• 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 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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.5
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• pp.1004-1009
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• 2004

Precise time synchronization is a main technology in high-speed communications, parallel and distributed processing systems, Internet information industry and electronic commerce. Synchronized clocks are useful for many leasers. Often a distributed system is designed to realize some synchronized behavior, especially in real-time processing in factories, aircraft, space vehicles, and military applications. Nowadays, time synchronization has been compulsory thing as distributed processing and network operations are generalized. A network time server obtains, keeps accurate and precise time by synchronizing its local clock to standard reference time source and distributes time information through standard time synchronization protocol. This paper describes design issues and implementation of a network time server for time synchronization especially based on a clock model. The system uses GPS (Global Positioning System) as a standard reference time source and offers UTC (universal Time coordinated) through NTP (Network Time protocol). Implementation result and performance analysis are also presented.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.3
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• pp.216-223
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• 2005

A computer clock has limits in accuracy and precision affected by its inherent instability, the environment elements, the modification of users, and errors of the system. So the computer clock needs to be synchronized with a standard clock if the computer system requires the precise time processing. The purpose of synchronizing clocks is to provide a global time base throughout a distributed system. Once this time base exists, transactions among members of distributed system can be controlled based on time. This paper discusses the integrated approach to clock synchronization. An embedded system is considered for time synchronization based on the GPS(Global Positioning System) referenced time distribution model. The system uses GPS as standard reference time source and offers UTC(Universal Time Coordinated) through NTP(Network Time Protocol). A clock model is designed and adapted to keep stable time and to provide accurate standard time with precise resolution. Private MIB(Management Information Base) is defined for network management. Implementation results and performance analysis are also presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1B
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• pp.86-97
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• 2009

RTLS is a system for automatically locating and tracking people and objects. The TDOA-based RTLS determines the location of the tag by calculating the time differences of a signal received from the tag. In TDOA-based RTLS, time synchronization is essential to calculate the time difference between readers. This paper presents a precision time synchronization method for TDOA-based RTLS over IEEE 802.15.4. In order to achieve precision time synchronization in IEEE 802.15.4 radio, we analyzed the error factors of delay and jitter. We also deal with the implementation of hardware assisted time stamping and the Kalman filtering method to minimize the error factors. In addition, this paper described the experiments and performance evaluation of the proposed precision time synchronization method in IEEE 802.15.4 radio. The results show that the nodes in a network can maintain their clocks to within 10 nanoseconds offset from the reference clock.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.715-718
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• 2016

SpaceWire invented for on-board data handling in a spacecraft has Time-Code defined for time synchronization over SpaceWire network. Delay and jitter of the transmission of Time-Code caused when a Time-Code travels through a network are the main reasons of time synchronization error. This work proposes a scheme that can reduce the time synchronization error by using extended Time-Codes. The proposed scheme can remove both transmission jitter and transmission delay. The scheme will be validated in a simulation environment built with OMNeT++.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.104-108
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• 2004

The most of the CDMA mobile communication depends on the GPS for the time synchronization. Then, we must prepare alternative system against the unusable GPS like a unexpectable accident or strategic purpose by the USA government. In this study, we have constructed ground test segment for the time synchronization system using the geostationary satellite. In addition. we have designed, manufactured and tested the transmitting and receiving board to receive 1 PPS signal from atomic clock for transmitting stored data in buffer to satellite modem and to produce 1 PPS signal from satellite modem for measuring time delay.

• KIPS Transactions on Software and Data Engineering
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• v.4 no.9
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• pp.385-392
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• 2015

In IoT(Internet of Things), it is important for wireless networks to communicate data created among resource-constrained wireless nodes, where time synchronization is needed for meaningful data creation and transmission. Time Synchronization by flooding is one of the mostly used protocols for WSN(Wireless Sensor Networks). Even though this type of scheme has some advantages over other types (i.e. a simple algorithm and independency of topology and so on), too many data transmission is required, leading to large power consumption. So, reducing transmission data is an important issue for energy efficiency in this kind of networks. In this paper, a new Flooding-based time synchronization protocol is proposed to use energy efficiently by reducing a transmitted traffic. The proposed scheme's performance has been evaluated and compared with an representative scheme, FTSP(Flooding Time Synchronization Protocol) by simulation. The results are shown that the proposed scheme is better than FTSP.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.7
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• pp.273-281
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• 2003

This paper proposes a new time synchronization scheme for the Automatic Identification System(AIS). The proposed scheme utilizes a Temperature Compensated Crystal Oscillator(TCXO) as a local reference clock, and consists of a Digitally Controlled Oscillator(DCO), a divider, a phase comparator, and register blocks. Primary time reference is IPPS from GPS receiver that is synchronized to Universal Time Coordinated(UTC). And if GPS is unavailable, other station's signal is utilized as secondary time reference. The phase comparator measures time difference between the 1PPS and the generated transmit clock. The measured time difference is compensated by controlling the DCO and the transmit clock is synchronized to the Universal Time Coordinated(UTC). The synchronized transmit clock(9600Hz) is divided into the transmitting time slot(37.5Hz). The proposed scheme is tested in an experimental AIS transponder set. The experimental result shows that the proposed module satisfies the timing specification of the AIS technical standard, ITU-R M.1371-1.

• 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.