• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.429-436
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• 2014

This paper proposes three methods of the time synchronization for Pseudolite and GPS and analyzes pseudolite time synchronization error factors for software based performance evaluation on proposed time synchronization methods. Proposed three time synchronization methods are pseudolite time synchronization station construction method, method by using UTC(KRIS) clock source and GPS timing receiver based time synchronization method. Also, we analyze pseudolite time synchronization error factors such as errors of pseudolite clock and reference clock, time delay as clock transmission line, measurement error of time interval counter and error as clock synchronization algorithm to design simulation platform for performance evaluation of pseudolite time synchronization.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.394-400
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• 2016

It is well known that the encrypted ranging signal, such as GPS P(Y) code, is immune to spoofing attack. However, in order for users to use the signal, there needs permission from the operator. And also there are many restrictions for use because of security issues. In this paper, a ground reference station equipped with high-gain directional antenna and a user receiver were simulated. In the reference station, the encrypted code can be demodulated from the high-gain signal. And then the code can be used to detect spoofing attack in the user receiver. This paper proposes the spoofing detection method using the encrypted signal and deals with simulation results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.7
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• pp.629-635
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• 2012

This paper presents a performance analysis of the GPS(Global Positioning System) receiver on board in LEO satellites, based on the comparison of its in-orbit performances and corresponding ground test results. An extensive ground tests on the subject GPS receiver has been performed in diverse conditions under the right frame of ground test environments and the analysis of in-orbit performances has also been performed with the huge amount of accumulated GPS data which has been in operation for 6 years since its launch on 2006. For this analysis, we chose three sets of in-orbit data; the data during the early mission period, the data at the 3-year mission completion time, and the most recent in-orbit data. As the performance measures, we selected the position and time synchronization accuracy, and the comparative analysis shows the concurrency between the in-orbit performances and the ground test results with in these performance measures, verifying the validity of the ground test. It is expected that the test configuration and analysis method presented in this paper can be applied to developing and verifying the future Koreanized satellite GPS receivers.

• The Korean Journal of Air & Space Law and Policy
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• v.35 no.3
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• pp.127-150
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• 2020

A Basic Plan for the Promotion of Space Development (hereinafter referred to as "basic plan"), which prescribes mid- and long-term policy objectives and basic direction-setting on space development every five years, is one of the matters to be deliberated by the National Space Committee. Confirmed February 2018 by the Committee, the 3rd Basic Plan has a unique matter, compared to the 2nd Basic Plan. It is to construct "Korean Positioning System(KPS)". Almost every country in the world including Korea has been relying on GPS. On the occasion of the shooting down of a Korean Air flight 007 by Soviet Russia, GPS Standard Positioning Service has been open to the world. Due to technical errors of GPS or conflict of interests between countries in international relations, however, the above Service can be interrupted at any time. Such cessation might bring extensive damage to the social, economic and security domains of every country. This is why some countries has been constructing an independent global or regional satellite navigation system: EU(Galileo), Russia(Glonass), India(NaVic), Japan(QZSS), and China(Beidou). So does South Korea. Once KPS is built, it is expected to make use of the system in various areas such as transportation, aviation, disaster, construction, defense, ocean, distribution, telecommunication, etc. For this, a pan-governmental governance is needed to be established. And this governance must be based on the law. Korea is richly experienced in developing and operating individually satellite itself, but it has little experience in the simultaneous development and operation of the satellites, ground, and users systems, such as KPS. Therefore we need to review overseas cases, in order to minimize trial and error. U.S. GPS is a classic example.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.87-90
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• 2003

