• Journal of Positioning, Navigation, and Timing
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• 제4권2호
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• pp.43-55
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• 2015

In the case of satellite navigation positioning, the shielding of satellite signals is determined by the environment of the region at which a user is located, and the navigation performance is determined accordingly. The accuracy of user position determination varies depending on the dilution of precision (DOP) which is a measuring index for the geometric characteristics of visible satellites; and if the minimum visible satellites are not secured, position determination is impossible. Currently, the GLObal NAvigation Satellite system (GLONASS) of Russia is used to supplement the navigation performance of the Global Positioning System (GPS) in regions where GPS cannot be used. In addition, the European Satellite Navigation System (Galileo) of the European Union, the Chinese Satellite Navigation System (BeiDou) of China, the Quasi-Zenith Satellite System (QZSS) of Japan, and the Indian Regional Navigation Satellite System (IRNSS) of India are aimed to achieve the full operational capability (FOC) operation of the navigation system. Thus, the number of satellites available for navigation would rapidly increase, particularly in the Asian region; and when integrated navigation is performed, the improvement of navigation performance is expected to be much larger than that in other regions. To secure a stable and prompt position solution, GPS-GLONASS integrated navigation is generally performed at present. However, as available satellite navigation systems have been diversified, finding the minimum satellite constellation combination to obtain the best navigation performance has recently become an issue. For this purpose, it is necessary to examine and predict the navigation performance that could be obtained by the addition of the third satellite navigation system in addition to GPS-GLONASS. In this study, the current status of the integrated navigation performance for various satellite constellation combinations was analyzed based on 2014, and the navigation performance in 2020 was predicted based on the FOC plan of the satellite navigation system for each country. For this prediction, the orbital elements and nominal almanac data of satellite navigation systems that can be observed in the Korean Peninsula were organized, and the minimum elevation angle expecting signal shielding was established based on Matlab and the performance was predicted in terms of DOP. In the case of integrated navigation, a time offset determination algorithm needs to be considered in order to estimate the clock error between navigation systems, and it was analyzed using two kinds of methods: a satellite navigation message based estimation method and a receiver based method where a user directly performs estimation. This simulation is expected to be used as an index for the establishment of the minimum satellite constellation for obtaining the best navigation performance.

• Journal of Astronomy and Space Sciences
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• 제32권4호
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• pp.403-409
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• 2015

The Quasi-Zenith Satellite System (QZSS), a dedicated regional Japanese satellite system currently under development, was designed to complement the performance of the Global Positioning System (GPS). The high elevation angle of the QZSS satellite is expected to enhance the effectiveness of GPS in urban environments. Thus, the work described in this paper, aimed to investigate the effect of QZSS on GPS performance, by processing the GPS and QZSS measurements recorded at the Bohyunsan reference station in South Korea. We used these data, to evaluate the satellite visibility, carrier-to-noise density (C/No), performance of single point positioning, and Dilution of Precision (DOP). The QZSS satellite is currently available over South Korea for 19 hours at an elevation angle of more than 10 degrees. The results showed that the impact of the QZSS on users' vertical positioning is greatest when the satellite is above 80 degrees of elevation. As for Precise Point Positioning (PPP) performance, the combined GPS/QZSS kinematic PPP was found to improve the positioning accuracy compared to the GPS only kinematic PPP.

• 한국측량학회지
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• 제34권1호
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• pp.71-78
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• 2016

본 논문에서는 2015년을 기준으로 GPS(Global Positioning System) 단독측위 및 통합항법 성능 현황을 분석하고, 2020년까지의 항법성능을 연도별로 예측하였다. 이러한 예측을 위하여 한반도 지역에서 관측할 수 있는 위성항법시스템의 궤도요소 및 궤도정보 설계 값을 이용하여 Matlab을 기반으로 DOP(Dilution Of Precision)관점에서 성능을 예측하였다. 통합항법의 경우, 항법시스템 간의 시계오차 추정을 위해 시각오프셋 결정 알고리즘을 고려해야 하는데, 위성항법 메시지 기반 추정방식과 사용자가 직접 추정하는 두 가지 방법으로 나누어 분석하였다. 또한 현실감 있는 시뮬레이션 수행을 위하여 3차원 지도정보를 사용하였다. 본 시뮬레이션결과는 도심지역에서의 항법성능을 예측할 수 있는 지표로 활용될 것이라 기대된다.

• 한국측량학회지
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• 제25권3호
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• pp.231-238
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• 2007

본 연구에서는 가까운 장래에 실현될 GNSS(Global Navigation Positioning System) 결합측위의 가용성을 평가하기 위하여, GPS(Global Positioning System), Galileo 및 QZSS(Quasi-Zenith Satellites System)의 직달파(direct signal), 반사파(reflected signal), 회절파(diffracted signal) 식별을 위한 신호 전달 모형을 수립하고 이를 3차원 지리정보시스템과 결합함으로써, 위성 가시도와 측위 오차 요소를 모사 측정하였다. 중고층 빌딩이 밀집한 일본 동경도청 부근의 $1km{\times}1km$ 구역을 40,000개의 $5m{\times}5m$ 격자로 구획하여 실시한 시뮬레이션을 통해, GPS 측위와 GNSS 결합측위에 있어서 가시위성의 개수, 위성 고도, 정밀도 저하율(dilution of position : DOP), 의사거리 다중 경로 오차(pseudorange multipath error : PME)를 비교 평가하였다. GNSS 결합측위에서는 가시위성 및 직달파 위성의 개수가 현격히 증가함을 확인할 수 있었으며, 위성고도의 평균은 GPS 측위에서보다 약간 낮게 나타나지만, 위성들의 기하학적 배치가 양호하게 이루어져 정밀도 저하율이 매우 감소함을 알 수 있다. 고밀도 도시공간에서는 빌딩 등의 전파 반사로 인해 발생하는 의사거리 다중경로 오차를 완화하는 것이 사용자 위치 정확도를 향상시키기 위한 핵심적인 요소이므로, 수신기 안테나의 설계 및 배치, 신호처리 및 공간통계 기법 등을 GNSS 결합측위에 적합하도록 개선하는 것이 필요할 것이다.

