Mi-Young Shin

Atomic clock error modeling for GNSS software platform

This paper presents satellite atomic clock error model for generating the satellite clock error in GNSS software platform for the GPS Ll C/A code signal, L2 civil signal, L5 signal, and Galileo El, E5a signals. Scheme to simulate the clock error through phase error characteristics of the atomic clock are given. Rubidium, cesium and hydrogen maser clock are considered for GPS or Galileo satellites and Quartz oscillator is considered for user receiver. The clock error consists of five typical noises such as white noise on phase, flicker noise on phase, white noise on frequency, flicker noise on frequency, random walk on frequency. The analysis software for the Allan variance, the Hadamard variance and the PSD (power spectral density) of the clock error is also included. The clock error model is implemented and its validity is analyzed by comparing with theoretical ones.

Detection algorithm of ionospheric delay anomaly based on multi-reference stations for ionospheric scintillation

Radio waves including GPS signals, various TV communications, and radio broadcasting can be disturbed by a strong solar storm, which may occur due to solar flares and produce an ionospheric delay anomaly in the ionosphere according to the change of total electron content. Electron density irregularities can cause deep signal fading, frequently known as ionospheric scintillation, which can result in the positioning error using GPS signal. This paper proposes a detection algorithm for the ionosphere delay anomaly during a solar storm by using multi-reference stations. Different TEC grid which has irregular electron density was applied above one reference station. Then the ionospheric delay in zenith direction applied different TEC will show comparatively large ionospheric zenith delay due to the electron irregularity. The ionospheric slant delay applied an elevation angle at reference station was analyzed to detect the ionospheric delay anomaly that can result in positioning error. A simulation test was implemented and a proposed detection algorithm using data logged by four reference stations was applied to detect the ionospheric delay anomaly compared to a criterion.

A Comparative Analysis of Performance of Ambiguity Validation Methods

반송파를 이용한 정밀 측위의 성능은 미지정수 결정에 큰 영향을 받는다. 미지정수가 정확하게 결정되면 수 mm에서 수 cm 정도의 정밀한 위치해를 얻을 수 있지만 미지정수가 잘못 결정되면 위치해의 정밀도와 정확도를 보장할 수 없다. 미지 정수 결정은 Integer Rounding(IR), Integer Bootstrapping (IB), Integer Least Squares(ILS) 등의 기법을 기반으로 발전 되어 왔다(Blewitt, 1989; Dong and Bock, 1989; Teunissen, 1993). 이 중에서 ILS를 기반으로 하는 기법이 이론과 실험의 모든 측면에서 다른 기법들보다 좋은 성능을 보이기 때문에 많은 연구에서 언급되고 있다. 특히, Teunissen(1995)은 ILS 를 수행하기 전에 비상관화 과정을 이용하여 미지정수 결정 성공률 및 효율성을 비약적으로 발전시켰다. ILS를 기반으로 하는 미지정수 결정은 다음과 같은 단계로 이루어진다. 첫 번 째는 미지정수가 정수라는 제약조건을 실수영역으로 완화하 여 실수 미지정수(floating ambiguity)와 실수 미지정수의 공 분산행렬을 추정한다. 두 번째는 앞서 추정한 실수 미지정수 와 실수 미지정수의 공분산행렬로 표현되는 비용함수를 최소 화시키는 정수 미지정수(integer ambiguity) 후보를 정수영역 에서 검색한다. 세 번째는 정수 미지정수 후보에 대한 검정을 통해 최종적으로 미지정수를 결정한다. IR, IB를 기반으로 하 는 방법들은 하나의 정수 미지정수 후보를 계산한다. 이에 반 해 ILS는 검색을 통해 여러 개의 정수 미지정수 후보를 찾으 므로, 후보 간의 검정을 통해 신뢰성이 가장 높게 평가된 하나 의 후보를 최종적인 미지정수로 결정하거나 모든 후보가 신뢰 성이 같게 평가되는 경우에는 미지정수를 결정하지 못하는 상 황으로 판단한다. 후보에 대한 검정이 견고하지 못하면 잘못 미지정수 후보 타당성 검정 기법간의 비교 분석

Design of Monitoring System for Network RTK

Network RTK is a precise positioning technique using carrier phase correction data from reference stations within the network, and is constantly being researched for improved performance. However, the study for the system accuracy has been performed but system integrity research has not been done as much as system accuracy, because network RTK has been mainly used on surveying for static or kinematic positioning. In this paper, adequate monitoring system for network RTK is designed as basis research for integrity monitoring on network RTK. To this, fault tree on network RTK is analyzed, and a countermeasure is prepared to detect and identify the each fault items. Based these algorithms, monitoring system to use on central processing facility is designed for network RTK service.

