Frequency GNSS Research Articles

“卫星导航定位理论与方法”的教学实践探讨

当下多系统多频GNSS高精度数据处理已成为卫星导航研究领域的热点问题，其目的在于培养学生的综合能力与创新能力。文章针对“卫星导航定位理论与方法”课程中的主要内容和典型问题，提出了改进的教学模式和考核方法，并在实践中取得了较好的教学实践效果。 Multi frequency GNSS high precision data processing has become a hot issue in the field of satellite navigation. The purpose is to cultivate students’ comprehensive ability and innovative ability. In this paper, the main content and typical problems in the course of the theory and method of satellite navigation and positioning are presented, and the improved teaching mode and the method of assessment are put forward, and has achieved good teaching practice effect in the practice.

Attitude Determination using Single Frequency GNSS Receivers for Small UAVs

Attitude Determination using Single Frequency GNSS Receivers for Small UAVs

Uso de información ionosférica obtenida por GNSS para detectar y medir fulguraciones solares

The Ionosphere, the partially ionized atmospheric region ranging from approximately 60 to +1000 km height, is typically affected by spatial and temporal variations, driven by Local Time (solar illumination), Latitude (magnetic field and solar illumination) and time (space weather, among seasonal and solar cycle dependence). It can be indirectly studied from the dual L-band frequency GNSS measurements by assuming the first order ionospheric delay approximation (the higher order ionospheric effects in GNSS typically constitute less than 0.1% of the overall ionospheric effect and only affects very precise applications). Moreover, the Ionosphere is affected as well by ionospheric waves, ,solar flares and other space weather effects. Recent modeling techniques and corresponding results are going to be summarized regarding to the daylight sudden overionization generated by the radiation associated to Solar Flares facing the Earth, and its measurement by means of Global Navigation Satellite Systems. This approach has already been implemented in real-time by the authors.

Demonstration of a Space Capable Miniature Dual Frequency GNSS Receiver

A low cost, miniature, dual frequency, software defined Global Navigation Satellite System receiver was developed and flown on a sounding rocket. The receiver, known as the Fast, Orbital, TEC, Observables, and Navigation (FOTON) receiver, is intended for use in space applications. In this paper, the receiver design is described and flight test results are presented. On its maiden sounding rocket demonstration flight in 2012, FOTON demonstrated GPS-based ionospheric sounding, including: (1) use of a dual frequency GPS receiver onboard a sounding rocket experiment, (2) estimation of spacecraft spin rate by exploiting differential GPS phase windup in a dual frequency receiver, and (3) GPS-based measurement of the vertical electron density profile in aurora. In preparation for upcoming space flights, FOTON was also designed for operation in low Earth orbit. Copyright © 2014 Institute of Navigation.

An Assessment of Ionospheric Error Mitigation Techniques for GNSS Estimation in the Low Equatorial African Region

Single frequency GNSS receivers are the most widely used tools for tracking, navigation and geo-referencing around the world. It is estimated that over 75% of all GNSS receivers used globally are single frequency receivers and users experience positioning error due to the ionosphere. To enable GNSS Single Frequency Precise Point Positioning (SFPPP), accurate a-prior information about the ionosphere is needed. The variation of the ionosphere is larger around the magnetic equator and therefore depends on latitude. It will be expected that SFPPP works better on latitude further from the magnetic equator. This present study aims to investigate the accuracy of some ionospheric error mitigation approaches used in single frequency precise point positioning (SFPPP) at several GNSS station in the new Nigerian GNSS Network (NIGNet) and two IGS sites in the low equatorial African region. This study covers two epochs of observation. The first consists of observation from three consecutive days (GPS week 1638; days 0, 1 and 2) that belongs to a period of low solar activities. The second epoch consists of observation from three consecutive days (GPS week 1647; days 2, 3 and 4) that belongs to a high solar activity and intense geomagnetic conditions. The estimated position for the GNSS stations from dual frequency measurement and their known ITRF solutions were used as a benchmark to assess the accuracy of SFPPP under four conditions i.e., SFPPP without ionospheric correction, SFPPP using final GIM models from the Centre for Orbit Determination in Europe( CODE), SFPPP with Klobuchar model, and SFPPP with a computed (local) model at each station. All computation was done using Leica Geo-office software. The result of the study clearly demonstrates the significance of removing or correcting for the effect of the ionosphere, which can result in up to 7 m displacement. It was recommended that GIMs from different organization should be investigated and also efforts should be towards improvement in algorithms and clock error modeling.

