• Journal of Satellite, Information and Communications
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• v.8 no.1
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• pp.14-22
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• 2013

GPS radio occultation is a remote sensing technique probing atmospheric properties based on the fact that GPS signal is refracted and delayed by atmosphere. The FORMOSAT-3/COSMIC mission jointly developed by the USA and Taiwan is providing about 2500 occultation soundings a day on the near real-time basis. The Korean KOMPSAT-5/AOPOD system is preparing to launch for monitoring troposphere and ionosphere using a dual frequency GPS receiver and the antenna for occultation data acquisition. In this paper, we examine the methods for signal processing and the geometry analysis for GPS radio occultation, and look into the retrieval techniques for the temperature and humidity of troposphere and the electron density and scintillation of ionosphere. Using these atmospheric properties, we aim to derive the strategies for applying GPS radio occultation to space weather, for example, ionospheric TEC(total electron content) analysis for earthquake monitoring and the Open API(application programming interface) development for more effective data service.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.5
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• pp.535-544
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• 2009

Signals from the Global Positioning System(GPS) satellite are used to retrieve the integrated amount of water vapor or the precipitable water vapor(PWV) along the path between a transmitting satellite and ground-based receiver. In order to retrieve the PWV from GPS signal delay in the troposphere, the actual zenith wet delay, which can be derived by extracting the zenith total delay and subtracting the actual zenith hydrostatic delay computed using surface pressure observing, will be needed. Since it has been not co-located between GPS permanent station and automated weather station, the air-pressure on the mean sea level has been used to determine the actual zenith hydrostatic delay. The directly use of this air-pressure has been caused the dilution of precision on GPS PWV retrieval. In this study, Korean reverse sea level correction method of air-pressure was suggested for the improving of GPS PWV retrieval capability and the accuracy of water vapor estimated by GPS was evaluated through a comparison with radiosonde PWV.

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.429-438
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• 2001

GPS (Global Positioning System) is the most ideal navigation system which can be used on the earth irrespective of time and weather conditions. GPS has been used for various applications such as construction, survey, environment, communication, intelligent vehicles and airplanes and the needs of GPS are increasing in these days. This paper deals with the design and implementation of the RTOS (Real-Time Operating System) for a GPS navigation computer in the GPS/INS integrated navigation system. The RTOS provides the optimal environment for execution and the base platform to develop GPS application programs. The key facilities supplied by the RTOS developed in this paper are priority-based preemptive scheduling policy, dynamic memory management, intelligent interrupt handling, timers and IPC, etc. We also verify the correct operations of all application tasks of the GPS navigation computer on the RTOS and evaluate the performance by measuring the overhead of using the RTOS services.

• Proceedings of the Korean Society of Computer Information Conference
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• 2024.01a
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• pp.109-111
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• 2024

군사 목적으로 개발된 드론은 최근 다양한 산업 및 민간 분야로 확대되고 있으며, 이러한 확대에 따라, 드론이 급격하게 발전하여, 농업이나 무인 드론 택배와 같은 산업 전반적으로 긍정적인 효과를 창출하는 추세이다. 그러나 이러한 발전에 반하여, 드론에 장착된 카메라를 통한 사생활 침해나 테러 목적으로 활용하는 것과 같은 부정적인 측면이 드러나기 시작하였다. 특히, 드론의 위치와 밀접한 연관이 있는 GPS와 관련하여, 무인 이동체의 특성상, GPS 신호에 의존하여 사용자에게 드론의 위치를 전달하지만, 이러한 GPS 신호를 송신하는 위성은 거리가 매우 멀리 위치하고, 이에 따라, 신호 세기가 비교적 약한 문제점을 가진다. 이와 같은 문제점을 악용하는 GPS 스푸핑 공격이 등장하였으며, 이 공격은 만약 공격자가 GPS 신호를 조작하여 송신한다면, 드론에 장착된 GPS 수신기는 조작된 GPS 위치를 수신하며, 이에 따라, 드론의 제어권을 탈취하거나 충돌 유발, 비정상적인 비행 경로 유도와 같은 문제점이 발생한다. 본 논문에서는 최신의 상용화된 드론을 대상으로, GPS 스푸핑 공격의 취약점을 분석하고 실증한다. 이를 위하여, 공격자가 비행 금지 구역에 해당하는 GPS 신호를 조작하는 것으로 공격을 시도하고, 이에 따른 드론에서 준비된 동작인 강제 착륙과 같은 비정상적인 행위를 유발하여, 드론의 임무 수행 능력을 제한하는 취약점을 분석하고 실험을 통하여 실증한다. 본 논문의 결과를 토대로, 최신 드론에서 발생 가능한 보안 위협을 도출함으로써, 드론의 안전성을 향상시키기 위한 자료로 활용될 수 있을 것으로 사료된다.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.275-284
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• 2007

