• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.588-590
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• 2003

For the normal operations, KOMPSAT-1 orbits are determined using GPS navigation solutions data such as position and velocity vectors. Currently, the accuracy of GPS navigation solution data is generally known as on the order of 10~30 m with the removal of S/A. In this paper, an estimate of the current orbit determination accuracy for the KOMPSAT-1 is given. For the evaluation of orbit determination accuracy, the orbit overlap comparison is used since no independent orbits of comparable accuracy are available for comparison. As a result, It is shown that the orbit accuracy is on the order of 5 m RMS with 4 hrs arc overlap for the 30 hr arc.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.109-109
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• 2004

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2004.02a
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• pp.82-94
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• 2004

This paper addresses solutions to the challenges of carrier phase integer ambiguity resolution and cycle slip detection/identification, for maintaining high accuracy of an integrated GPS/Pseudolite/INS system. Such a hybrid positioning and navigation system is an augmentation of standard GPS/INS systems in localized areas. To achieve the goal of high accuracy, the carrier phase measurements with correctly estimated integer ambiguities must be utilized to update the system integration filter's states. The occurrence of a cycle slip that is undetected is, however, can significantly degrade the filter's performance. This contribution presents an effective approach to increase the reliability and speed of integer ambiguity resolution through using pseudolite and INS measurements, with special emphasis on reducing the ambiguity search space. In addition, an algorithm which can effectively detect and correct the cycle slips is described as well. The algorithm utilizes additional position information provided by the INS, and applies a statistical technique known as the cumulative-sum (CUSUM) test that is very sensitive to abrupt changes of mean values. Results of simulation studies and field tests indicate that the algorithms are performed pretty well, so that the accuracy and performance of the integrated system can be maintained, even if cycle slips exist in the raw GPS measurements.

• Journal of Astronomy and Space Sciences
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• v.19 no.3
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• pp.197-206
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• 2002

NORAD Two Line Elements (TLE) are widely used for the increasing number of small satellite mission operations and analysis. However, due to the irregular periodicity of generation of the NORAD TLE, a new TLE that is independent of NORAD is required. A TLE type Orbit Determination (TLEOD) has been developed for the generation of a new TLE. Thus, the TLEOD system can provide an Antenna Control Unit (ACU) with the orbit determination result in the type of a TLE, which provides a simple interface for the commercialized ACU system. For the TLEOD system, NORAD SGP4 was used to make a new orbit determination system. In addition, a least squares method was implemented for the TLEOD system with the GPS navigation solutions of the KOMPSAT-1. Considering both the Orbit Propagation (OP) difference and the tendency of $B^{*}$ value, the preferable span of the day in the observation data was selected to be 3 days. Through the OD with 3 days observation data, the OP difference was derived and compared with that of Mission Analysis and Planning (MAPS) for the KOMPSAT-1. It has the extent from 2 km after sit days to 4 km after seven days. This is qualified enough for the efficiency of an ACU in image reception and processing center of the KOMPSAT-2.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.4
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• pp.369-377
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• 2023

This paper presents the analysis results of navigation performance of Korea Augmentation Satellite System (KASS) test signals. Performance analysis was performed with Global Positioning System (GPS) and Satellite Based Augmentation System (SBAS) signals received from 7 KASS reference stations. And the performances were analyzed in terms of the signal strength, statistics for each SBAS message, coverage of ionospheric correction, accuracy, integrity, continuity, and availability. In addition, the navigation solutions provided by commercial receiver was analyzed and the performance experienced by general users was presented. Lastly, directions for further improvement of the KASS system were addressed. These performance analysis results can be used to confirm the feasibility of utilizing KASS in user applications.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.2
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• pp.296-303
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• 2010

