• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.601-607
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• 2017

This study performed fault test on global positoining system (GPS) carrier phase measurements, which is a preprocessing step to generate the positioning correction information based on the global navigation satellite system (GNSS) infrastructure. The existing carrier acceleration ramp step test (CARST) method affects the test result by using the mean value to eliminate the receiver clock error. In this regard, this study applied differencing and compared its results with those of the existing CARST. The fault simulation that applied artificial faults to the actual data found that the fault could be detected independently on each satellite when difference method was applied, and the single difference CARST and the double difference CARST produced similar results. The comparison with the existing method using actual data demonstrated the strengths and weaknesses of satellite and station single difference. Nevertheless, it is our understanding that it would require an additional analysis to determine whether the results were affected by the satellite or receiver clock error.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.225-231
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• 2011

The satellite clock anomalies, one of the abnormal signal factors of the GPS satellites, can have a significant impact on the GPS measurements. However, it can be difficult to detect the anomalies of the satellites clock before the range of the satellites clock error becomes bigger than the range of the other factors, due to the measurement including error of the orbit, ionosphere delay, troposphere delay, multipath and receiver clock. In order to perform quick and accurate detection by minimization of critical range in anomalies of the satellites clock, this paper suggested a solution to detect precise anomalies of the satellites clock after application of carrier smoothing filter from measurement by dual-frequency and adjustment of errors which can be occurred by other factor and the receiver clock errors. The performance of the proposed method was confirmed by comparing to the satellite clock biases which are provided by IGS.

• Journal of Navigation and Port Research
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• v.39 no.1
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• pp.7-13
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• 2015

The number of mobile terminals equipped with a GPS module is steadily increasing today. However, because they using code pseudorange measurements in positioning, the positioning accuracy of mobile terminals is lower than that of those receivers using carrier phases. Especially, the multipath signal causes more significant errors in code pseudoranges. Therefore, the techniques of multipath detection and elimination is necessary. In this study, as an initial analysis of multipath detection and elimination technique development, we tested the feasibility of multipath signal detection using GPS signal strength information. We found that the GPS signal strength increases as the elevation angle gets higher in the open-sky environment. Also, we found that the signal strength decreases when there were some signal reflectors nearby. We checked the repeatability of the signal strength variation characteristics by reflecting repeat time of GPS satellites. As a result, this characteristics repeats almost perfectly when GPS satellites pass the same orbit. Therefore, we found that it is not a temporary phenomenon and the multipath signal detection should be possible by using GPS signal strength information.

• Journal of Korean Society for Geospatial Information Science
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• v.17 no.1
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• pp.149-155
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• 2009

To quantitatively analyze the positioning error due to the ionosphere over the Korean peninsula, we created 2-dimensional ionosphere map using 44 permanent Global Positioning System(GPS) stations operated by Ministry of Land, Transport, and Maritime Affairs. We estimated Vertical Total Electron Content(VTEC) in a fine rectangular grids of $0.1^{\circ}{\times}0.1^{\circ}$ resolution. The observables we used were phase-leveled pseudoranges which are linear combinations of pseudoranges and carrier phases. VTECs were computed for five days during January 25-29, 2003 using the data from 45 permanent stations. In comparison with the Global Ionosphere Map of the Center for Orbit Determination in Europe, RMS differences were at the level of 8 TECU(TEC Unit).

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.54-54
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• 2000

For its synergistic relationship, an integrated SDINS/GPS system has been adopted in many navigation areas. As an application of SDINS/GPS integration, the in-flight alignment process of a SDINS utilizing GPS carrier phase measurements is introduced and analyzed via an observability analysis using nul1 space method. A measurement model of double-differenced GPS carrier phase measurements is newly derived in order to be used with a SDINS error model. Also, conditions for determining the complete observability of a SDINS/GPS system are suggested and proved. Consequently, it is shown that the system is not completely observable in case of one basel me. With one baseline aligned with y-axis of body frame, pitch error and x-axis accelerometer bias are unobservable states. Also shown is that al1 states are completely observable when sequential maneuver is performed. Above results are confirmed by a covariance analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.11
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• pp.1044-1050
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• 2013

