• Journal of Positioning, Navigation, and Timing
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• 제3권4호
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• pp.163-170
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• 2014

A pseudolite is used as a GPS backup system, and is also used for the purpose of indoor navigation and correction information transmission. It is installed on the ground, and transmits signals that are similar to those of a GPS satellite. In addition, in recent years, studies on the improvement of positioning accuracy using the pseudorange measurement of a pseudolite have been performed. As for the effect of the time synchronization error between a pseudolite and a GPS satellite, a time synchronization error of 1 us generally induces a pseudorange error of 300 m; and to achieve meter-level positioning, ns-level time synchronization between a pseudolite and a GPS satellite is required. Therefore, for the operation of a pseudolite, a time synchronization algorithm between a GPS satellite and a pseudolite is essential. In this study, for the time synchronization of a pseudolite, "a pseudolite time synchronization method using the time source of UTC (KRIS)" and "a time synchronization method using a GPS timing receiver" were introduced; and the time synchronization performance depending on the pseudolite time source and reference time source was evaluated by designing a software-based pseudolite time synchronization performance evaluation simulation platform.

• 한국통신학회논문지
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• 제38C권2호
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• pp.141-154
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• 2013

신호수신장치들간 시각 동기화는 TDoA를 이용한 위치 탐지에 있어 가장 중요한 전제 사항이 된다. 본 논문에서는 시스템의 시각동기 정확도를 위하여 고정밀도의 OCXO와 DPLL을 이용하여 원자 클럭을 사용하는 GPS 위성으로부터 수신되는 1 pps(pulse per second) 신호에 위상동기 되는 방식을 제안한다. GPS 기반 고정밀 타이밍 레퍼런스의 성능은 근본적으로 매우 우수한 장기간에 걸친 주파수 안정도(long-term frequency stability)를 갖는 GPS 타이밍 신호의 특성을 따라간다고 볼 수 있으며, GPS 타이밍 신호에 동기가 되면 0.001 ppb(part per billion) 급의 초정밀 타이밍 레퍼런스를 통해 시각 동기의 정확도를 향상시킨다. 제안하는, 향상된 시각 동기 정확도를 통해 TDoA 기반의 위치 탐지 기술에서의 측정 오차를 평가하고, 시각동기 오차 개선 방법이 TDoA 기반의 위치 측정 오차를 크게 개선함을 보인다.

• Journal of Positioning, Navigation, and Timing
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• 제4권2호
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• pp.67-72
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• 2015

Power grid techniques are distributed over general power systems ranging from power stations to power transmission, power distribution, and users. To monitor and control the elements and performance of a power system in real time in the extensive area of power generation, power transmission, wide-area monitoring (WAM) and control techniques are required (Sattinger et al. 2007). Also, to efficiently operate a power grid, integrated techniques of information and communication technology are required for the application of communication network and relevant equipment, computing, and system control software. WAM should make a precise power grid measurement of more than once per cycle by time synchronization using GPS. By collecting the measurement values of a power grid from substations located at faraway regions through remote communication, the current status of the entire power grid system can be examined. However, for GPS that is used in general national industries, unexpected dangerous situations have occurred due to its deterioration and jamming. Currently, the power grid is based on a synchronization system using GPS. Thus, interruption of the time synchronization system of the power system due to the failure or abnormal condition of GPS would have enormous effects on each field such as economy, security, and the lives of the public due to the destruction of the synchronization system of the national power grid. Developed countries have an emergency substitute system in preparation for this abnormal situation of GPS. Therefore, in Korea, a system that is used to prepare for the interruption of GPS reception should also be established on a long-term basis; but prior to this, it is required that an evaluation technique for the time synchronization performance of a GPS receiver using an atomic clock within the power grid. In this study, a monitoring system of time synchronization based on GPS at a power grid was implemented, and the results were presented.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2006년도 하계학술대회
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• pp.235-240
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• 2006

In order to enhance receive sensitivity in noisy environment, the previous initial synchronization method of GPS receiver for reference stations adopts not only the coherent integration method but also the non-coherent integration method. However, the previous GPS initial synchronization method causes the non-coherent integration loss, which is a dominant factor among the signal acquisition losses in noisy environment. And the non-coherent integration loss increases with the strength of noise signal. In this pa-per, a GPS initial synchronization method is proposed to enhance receive sensitivity of GPS receiver for reference stations in noisy environment. This paper presents that the proposed GPS initial synchronization method suppresses the non-coherent integration loss. Furthermore, with regard to the mean acquisition time, it is shown that the number of the search cells of the proposed GPS initial synchronization method is much fewer than that of the previous GPS initial synchronization method.