이중 주파수 및 다중 위성항법 광역보강시스템 한반도 지역 성능 예측

최근에 GPS의 현대화, GLONASS의 정상화, Galileo 및 Beidou의 개발 등으로 기존에 GPS에만 의존하였던 것과 달리 사용자가 다양한 항법위성을 활용할 수 있게 되었다. 또한 새로운 항법위성에는 기존의 L1 주파수 신호 뿐만 아니라 새로운 민간 신호인 L5 주파수 신호도 방송하기 때문에 사용자는 이중 주파수 측정치를 활용하여 직접 자신의 전리층 지연을 추정하여 가용성 성능을 향상 시킬 수 있을 것으로 예상된다. 이에 따라 기존의 GPS L1 주파수 사용자만 고려하던 광역보강시스템도 이중 주파수 및 다중 위성항법시스템을 고려하도록 개발이 진행되고 있다. 본 논문에서는 미래의 L1/L5 이중 주파수 및 다중 위성항법 시스템 사용자를 고려한 위성기반 광역보강시스템 (Satellite Based Augmentation System, SBAS)의 주요 알고리즘을 설명하고, 한반도 주변의 성능을 시뮬레이션을 통해 예측하였다. Recently, GNSS users can utilize various navigation satellite thanks to GPS modernization, renewal of GLONASS, and development of Galileo and Beidou. And availability performance of users is expected to be improved because these new navigation satellites transmit L5 signal as well as L1 signal, and users can directly estimate the ionospheric delays. In accordance with these changes existing Satellite Based Augmentation System (SBAS) which considers only GPS L1 signal is being developed to support dual frequency and multi-constellation GNSS users. This paper describes the main features of dual-frequency, multi-constellation SBAS algorithms and estimates the performance in Korean region by simulation.

A GNSS Interference Monitoring Method with Low False Alarm and Low Missed Detection Probability

Interference monitoring and analysis for GNSS frequency bands plays an important role in construction and development of satellite navigation systems, which can promote interference source locating, and has much benefit for system construction and the development of anti-jamming equipments. Due to high satellite orbits, GNSS signals reached the ground are very weak and submerged below the thermal noise, which makes it vulnerable to interference. Interference sources for satellite navigation system require only a small transmission power; however, a significant interference effect can be obtained. Therefore, a high sensitivity is needed by interference monitoring for satellite navigation system. The interference judgment threshold is close to thermal noise power, which often causes a higher probability of false alarm. It is very important to reduce the probability of false alarm at the same time to ensure high sensitivity. In this paper, a high sensitivity (low missed detection probability) and low false alarm interference monitoring method is proposed, a dual decision threshold is designed, thus the probability of false alarm can be effectively reduced at the same time of identifying interference accurately. The experimental results demonstrated the effectiveness of the algorithm.

Ambiguity resolution for triple-frequency geometry-free and ionosphere-free combination tested with real data

The recent GPS Block IIF satellites SVN62 and SVN63 and the Galileo satellites GIOVE-A, GIOVE-B, PFM and FM2 already send signals on more than two frequencies, and more GNSS satellites will provide tracking data on at least three frequencies in the near future. In this paper, a simplified general method for ambiguity resolution minimizing the noise level for the triple-frequency geometry-free (GF) and ionosphere-free (IF) linear combinations is presented, where differently scaled code noise on the three frequencies was introduced. For the third of three required linear combinations, the most demanding one in triple-frequency ambiguity resolution, we developed a general method using the ambiguity-corrected phase observations without any constraints to search for the optimal GF and IF linear combination. We analytically demonstrate that the noise level of this third linear combination only depends on the three frequencies. The investigation concerning this frequency-dependent noise factor was performed for GPS, Galileo and Compass frequency triplets. We verified the theoretical derivations with real triple-frequency GPS and Galileo data from the Multi-GNSS Experiment (M–GEX) of the International GNSS Service (IGS). The data of about 30 M–GEX stations around the world over 11 days from 29 April 2012 to 9 May 2012 were used for the test. For the third linear combinaton using Galileo E1, E5b and E5a, which is expected to have the worst performance among all the GNSS frequency triplets in our investigation, the formal errors of the estimated ambiguities are in most cases below 0.2 cycles after 400 observation epochs. If more GPS satellites sending signals on three frequencies or more stations tracking Galileo E6 signal are available in the future, an improvement by a factor of two to three can be expected.