This paper analyzes what is mitigated as spoofing attack using the U-Blox Receiver and GPS RF signal generator developed at ETRI. Generally the spoofing attack made the target receiver to be wrong navigation solution by providing false measurement of code and carrier. So we analyzed the impact of spoofing attack through the signal strength and navigation solution. In oder to test of effect of anti-spoofing signal, we consider the signal with antiphase code to spoofing signal and generated GPS normal signal and spoofing signal and anti-spoofing signal using GPS RF signal generator. This paper analyzed that the GPS receiver was responded to the spoofing attack according to code phase difference between spoofing and anti-spoofing signal. We confirmed that the spoofing signal was disappeared by anti-spoofing signal if code phase is an exact match.

• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.29-29
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• 2003

GPS의 민간수요에 따른 응용분야가 날로 증가함에 따라 중저가 GPS 수신기를 이용한 실시간 정밀측위 기술의 필요성이 점차 부각되고 있다. 이에 한국천문연구원은 iRTK 기법을 이용한 준 실시간 정밀측위 시스템을 개발한 바 있다. 반송파 위상데이터를 이용한 정밀측위는 모호수를 결정해야하는 어려움이 있고 특히 짧은 시간 내에 정확한 모호수를 찾는 것은 쉽지 않다. 본 연구는 한국천문연구원이 개발한 iRTK시스템의 자료처리능력을 향상시키기 위한 것으로 실시간 모호수 결정 알고리즘 개발에 중점을 두었다. 이를 위해 2003년 7월부터 9월 사이에 실험이 이루어졌고 중저가 GPS 수신기를 이용해 측정한 데이터를 모호수 결정 알고리즘으로 구한 값과 이미 알고 있는 정밀좌표 값을 비교 분석하였다. 새로운 모호수 결정 알고리즘을 이용해 구한 결과 값이 기존의 iRTK시스템 결과보다 정밀하고 안정적으로 산출됨을 알 수 있었다. 개선된 모호수 결정 알고리즘은 iRTK시스템의 준 실시간 자료처리부분에 적용할 수 있도록 보완할 것이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.66-72
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• 2005

As one of the methods that determine position using GPS carrier phase without the resolution of integer ambiguity, the characteristics of the time difference is analyzed in this paper. When determining position by the needed accuracy, the difference time gap becomes an important factor. It is said that accuracy is improved as the difference time gap is getting large, and finally the centimeter level accuracy is achieved after a certain difference time gap. In this paper, the characteristics of the time difference is analyzed using real data and a new parameter is proposed to predict the resulting position accuracy. The difference time gap when position error is converged to the centimeter level is estimated with the proposed parameter.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.6
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• pp.602-612
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• 1997

With GPS carrier phase measurements from more than two antenna which attached to the vehicle, precise attitude can be easily obtained if the integer ambiguity included in carrier phase measurement is resolved. Recently some special products which use dual frequencies or has one receiver engine with multiple antenna are announced. But there are still strong requirements for the conventional single frequency off-the-shelf receiver. To meet these requirements, an efficient integer ambiguity resolution technique is indispensable. In this paper, a new technique to resolve integer imbiguity with single frequency receivers is proposed. The proposed method utilize the known baseline length as a constraint of independent elements of integer ambiguities. With this constraints, the size of search volume can be greatly reduced. Thus the true integer ambiguity can be easily determined with less computational burden and number of measurements. The proposed method is applied to real data to show its effectiveness.

• Journal of Navigation and Port Research
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• v.26 no.3
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• pp.303-310
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• 2002

Nowadays, the combined land navigation system using GPS(Global Positioning System) and DR(Deduced Reckoning), etc. has been used. Although GPS is popular with the land navigation system, this is not useful for the kinematic positioning of the vehicles in the urban canyon because of its few satellites. Thus, this study deals with the kinematic positioning of the vehicles with the combined GPS/GLONASS(GLObal Navigation Satellite System) to compliment the drawbacks of GPS. So the kinematic positioning of the vehicles can be performed constantly by the combined GPS/GLONASS based on the high acquisition rate of data with the help of GLONASS despite of many obstacles and few satellites tracked in the test sites. Consequently, the combined GPS/GLONASS can be applicable to the control of traffic flow and the effective management of read system.