• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.9
• /
• pp.1846-1855
• /
• 2015

In this paper, a precise relative positioning with TD(time differenced) carrier phase measurements from a low-cost GNSS(Global Navigation Satellite System) receiver is proposed and analysed. The proposed method is using carrier phase measurement from a single GNSS receiver that reference receiver is not required and stand alone positioning is possible. TD operation removes the troublesome integer ambiguity resolution problem, and if the time interval is short, other error, such as, ionospheric, tropospheric delay and ephemeris error are effectively eliminated. The error analysis of the proposed method shows that a precise and positioning with carrier phase is possible. The implemented system is evaluated using a real car experiments. The results show that the horizontal positioning error was less than 3m during 10 minutes experiments, which is 4 times more precise than the results of normal code based absolute positioning.

• Proceedings of the KSRS Conference
• /
• 2005.10a
• /
• pp.87-90
• /
• 2005

The FORMOSAT-3/COSMIC mission is a micro satellite mission to deploy a constellation of six micro satellites at low Earth orbits. The final mission orbit is of an altitude of 750-800 lan. It is a collaborative Taiwan-USA science experiment. Each satellite consists of three science payloads in which the GPS occultation experiment (GOX) payload will collect the GPS signals for the studies of meteorology, climate, space weather, and geodesy. The GOX onboard FORMOSAT -3 is designed as a GPS receiver with 4 antennas. The fore and aft limb antennas are installed on the front and back sides, respectively, and as well as the two precise orbit determination (POD) antennas. The precise orbit information is needed for both the occultation inversion and geodetic research. However, the instrument associated errors, such as the antenna phase center offset and even the different cable delay due to the geometric configuration of fore- and aft-positions of the POD antennas produce error on the orbit. Thus, the focus of this study is to investigate the impact of POD antenna parameter on the determination of precise satellite orbit. Furthermore, the effect of the accuracy of the determined satellite orbit on the retrieved atmospheric and ionospheric parameters is also examined. The CHAMP data, the FORMOSAT-3 satellite and orbit parameters, the Bernese 5.0 software, and the occultation data processing system are used in this work. The results show that 8 cm error on the POD antenna phase center can result in ~8 cm bias on the determined orbit and subsequently cause 0.2 K deviation on the retrieved atmospheric temperature at altitudes above 10 lan.

• Journal of Advanced Navigation Technology
• /
• v.24 no.2
• /
• pp.92-100
• /
• 2020

Satellite-based argumentation systems (SBAS) is a system that enhances the accuracy, integrity, availability and continuity of GNSS navigation users by using geostationary orbit (GEO) satellites to send correction information and the failures of global navigation satellite system (GNSS) satellites in the form of messages. The correction information provided by SBAS is pseudorange error, satellite orbit error, clock error, and ionospheric delay error at 250 bps. Therefore, A lot of message processing are required for the SBAS navigation. There is a need to reduce SBAS time to first fix (TTFF) for using SBAS navigation in systems with short operating time. In this paper, A-SGNSS operation method was proposed for reducing SBAS TTFF. Also, A-SGNSS TTFF and availability were analyzed.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.90-94
• /
• 2007

The conventional single-reference station positioning is affected by systematic errors such as ionospheric and tropospheric delay, so that the rover must be located within 10 km from the reference station in order to acquire centimeter-level accuracy. The medium-range real-time kinematic has been proven feasible and can be used for high precision applications. However, the longer of the baseline, the more of the time for resolving the integral ambiguity is required. This is due to the fact that systematic errors can not be eliminated effectively by double-differencing. Recently, network approaches have been proposed to overcome the limitation of the single-reference station positioning. The real-time systematic error modeling can be achieved with the use of GPS network. For expanding the effective range and decreasing the density of the reference stations, Land Survey Bureau, Ministry of the Interior in Taiwan set up a national GPS network. In order to obtain the high precision positioning and provide the multi-goals services, a GPS network including 66 stations already been constructed in Taiwan. The users can download the corrections from the data center via the wireless internet and obtain the centimeter-level accuracy positioning. The service is very useful for surveyors and the high precision coordinates can be obtained real time.

