• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4A
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• pp.402-411
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• 2006

In OFDMA system, multiple users transmit signal through the subcarriers assigned to the user. Capabilities of high data-rate transmission in OFDMA system come from the ability to compensate the ICI (Inter Carrier Interference) using a single-tap equalizer and to implement transmitter and receiver by employing high speed FFT circuitry. Issues of time and frequency synchronization in OFDM system is quite essential to preserve the orthogonality among subcarriers not to produce ICI. In this paper, we Int analyze the preamble used in 802.16 d/e and WiBro system. Then we propose an effective timing synchronization algorithm, which is more accurate than the conventional one in the sense of timing position, and integral frequency offset estimation scheme for the simultaneouse estimation of the fractional and integral frequency offset. Through the simulation utilizing the proposed synchronization algorithm and structure, we show that the performance degradation due to the adjacent channel interference can be mitigated for the than conventional ones.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.1
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• pp.114-122
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• 2011

In this paper, we have identified the system instability factors in a bistatic radar system using pulse chasing and considered their effects on the bistatic receiver's MTI(Moving Target Indication) improvement performance. The pulse chasing is a method to efficiently scan a restricted search area within the limited transmitter power and time in a bistatic radar and to track a series of transmitted pulses using the receiver beam which has ideally matched to the pulse propagation rate. In this paper, we have discussed the interrelationship between the pulse chasing and time and frequency/phase synchronization and described the effects of the identified system instability factors on two kinds of MTI filter configuration, single delay-line and double delay-line, in the bistatic radar. And also, we have confirmed that the overall system improvement is restricted by a lower improvement factor among identified them, and discussed the allowable tolerance of the time and frequency/phase synchronization in the bistatic system.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.05a
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• pp.68-71
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• 2018

In this paper, we propose a synchronization protocol for underwater acoustic networks which aims to minimize the effects of long propagation delay and uncertain delay variations and employs packet train scheme with considering low data rate. The proposed protocol uses an one-way delay measurement method by transmitting consecutive packets and acquires synchronization only considering propagation delay variations by calculating packet arrival time differences. We perform simulations under various network conditions, such as node mobility, time interval for packet transmission, network range, and elapsed time after synchronizing. The simulation results shows the superiority of our protocol, compared with a previously proposed protocol.

• Journal of KIISE
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• v.42 no.11
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• pp.1332-1338
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• 2015

Recently, growing attention has been paid to multi-GPU rendering to support real-time high-quality rendering at high resolution. In order to attain high performance in real-time multi-GPU rendering, great care needs to be taken to reduce the overhead of data transfer among GPUs and frame composition. This paper presents a novel multi-GPU algorithm that greatly enhances split frame rendering with implicit query-based synchronization. In order to support implicit synchronization in frame composition, we further present a message queue-based scheduling algorithm. We carried out an experiment to evaluate our algorithm, and found that our algorithm improved rendering performance up to 200% more than previously existing algorithms.

• Journal of Astronomy and Space Sciences
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• v.21 no.2
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• pp.109-120
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• 2004

STSAT-1 was launched on sep. 2003 with the main payload of Far Ultra-violet Imaging Spectrograph(FIMS). The mission of FIMS is to observe universe and aurora. In this paper, we suggest a simple and reliable strategy adopted in STSAT-1 to synchronize time between On-board Computer(OBC) and FIMS. For the characteristics of STSAT-1, this strategy is devised to maintain reliability of satellite system and to reduce implementation cost by using minimized electronic circuits. We suggested two methods with different synchronization resolutions to cope with unexpected faults in space. The backup method with low resolution can be activated when the main has some problems.

• Journal of the Korea Society of Computer and Information
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• v.15 no.5
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• pp.133-141
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• 2010

Contents adaptation is a technology which converts one content to another content used in various devices. Specially, synchronization of inter-media which are included in a document is needed. There are various proposals and solutions for synchronization of inter-media. In the paper, I present "TATS : Temporal Aggregate Tree Strategy" model, which is used for specifying the temporal relationship among media in series of time. In the TATS model, aggregate tree, a sort of a binary tree, is generated from the execution time of those media. Using this aggregate tree, I implemented the inter-media synchronizations.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.3 no.2
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• pp.11-17
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• 2004

In this paper we propose a new conceptual system for a network clock in which all node clocks are simultaneously synchronized to the national standard by intermediation parameter of satellite time. Experiments have shown the possibility of its adoption by real networks. The new proposed method has various structural benefits, in particular all node clocks can be kept at the same hierarchical quality in contrast to the existing method. The measurement results show that the accuracy of the experimental slave clock system can be kept within a few parts In 1012 and the MTIE (Maximum Time Interval Error) sufficiently meets ITU-T G.811 for the primary reference clock. A prototype system with fully automatic operational functions has been realized at present and is expected to be directly used for communication network synchronization in the near future.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.647-656
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• 2012

TDMA MAC protocol in MANET requires precise network synchronization between nodes though network topology changes continuously due to node mobility and the effect of propagation environment. In this paper we propose in-band cross-layer network synchronization architecture for TDMA-based MANETs. In the proposed architecture TDMA MAC protocol and proactive routing protocol cooperate closely to rapidly detect network partition and merge caused by node mobility and to precisely maintain network synchronization. We also implement the proposed synchronization architecture in OPNET simulator and evaluate the performance of it in various simulation scenarios. Simulation results show that our architecture stably maintains network time synchronization in both network partition and merge situations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.497-500
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• 2010

Wireless sensor network is the system for data collection and data process between many nodes. For this work, Synchronization of operation execution and ordering many events are needed. Reference the external time information is the most accurate way to have same time information for all nodes but it's hard to apply these to sensor network. So there are many study of time synchronization there are many error occurred when the time synchronization is executed in the sensor network and minimizing these errors is important. In this paper, we propose how to minimize errors using several time stamp information exchanging when the network is initialized. When the big difference is occurred between receive time and send time in the node communication(cause of traffic overhead and etc), it shows big error of time correction and transfer delay time. but it's hard to detect these errors when it exchanges time stamp information just one time. so we try to reduce these errors using the median value of transfer delay and time correction value with many times of time stamp information exchange.