• 한국항행학회논문지
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• 제18권5호
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• pp.429-436
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• 2014

본 논문에서는 의사위성과 GPS 위성 사이의 시각동기를 위한 세가지 동기 방안을 제안하고 시각동기 기법의 성능 분석에 필요한 의사위성 시각동기 오차요소에 대해 분석한다. 제시한 세가지 시각동기 방안으로는 의사위성 시각동기 스테이션 구축 방안, UTC(KRIS)의 시각정보원을 활용한 의사위성 시각동기 방안, GPS 시각용 수신기를 활용한 시각동기 방안이 있다. 또한 제안한 의사위성 시각동기 방안의 성능평가를 위한 시뮬레이션 구성을 위해 의사위성 시각동기 방안의 오차요소를 의사위성 및 기준 클럭의 오차, 전송선로에 의해 발생하는 오차, TIC에 의해 발생하는 오차, 클럭 동기 알고리즘에 의해 발생하는 오차로 구분하고 각 오차 요소를 분석하였다.

• ETRI Journal
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• 제30권1호
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• pp.59-67
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• 2008

The necessity for the precise time synchronization of measurement data from multiple sensors is widely recognized in the field of global positioning system/inertial navigation system (GPS/INS) integration. Having precise time synchronization is critical for achieving high data fusion performance. The limitations and advantages of various time synchronization scenarios and existing solutions are investigated in this paper. A criterion for evaluating synchronization accuracy requirements is derived on the basis of a comparison of the Kalman filter innovation series and the platform dynamics. An innovative time synchronization solution using a counter and two latching registers is proposed. The proposed solution has been implemented with off-the-shelf components and tested. The resolution and accuracy analysis shows that the proposed solution can achieve a time synchronization accuracy of 0.1 ms if INS can provide a hard-wired timing signal. A synchronization accuracy of 2 ms was achieved when the test system was used to synchronize a low-grade micro-electromechanical inertial measurement unit (IMU), which has only an RS-232 data output interface.

• 항공우주기술
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• 제2권1호
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• pp.98-107
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• 2003

멀리 떨어진 장소의 시계를 동기시키기 위해 사용하는 일반적인 방법에 대한 조사 연구를 수행하였다. 현재까지 사용되었거나 사용 중인 시각동기 방법은 여러 가지가 있는데 크게 세가지 범주로 분류할 수 있다. 첫 번째는 지상망에 의한 방법, 두 번째는 GPS/NAVSTAR 위성망에 의한 방법, 그리고 세 번째, 정지위성에 의한 시각동기 방법이다. 특히 GPS/NAVSTAR 위성망은 무선 디지털 통신용 기지국의 시각동기에 사용되고 있으며, 이것의 백업 시스템으로써 정지위성에 의한 시각동기 방법이 연구되고 있다. 본 논문에서는 세 가지로 분류된 각각의 시각동기 방법에 대해 설명한다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.367-370
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• 2006

A GPS-based time synchronization technique employing a refined HW circuitry and SW algorithm is considered as fine time-management system for Low Earth Orbit (LEO) remote sensing satellites. By synchronizing the On-Board Time (OBT) within satellites to the GPS 1PPS, a very expensive, highly accurate on-board clock is not required to determine the precise on-board time management. Also, the satellite command generation in ground stations and postprocessing of earth observation data which a particular image is acquired. This paper analyses on-orbit verification of the existing satellite time sync architecture and presents a new time sync architecture, operation and relation between the OBT and the GPS time.

• 제어로봇시스템학회논문지
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• 제8권2호
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• pp.185-192
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• 2002

A novel GPS initial synchronization scheme with low hardware complexity is proposed. The proposed method has the decomposed differential matched filter, which consists of 25% multiplier and adder of the conventional matched filter. This paper presents the generalized mean acquisition time of initial synchronization scheme with multiple correlator. It is shown that the proposed method, in spite of its low hardware complexity, has the equal performance to the conventional method. The performance of the proposed method is verified through the simulation test by the GPS simulator. It is shown that the proposed method prevents the squaring loss of non-coherent integration.

• 항공우주기술
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• 제3권1호
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• pp.109-116
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• 2004

일반적으로 위성에 장착된 GPS 수신기는 GPS 위성으로부터 항법 신호를 받아서 위성의 위치, 시간 및 속도 정보를 제공하는 것을 주요 목적으로 하고 있다. 이러한 정보를 근거로 위성의 현재 위치정보 및 임무 수행을 위한 정보를 유도하게 된다. 2005년 발사예정인 아리랑 위성2호는 GPS 수신기에서 나오는 IPPS 신호를 위성체 각 프로세서의 기준시간으로 사용되며 DPLL, FEP회로 및 운용소프트웨어(FSW)에 의하여 동작된다. 본 논문에서는 아리랑 위성2호(KOMPSAT-2,이하 K2)의 시간동기구조에 대한 구조 및 설계에 대한 뿐 아니라 정밀도 분석 및 시험결과등 전 과정에 대한 내용을 기술하였다.