• 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 Astronomy and Space Sciences
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• v.29 no.1
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• pp.1-10
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• 2012

In this study, global positioning system (GPS)-derived precipitable water vapor (PWV) and microwave radiometer (MWR)-measured integrated water vapor (IWV) were compared and their characteristics were analyzed. Comparing those two quantities for two years from August 2009, we found that GPS PWV estimates were larger than MWR IWV. The average difference over the entire test period was 1.1 mm and the standard deviation was 1.2 mm. When the discrepancies between GPS PWV and MWR IWV were analyzed depending on season, the average difference was 0.7 mm and 1.9 mm in the winter and summer months, respectively. Thus, the average difference was about 2.5 times larger in summer than that in winter. However, MWR IWV measurements in the winter months were over-estimated than those in the summer months as the water vapor content got larger. The results of the diurnal analysis showed that MWR IWV was underestimated in the daytime, showing a difference of 0.8 mm. In the early morning hours, MWR IWV has a tendency to be over-estimated, with a difference of 1.3 mm with respect to GPS PWV.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.335-340
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• 2021

A constant envelope multiplexing via constellation tailoring scheme is proposed for flexible power allocation of Global Navigation Satellite System (GNSS) signals. The proposed scheme is compared with the coherent adaptive subcarrier modulation (CASM) adopted in the L1 band signals of the Global Positioning System (GPS) in terms of power difference and power loss. Analysis of the constellation optimization results on the power difference and power loss show that the proposed scheme outperforms the CASM of the GPS signals in the allowable power difference of less than 0.1 dB.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.2
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• pp.73-77
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• 2015

Global Positioning System (GPS) Precise Point Positioning (PPP) has been extensively used for geodetic applications. Since December 2012, BeiDou navigation satellite system has provided regional positioning, navigation and timing (PNT) services over the Asia-Pacific region. Recently, many studies on BeiDou system have been conducted, particularly in the area of precise orbit determination and precise positioning. In this paper PPP method based on BeiDou observations are presented. GPS and BeiDou data obtained from Mokpo (MKPO) station are processed using the Korea Astronomy and Space Science Institute Global Navigation Satellite System (GNSS) PPP software. The positions are derived from the GPS PPP, BeiDou B₁/B₂ PPP and BeiDou B₁/B₃ PPP, respectively. The position errors on BeiDou PPP show a mean bias < 2 cm in the east and north components and approximately 3 cm in the vertical component. It indicates that BeiDou PPP is ready for the precise positioning applications in the Asia-Pacific region. In addition, BeiDou tropospheric zenith total delay (ZTD) is compared to GPS ZTD at MKPO station. The mean value of their difference is approximately 0.52 cm.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.3
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• pp.180-185
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• 2005

Microstrip antennas generally have a lot of advantages that are thin profile, lightweight, low cost, and conformability to a shaped surface application with integrated circuitry. In addition to military applications, they have become attractive candidates in a variety of commercial applications such as mobile satellite communications, the direct broadcast system (DBS), global positioning system (GPS), and remote sensing. Recently, many of the researches have been achieved for improving the impedance bandwidth of microstrip antennas. The basic form of the microstrip antenna, consisting of a conducting patch printed on a grounded substrate, has an impedance bandwidth of $1\~2\%$. For improvement of narrow bandwidth of microstrip patch, we were designed U-slot microstrip patch antenna in this paper. This antenna had wide bandwidth for all personal communication services (PCS) and IMT-2000. For the design of U-slot microstrip patch antenna using a finite difference time domain(FDTD) method. This numerical method could get the frequency property of U-slot patch antenna and the electromagnetic fields of slots.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2010.04a
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• pp.169-171
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• 2010

The goal of this study is to evaluate the performance of different solution types(a GPS-only, a GLONASS-only, and a GNSS solution) on GNSS positioning modes which are point positioning and relative positioning(DGNSS-, Static-, and Kinematic-solutions). I started with GNSS sites of seoul metropolitan government's RTK network which providing combined GPS/GLONASS observations : Gangseo(GANS), Dobong(DBON). The positioning accuracy of different solution types on positining modes are compared. Considering the compared results of all cases, can find not only the difference of the performance between the GNSS solution and the GPS-only solution is very small, but also the GLONASS-only solution is not far from the other solution types taking into consideration that GLONASS system is not (yet) a complete system.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.363-369
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• 2021

