• Journal of Positioning, Navigation, and Timing
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• 제7권4호
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• pp.217-226
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• 2018

According to the Korea Coast Guard's maritime disaster statistics (Korea Coast Guard 2017, Korean Statistical information Service 2018), an average of 2,140 marine accidents occurred every year for the past 6 years and the number of accidents is increasing every year. Among them, maritime accidents of fishing vessels are the most frequent, and recently accidents involving fishing boat and leisure vessels are rapidly increasing as well. In particular, the number of accidents involving leisure vessels increased to about one-third of the accidents of fishing vessels, and emergency rescue requests are increasing every year accordingly. However, the number of crash accidents involving users of small vessels and marine leisure activities are increasing because of the difficulties of installing navigation equipment and electronic navigation charts. Recently, the demand for precise positioning using mobile devices is increasing in the fields of maritime safety, piloting support, and coastal survey. Although various applications of smart devices provide location-based services for users, the measurement results are discontinuous when using the position coordinates of the National Marine Electronics Association (NMEA) calculated by smartphone. Recently, Google announced that they will provide GPS raw data to developers from Android 7.0 Nougat. As a result, developers have an opportunity to receive precise carrier phase and code measurements to make more accurate positioning according to the performance of Android devices. This study analyzed GPS positioning performance using Android devices, and compared and analyzed the positioning performance at sea with high-performance GPS receivers.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.535-540
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• 2006

The relationship between the observable noise model and the satellite elevation angle can be modeled quite well by an exponential function.[Jin, 1996] Noise size and dependence on the elevation angle are, however, different for each observation and receiver type. Therefore, the coefficient determination of this model is an issue, and various methods including PR-CP, single difference, and time difference have been suggested. The limitations of them are difficulty to model the carrier phase noise and to eliminate bias. To overcome these disadvantages for using Jin's model, we suggest zero baseline double difference (DD) and noise sorting algorithm. Data DD technique in zero baseline is useful to eliminate all the troublesome GPS biases, and the remaining error is the sum of GPS measurement noises from two satellites. These DD residuals for hours should be sorted by the combination of satellite elevation angles, and then variance value of the residual for each combination can be estimated. Using these values, we construct an over-determined linear equation whose solution is a set of noise variance for each satellite elevation angle. With 24hr Trimble 4000ssi data, we easily worked out the coefficients of the noise model not only for pseudorange but also for carrier phase. We estimated the standard deviation of the measurement DD using our model, and plotted 1 and 3 sigma lines for every epoch to verify the representation of the residual error. 63.3% of pseudorange residual and 65.9% of phase error did not exceed the 1 sigma lines. Additionally, 99.2% and 99.5% of them lied within 3sigma line. These figures prove that the Gaussian property of measurement noise, and that the suggested model by our algorithm corresponds to the observable noise information.

• 제어로봇시스템학회논문지
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• 제5권1호
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• pp.69-78
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• 1999

The attitude determination system is indispensable for navigation, guidance and control tasks. In order to construct this system some special products that use dual frequencies or have on receiver engine with multiple antennas are used. But they are so expensive. Thus there are still strong requirements for the conventional low cost single frequency off-the-shelf receiver. This paper will propose a new technique to resolve integer ambiguity with single frequency GPS receiver and will show the problems of the attitude applications in which low cost receiver are being used. Also, based on this new technique precise attitude determination is presented.

• 한국환경과학회지
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• 제11권2호
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• pp.103-110
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• 2002

The position fixing usually is determined by triangulation, traverse surveying and astronomy surveying. However, when the station is moving, it is impossible to determine its position continuously by the former method. By a satellite positioning method(GPS), this problem can be solved. In our study, we used two methods to determine the length and coordinate of a point position. One is a kinematic GPS method and the other is a static one. Each is based on carrier phase measurement and employs a relative position technique. We implemented observation experiments such as Geodimeter and DGPS(Differential GPS) successfully. To estimate the accuracy between the kinematic and static methods, we compared the results of Geodimeter, the kinematic, and the static. The results showed that the static is relatively a little more accurate than the kinematic. However, in the kinematic mode, when we received the GPS data for a long time, we found that the kinematic also had a high accuracy value for the length survey Finally, we applied the GPS to Jeju Harbor Breakwater to examine the applicability of GPS for coastal ocean structure based on the kinematics and the statics, respectively.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.113-116
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• 2006

In order to fully utilize the inherent precision that GPS observables could offer, accurate estimation of dynamic and measurement parameters is vital. Among these parameters some are indispensable in virtually every form of GPS processing, while some are limitedly relevant to a particular application. In the context of time transfer by GPS, the transmission-related errors such as ionospheric and tropospheric delays, and the integer ambiguity of the carrier phase observables belong to the former, the atomic clock parameters and data batch-related parameters to the latter. Obviously the atomic clock parameters are of prime importance in GPS time transfer. In this study some of important parameters in conducting time transfer experiments by use of GPS were characterized and their effects on time transfer performance were investigated in detail

• 한국통신학회논문지
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• 제38C권11호
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• pp.1044-1050
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• 2013

