• Journal of Advanced Navigation Technology
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• v.15 no.4
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• pp.517-522
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• 2011

Global Navagation Satellite System(GNSS) is divided into Local Area Differential GNSS and Wide Area Differential GNSS. Wide Area DGNSS has more complicated structure and massage type. And transfer rate is limited, so efficient message scheduling algorithm is needed to guarantee user's accuracy and integrity. There are about 30 message types in Wide Area DGNSS. Each message type has different update interval. In this paper, the performances of message scheduling algorithm for Wide Area Differential GNSS are investigated. For all message types, results show that max update time interval requirement is satisfied.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.297-300
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• 2016

The typical Differential Global Navigation Satellite System service of South Korea is the Ground Based Differential GNSS service. South Korea building the Satellite-Based Augmentation System for GNSS to expand the Differential GNSS service. The satellite-based differential GNSS serive is called the SBAS(Satellite Based Augmentation System). The SBAS reference station on ground should be installed to operate the SBAS service alike the ground based augmentation system. That SBAS reference station can be installed with ground based DGNSS reference station. To make the SBAS reference station combined with the ground based DGNSS reference station, DGNSS system should be connected to NovAtel's G-III receiver. In this paper, the DGNSS software reference station's software module architecture was changed and G-III interface module was designed to use the G-III receiver.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.307-313
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• 2021

Modernized GNSS signal structures tend to use tiered codes, and all GNSSs use binary codes as secondary codes. However, recently, signals using polyphase codes such as Zadoff-Chu sequence have been proposed, and are expected to be utilized in GNSS. For example, there is Tiered Differential Polyphase Code (TDPC) using polyphase code as secondary code. In TDPC, the phase of secondary code changes every one period of the primary code and a time-variant error is added to the carrier tracking error, so carrier tracking ambiguity exists until the secondary code phase is found. Since the carrier tracking ambiguity cannot be solved using the general GNSS receiver architecture, a new receiver architecture is required. Therefore, in this paper, we describe the carrier tracking ambiguity and its cause in signal tracking, and propose a receiver structure that can solve it. In order to prove the proposed receiver structure, we provide three signal tracking results. The first is the differential decoding result (secondary code sync) using the general GNSS receiver structure and the proposed receiver structure. The second is the IQ diagram before and after multiplying the secondary code demodulation when carrier tracking ambiguity is solved using the proposed receiver structure. The third is the carrier tracking result of the legacy GPS (L1 C/A) signal and the signal using TDPC.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.433-439
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• 2016

Several low-cost global navigation satellite system (GNSS) receivers do not support general range-domain correction, and DGNSS-CP (differential GNSS) method had been suggested to solve this problem. It improves its position accuracy by projecting range-domain corrections to the position-domain and then differentiating the stand-alone position by the projected correction. To project the range-domain correction, line-of-sight vectors from the receiver to each satellite should be calculated. The line-of-sight vectors can be obtained from GNSS broadcast ephemeris data or satellite direction information, and this paper shows positioning performance for the two methods. Stand-alone positioning result provided from Septentrio PolaRx4 Pro receiver was used to show the difference. The satellite direction information can reduce the computing load for the DGNSS-CP by 1/15, even though its root mean square(RMS) of position error is bigger than that of ephemeris data by 0.1m.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.260-267
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• 2014

For the purpose of improving the accuracy of Wide Area Differential GNSS (WA-DGNSS), estimation performance of ionospheric delay error which has a great impact on GPS error sources should be enhanced. This paper applied multi-constellation GNSS which represents GPS in USA, GLONASS in Russia, and Galileo in Europe to WA-DGNSS algorithm in order to improve performance of ionospheric delay estimation. Furthermore, we conducted simulation to analyze ionospheric delay estimation performance in Korean region by increasing the number of reference stations. Consequently, using multi-constellation GNSS to improve performance of ionospheric delay estimation is more effective than increasing the number of reference stations in spite of similar number of measurements which are in use for estimation. We expect this result can contribute to improvement for ionospheric delay estimation performance of single-frequency SBAS (Satellite Based Augmentation System) user.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.1
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• pp.8-14
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• 2013

