• Journal of Advanced Navigation Technology
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• v.16 no.1
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• pp.16-26
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• 2012

Pseudolites are ground-based transmitters that can be configured to emit GPS-like signals for enhancing the GPS by providing increased accuracy, integrity, and availability. However, a pseudolite (PL) can interfere with GPS satellite signals while it is transmitting or cause saturation to automatic gain control circuit. To solve these problems pulsing scheme is used, which transmits PL signal during a short period of time. In this paper the effect of the number of PL and pulsing scheme on the software GPS L1 and L2C signal acquisition performance is studied for the three pulsing schemes such as static pulsing, sweep pulsing, and pseudo random pulsing. For GPS L1 signal, static pulsing shows the best signal acquisition and tracking performance with one PL, and random pulsing shows the best performance with more than or equal to two PLs. For GPS L2C signal, all three pulsing schemes show the similar signal acquisition and tracking performance, but static pulsing shows a little better performance. For GPS L1 and L2C signals, software GPS receivers can do positioning with up to three PLs.

• Bulletin of the Korean Space Science Society
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• 2002.10a
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• pp.35.2-35
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• 2002

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.21 no.1
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• pp.9-17
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• 2003

Typhoon RUSA, which caused serious damage was passed over in Korea peninsula during 30 August to 1 September, 2002. We estimated tropospheric wet delay using GPS data and meteorological data during this period. Integrated Water Vapor(IWV) gives the total amount of water vapor from tropospheric wet delay and Precipitable Water Vapor(PWV) is calculated the IWV scaled by the density of water. We obtained GPS PWV at 13th GPS permanent stations(Seoul, Wonju. Seosan, Sangju, Junju, Cheongju, Taegu, Wuljin, Jinju, Daejeon, Mokpo, Sokcho, Jeju). We retrieve GPS data hourly and use Gipsy-Oasis II software and we compare PWV and precipitation. GPS observed PWV time series demonstrate that PWV is, in general, high before and during the occurrence of the typhoon RUSA, and low after the typhoon RUSA. GPS PWV peak time at each station is related to the progress of a typhoon RUSA. We got very near result as we compare GMS Satellite image with tomograph using GPS PWV and we could present practical use possibility by numerical model for weather forecast.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.2
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• pp.157-164
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• 2008

GPS baseline analysis is a mathematical procedure which estimates a baseline vector from carrier-phase double-differenced observations. Least squares technique is generally applied for the processing and integer ambiguities in the observations should be resolved to obtain maximum accuracy of the solution. In GPS control surveying, after assembling the baseline solutions into a network, adjustment is performed to derive final coordinate sets of unknown points. This paper deals with details of GPS baseline analysis for the $2^{nd}$ order national geodetic network adjustment. After reviewing GPS campaigns carried out by National Geographic Information Institute (NGII) and their observations. technical issues and considerations for the GPS baseline analysis are presented with emphasis of selecting the processing strategies and software. Finally, the analyzed results will be evaluated by examining the close of figures formed by joining the processed baseline vectors.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.285-296
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• 2007

The Precipitable Water Vapor (PWV) from GPS with high resolution in terms of time and space might reduce the limitations of the numerical weather prediction (NWP) model for easily variable phenomena, such as precipitation and cloud. We have converted to PWV from Global Positioning System (GPS) data of Korea Astronomy and Space Science Institute (KASI) and Ministry of Maritime Affairs & Fisheries (MOMAF). First of all, we have selected the heavy rainfall case of having a predictability limitation in time and space due to small-scale motion. In order to evaluate the effect for GPS PWV, we have executed the sensitivity experiment with PWV from GPS data over Korean peninsula in the Weather Research & Forecasting 3-Dimensional Variational (WRF-3DVAR). We have also suggested the direction of further research for an improvement of the predictability of NWP model on the basis of this case.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.2
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• pp.195-202
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• 2014

The Global Positioning System (GPS), which has various military and commercial applications, is designed to estimate the location of the specific user or object. In order to accurately estimate the location, GPS requires at least four satellite signals. The GPS receiver operates on extremely low signal-to-noise ratio (SNR) environment and it may suffer from various interference signals with the extremely high power. In this paper, we introduce a blind adaptive receiver based on the modified despreader, which suppress interference signals and detect GPS signals of interest without requiring explicit angle-of-arrival (AOA) information. We, also, provide the mathematical analysis for the signal-to-interference and noise ratio (SINR) of the modified despeader beamformer output. A representative computer simulation example is presented to illustrate the interference suppression performance of the considered GPS receiver and mathematical analysis of the SINR.