Cycle Slip Detection and Correction Methods with Time-Differenced Model for Single Frequency GNSS Applications

Cycle Slip Detection and Correction Methods with Time-Differenced Model for Single Frequency GNSS Applications

Accuracy Analysis of Absolute Positioning by GNSS

정밀단독측위(PPP)의 정확도에 영향을 주는 주요변수는 위성궤도력의 정확도, 위성시계오차, 관측자 환경에 종속된 오차(전리층 및 대기층 지연, multipath, tides 등) 및 이들과 관련한 모호정수의 해석 문제 등이다. 따라서 정밀단독측위의 정확도를 향상시키기 위해서는 여러 주파수의 GNSS 관측 자료에 정밀한 위성궤도 및 시계 보정정보와 관측자에 종속된 보정정보를 적용하여 전리층지연 및 모호정수를 실시간 해석해야 한다. 현재, 지역 및 광역 실시간 GNSS 관측망으로 부터 정밀 보정정보를 제공하는 여러 해석센터가 있다. 본 연구는 지역 또는 광역 GNSS 관측망의 해석센터들로부터 산출된 RTCM 보정정보를 NTRIP으로 수신하여 실시간으로 검사점에 개별 및 조합 적용하고 표준단독측위(SPP) 및 다양한 보정정보의 적용에 따른 정밀단독측위의 정확도를 시간대별로 비교 분석하여 GNSS위성에 의한 실시간 절대측위의 정확도를 검토하였다. The main limiting factors of Precise Point Positioning(PPP) accuracy are errors in broadcast satellite orbits, clock errors, and the others, which are receiver-dependent errors(ionospheric, tropospheric refraction, multipath, and tides, etc.). Therefore, to facilitate high precision PPP, precise orbits/clocks corrections, the receiver-dependent errors corrections have to apply to multi frequency GNSS measurements for an ionosphere free combination and integer ambiguity resolution in real-time. Currently, there are many Analysis Centers, which offer the precise corrections stream computed in real-time using the global or regional GNSS tracking network. The goles of this research considered performances of the real-time static PPP with using RTCM corrections from NTRIP casters. For this, the corrections streams of Analysis Centers received via NTRIP does apply to GNSS data of check points individually, as well as jointly, in accordance with various session lengths. After that, have compared the PPP results from the corrections streams with each other, and with Standard Point Positioning(SPP) results.

A PRECISE, LOW-COST RTK GNSS SYSTEM FOR UAV APPLICATIONS

Abstract. High accuracy with real-time positioning of moving objects has been considered a standard task of engineering geodesy for 10 to 15 years. An absolute positioning accuracy of 1–3 cm is generally possible worldwide and is further used in many areas of machine guidance (machine control and guidance), and farming (precision farming) as well as for various special applications (e.g. railway trolley, mining, etc.). The cost of the measuring instruments required for the use of geodetic L1/L2 receivers with a local reference station amounts to approximately USD 30,000 to 50,000. Therefore, dual frequency RTK GNSS receivers are not used in the mass market. Affordable GPS/GNSS modules have already reached the mass market in various areas such as mobile phones, car navigation, the leisure industry, etc. Kinematic real-time positioning applications with centimetre or decimetre levels could also evolve into a mass product. In order for this to happen, the costs for such systems must lie between USD 1,000 to 2,000. What exactly low-cost means is determined by the precise specifications of the given individual application. Several university studies in geodesy focus on the approach of high-accuracy positioning by means of single frequency receivers for static applications [e.g. GLABSCH et. al. 2009, SCHWIEGER and GLÄSER 2005, ALKAN 2010, REALINI et. al. 2010, KORTH and HOFMANN 2011]. Although intelligent approaches have been developed that compute a trajectory in the post-processing mode [REALINI et. al., 2010], at present, there are only a very few GNSS Low-Cost Systems that enable real-time processing. This approach to precise position determination by means of the computation of static raw data with single frequency receivers is currently being explored in a research project at the Beuth Hochschule für Technik Berlin – and is being further developed for kinematic applications. The project is embedded in the European Social Fund. It is a follow-up project in the area of static positioning with single GNSS frequency receivers [KORTH and HOFMANN, 2011].

