• Journal of Satellite, Information and Communications
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• v.9 no.3
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• pp.80-85
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• 2014

In this paper, we propose and analyze a novel synchronization scheme for ubiquitous home network system. In ubiquitous home network system, synchronization method is very important because many consumer electronic devices send the data simultaneously to each other through infrastructure such as access point. We employ digital watermarking sequence to improve synchronization performance without system overhead. The performance of proposed scheme is analyzed in terms of correlation performance. The results of the paper can be applied to design of various applications for ubiquitous home network systems.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.292-298
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• 2013

This paper considers synchronization problem of a complex dynamical network with nonidentical nodes. For the problem, the target node is chosen as one of nodes in the complex network instead of an isolate node. Moreover, our synchronization scheme does not need additional conditions and information of coupling matrix comparing with existing works. Based on Lyapunov stability theory, a design criterion for a novel adaptive feedback controller for the synchronization between the target node and another nodes of the complex network is proposed. Finally, the proposed method is applied to a numerical example in orther to show the effectiveness of our results.

• Journal of Korea Multimedia Society
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• v.22 no.8
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• pp.887-896
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• 2019

In this paper, we discuss an optimization approach for time-synchronizations in networked simulators. This method is a sub-technology that is required to combine heterogeneous simulators into a single simulation. In previous time-synchronization studies, they had built a network system among networked simulators. The network system collects network packets and adds time-stamps to the networked packets based on the time that occurs in events of simulation objects in the individual simulators. Then, it sorts them in chronological order. Finally, the network system applies time-synchronization to each simulator participating in interworking sequentially. However, the previous approaches have a limitation in that other participating simulators should wait for while processing an event in a simulator in a time stamp order. In this paper, we attempt to solve the problem by optimizing time-synchronizations in networked simulation environments. In order to prove the practicality of our approach, we have conducted an experiment. Finally, we discuss the contributions of this paper.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.5
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• pp.161-169
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• 2018

This study presents a time synchronization system in decentralized structure by using the blockchain, a core technology of Bitcoin introduced by Satoshi Nakamoto in 2008. In this study, Getting away from existing time synchronization system in centralized structure, A blockchain network has completely decentralized structure using public blockchain. In decentralized structure, Only certain peers among the peers that participate in a blockchain network access the NTP server. Therefore, others can synchronize time without having to go to public network. Furthermore if appropriate time synchronization cycles are established for each peer, time synchronization can be maintained even when connection to public network is completely lost. A time synchronization system in this study has advantages of p2p system and can be also guaranteed reliability and stability because it used digital signature, merkle tree, consensus algorithm which are core characteristics of block chains.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.724-730
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• 2017

SpaceWire invented for spacecrafts has Time-Code defined for time synchronization over SpaceWire network. A Time-Code suffers transmission delay of 14[bit-period] and jitter up to 10[bit-period] whenever it passes through a SpaceWire link, which is the primary cause of time synchronization error. This work presents a simple method to improve the time synchronization which uses two extended Time-Codes. Nodes on a SpaceWire network can find how much delay and jitter a received Time-Code has suffered while it passes through the network, and they can correct time synchronization error with this information. The proposed method was validated in a simulation environment developed based on OMNeT++. The simulation result showed that time synchronization error less than a few bit-periods can be achieved. The proposed method is cost effective and suitable for small-scale SpaceWire network systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.5
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• pp.486-496
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• 2013

Time synchronization in underwater environment is challenging due to high propagation delay and mobility of sensor nodes. Previous researches do not consider practical issues affecting on the accuracy of time synchronization such as high-channel access delay and relative position between sensor nodes. Also, those protocols using bidirectional message exchange shorten the network lifetime and decrease the network throughput because numerous transmission, reception and unnecessary overhearing can be occurred. Therefore, in our research, we suggest enhanced time synchronization based on features of underwater environment. It controls the instant of transmission by exploiting the feature of an oceanic movement and node deployment. Moreover, the protocol uses more accurate time information by removing channel access delay from the timestamp. The proposed scheme is also practical on the underwater sensor network requiring low-power consumption because the scheme conducts time-synchronization with smaller transmission and reception compared with previous works. Finally, simulation results show that the proposed protocol deceases time error by 2.5ms and 0.56ms compared with TSHL and MU-Sync respectively, reducing energy consumption by 68.4%.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.5
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• pp.219-231
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• 2005