• Journal of Satellite, Information and Communications
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• v.10 no.4
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• pp.58-63
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• 2015

Due to GPS signal's vulnerability of jamming attack, various enhancement techniques are needed. Among variety of techniques, we focused on GPS receiver's anti-jamming techniques. There are many anti-jamming methods at GPS receivers which include filtering methods in time domain, frequency domain and space domain. However, these methods are ineffective to signals, which include both jamming and noise. To solve the problem, this paper proposes a jamming separation scheme by using a BSS method in a jamming environment. As separated GPS signals include noise after the jamming separation method, it is difficult to receive accurate GPS signals. For this reason, this paper also proposes a wavelet de-noising method to effectively eliminate noise. Experimental results of this paper are based on a real field test data of an integrated GPS/QZSS/Wi-Fi positioning system. At the end, the simulation result demonstrates its superiority by showing improved positioning accuracy.

• Journal of IKEEE
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• v.17 no.4
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• pp.440-445
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• 2013

This paper proposes a local estimation system which combines Cell Divide Algorithm with low-cost GPS/INS fused by Extended Kalman Filter(EKF) for localization of Quad-rotor when it returns to the departure point. In the research, the low-cost GPS and INS are fused by EKF to reduce the local error of low-cost GPS and the accumulative error of INS due to continuous integration of sensor error values. When the Quad-rotor returns to the departure point in the fastest path, a moving path can be known because it moves straight, where Cell Divide Algorithm is used to divide moving route into the cells. Then it determines the closest position of data of GPS/INS system fused by EKF to obtain the improved local data. The proposed system was verified through comparing experimental localization results obtained by using GPS, GPS/INS and GPS/INS with Cell Divide Algorithm respectively.

• Journal of the Korea Institute of Building Construction
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• v.10 no.3
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• pp.65-70
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• 2010

Steel frame construction in high places entails many risk factors. In order to improve the safety and productivity of steel frame construction, a project to develop a robotic tower-crane has been undertaken. As the first step, a real-time lifting-path tracking system is being developed. In a previous study, a laser-based tracking system was proposed. While a laser-based tracking system requires at least three laser sensors to detect the x, y, z coordinates of a lifted steel member, a GPS-based system has an advantage over the laser-based system, in that the x, y, z coordinates of a lifted steel member can be detected by a single GPS sensor. To improve the accuracy, arelative positioning method using two GPS sensors was proposed in a previous study. This paper reports an improved GPS-based lifting-path tracking system of a tower crane based on an integrated RF modem and GPS system. The results showedthat the RF modem could successfully send the identifier information to a server a maximum distance of 1 km away from the lifted steel beam, and the lifting path information of each beam captured by the GPS-based tracking system was successfully saved together. Also, byusing an improved algorithm for the GPS relative positioning method, the deviation was reduced to 0.61 m on average.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.21 no.3
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• pp.199-207
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• 2003

In the study, the open area keeping a few visible satellites and the urban area covered with the high building, an electric pole were chosen far evaluation of accuracy of satellite positioning. First, suggest the validity of GPS/GLONASS, TS/RTK-GPS, and compared the accuracy with that of the classical surveying method. As a result, In static relative surveying, the difference of between the known cadastral supplementary control station and that of the acquired is 0.000∼.0006m in GPS alone, GPS/GLONASS, and In the RTK-GPS/TS, 0.010∼0.077m on the non-ambiguity fixed solutions in the urban area 0.008∼0.078m in the open area. it proved to be valid because it is within the allowed connecting errors, i.e 12cm on the baseline of loom in l/l,200 cadastral map.