reducing the required time for synchronization. In this paper, we propose a fast scattered pilot synchronization algorithm, which detects the pilot pattern of currently received OFDM symbol. The proposed scheme is based on the correlation between the adjacent subcarriers of potential scattered pilot position in two consecutively received OFDM symbols. Therefore, it can reduce the time for the scattered pilot synchronization within two symbols as com-pared with the conventional method used for DVB-T. And the proposed algorithm has better performance than the two schemes proposed by Nokia for DVB-H and the method using correlation with reference signal. Extensive com-puter simulation is performed based on ETSI EN300 744 ETSI and performance results show that the proposed algorithm has more efficient and stable operation than the conventional schemes.

• Journal of KIISE:Computer Systems and Theory
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• 제29권6호
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• pp.331-339
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• 2002

This paper presents a garbage collection protocol for checkpoints and message logs which are staved on the stable storage or volatile storage for fault tolerancy. The previous works of garbage collections in coordinated checkpointing protocol delete all the checkpoints except for the last checkpoints on earth processes. But implemented in top of reliable communication protocol like as TCP/IP, rollback recovery protocol based on only last checkpoints makes sympathetic rollback. We show that the old checkpoints or message logs except for the last checkpoints have to be preserved in order to replay the lost message. And we define the conditions for garbage collection of checkpoints and message logs for lost messages and present the garbage collection algorithm for checkpoints and message logs in coordinated checkpointing protocol. Since the proposed algorithm uses process information for lost message piggybacked with messages, the additional messages for garbage collection is not required The proposed garbage collection algorithm makes 'the lazy garbage collectioneffect', because relying on the piggybacked checked checkpoint information in send/receive message. But 'the lazy garbage collection effect'does not break the consistency of the whole systems.

• The Transactions of the Korea Information Processing Society
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• 제3권7호
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• pp.1697-1706
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• 1996

This paper presents the design and the implementation of a MissCW(Multi user Interactive System for Synchronous Collaborative Writing). The document model DMDA(Distributed Multimedia Document Architecture) of MissCW consists of the logical structure, presentation style object, and mark object. The windows. The collaborative editor of this system proposes a structure oriented editing mechanism to combine distrbuted objects into one document. The middleware SOM(Shared Object Manager) maintains shared objects consistently and helps application programs use objects efficiently. The infrastructure of this system is a hybrid structure of replicated and centralized architectures, that is to maintain shared objects consistently inside of SOM and to reduce the overhead of network traffic. The central part is a virtual node which corresponds to the Object Controller of SOMwith the SOT(Shared Objet Table).

• Journal of the Korea Institute of Information and Communication Engineering
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• 제1권2호
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• pp.145-158
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• 1997

Method for synchronizing multimedia data is needed to support continuous transmission of multimedia data through a network in a bounded time and it also required for supporting continuous presentation of multimedia data with the required norminal playout rate in distributed network environments. This paper describes a new synchronization method for supporting delay-sensitive multimedia Presentation without degration of Quality of services of multimedia application. It mainly aims to support both intermedia and intermedia synchronization by absorbing network variations which may cause skew or jitter. In order to remove asynchonization problems, we make use of logical time system, dynamic buffer control method, and adjusting synchronization intervals based on the quality of services of a multimedia. It might be more suitable for working on distribute[1 multimedia systems where the network delay variation is changed from time to time and no global clock is supported. And it also can effectively reduce the amount of buffer requirements needed for transfering multimedia data between source and destination system by adjusting synchronization intervals with acceptable packet delay limits and packet loss rates.

• The KIPS Transactions:PartD
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• 제10D권1호
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• pp.109-116
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• 2003

In this paper, a CORBA-based collaborative medical image analysis and visualization system, which provides high accessibility and usability of the system for the users on distributed environment is introduced. The system allows us to manage datasets and manipulates medical images such as segmentation and volume visualization of computed geometry from biomedical images in distributed environments. Using Bayesian classification technique and an active contour model the system provides classification results of medical images or boundary information of specific tissue. Based on such information, the system can create real time 3D volume model from medical imagery. Moreover, the developed system supports collaborative work among multiple users using broadcasting and synchronization mechanisms. Since the system is developed using Java and CORBA, which provide distributed programming, the remote clients can access server objects via method invocation, without knowing where the distributed objects reside or what operating system it executes on.

• Journal of KIISE:Computer Systems and Theory
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• 제32권5호
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• pp.209-218
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• 2005

In this paper, we propose CIVE, context-based interactive system for heterogeneous distributed virtual environments that delivers contexts irom real world to virtual environment and vice versa. The proposed system ronsists of obi-UCAM for generating user's contexts, NAVER for managing virtual environment, and Interface for linking obi-UCAM with NAVER. The connection between real and virtual worid through context is brneficial in following ways. Firstly. CIVE Provides a personalized user interface for virtual environment according to a user profile such as identity, age and vernacular. Secondly, translating all input signals into context, it guarantees adaptive access that enables a user to exploit unencumbered input devices controlling a shared object in virtual environment even if he moves with his own device from a virtual system to another. Finally, it provides a mechanism for synchronizing distributed virtual systems that share context representing changes at remote nodes. The context reduces the inconsistency of representing the same data among heterogeneous systems. Therefore, CIVE plays an important role in implementing VR applications such as teleconference, game and entertainment.