The term "spoofing" refers to the transmission of counterfeit signals to provide undetectable falsification of GPS service. A spoofing can be accomplished using information from open literature which defines the signal format and the data structure. Spoofing is intended either to produce erroneous navigation solutions or saturate the processor of the victim receiver. The GPS receiver has no way to get rid of the effect of a spoofing because GPS receivers for civil service do not have an anti-spoofing scheme. This paper analyzes the spoofing characteristics, spoofing methods and environment conditions. And the spoofing effects on GPS receiver are analyzed in detail using the designed software-based spoofer and the Nordnav receiver.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.2
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• pp.163-171
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• 2014

Based on the GPS/IMU integration, the car navigation has unstable conditions as well as drastically reduces accuracies in urban region. Nowadays, many cars mounted the camera to record driving states. If the ground coordinates of street furniture are known, the position and attitude of camera can be determined through SPR(Single Photo Resection). Therefore, an estimated position and attitude from SPR can be applied measurements in Kalman filter for updating errors of navigation solutions from GPS/IMU integration. In this study, the GPS/IMU/SPR integration algorithm was developed in loosely coupled modes through extended Kalman filters. Also, in order to analyze performances of GPS/IMU/SPR, simulation tests were conducted in GPS signal reception environments and the GCPs (Ground Control Points) distributions. In fact, the position and attitude gathered from GPS/IMU/SPR integration are more precise than the position and attitude from GPS/IMU integration. When IPs (image points), corresponded to GCPs, were concentrated in the center of image, the position error in the optical axis respectively increased. To understand effects from SPR, we plan to carry additional test on the magnitude of GCP, IP and initial exterior orientation errors.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.1
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• pp.15-21
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• 2020

In October 2019, the European Galileo navigation system operates a total of 24 satellites, two of them are in the testing phase. There are enough satellites in operation to enable precise point positioning (PPP) using Galileo signals. The number of visible satellites for Galileo in South Korea is investigated. In addition, to assess the latest performance of the Galileo kinematic PPP, data received at DAEJ reference station from October 1 to October 7, 2019, are analyzed. Galileo kinematic PPP presents some results in two categories, single-frequency PPP (SPPP) and dual-frequency PPP (DPPP). The positioning accuracy for Galileo kinematic SPPP solutions is less than 1 m root mean square (RMS) in all direction components. The Galileo kinematic DPPP achieves the positioning accuracy with an RMS value of less than 7 cm in all direction components. The results show that the latest performance of Galileo kinematic PPP at DAEJ station in South Korea is still relatively poor compared to GPS kinematic PPP. However, the residuals of Galileo code measurements are smaller than those of GPS code measurements.

• Journal of Advanced Navigation Technology
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• v.11 no.3
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• pp.239-251
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• 2007

This thesis is about the reduction of the power consumption in GPS embedded terminals with periodic position fix to improve the time delay of position determination. In order to improve time delay of position determination during the wireless terminal is powered on, it needs to be set such that it can be periodically recalibrated by the GPS and those recalibrated values need to be saved in the terminal's memory so that it can reduce the time delay from the request of location. By using the trace of the information that's been saved in the terminal's memory, it can be set so that it'll be easier to determine whether the wireless terminal has gone into buildings and have the capability of checking if it has gone into a specific building. Likewise, while the terminal is turned on, in order calibrate the location, it needs to continuously work the GPS engine which leads to a rapid decrease in terminal's idle time. This thesis proposes some solutions regarding these issues - reducing 20 ~ 30% of the battery consumption for GPS visible situation that can occur when the wireless terminal periodically calibrates its location to determine the in-building status, and extending the idle time of the terminal by flexibly using the suggested GPS calibration time method according to wireless terminal's mobility.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.114.6-114
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• 2001

According to expansion of wireless communication system and mobile device, interest has been growing in personal navigation system integrated with wireless system. In portable consumer electronics, such as cellular phones, GPS and PDA, one of major design factors is the power consumption. Solutions of reducing the power dissipation are low voltage, low system clock power management and so on. This paper develops a GPS receiver based on the advanced power management algorithm that achieves very low average power consumption. Both RF and DSP chips are powered down and reactivated only when the position fixing is required. In order to run, the developed includes the RTC calibration function and the fast reacquisition function using XMC (eXtended Multiple Correlator) ...