A feasibility study of PNT integrity provision for maritime applications

This paper focuses on provision of maritime position, navigation, and timing (PNT) integrity information in order to support safe maritime navigation and application. A simulation system for a feasibility study is used to evaluate the performance of the system according to the requirements set by the International Maritime Organization (IMO) resolution A.915 (22) on accuracy, integrity, and availability. In order to assess the performance requirements and service level of the system, a concept for maritime PNT integrity monitoring is proposed, and the considerations necessary to meet performance requirements are summarized. Related studies are analyzed, and their limitations in monitoring the integrity of the satellite signals are presented. To overcome these limitations, the port PNT information reliability is presented in this work, consisting of the Stanford plot. Finally, this feasibility study determines the reliability level of maritime PNT information, and simulation results are shown.

A study on the optimal geometrical placement of eLoran stations in Korea

In the eLoran navigation system, the dominant deterioration factors of navigation accuracy are the TOA measurement errors on user receiver and the GDOP between the receiver and the transmitters. But if the ASF data measured at dLoran reference station are provided for users through the Loran data channel, it will be possible to correct the TOA measurement errors. The position accuracy can be determined by the DOP depending on the geometry of receiver-transmitters, and their optimal placement improves the navigation accuracy. In this study we determined the geometric placement in case of up to six stations, and evaluated the performance of position accuracy for the receiver-transmitter geometry set of eLoran stations. The proposed geometry of eLoran stations can be referred for the construction of eLoran infrastructure meeting the capability of HEA for maritime, and time/frequency users in Korea.

The Integrated eLoran/GPS Navigation Algorithm for Reduced Calculational Complexity and High Accuracy

Satellite navigation system such as GPS is becoming more important infrastructure for positioning, navigation and timing. But satellite navigation system is vulnerable to interferences because of the low received power, complementary navigation system such as eLoran is needed. In order to develop eLoran/GPS navigation system, integrated eLoran/GPS navigation algorithm is necessary. In this paper, new integrated eLoran/GPS navigation algorithm is proposed. It combines the position domain integration and the range domain integration to get accurate position with less computational burden. Also an eLoran/GPS evaluation platform is designed and performance evaluation of the proposed algorithm using the evaluation platform is given. The proposed algorithm gives an accuracy of the range domain integration with a computational load of the position domain integration.

Comparison of Predicted and Measured ASF

In the almost application parts, GNSS being used the primary navigation system on world-widely. However, some of nations attempt or deliberate to enhance current Loran system, as a backup to satellite navigation system because of the vulnerability to the disturbance signal. Loran interests in supplemental navigation system by the development and enhancement, which is called eLoran, and that consists of advancement of receiver and transmitter and of differential Loran in order to increase the accuracy of current Loran-C. A significant factor limiting the ranging accuracy of the eLoran signal is the ASF in the TOAs observed by the receiver. The ASF is mostly due to the fact that the ground-wave signal is likely to propagate over paths of varying conductivity and topography. This paper presents comparison results between the predicted ASF and the measured ASF in a southern east region of Korea. For predicting ASF, the Monteath model is used. Actual ASF is measured from the legacy Loran signal transmitted Pohang station in the GRI 9930 chain. The test results showed the repeatability of the measured ASF and the consistent characteristics between the predicted and the measured ASF values.

Development of a GPS Receiver Platform with High Resolution to Design of Interference Excision Filters

A GPS receiver platform has been developed to design an interference rejection filter and the platform is also able to evaluate performance of those filters. This platform consists of RF/IF part, data acquisition part and PC part. The RF/IF part converts RF signals to IF signals, the data acquisition part transmits the IF signals to PC using USB device. The PC part rejects the interferences with a filter and then it does navigation with GPS software receiver. The RF/IF part and data acquisition part had been validated with signal spectrum, and the PC part had been validated with the navigation results of GPS receiver. Finally, the entire platform including interference rejection filter has been confirmed with the navigation results in case that the GPS signals and interference entered this platform. As a result, the GPS receiver operated well against interference with 45dB JSR.

A Navigation Method Based on the NDGPS and LORAN-C

The coverage of the NDGPS is nationwide currently and by 2007 more than 2 NDGPS signal will be available in most of Korean peninsula both coastal area and inland. The role of NDGPS beacon is transmitting pseudorange corrections however if range or pseudorange can be measured from NDGPS beacon signal, it might be possible to construct an independent regional navigation system: The range from NDGPS beacon signal can be used as additional measurements to remove GPS shadow area and to improve accuracy and reliability of GPS. Furthermore, by adding Loran-C, a regional radio navigation system without GPS can be possible. In this paper, a feasibility study on the regional positioning system using NDGPS and LORAN-C are given. The results show that the NDGPS and LORAN-C can be used as a ground based regional navigation system if requirements such as synchronization of NDGPS network, dual coverage of NDGPS, navigation algorithm for both NDGPS and LORAN-C measurements and an efficient ASF compensation method are met.