• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.392-399
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• 2019

In this paper, we have studied wireless time division duplex(TDD) time synchronization technique considering the propagation delay between mobile vehicles. The existing IEEE 1588 precision time protocol(IEEE 1588 PTP) algorithm was applied and the time synchronization between the two nodes was achieved through the propagation delay and clock offset time correction calculated between master slave nodes during wireless TDD communication. The time synchronization process and procedure of IEEE 1588 PTP algorithm were optimized, thereby reducing the propagation delay error sensitivity for real-time moving vehicles. The sync flag signal generated through the time correction has a time synchronization accuracy of max +252.5 ns within 1-symbol(1.74 M symbol/sec, ${\pm}287.35ns$) through test and measurement, and it was confirmed that the time synchronization between master slave nodes can be achieved through sync flag signal generated during GPS disturbance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.971-981
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• 2009

The coordination of distributed entities and events requires time synchronization. Precision time synchronization enables a variety of extensions of applications and provides much accurate information. The IEEE 1588 precision time protocol (PTP) provides a standard method to synchronize devices in a network. This paper deals with the design and implementation of a PTP gateway to extend IEEE 1588 to Zigbee networks. The PTP gateway can not only extend IEEE 1588 to Zigbee networks but also share the same time reference using IEEE 1588 between two or more Zigbee networks. This paper also presents experiments and performance evaluation of time synchronization using the PTP gateway. Our result established a method for nodes in a network to maintain their clocks to within a 300 nanosecond offset from the reference clock of a master node via Ethernet.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2009.04a
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• pp.325-326
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• 2009

다각촬영카메라를 제어하고 GPS/INS와 동기화하기 위해서 다각촬영 카메라 제어 장비(MLCC)를 개발하였다. 이는 5대의 카메라에 촬영신호를 보내고 촬영시각을 GPS/INS와 동기화 하여 정확한 촬영시각을 기록하기 위한 장비이다. 개발 결과를 검증하기 위하여 Applanix사의 POS 시스템과 Leica-Geosystem의 IPAS20을 병렬로 연결하여 그 결과를 비교하였다. 비교 결과 다각촬영 카메라를 제어하기에 충분한 정밀도를 보여 주었으며, 차기년도 경량화를 진행하고자 한다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.6
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• pp.446-455
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• 2001

In this paper, the precise synchronized clock generator using GPS receiver is presented. The GPS receiver provides a synchronized IPPS signal which guaranties a reliable standard time mark. This signal allows us to do time synchronization and correct the time step. We designed and implemented the precise synchronized clock generator based on DPLL in order to generate a high-resolution clock from a low-cost inaccurate oscillator with ALTERA FLEX EPM6016TC144-3. We also implemented a hardware unit and proved that the unit provides 1MHz clock output which had a high resolution and accuracy when it was combined with GPS receiver.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.39 no.6
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• pp.587-598
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• 2021

This study aims to develop a multi-camera based MMS (Mobile Mapping System) technology for building a HD (High Definition) map for autonomous driving and for quick update. To replace expensive lidar sensors and reduce long processing times, we intend to develop a low-cost and efficient MMS by applying multiple cameras and real-time data pre-processing. To this end, multi-camera storage technology development, multi-camera time synchronization technology development, and MMS prototype development were performed. We developed a storage module for real-time JPG compression of high-speed images acquired from multiple cameras, and developed an event signal and GNSS (Global Navigation Satellite System) time server-based synchronization method to record the exposure time multiple images taken in real time. And based on the requirements of each sector, MMS was designed and prototypes were produced. Finally, to verify the performance of the manufactured multi-camera-based MMS, data were acquired from an actual 1,000 km road and quantitative evaluation was performed. As a result of the evaluation, the time synchronization performance was less than 1/1000 second, and the position accuracy of the point cloud obtained through SFM (Structure from Motion) image processing was around 5 cm. Through the evaluation results, it was found that the multi-camera based MMS technology developed in this study showed the performance that satisfies the criteria for building a HD map.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.737-738
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• 2011