정밀한 위치결정에 사용되는 GPS는 초기 군사목적을 벗어나 자동차, 선박, 비행기 등의 항법은 물론 측량분야, 지각 및 구조물의 변위 감시, 우주, 통신, 국방 분야 등 매우 광범위한 분야에서 활용되고 있으며, 그 이용도가 급속히 증가하는 추세이다. 그러나 GPS 관측값은 부정오차와 정오차 등 많은 오차를 포함하고 있기 때문에 이를 소거하거나 최소화하여야 한다. GPS 오차는 크게 위성궤도나 위성시간 오차등 위성에 관련된 오차, 수신기 잡음이나 다중경로 등 수신기 관련 오차, 그리고 대류권이나 전리층에 의한 전파 오차로 구분할 수 있다. 이들 오차들은 대부분 차분방법과 수학적 알고리즘에 의해 소거되거나 최소화되지만, 다중경로와 수신기 잡음은 소거하거나 축소할 수 없다. 다중경로는 관측당시의 수신기 주변환경에 따라 바뀌기 때문에 수학적으로 소거할 수 없으며, 수신기 잡음은 수신기 내부의 노이즈로 인하여 발생하기 때문에 소거하기가 상당히 어렵다. 본 연구에서는 다중경로에 의한 GPS 기선변화를 알아보기 위해서 여러 조건하에서 정적 GPS 측량을 실시하였다. 먼저 정확한 좌표를 알고 있는 한 점에 GPS를 설치하고 다른 두 대의 GPS을 임의 점에 설치하였고, 이들 두 GPS 중에 하나의 수신기에 다중경로 환경을 설정하였다 정적 GPS 관측시 기선에 어떠한 변화가 오는 파악하기 위해서 기선처리와 망조정을 통해 기선길이와 좌표값을 산출하였다. 이러한 다중경로 실험은 구조물 모니터링 등 mm 정확도를 요구하는 GPS 측량에 유용하게 사용될 수 있을 것이다.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.66-72
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• 2009

In order to verify the operability of a GPS receiver which is one of the KSLV-I onboard electrical equipments under the vacuum conditions, this paper describes the operation methods and performance results of the GPS receiver under the thermal-vacuum and vacuum environments. The damages and degradations of electrical parts of the GPS receiver caused by the pressure change and high-degree vacuum conditions are analyzed in terms of tracking and navigation capabilities through the signal-to-noise ratio and navigation error.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.2
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• pp.149-157
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• 2009

The orbit ephemeris of Global Positioning System(GPS) is one element to determine the surveying accuracy and there are broadcasting ephemeris and precise ephemeris, IGS rapid orbit and IGS ultra rapid orbit in the orbit ephemeris of GPS. In this study, test area was selected in Uljin, Kyungsanbukdo and GPS surveying was accomplished at 37 points in the test area. Then baseline solution was done on 74 baseline using broadcasting ephemeris and precise ephemeris and analysis by TGO and the results were compared. Comparison results were showed that there were nearly no difference between the two results but in case of relative precision of the baseline, it was slightly better the baseline results of precise ephemeris which showed 0.706ppm than the baseline results of broadcasting ephemeris which showed 0.708ppm.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.2 s.25
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• pp.96-102
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• 2006

In this paper, the design, construction and basic characteristics of an electronically adaptive array antenna for the GPS receiver is described. The susceptibility of the GPS signals to the interference is of concern to the GPS user community. Because of the low received power of the GPS signals, outages can easily occur due to the unintentional interference and the easily obtainable low cost GPS jammer denying access to the GPS signals. We propose a technique of the adaptive array antenna that detects the GPS interference sources and controls the null beam pattern only toward the jamming sources to acquire GPS navigation data after acquisition and tracking of the GPS signals.

• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.421-428
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• 2014

GPS satellite positions can be obtained from the navigation message transmitted from the GPS satellite. In this paper, the accuracy of broadcast orbit and clock are analyzed by comparing with the NGA precise ephemeris. For analyzing global and local orbit errors in 2004 to 2013, GPS satellite visibilities are calculated in Korea. Local RMS of 3D orbit error and SISRE are 4 cm and 3 cm less than global RMS of 3D orbit errors and SISRE. Orbit and clock errors are calculated for each GPS satellite Block for 10 years. SISRE of Block IIA satellites are 2.8 times greater than Block IIF satellites. The correlation between orbit errors and shadow condition is analyzed. The orbit errors in shadow is 2.1% higher than that in sunlight. Correlation analysis between the orbit errors and solar/geomagnetic index shows that orbit errors has a high correlation with from 2004 to 2008. However, the correlation became low since 2009.

• Journal of Advanced Navigation Technology
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• v.22 no.6
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• pp.585-590
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• 2018

GPS satellite orbits could be estimated precisely using GPS dynamics as well as GPS observations. Most of the perturbations are available to be generated using satellite position, velocity, well known model equations and coefficients. However, who wants to calculate solar radiation pressure (SRP) should choose a SRP model and estimate the coefficients of a SRP model. The accuracy of SRP model depends on the model characteristics. Therefore this paper has estimated coefficients of SRP models using CODE precise orbit product and compared the accuracy of orbit propagator depending on SRP model. The results show that the extended CODE orbit model (ECOM) and the reduced ECOM achieved cm level fitting orbit for the CODE 1-day orbit. Also orbit propagation model without SRP model consideration could get tens of meter orbits compared to CODE orbits.