본 논문은 ETRI에서 개발한 GPS RF 신호생성기와 상용수신기인 U-Blox 수신기를 이용하여 기만신호의 공격을 완화하는 방법에 대하여 분석하였다. 기만신호는 대상 수신기의 코드 및 반송파 성분의 변이를 이용하여 대상수신기가 비정상적인 위치를 생성하도록 하는 것이다. 우리는 이러한 기만신호 공격에 따른 수신기에서의 신호세기 및 항법해 영향을 분석하였다. 또한 기만신호를 제거하기 위하여 기만신호와 역위상 코드를 가지는 신호를 고려하였다. GPS RF 신호생성기를 이용하여 정상적인 GPS 신호, 기만신호, 기만신호와 역위상을 가지는 항기만신호를 생성하였고 기만신호와 항기만신호간의 코드 위상차이에 따른 기만신호 공격의 영향을 수신기를 통하여 확인하였다. 기만 신호의 코드 지연과 동일한 코드지연의 신호를 생성할 경우 기만신호가 상쇄되는 것을 확인하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.309-314
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• 2006

In general DGPS system, the correction message is transferred to users by wireless modem. To cover wide area, many DGPS station should be needed. And DGPS users must have a wireless modem that is not necessary in standalone GPS. But SBAS users don't need a wireless modem to receive DGPS corrections because SBAS correction message is transmitted from the GEO satellite by L1 frequency band. SBAS signal is generated in the GUS(Geo Uplink Subsystem) and uplink to the GEO satellite. This uplink transmission process causes two problems that are not existed in GPS. The one is a time delay in the uplink signal. The other is an ionospheric problem on uplink signal, code delay and carrier phase advance. These two problems cause ranging error to user. Another critical ranging error factor is clock synchronization. SBAS reference clock must be synchronized with GPS clock for an accurate ranging service. The time delay can be removed by close loop control. We propose uplink ionospheric error correcting algorithm for C/A code and carrier. As a result, the ranging accuracy increased high. To synchronize SBAS reference clock with GPS clock, I reviewed synchronization algorithm. And I modified it because the algorithm didn't consider doppler that caused by satellites' dynamics. SBAS reference clock synchronized with GPS clock in high accuracy by modified algorithm. We think that this paper will contribute to basic research for constructing satellite based DGPS system.

• Korean Journal of Geomatics
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• 제4권2호
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• pp.47-52
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• 2004

We can process and compute the position, velocity and time by satellite signals of GPS. The signals are used to compute positioning of three dimensions and timing offset of the receiver clock when we can track the tour satellite signals at least. One of the specified aims is to use less expensive single frequency code/carrier phase GPS receivers, which are typically around half the price of dual frequency receivers. In the study, the author analyzed the accuracy and applicability of frequence linear combination using triangulation points evaluated distance limitation.

• Journal of Astronomy and Space Sciences
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• 제26권2호
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• pp.229-236
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• 2009

다목적실용위성-5호는 2010년 발사를 목표로 고도 550km의 저궤도에 위치하게 될 것이다. 다목적실용위성-5호의 임무인 고정밀 SAR(Synthetic Aperture Radar) 영상을 처리하기 위해서는 정확한 위성의 위치(20cm) 와 속도(0.03cm/s)가 결정되어야 한다. 이러한 요구 조건은 한국 전자통신연구원에서 개발한 ETRI GNSS Precise Orbit Determination(EGPOD) 소프트웨어로 검증하였다. 0.1Hz 수신 주기의 SAC-C 위성 반송파위상 데이터로 정밀궤도결정을 수행하였다. 이중 주파수 GPS 데이터를 사용하여 수신 선호의 전리층 오차를 대부분 제거하고 이중 차분된 데이터를 생성함으로써 GPS 위성과 수신기의 공통된 시계 오차를 없앴다. 동역학 모델 접근 방법을 이용하였고, Batch Least Square Estimator(BLSE) 필터로 각 데이터 아크(arc) 에 해당하는 위성의 위치와 속도, 대기저항 계수, 태양풍 계수를 추정하였다. 또한 정밀한 동역학 모델을 위하여 모델 되지 않은 부정확한 가속도 항을 보충하는 경험 가속도를 추가하였다. 경험 가속도는 위성의 공전 주기(revolution) 당 한번씩 시선방향(radial), 진행방향(along-track), 수직방향(cross-track)으로 추정하고, 수직방향의 상수 항에 대해서는 해당 데이터 아크에 관하여 부가적으로 추정하였다. 정밀궤도결정 결과 검증을 위하여 EGPOD 소프트웨어에서 얻어진 결과와 JPL에서 제공하는 정밀궤도력(Precise Orbit Ephemeris)을 비교하였다.

• Journal of Astronomy and Space Sciences
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• 제26권1호
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• pp.59-74
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• 2009

Relative navigation system is presented using GPS measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide the real-time inter-satellite relative positions as well as absolute positions for two formation flying satellites in low earth orbit. To improve the navigation performance, the absolute states are estimated using ion-free GRAPHIC (group and phase ionospheric correction) pseudo-ranges and the relative states are determined using double differential carrier-phase data and singled-differential C/A code data based on the extended Kalman filter and the unscented Kalman filter. Furthermore, pseudo-relative dynamic model and modified relative measurement model are developed. This modified EKF method prevents non-linearity of the measurement model from degrading precision by applying linearization about absolute navigation solutions not about the priori estimates. The LAMBDA method also has been used to improve the relative navigation performance by fixing ambiguities to integers for precise relative navigation. The software-based simulation has been performed and the steady state accuracies of 1 m and 6 mm ($1{\sigma}$ of 3-dimensional difference errors) are achieved for the absolute and relative navigation using EKF for a short baseline leader/follower formation. In addition, the navigation performances are compared for the EKF and the UKF for 10 hours simulation, and relative position errors are mm-level for the two filters showing the similar trends.