Since the Global Navigation Satellite System (GNSS) signal received from the low Earth orbit (LEO) satellite is only affected by the upper ionosphere, the magnitude of the ionospheric delay of Global Positioning System (GPS) signal received from ground user is different. Therefore, the ground-based two-dimensional ionospheric model cannot be applied to LEO satellites. The NeQuick model used in Galileo provides the ionospheric delay according to the user's altitude, so it can be used in the ionospheric model of the LEO satellites. However, the NeQuick model is not suitable for space receivers because of the high computational cost. A simplified NeQuick model with reduced computing time was recently presented. In this study, the computing time of the NeQuick model and the simplified NeQuick model was analyzed based on the GPS Klobuchar model. The NeQuick and simplified NeQuick model were applied to the GNSS data from GRACE-B, Swarm-C, and GOCE satellites to analyze the performance of the ionospheric correction and positioning. The difference in computing time between the NeQuick and simplified NeQuick model was up to 90%, but the difference in ionospheric accuracy was not as large as within 4.5%.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.2
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• pp.113-119
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• 2023

Satellite navigation systems, with the exception of the GLObal NAvigation Satellite System (GLONASS), adopt ionosphere models and provide ionospheric coefficients to single-frequency users via navigation messages to correct ionospheric delay, the main source of positioning errors. A Global Navigation Satellite System (GNSS) mostly has its own ionospheric models: the Klobuchar model for Global Positioning System (GPS), the NeQuick-G model for Galileo, and the BeiDou Global Ionospheric delay correction Model (BDGIM) for BeiDou satellite navigation System (BDS)-3. On the other hand, a Regional Navigation Satellite System (RNSS) such as the Quasi-Zenith Satellite System (QZSS) and BDS-2 uses the Klobuchar Model rather than developing a new model. QZSS provides its own coefficients that are customized for its service area while BDS-2 slightly modifies the Klobuchar model to improve accuracy in the Asia-Pacific region. In addition, BDS broadcasts multiple ionospheric parameters depending on the satellites, unlike other systems. In this paper, we analyzed the different ionospheric models of GPS, QZSS, and BDS in Korea. The ionospheric models of QZSS and BDS-2, which are based in Asia, reduced error by at least 25.6% compared to GPS. However, QZSS was less accurate than GPS during geomagnetic storms or at low latitude. The accuracy of the models according to the BDS satellite orbit was also analyzed. The BDS-2 ionospheric model showed an error reduction of more than 5.9% when using GEO coefficients, while in BDS-3, the difference between satellites was within 0.01 m.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.6
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• pp.550-557
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• 2001

There are several applications and error analysis methods using GPS(Global Positioning System) In most analysis positioning and timing errors are represented as the multiplication of DOP(Dilution Of Precision) and measurement errors, which are affected by the receiver and measurement type. Therefore, lots of DOPs are defined and used to analyze and predict the performance of positioning and timing systems. In this paper, the relationships between these DOPs are investigated in detail, The relationships between GDOP(Geometric DOP), PDOP(Position DOP) and TDOP(Time DOP) in the absolute positioning are de-rived. Using these relationships, the affect of clock bias is analyzed. The relationships between RGDOP(Relative DOP) and PDOP are also derived in relative positioning where the single difference and double dif-ference techniques are used. From the results, it is expected that using the common clock will give better performance when the single difference technique is used while the effects of clock is eliminate when the double difference technique is used. Finally, the error analyses of dual frequency receivers show that the narrow lane measurements give more accurate results than wide line of or L1. L2 independent measurements.

• IEMEK Journal of Embedded Systems and Applications
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• v.10 no.2
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• pp.101-108
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• 2015

In this paper, a robust traffic light detection method is proposed by using vision sensor and DGPS(Difference Global Positioning System). The conventional vision-based detection methods are very sensitive to illumination change, for instance, low visibility at night time or highly reflection by bright light. To solve these limitations in visual sensor, DGPS is incorporated to determine the location and shape of traffic lights which are available from traffic light database. Furthermore the geometric relationship between traffic light and vision sensor is used to locate the traffic light in the image by using DGPS information. The empirical results show that the proposed method improves by 51% in detection rate for night time with marginal improvement in daytime environment.