• The KIPS Transactions:PartC
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• 제10C권6호
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• pp.711-716
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• 2003

We propose a new Interet time synchronization model using danamic linear model and introduce the characteristics of internet transmission delays. SNTP(Simple Network Time Protocol) has been widely used as a time synchronization method on the Internet. While SNTP provides a very simple usage, SNTP may not provide the stable services, since SNTP does not consider the several essential error factors. In order to overcome the instabitily of SNTP, we analyze the process of time estimation of SNTP and find the difference between forward transmission delay and backward transmission delay operates the main error on the estimation of an time offset.

• Proceedings of the Korean Information Science Society Conference
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• 한국정보과학회 1999년도 가을 학술발표논문집 Vol.26 No.2 (2)
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• pp.295-297
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• 1999

인터넷에 대한 사용자의 관심이 증가하면서 WWW에 관련된 기술이 급격히 증가하고 있다. 이러한 웹을 기반으로 하는 작업은 분산되어 있는 작업그룹의 여러 사용자들이 공동의 프로젝트에 관하여 효율적으로 공동작업을 하기에 충분한 기반환경을 제공할 수 있다. CoDocs 시스템은 웹에서 공동작업을 하는 작업그룹의 사용자들이 서로의 정보를 공유하고 교환함으로써 효율적으로 공동작업을 할 수 있는 기반 환경을 제공한다. 그러나, 이러한 CoDocs 시스템에서는 각 작업그룹 사용자들이 서로간의 의사전달을 위해 다지 비동기적인 통신 방법을 제공하고 있을 뿐 실시간적인 통신 방법을 갖추고 있지 않다. 하지만 보다 효과적인 공동작업을 위해서는 각 작업그룹의 사용자들간에 실시간으로 의사전달을 하고 서로의 정보를 교환하여 공유할 수 있는 통신 수단을 필요로 한다. 본 논문에서는 CoDocs 시스템에서 각 작업그룹 사용자들간에 이루어질 수 있는 실시간 의사전달 및 정보 교환을 가능하게 함으로써 공동작업을 효율적으로 지원할 수 있는 메신저 시스템을 설계하고 구현하였다.

• ICROS
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• 제3권1호
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• pp.41-52
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• 1997

초고속 정보 통신망의 구축, 각종 표준 제정 움직임, 그리고 이들을 배경으로 한 최근의 CALS 관련 활동들과 사내/외 정보 공유를 지원하는 PDM 및 ERP 시스템이 궁극적으로 지향하는 바는 "정보 공유"이다. 그러나 아직까지 CALS에서 채택한 표준을 이용하여 정보 공유를 지원하는 시스템에 대한 연구는 매우 제한적이다. 그리고 분산환경에서의 멀티미디어 정보 공유를 통한 실질적인 업무 추진을 지원하는 시스템의 구현에 관한 연구도 상대적으로 부족한 실정이다. 결국 실제로 이를 이용하는 것도 아직은 초보적인 단계에 있다. 그러나 최근의 글로벌화와 경영 환경의 변화는 정보 공유를 통한 조직 경쟁력 강화의 필요성을 한 층 더 부각시키고 있고, 이는 결국 필요한 정보기술 발전에 충분한 동기가 될 수 있으며, 그 발전의 속도를 가속시킬 것이 확실하다. 과거 개인 또는 부서 차원에서 생성되고 활용되던 자료, 정보, 지식들이 기업 전체의 차원에서 전자적으로 교환됨으로써 훨씬 효율적인 정보의 공유가 가능하게 되는 것이다. 결국 이는 제한된 자원을 효과적으로 활용하면서, 제품 개발 기간을 단축시키게 되므로, 과거에는 불가능했던 새로운 형태의 부가가치를 소비자에게 제공하게 될 것이다.

• Proceedings of the Korea Information Processing Society Conference
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• 한국정보처리학회 2001년도 추계학술발표논문집 (상)
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• pp.191-194
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• 2001

멀티미디어 응용의 확산에 따라 MOD와 같은 서비스와 이를 뒷받침하기 위해 네트웍 환경이 급증하고 있다. 이러한 서비스는 네트웍을 이용하므로 실시간성과 최적의 스케줄링 알고리즘이 필요하다. 본 논문에서는 가변적인 네트웍 상황을 고려한 전역시간 동기화 방법을 제안한다. 제안한 알고리즘은 UDP환경 하에서의 설계 및 구현하였다. 성능 측정은 여러 가지 네트웍 환경에서 측정하였다. 제안한 알고리즘을 통해 측정된 데이터분석에 의해 서버 시간에 근접한 시간동기화를 얻을 수 있으므로 클라이언트의 QoS를 높일 수 있다.