• 한국항공운항학회지
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• 제11권2호
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• pp.7-21
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• 2003

The objective of this study is to evaluate a feasibility of navigation systems appropriate for the Asia-Pacific region. As an independent navigation system, four, five, and six geosynchronous satellite constellations are simulated to provide a navigation system for the region and dilutions of precision of the proposed systems are analyzed and compared.

• Journal of Positioning, Navigation, and Timing
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• 제9권2호
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• pp.79-88
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• 2020

We determined Global Positioning System (GPS) satellite visibilities in signal-blockage simulations and then analyzed Position Dilution of Precision (PDOP) fluctuations obtained from those simulated satellite geometries. PDOP values under harsh signal-blockage simulation conditions become very high compared to those calculated with real observations. Especially when the number of observed satellites is four, which is the minimum requirement for GPS positioning, PDOP values instantaneously reached several hundreds or even several tens of thousands. It was also found that the volume of the tetrahedron composed with four satellites decreases significantly. When the correlation of the tetrahedron volume and PDOP was analyzed, we reached the following conclusions: PDOP values less than 4 can be acquired when the volume is larger than 103.2 × 10¹⁹ ㎥, and PDOP values increase beyond 50 when the volume is less than 6.0 × 10¹⁹ ㎥.

• 제어로봇시스템학회논문지
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• 제20권1호
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• pp.101-105
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• 2014

For a localization system, the TDOA (Time Difference of Arrival) measurement and AOA (Angle of Arrival) measurement are often used for estimating target's positions. Although it is known that the accuracy of TDOA based localization is superior to that of AOA based one, it may have a poor vertical accuracy in bad geometrical conditions. This paper, therefore, proposes a localization algorithm in which the vertical position is estimated by AOA measurements and the horizontal one is estimated by TDOA measurement in order to achieve high 3D-location accuracy. And this algorithm is applied to a GPS jammer localization systems because it has a large value of the DOP (Dilution of Precision) when the jammer is located far away from the system. Simulation results demonstrate that the proposed hybrid TDOA/AOA location algorithm gives much higher location accuracy than TDOA or AOA only location.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1015-1017
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• 2003

Recently, DGPS or RTK-GPS techniques enable us to use satellite based positioning systems with high accuracy. But in urban area, navigation systems suffer from problems such as signal blockage by high-rise buildings, multi-path problems, and so on. So we have to know numbers of visible satellites and quality of signals received at the ground level in urban area as accurate as possible. In this paper, we developed a simulation system called LoQAS [Location service Quality Assessment System, 2002, the University of Tokyo] which can simulate numbers of visible satellites and DOP values using accurate satellite orbital data and 3-D digital map. In this time, we evaluated this system and extended it to deal with reflected signals to assess multi-path problems.

• 한국측량학회지
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• 제27권6호
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• pp.659-667
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• 2009

이 연구에서는 3차원 건물좌표를 이용한 통합 GNSS 시뮬레이터 IGSS(Inha GNSS Simulation System)를 개발하고 정확도를 검증하였다. 또한 IGSS를 이용하여 통합 GNSS 환경에서의 측위 가용성 및 정확도 향상을 평가하였다. GPS와 GLONASS의 예측결과를 실제관측 결과와 비교하여 시뮬레이터를 검증하였으며 그 결과, GPS와 GLONASS의 오차 발생빈도가 각각 6.4%와 7.5%로 나타났다. 통합 GNSS 환경에서의 측위 가용성과 정확도 향상에 관한 평가는 중고층 건물에 의한 신호차폐현상이 심한 정부대전청사를 대상으로 하였다. GPS를 단독으로 사용하였을 경우, GPS와 GLONASS를 동시에 사용하였을 경우, GPS, GLONASS, 그리고 Galileo를 함께 사용하였을 경우를 구분하여 가시위성의 개수와 정밀도 저하율을 산출하고 그 결과를 비교 및 평가하였다.

• Journal of Positioning, Navigation, and Timing
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• 제8권4호
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• pp.183-192
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• 2019

In fingerprint-based wireless positioning, it is necessary to establish a DB of the unmeasured area. To this end, a method of estimating the position of a base station based on a signal propagation model, and a method of estimating the information of the received signal in the unmeasured area based on the estimated position of the base station have been investigating. The purpose of this paper is to estimate the position of the base station using the measured information and to analyze the performance of the positioning. Vehicles equipped with a GPS receiver and signal measuring equipment travel the service area and acquire location-based Reference Signal Received Power (RSRP) measurements. We propose a method of estimating the position of the base station using the measured information. And the performance of the proposed method is analyzed on a simulation basis. The simulation results confirm that the accuracy of the positioning is affected by the measured area and the Dilution of Precision (DOP), the accuracy of the position information obtained by the GPS receiver, and the errors of the signal included in the RSRP. Based on the results of this paper, we can expect that the position of the base station can be estimated and the DB of the unmeasured area can be constructed based on the estimated position of the base stations and the signal propagation model.