• International Journal of Aeronautical and Space Sciences
• /
• v.6 no.1
• /
• pp.44-51
• /
• 2005

To provide more accurate and reliable positioning and timing services to Korean nationwide users, the Ministry of Maritime Affairs and Fisheries of Korea is implementing Korean NDGPS (Nationwide DGPS), which is operational partly. And it also has a plan to construct WADGPS (Wide Area Differential GPS) system using sites and equipments of the NDGPS reference stations. For that, Seoul National University GNSS Laboratory is implementing and testing prototypes of WRS (Wide-area Reference Station) and WMS (Wide-area Master Station). Until now, because there are not enough installed WRSs to be used for computing wide area correction information, we cannot test algorithms of WMS with the data processed actually in WRSs. Therefore to evaluate the performance of the algorithms, we made a MATLAB program which can process RINEX (Receiver INdependent Exchange) format data with WADGPS algorithm. Using that program which consists of WRS, WMS and USER modules, we processed the data collected at NDGPS reference stations, which are saved in RINEX format. In WRS module, we eliminate the atmospheric delay error from the pseudorange measurement, smooth the measurement by hatch filter and calculate pseudorange corrections for each satellite. WMS module collects the processed data from each reference stations to generate the wide area correction information including estimated satellite ephemeris errors, ionospheric delays at each grid point, UDRE (User Differential Range Error), GIVE (Grid Ionosphere Vertical Error) and so on. In USER part, we use the measurements of reference stations as those of users and estimate the corrected users' positions and protection levels (HPL, VPL). With the results of estimation, we analyzed the performance of the algorithms. We assured the estimated UDRE /GIVE values and the protection levels bound the corresponding errors effectively. In this research, we can expect the possible performance of WADGPS in Korea, and the developed modules will be useful to implementation and improvement of the algorithms.

• Journal of Korean Society for Geospatial Information Science
• /
• v.22 no.1
• /
• pp.47-54
• /
• 2014

Precise Point Positioning (PPP) algorithms using GPS code pseudo-range measurements were developed and their accuracy was validated for the purpose of implementing them on a portable device. The group delay, relativistic effect, and satellite-antenna phase center offset models were applied as fundamental corrections for PPP. GPS satellite orbit and clock offsets were taken from the International GNSS Service official products which were interpolated using the best available algorithms. Tropospheric and ionospheric delays were obtained by applying mapping functions to the outputs from scientific GPS data processing software and Global Ionosphere Maps, respectively. When the developed algorithms were tested for four days of data, the horizontal and vertical positioning accuracies were 0.8-1.6 and 1.6-2.2 meters, respectively. This level of performance is comparable to that of Differential GPS, and further improvements and fine-tuning of this suite of PPP algorithms and its implementation at a portable device should be utilized in a variety of surveying and Location-Based Service applications.

• Journal of Navigation and Port Research
• /
• v.37 no.4
• /
• pp.367-373
• /
• 2013

Wide area differential GNSS(WA-DGNSS) collects GPS measurements from the several reference stations and estimates 3-D satellite orbit error, satellite clock error, ionospheric delay. These correction messages are broadcasted to user, then user can have more accurate and reliable position estimates. The performance of WA-DGPS can be changed depending on the position of reference stations. To select proper reference stations, performance analysis with the change of reference stations is necessary. In this paper, changing the geographical location of reference stations, we carried out simulation based test and show the performance of WA-DGNSS in Korea.

• Journal of Positioning, Navigation, and Timing
• /
• v.5 no.4
• /
• pp.181-191
• /
• 2016

A Satellite Based Augmentation System (SBAS) provides differential correction and integrity information through geostationary satellite to users in order to reduce Global Navigation Satellite System (GNSS)-related errors such as ionospheric delay and tropospheric delay, and satellite orbit and clock errors and calculate a protection level of the calculated location. A SBAS is a system, which has been set as an international standard by the International Civilian Aviation Organization (ICAO) to be utilized for safe operation of aircrafts. Currently, the Wide Area Augmentation System (WAAS) in the USA, the European Geostationary Navigation Overlay Service (EGNOS) in Europe, MTSAT Satellite Augmentation System (MSAS) in Japan, and GPS-Aided Geo Augmented Navigation (GAGAN) are operated. The System for Differential Correction and Monitoring (SDCM) in Russia is now under construction and testing. All SBASs that are currently under operation including the WAAS in the USA provide correction and integrity information about the Global Positioning System (GPS) whereas the SDCM in Russia that started SBAS-related test services in Russia in recent years provides correction and integrity information about not only the GPS but also the GLONASS. Currently, LUCH-5A(PRN 140), LUCH-5B(PRN 125), and LUCH-5V(PRN 141) are assigned and used as geostationary satellites for the SDCM. Among them, PRN 140 satellite is now broadcasting SBAS test messages for SDCM test services. In particular, since messages broadcast by PRN 140 satellite are received in Korea as well, performance analysis on GPS/GLONASS Multi-Constellation SBAS using the SDCM can be possible. The present paper generated correction and integrity information about GPS and GLONASS using SDCM messages broadcast by the PRN 140 satellite, and performed analysis on GPS/GLONASS Multi-Constellation SBAS performance and APV-I availability by applying GPS and GLONASS observation data received from multiple reference stations, which were operated in the National Geographic Information Institute (NGII) for performance analysis on GPS/GLONASS Multi-Constellation SBAS according to user locations inside South Korea utilizing the above-calculated information.