• Journal of rehabilitation welfare engineering & assistive technology
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• v.5 no.1
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• pp.111-115
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• 2011

In this paper, we present a novel time-synchronization method for distributed systems to measure the body motion. The distributed system scheme is considered because human data acquisition systems tend to have a centralized controller with sensors connected with a long range of electric wires running through the subject's body, which results in inconvenience. Utilizing simple key switches and digital input ports for reading the key, the proposed method requires a very simple hardware structure, which means less power consumption compared with the well-known ubiquitous sensor network. After measuring the motion data as well as the synchronization pulses, the proposed method compensates, in offline, the difference of the sampling instance between the two systems by scaling the time difference. The paper presents experimental results to show the validity of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.4
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• pp.303-310
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• 2008

Recently, IEC 61850 supports the standardized communication technique in both station bus and process bus, and presents substation automation model. In order to implement the IEC 61850 based communication in a substation using the MU (merging unit) which is one of the important data acquisition equipments in substation automation, the time synchronization is demanded for cooperative operation between the devices. This paper proposes the precision time synchronization technique using IRIG-B protocol to develop the MU under IEC 61850 communication protocol. The proposed technique is implemented and its performance is verified experimentally.

• Journal of Advanced Navigation Technology
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• v.24 no.4
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• pp.267-272
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• 2020

In order to monitor in large area of a ship without any concerns of spacial environments, there can be the use of many sensors that support wireless network technologies. Through the deployment of the wireless sensors and their autonomous network formations, the status of a ship can be easily monitored in real time. Moreover, if all the sensors are timely synchronized with each other, the locations and the moving directions of certain events can be estimated. Thus, the time synchronization amongst wireless sensors are crucial. In this paper, we propose an algorithm which supports reduced message transmissions between the sensors for synchronization.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.1
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• pp.7-14
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• 2013

Presently, there are many different technologies used for position detection. However, as signal-receiving devices operating in different locations must detect the precise position of objects located at long distances, it is essential to know the precise time at which an object's or a user's terminal device sends a signal. For this purpose, the existing time of arrival (ToA) technology is not sufficiently reliable, and the existing time difference of arrival (TDoA) technology is more suitable. If a TDoA-based electric surveillance system and other tracking devices fail to achieve precise time-synchronization between devices with separation distance operation, it is impossible to obtain correct TDoA values from the signals sent by the signal-receiving devices; this failure to obtain the correct values directly affects the location estimation error. For this reason, the technology for achieving precise time synchronization between signal-receiving devices in separation distance operation, among the technologies previously mentioned, is a core technology for detecting TDoA-based locations. In this paper, the accuracy of the proposed time synchronization and the measurement error in the TDoA-based location detection technology is evaluated. The TDoA-based location measurement error is significantly improved when using the proposed method for time-synchronization error reduction.

• International journal of advanced smart convergence
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• v.9 no.1
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• pp.109-112
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• 2020

Many devices are connected on the internet to give functionalities for interconnected services. In 2020', The number of devices connected to the internet will be reached 5.8 billion. Moreover, many connected service provider such as Google and Amazon, suggests edge computing and mesh networks to cope with this situation which the many devices completely connected on their networks. This paper introduces the current state of the introduction of the wireless mesh network and edge cloud in order to efficiently manage a large number of nodes in the exploding Internet of Things (IoT) network and introduces the existing Network Time Protocol (NTP). On the basis of this, we propose a relatively accurate time synchronization method, especially in heterogeneous mesh networks. Using this NTP, multiple time coordinators can be placed in a mesh network to find the delay error using the average delay time and the delay time of the time coordinator. Therefore, accurate time can be synchronized when implementing IoT, remote metering, and real-time media streaming using IoT mesh network.

• Journal of IKEEE
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• v.23 no.3
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• pp.1096-1099
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• 2019

In this paper, we propose the protocol for construction of smart factory. The proposed protocol for construction of smart factory consists of an OPC UA Server/Client, a technology of TSN realtime communication, a NTP & PTP time synchronization protocol, a FieldBus protocol and conversion module, a technology of saving data for data transmit latency and synchronization protocol. OPC UA server/client is a system integration protocol which makes interface industrial hardware device and supports standardization which allows in all around area and also in not independent from any platform. A technology of TSN realtime communication provides an high sensitive time management and control technology in a way of sharing specific time between devices in the field of high speed network. NTP & PTP time synchronization protocol supports IEEE1588 standardization. A fieldbus protocol and conversion module provide an extendable connectivity by converting industrial protocol to OPC. A technology of saving data for data transmit latency and synchronization protocol provide a resolution function for a loss and latency of data. Results from testing agencies to assess the performance of proposed protocol for construction of smart factory, response time was 0.1367ms, synchronization time was 0.404ms, quantity of concurrent access was 100ea, quantity of interacting protocol was 5ea, data saving and synchronization was 1,000 nodes. It produced the same result as the world's highest level.

• 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 the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1312-1317
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• 2013

Pseudolite is a contraction of the term "pseudo-satellite", used to refer to something that is not a satellite which performs a function commonly in the domain of satellites. Pseudolite are most often small transceivers that are used to create a local, ground-based GPS alternative. Pseudo-range measurement of pseudolite has around 300m range error, when time synchronization error of $1{\mu}sec$ occurs. Therefore the time synchronization methods play an important part in navigation augmentation using pseudolite. This paper proposes three clock synchronization methods that are installation method of pseudolite station, method using KRISS-UTC and method using PRN code phase difference for pseudolite. The simulation platform structure is presented for evaluating proposed clock synchronization performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.165-176
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• 2015

Clock or time synchronization protocol is one of the crucial factors that could determine the quality of the communication. With the rapid development of the network technology, more robust clock synchronization algorithm is required. IEEE 1588 is one of the possible solutions for a robust clock synchronization algorithm; however, there are still some challenges that need to be concerned in IEEE 1588 in term of reducing and stabilizing the PDV value. This survey paper shows several solutions that could improve the performance of IEEE 1588, including modifying the PTP message transmission, optimizing PTP method, filtering techniques, and using the hardware timestamp instead of application layer timestamp, and so on. Despite the improvement that is created with these techniques, the clock synchronization algorithm is still an open issue in the network communication.

• Journal of Advanced Navigation Technology
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• v.5 no.1
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• pp.45-53
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• 2001

We present the frame synchronization scheme using the FFT window position restoration algorithm appropriate for wireless OFDM systems under multipath fading environment. From the restoration of the synchronization parameters of previous several frames, the algorithm can extract the synchronization parameters for the next frames. To analyze the performance of the proposed algorithm, we compare the probability of synchronization failure under time and frequency domains, respectively. From the simulation results, one can see that the algorithm in the time domain shows better performance than in the frequency one, for the $E_b/N_o$ of 6.0dB or more.