• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.402-408
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• 2021

GNSS-Reflectometry (GNSS-R) is a technique for measuring and analyzing signals transmitted from satellites, reflecting on the surface of land or sea. GNSS-R is mainly used for measuring the water level variation, typhoon and meteorological anomaly, soil moisture, and snow depth. This paper describes the concept and measurement principle of GNSS-R technology, especially focusing on the field of marine utilization and its feasibility. In particular, it presents the applications of this technique for monitoring the safety of marine environment as well as the marine vessel and their utilization areas based on currently available infrastructure on the ground and maritime reference stations, such as the existing differential GNSS reference stations and integrity monitors (DGNSS RSIM), and GNSS reference station infrastructure, using the ground-based and the satellite-based GNSS-R approaches.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.5
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• pp.527-537
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• 2014

In 2013, NGII(National Geographic Information Institute) has developed and provided the KNGeoid13(Korean National Geoid Model 2013) to support the fundamental computation of GNSS-derived orthometric height. In this study, the adjusted ellipsoidal height, the sum of geoidal height and height by the leveling, is applied to calculate the GNSS-derived orthometric height without the local bias, based on GNSS static surveying and KNGeoid13. The mean of errors in GNSS-derived orthometric heights could be verified with the leveling data, which was actually less than 0.5 cm with using the adjusted ellipsoidal heights, but 3 cm by calculating differences between ellipsoidal heights and geoidal heights. By analyze the accuracy of GNSS-derived orthometric height depending on the duration of observation, we could realized 95% of data shows less than 4 cm accuracy, when the GNSS survey conducting for 4 hours spread over two days, but while the case of GNSS survey conducting for 4 hours and 2 hours respectively, resulted in 95% of data less than 5cm level of accuracy. Also, if the ambiguity is fixed, less than 10cm of accuracy could be obtained at 95% of data for only 30 minutes GNSS survey over a day. Following the study, we expected that the height determination by GNSS and geoid models can be used in the public benchmark surveying.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.24 no.4
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• pp.1-5
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• 2016

As a dependency on Global Navigation Satellite System (GNSS) becomes increase in various applications, its reliability has been very important. However, in South Korea, Global Positioning System (GPS) jamming incident happened four times since 2010. GNSS signal is so weak that it is highly susceptible to all types of the jamming. GNSS jamming can cause serious damage in the safety-critical applications based on the GNSS. In this paper, we present the GNSS jamming signal propagation prediction simulator based on ITU-R P.1546 model. This simulator is developed for preventing or reducing the damage from the GNSS jamming attack by predicting the jamming propagation strength based on the geographical information in Korean peninsula.

• Journal of Positioning, Navigation, and Timing
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• v.6 no.4
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• pp.205-210
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• 2017

Multi-Global Navigation Satellite System (GNSS) can significantly improve the positioning accuracy and convergence speed. The reliability and availability of multi-GNSS precise point positioning (PPP) is steadily increasing with the rapid development of GNSS satellites. In this study, multi-GNSS PPP analysis is performed to compare the positioning precision by processing the observations from different GNSS systems (GPS, GLONASS, Galileo and BeiDou). To improve the positioning performance of the multi-GNSS PPP, we employed the weighed measurement noise (WMN) method. After applying WMN method to multi-GNSS PPP, positioning precision is improved by approximately 26.3% compared to the GPS only solutions, and by approximately 9.1% compared to combined GPS, GLONASS, and Galileo PPP.

• Journal of Satellite, Information and Communications
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• v.2 no.1
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• pp.41-47
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• 2007

Software GNSS digitized IF signal simulator is being developed by ETRI as a part of development of software-based GNSS Test & evaluation Facility which will provide test and evaluation environment for various software level application and navigation algorithm in GNSS. Software GNSS IF signal simulator will provide digitized GNSS signal including GPS and Galileo. The requirement analysis and conceptual design for the Software GNSS IF signal simulator is presented in this paper.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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• pp.295-306
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• 2023