For the application to the numerical weather prediction (NWP) in active service, it is necessary to ensure that the GPS precipitable water vapor (PWV) data has less than one hour latency and three millimeter accuracy. The comparison and the verification between the daily products from GPS measurement by using the IGS final ephemeris and the conventional meteorological observation has been done in domestic researches. In case of using IGS final ephemeris, GPS measurements can be only post processed in daily basis in three weeks after the observation. Thus this method cannot be applied to any near real-time data processing. In this paper, a GPS data processing method to produce the PWV output with three mm accuracy and one hour latency for the data assimilation in NWP has been planned. For our new data processing strategy, IGS ultra-rapid ephemeris and the sliding window technique are applied. And the results from the new strategy has been verified. The GPS measurements during the first 10 days of January, April, July and October were processed. The results from the observations at Sokcho, where the GPS and radiosonde were collocated, were compared. As the results, a data processing strategy with 0.8 mm of mean bias and 1.7 mm of standard deviation in three minutes forty-three seconds has been established.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.10a
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• pp.279-282
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• 2015

Fisheries development of the basic law pursuant to article 15 (marine safety management, etc.) one of maritime safety and maritime traffic facilities nationwide network of DGPS in accordance with the building maximize infrastructure utilization and country. Source technology has been improving steadily raised for the benefit daegukmin. In particular, look at the type of product for the marine supply medium-wave receiver Performance products that satisfy most of the IMO Advisory. The antenna and receiver are separate structural supply for some integrated model with a very high Rather it is used as a portable receivers for marine positioning cheap integrated model development is needed. Correction of satellite navigation receivers for the current Marine GPS module, medium-wave modules can be developed one low cost Integrated in independent operating environments do not support the model development done look at what the problem is 285kHz ~ 315kHz in DGPS Beacon receiver structure using a medium wave or Beacon The medium-wave antenna and a GPS receiver signal to noise ratio was studied GPS signal attenuation on the DGPS performance looked at each GPS manufacturer medium-wave signal-to-noise ratio and normalized impact by GPS manufacturers noise power ratio per bandwidth for medium-wave GPS signals affect it was implemented to improve performance.

• Journal of Korean Society for Geospatial Information Science
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• v.12 no.1 s.28
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• pp.11-20
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• 2004

The purpose of this paper is to evaluate the applicability of GPS data for real-time traffic information collection especially after SA removal. Two major results have been reported. One is the GPS data availability and/or useful data point density for travel time estimation using Circle-X algorithm. 87.23% of data points can be mobilized after SA whereas only 29.94% of data was useful in calculating travel time. The other is the possible reduction of the buffer size that is used for screening the points of all GPS into useful and useless data, respectively. With these outcomes, it is safely expected that the regular GPS alone can provide the data points for real-time travel time estimation instead of the more expensive DGPS system.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.87-90
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• 2003

정밀한 위치결정에 사용되는 GPS는 초기 군사목적을 벗어나 자동차, 선박, 비행기 등의 항법은 물론 측량분야, 지각 및 구조물의 변위 감시, 우주, 통신, 국방 분야 등 매우 광범위한 분야에서 활용되고 있으며, 그 이용도가 급속히 증가하는 추세이다. 그러나 GPS 관측값은 부정오차와 정오차 등 많은 오차를 포함하고 있기 때문에 이를 소거하거나 최소화하여야 한다. GPS 오차는 크게 위성궤도나 위성시간 오차등 위성에 관련된 오차, 수신기 잡음이나 다중경로 등 수신기 관련 오차, 그리고 대류권이나 전리층에 의한 전파 오차로 구분할 수 있다. 이들 오차들은 대부분 차분방법과 수학적 알고리즘에 의해 소거되거나 최소화되지만, 다중경로와 수신기 잡음은 소거하거나 축소할 수 없다. 다중경로는 관측당시의 수신기 주변환경에 따라 바뀌기 때문에 수학적으로 소거할 수 없으며, 수신기 잡음은 수신기 내부의 노이즈로 인하여 발생하기 때문에 소거하기가 상당히 어렵다. 본 연구에서는 다중경로에 의한 GPS 기선변화를 알아보기 위해서 여러 조건하에서 정적 GPS 측량을 실시하였다. 먼저 정확한 좌표를 알고 있는 한 점에 GPS를 설치하고 다른 두 대의 GPS을 임의 점에 설치하였고, 이들 두 GPS 중에 하나의 수신기에 다중경로 환경을 설정하였다 정적 GPS 관측시 기선에 어떠한 변화가 오는 파악하기 위해서 기선처리와 망조정을 통해 기선길이와 좌표값을 산출하였다. 이러한 다중경로 실험은 구조물 모니터링 등 mm 정확도를 요구하는 GPS 측량에 유용하게 사용될 수 있을 것이다.

• Journal of Advanced Navigation Technology
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• v.1 no.1
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• pp.11-22
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• 1997

Determination of position, velocity and time from the satellite signals is the central problem of the GPS receiver. Generally, GPS receiver uses least square method for navigation filter algorithm. The Kalman filter has known as an optimal linear estimator, which uses the knowledge of the system dynamics and the statistical characteristics of the system noises and measurement error. In this paper, we design an 8 state Kalman filter for GPS navigation and employ some techniques that can reduce computational burden, increase numerical stability, and improve filtering performance. To show its effectiveness, the designed filter is implemented in a GPS receiver and tested in real-time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.1
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• pp.50-56
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• 2014

Recently Android apps utilizing location based services are widely used. Understanding the operation of the GPS location provider, among various location providers supported in the Android platform, is an essential task for developers using the Android. This paper, based on the analysis of source codes of the GPS subsystem in the Android platform, shows clearly and orderly the operation of the GPS location provider, in key threads' perspectives as well as in a stepwise fashion from the initialization up to the final location report steps.