PLANIALTIMETRIC EVALUATION OF A CARTOSAT-1 STEREO PAIR – CASE STUDY: SÃO SEBASTIÃO, SP, BRAZIL

Abstract. It is noticed a significant increase in the development of orbital and airborne sensors that enable the extraction of three-dimensional data. So, it's important the increment of studies about the quality of altimetric values derived from these sensors to verify if the improvements implemented in the acquisition of data may influence the results. In this context, as part of a larger project that aims to evaluate the accuracy of various sensors, this work aims to analysis the planialtimetric accuracy of DEM generated from Cartosat-1 stereo pair. The project was developed for an area near the city of São Sebastião, located in the basin of the North Coast of São Paulo state, in Brasil. The relief in this area is very steep, with a predominance of dense forest vegetation, typical of the Atlantic Forest. All points in this assessment have been established in the field, with the use of single frequency (L1) GNSS receivers, through static relative positioning. In this work it was considered the Brazilian standard specifications (PEC, in Portuguese) for classification of cartographic bases. Results may be considered very good and showed that Cartosat-1 orthoimage presents accuracy equivalent to class B for 1:10.000 scale. The DEM presents altimetric accuracy compatible with class A of the 1:25.000 scale. Results obtained are true for this specific area/study case, but may vary in case different scenes or other studies areas are considered.

Research on Time Keeping at NIM

UTC(NIM), which is developed and maintained by NIM, is the time and frequency primary standard in China. UTC(NIM) is generated originally by a clock ensemble, and is traced to UTC by participating in TAI cooperation with GNSS time and frequency transfer methods. TWSTFT earth station has been established at NIM new campus to join the Europe–Asia link. In this paper, the new development on the realization of UTC(NIM), the GNSS time and frequency transfer and TWSTFT and our briefly future plan are introduced.

Improving the Design of Frequency Lock Loops for GNSS Receivers

An analysis of the design and performance of the discrete-update GNSS frequency lock loop (FLL) is presented. Expressions for the design and the steady-state performance of one first-order and two second-order FLL loop filters are developed. Transient performance of the FLL in the presence of thermal noise is examined and the relative performance of four carrier frequency discriminators is studied. It is shown that careful discriminator choice can yield a 10 dB performance improvement relative to naive designs.

Total electron content monitoring using triple frequency GNSS: Results with Giove-A/-B data

Triple frequency GNSS will be fully operational within the next decade, opening opportunities for new applications. Dual frequency GNSS already allow to study the ionosphere through the estimation of Total Electron Content (TEC). However, the precision is limited by the ambiguity resolution process. This paper studies a triple frequency TEC monitoring technique in which the use of Geometry-Free and Iono-Free linear combinations improves the ambiguity resolution process and therefore the precision of TEC. We have tested it on a set of triple frequency Giove-A/-B data from January and December 2008. The conclusions achieved are (1) TEC values are affected by an error of about 2–2.5 TECU produced through the ambiguity resolution process; (2) the error caused by the Geometric Free phase combination delays (hardware, multipath, noise, antenna phase center) on TEC is about 0.2 TECU; (3) the total error on TEC approximately reach 2–3 TECU.

Estimate of higher order ionospheric errors in GNSS positioning

Precise navigation and positioning using GPS/GLONASS/Galileo require the ionospheric propagation errors to be accurately determined and corrected for. Current dual‐frequency method of ionospheric correction ignores higher order ionospheric errors such as the second and third order ionospheric terms in the refractive index formula and errors due to bending of the signal. The total electron content (TEC) is assumed to be same at two GPS frequencies. All these assumptions lead to erroneous estimations and corrections of the ionospheric errors. In this paper a rigorous treatment of these problems is presented. Different approximation formulas have been proposed to correct errors due to excess path length in addition to the free space path length, TEC difference at two GNSS frequencies, and third‐order ionospheric term. The GPS dual‐frequency residual range errors can be corrected within millimeter level accuracy using the proposed correction formulas.

Estimation of Ionospheric Delays in Dual Frequency GNSS Positioning

The correct estimation of ionospheric delays is very important in precise satellite-based kinematic positioning, especially over long baselines. In the case of triple frequency system, the ionospheric delays can be estimated from the measurements. However, in the case of dual frequency system, the situation becomes more complicated. The precision of those ionosphere models supplied by the external information source such as JPL IONEX Data is not sufficient, as the high frequency component is neglected. The precision of the low frequency component is not sufficient for the use in long baseline kinematic positioning. On the other hand, the high frequency component can be estimated from the phase range measurements. If the low frequency components are estimated by using an external information source or pseudo-range measurements, more reasonable estimates of ionospheric delays may be possible. In this paper, the estimation using the pseudo-range measurements is discussed. The accuracy of the estimates for ionospheric delays is not sufficient at present because of the bias errors in the pseudo-range measurements. However, if the accuracy of the pseudo-range measurements is improved in future by GPS Modernization and GALILEO, the method would become very promising and convenient, since any external informations are needed and realtime estimation of ionospheric delays becomes possible.