This paper presents a multi-frequency and multi-constellation Global Navigation Satellite System (GNSS) signal generator that simulates intermediate frequency level digital signal samples for testing GNSS receivers. GNSS signal generators are ideally suited for testing the performance of GNSS receivers and algorithms under development in the laboratory for specific user locations and environments. The proposed GNSS signal generator features a fully-reconfigurable structure with the ability to adjust signal parameters, which is beneficial to generate desired signal characteristics for multiple scenarios including multi-constellation and frequencies. Successful signal acquisition, tracking, and navigation are demonstrated on a verified Software Defined Radio (SDR) in this study. This work has implications for future studies and advances the research and development of new GNSS signals.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.20 no.3
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• pp.74-85
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• 2021

Global Navigation Satellite System (GNSS) receivers are intrinsically vulnerable to radio frequency jamming signals due to the fundamental property of radio navigation systems. A GNSS jamming monitoring system that is capable of jamming detection, classification and localization is essential for infrastructure for autonomous driving systems. For these 3 functionalities, a GNSS jamming monitoring network consisting of a multiple of low-cost GNSS receivers distributed in a certain area is needed, and the precise time synchronizaion between multiple independent GNSS receivers in the network is an essential element. This paper presents a precise time synchronization method based on the direct use of Time Difference of Arrival (TDOA) technique in signal domain. A block interpolation method is additionally incorporated into the method in order to maintain the precision of time synchronization even with the relatively low sampling rate of the received signals for computational efficiency. The feasibility of the proposed approach is verified in the numerical simualtions.

• Journal of Advanced Navigation Technology
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• v.25 no.3
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• pp.194-202
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• 2021

Ionosphere, one of the largest error sources, can pose potentially harmful threat to single-frequency GNSS (global navigation satellite system) user even after applying ionospheric corrections to their GNSS measurements. To quantitatively assess ionospheric impacts on the satellite navigation-based applications using simulation, the standard deviation of residual ionospheric errors is needed. Thus, in this paper, we determine conservative statistical quantity that covers typical residual ionospheric errors for nominal days. Extensive data-processing computes TEC (total electron content) estimates from GNSS measurements collected from the Korean reference station networks. We use Klobuchar model as a correction to calculate residual ionospheric errors from TEC (total electron content) estimate. Finally, an exponential delay model for residual ionospheric errors is presented as a function of local time and satellite elevation angle.

• Journal of Cadastre & Land InformatiX
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• v.52 no.2
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• pp.53-65
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• 2022

According to the advancement of the GNSS satellite positioning system, the module of hardware and operation software reflecting accuracy and economical efficiency is implemented in the user sector including the multi-channel GNSS receiver, the multi-frequency external antenna and the mobile app (App) base public positioning analysis software etc., and the multichannel GNSS RTK positioning of the active configuration method (DIY, Do it yourself) is possible according to the purpose of user. Especially, as the infrastructure of multi-GNSS satellite is expanded and the potential of expansion of utilization according to various modules is highlighted, interest in the utilization of multi-channel low-cost GNSS receiver module is gradually increasing. The purpose of this study is to review the multi-channel low-cost GNSS receivers that are appearing in the mass market in various forms and to analyze the utilization plan of the "address information facility investigation project" of the Ministry of Public Administration and Security by constructing the multi-channel low-cost GNSS positioning module based RTK survey system (hereinafter referred to as "multi-channel GNSS RTK module positioning system"). For this purpose, we constructed a low-cost "multi-channel GNSS RTK module positioning system" by combining related modules such as U-blox's F9P chipset, antenna, Ntrip transmission of GNSS observation data and RTK positioning analysis app through smartphone. Kinematic positioning was performed for circular trajectories, and static positioning was performed for address information facilities. The results of comparative analysis with the Static positioning performance of the geodetic receivers were obtained with 5 fixed points in the experimental site, and the good static surveying performance was obtained with the standard deviation of average ±1.2cm. In addition, the results of the test point for the outline of the circular structure in the orthogonal image composed of the drone image analysis and the Kinematic positioning trajectory of the low cost RTK GNSS receiver showed that the trajectory was very close to the standard deviation of average ±2.5cm. Especially, as a result of applying it to address information facilities, it was possible to verify the utility of spatial information construction at low cost compared to expensive commercial geodetic receivers, so it is expected that various utilization of "multi-channel GNSS RTK module positioning system"