Many applications in cluster computing require QoS (Quality of Service) services. Since performance predictability is essential to provide QoS service, underlying systems must provide predictable performance guarantees. One way to ensure such guarantees from network subsystems is to generate global schedules from applications'network requests and to execute the local portion of the schedules at each network interface. To ensure accurate execution of the schedules, it is essential that a global time base must be maintained by local clocks at each network interface. The task of providing a single time base is called a synchronization problem and this paper addresses the problem for system area networks. To solve the synchronization problem, FM-QoS (1) proposed a simple synchronization mechanism called FBS(Feedback-Based Synchronization) which uses built-in How control signals. This paper extends the basic notion of FM-QoS to a theoretical framework and generalizes it: 1) to identify a set of built-in network flow control signals for synchrony and to formalize it as a synchronizing schedule, and 2) to analyze the synchronization precision of FBS in terms of flow control parameters. Based on generalization, two application classes are studied for a single switch network and a multiple switch network. For each class, a synchroniring schedule is proposed and its bounded skew is analyzed. Unlike FM-QoS, the synchronizing schedule is proven to minimize the bounded skew value for a single switch network. To understand the analysis results in practical networks, skew values are obtained with flow control parameters of Myrinet-1280/SAN. We observed that the maximum bounded skew of FBS is 9.2 Usec or less over all our experiments. Based on this result, we came to a conclusion that FBS was a feasible synchronization mechanism in system area networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.4
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• pp.344-365
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• 2009

The performance of a tracking system is greatly increased if multiple types of sensors are combined to achieve the objective of the tracking instead of relying on single type of sensor. To conduct the multi-modal tracking, we have previously developed a multi-modal sensor-based tracking model where acoustic sensors mainly track the objects and visual sensors compensate the tracking errors [1]. In this paper, we find a network synchronization problem appearing in the developed tracking system. The problem is caused by the different location and traffic characteristics of multi-modal sensors and non-synchronized arrival of the captured sensor data at a processing server. To effectively deliver the sensor data, we propose a time-based packet aggregation algorithm where the acoustic sensor data are aggregated based on the sampling time and sent to the server. The delivered acoustic sensor data is then compensated by visual images to correct the tracking errors and such a compensation process improves the tracking accuracy in ideal case. However, in real situations, the tracking improvement from visual compensation can be severely degraded due to the aforementioned network synchronization problem, the impact of which is analyzed by simulations in this paper. To resolve the network synchronization problem, we differentiate the service level of sensor traffic based on Weight Round Robin (WRR) scheduling at the routers. The weighting factor allocated to each queue is calculated by a proposed Delay-based Weight Allocation (DWA) algorithm. From the simulations, we show the traffic differentiation model can mitigate the non-synchronization of sensor data. Finally, we analyze expected traffic behaviors of the tracking system in terms of acoustic sampling interval and visual image size.

• Journal of Korea Society of Digital Industry and Information Management
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• v.9 no.3
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• pp.67-78
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• 2013

In this paper, We proposed an development method of application framework for using the precision time protocol(PTP) based on physical layer devices to synchronize clocks across a network with IEEE1588 capable devices. The algorithm was not designed as a complete solution across all conditions, but is intended to show the feasibility of such a for the PTP(Precision Time Protocol) based on time synchronization of heterogeneous network between devices that support in IEEE 1588 Standard application framework. With synchronization messages per second, the system was able to accurately synchronize across a single heavily loaded switch. we describes a method of synchronization that provides much more accurate synchronization in systems with larger networks. In this paper, using the IEEE 1588 PTP support for object-oriented modeling techniques through the 'application framework development Development(AFDM)' is proposed. The method described attempts to detect minimum delays, or precision packet probe and packet metrics. The method also takes advantage of the Tablet PC(Primary to Secondary) clock control mechanism to separately control clock rate and time corrections, minimizing overshoot or wild swings in the accuracy of the clock. We verifying the performance of PTP Systems through experiments that proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.2
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• pp.123-132
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• 2014

In this paper, an IEEE1588 based clock synchronization technique for CAN (Controller Area Network) is presented. Clock synchronization plays a key role to the success of a networked embedded system. Recently, the IEEE1588 algorithm making use of dedicated chipsets has been widely adopted for the synchronization of various industrial applications using Ethernet. However, there is no chipset available for CAN. This paper presents the implementation of IEEE1588 for CAN, which is implemented using only software and CAN packets without any dedicated chipset. The proposed approach is verified by the comparison between the estimated synchronization precision with a simple model and the measured precision with experimental setup.