전력 계통현상 분석장치(DFR)에서 시각동기에 대한 중요성이 부각됨에 따라 장치의 시각동기가 중요하게 대두되고 있다. 본 연구내용에서 보여주고자 하는 DFR TimeSync Simulator는 GPS 수신기로부터 IRIG-B 신호와 1PPS 신호를 수신하여 계통현상 분석장치의 사고발생 이벤트를 위한 절대시각을 제공하는 장치이다. 이 절대시각은 계통현상 분석장치의 정밀성 및 품질을 검증하는데 적용한다. 그리고 개발된 Simulator가 정확한 1PPS 신호를 산출해 내는지를 검증하기 위해 GPS 수신기의 1PPS 신호와 Simulator에서 출력되는 1PPS 신호의 파형을 비교 실험하여 정확도 및 신뢰성을 확인하였다.

• Journal of Astronomy and Space Sciences
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• v.22 no.4
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• pp.491-500
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• 2005

Every time laboratory in the world follows an international standard time scale and GPS (Global Positioning System) is playing an important role. Korea Research Institute of Standards and Science is also operating a permanent GPS station for time transfer. To improve the accuracy and precision of the clock offsets derived from GPS we used carrier phase measurements. In addition, we tested four different kinds of GPS satellite orbits and compared the results. The precision of the time offsets using rapid and ultra-rapid orbits was about 0.5 nanoseconds (ns). Tn the case of broadcast orbits, the precision was better than 2 ns.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.6
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• pp.515-519
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• 2021

IEEE 1588 PTP is a precision time protocol in which two systems synchronize without the aid of GPS by exchanging packets including transmission/reception time information. In the time synchronization process, the propagation delay time can be calculated and the distance between the two systems can be measured using this. In this paper, we proposed a method to improve the distance measurement precision less than the modulation symbol period using the timing error information extracted from the preamble of the received packet. Computer simulations show that the distance measurement precision is proportional to the length of the preamble PN sequence and the signal-to-noise ratio.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.9
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• pp.2022-2028
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• 2015

SpaceWire is a standard for high-speed links and networks between spacecraft components, which was invented for better, cheaper and faster on-board data handling in spacecraft. The standard defines timecode and its distribution which can be used for time synchronization among the nodes in a SpaceWire network. A timecode output from the time master which provides standard time over a SpaceWire network travels through links and routers to reach every nodes. While traveling, a timecode suffers from transmission delay and jitter which cause some difference in time synchronization among nodes. In this work, a simulator was developed using OMNeT++ to simulate the operation of a SpaceWire network and some analyses were performed on the transmission delay and jitter accompanied with a transmission of a timecode. The result will be used in the near future for the research of a precise time synchronization technique over a SpaceWire network.

• Electronics and Telecommunications Trends
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• v.32 no.3
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• pp.98-106
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• 2017

GPS 등과 같은 위성항법 시스템은 정밀한 시각동기가 요구되는 동기식 이동통신망, 전력망, 금융망과 같은 분야와 사용자의 정밀한 위치를 요구하는 차량 내비게이션, 항공기 및 자동차, 측지 측량분야는 물론 향후 드론 및 자율주행 차량 등과 같은 다양한 응용분야에서 그 활용도가 증가될 것이다. 또한, 스마트폰에서는 기본적으로 위성항법 칩셋이 내장되어 사용자 위치를 제공하고 있다. 이렇듯 다양한 분야에서 활용되는 위성항법 수신 칩셋 또는 수신 시스템의 기능 및 성능을 다양한 환경에서 검증할 필요성이 대두되고 있다. 본고에서는 다양한 검증 환경을 제공할 수 있는 위성항법 신호생성기의 국외기술 동향을 살펴보고, 미래부 출연사업인 GNSS 전파교란 검증플랫폼 과제를 통해 개발된 GNSS 전파혼신 신호발생장치에서 확보한 실제 GPS 신호와 동기를 유지한 신호생성기술 개발 현황을 소개한다.