As GNSS(Global Navigation Satellite System) is used in various filed, many countries establish GNSS system independently. But GNSS system has the limitation of accuracy and stability in stand-alone mode, because this system has error elements which are ionospheric delay, tropospheric delay, orbit ephemeris error, satellite clock error, and etc. For overcome of accuracy limitation, the DGPS(Differential GPS) and RTK(Real-Time Kinematic) systems are proposed. These systems perform relative positioning using the reference and user receivers. ETRI(Electronics and Telecommunications Research Institute) is developing precision navigation system in point of extension of GNSS usage. The precision navigation system is for providing the precision navigation solution to common users. If this technology is developed, GNSS system can be used in the fields which require precision positioning and control. In this paper, we introduce the precision navigation system and perform design and algorithm verification.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.208-214
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• 2009

Using the GNSS data and tilt-meter data of Boeun (BOEN) and Goesan (GSAN) GNSS stations, we have calculated the differential distance vector variation with the calculation time span set to 1 hour and 3 hour and differential tilt vector variation along time and derived an indicator of similarity between the two variations along time. The similarity such calculated is rather lower than high. But as the existence of a circular type movement of the antenna's phase center's location due to the tilt's variation of the antenna tower because of the sunlight's diurnal change is certain, we recommend to take such diurnal variation of antenna's location into consideration when the correction error in DGNSS or the measured data at reference stations in VRS (Virtual Reference System) is broadcast.

• 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 Satellite, Information and Communications
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• v.7 no.3
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• pp.30-34
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• 2012

National Meteorological Satellite Center(NMSC) of Korea Meteorological Administration(KMA) has launched to implement the application development to get prepared for the space weather operation since 2010. As a action of KMA's space weather work, NMSC constructed Global Navigation Satellite System(GNSS) application system for meteorology and space weather. We will introduce NMSC's space weather application system which derives regional TEC(Total Electron Content) in near real time using nation-wide GNSS network data. First, We constructed system for collecting GNSS data, which is currently collecting about 80 stations operated by agencies like NGII(National Geographic Information Institute), Central Office of DGPS(Differential GPS), and KASI(Korea Astronomy and Space Science) including KMA's own data of 2 stations. In order to retreive regional TEC over Korean peninsular, we build up the automatic processes running every 1-hour. In these processes, firstly, GNSS data of every stations with 24 hours time window are processed to derive DCBs(Differential Code Biases) of each GNSS station and TEC values on every ionosphere piercing point(IPP). Then we made gridded regional TEC map with resolution of 0.25 degree from 31N, 121E to 41N, 135E by combination of all station results within 30 minutes window with assumption that TEC of a given point during a given 30 minutes window would have a constant value. The grid points without TEC value are interpolated using Barnes objective analysis. We presentour regional TEC maps, which can describe better on the status of ionosphere over Korean peninsular compared to IGS TEC maps.

• Journal of Navigation and Port Research
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• v.38 no.4
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• pp.373-378
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• 2014

In order to prepare for recapitalization of differential GNSS (DGNSS) reference station and integrity monitor (RSIM) due to GNSS diversification, this paper focuses on differential correction algorithm using GPS/Galileo pesudorange. The technical standards on operation and broadcast of DGNSS RSIM are described as operation of differential GPS (DGPS) RSIM for conversion of DGNSS RSIM. Usually, in order to get the differential corrections of GNSS pesudorange, the system must know the real positions of satellites and user. Therefore, for calculating the position of Galileo satellites correctly, using the equation for calculating the SV position in Galileo ICD (Interface Control Document), it estimates the SV position based on Ephemeris data obtained from user receiver, and calculates the clock offset of satellite and user receiver, system time offset between GPS and Galileo, then determines the pseudorange corrections of GPS/Galileo. Based on a platform for performance verification connected with GPS/Galileo integrated signal simulator, it compared the PRC (pseudorange correction) errors of GPS and Galileo, analyzed the position errors of DGPS, DGalileo, and DGPS/DGalileo respectively. The proposed method was evaluated according to PRC errors and position accuracy at the simulation platform. When using the DGPS/DGalileo corrections, this paper could confirm that the results met the performance requirements of the RTCM.