Satellite-based Navigation Systems Research Articles

Modeling of Low-Latitude Ionosphere Using GPS Data With SHF Model

The Indian ionosphere is characterized by large variations, irregularities, and equatorial anomaly conditions. Therefore, an appropriate ionospheric model is necessary for satellite-based navigation systems. An ionospheric model based on spherical harmonic function (SHF) is used for modeling. Using the basis functions and measured vertical total electron content (TEC) data, spherical harmonic coefficients are computed by a weighted least square method. Seventeen stations of GPS Aided Geo Augmented Navigation TEC data are considered in the analysis. The results of the SHF model are presented in terms of accuracy of the residual error and compared with other standard grid models. The diurnal TEC variations are well depicted using the SHF model. The summer- and autumn-equinox-season ionospheric delay variations are also presented. The results indicate that the SHF model is capable of estimating ionospheric delays well.

Global positioning system: A new tool to measure the distribution of anemia and nutritional status of children (5-10 years) in a rural area in south India

Global positioning system (GPS) is a satellite-based navigation system that is of late being used in health care. The aims of the study were to describe the geographical distribution and assess the prevalence of anemia and malnutrition in children aged 5-10 years with GPS. This exploratory study was conducted over a period of 2 months in the rural field practice area of a medical college situated in Bangalore during June-July 2012. Children aged 5-10 years were the study subjects. GPS was used for describing the geographical distribution of anemia and nutrition status on the Google earth map. The prevalence of anemia in the study subjects was 8.7%. The prevalence of underweight, stunting, thinness, and severe thinness among the study subjects was 52.8%, 28.5%, 23.5%, and 29.1%, respectively; however, overweight and obesity were observed only in 0.9% and 1.2% of the study subjects, respectively. GPS was easy to use and was able to demonstrate the actual distribution of morbidity at the household level in the rural area.

Positioning with Wide-Area GNSS Networks: Concept and Application

The use of Global Navigation Satellite Systems (GNSS) for positioning has revolutionized the way location data is be- ing collected. The NAVigation System with Time And Ranging Global Positioning System (GPS), which is a principal component of the global navigation satellite system (GNSS); is a satellite-based radio navigation system that provides positions of points of interest and time information to users. GPS positional accuracy can be improved by using differential corrections obtained through a technique called Differential GPS (DGPS), which is known to provide the most accurate positioning results. Differential correction can be applied in real time at the data collection phase or in the of- fice, at the post-processing phase. DGPS is generally used for positioning purposes through static or kinematics GPS surveys. In static GPS surveys, one receiver is placed at a point whose coordinates are known and the other receiver is placed over a point whose coordinates are desired. In kinematic surveys, one receiver remains at one point (base station) normally with known coordinates, and the other receiver (rover) moves from point to point in the project area. Kinematic surveys in which points positions are computed on-the-fly (OTF) are known as real-time kinematic (RTK). RTK surveys provide real-time locations of points of interest needed in many applications. Positioning with wide-area GNSS networks is basically based on the DGPS and RTK concepts. Observables from a network of a finite number of GPS receivers over an area are processed by a server at a central location (network server) and made available to the users of the network later or in real-time through radio-based, satellite, or wireless communications. This article provides a review of the concept and application of positioning with wide-area GNSS networks.

Sensor Architecture and Task Classification for Agricultural Vehicles and Environments

The long time wish of endowing agricultural vehicles with an increasing degree of autonomy is becoming a reality thanks to two crucial facts: the broad diffusion of global positioning satellite systems and the inexorable progress of computers and electronics. Agricultural vehicles are currently the only self-propelled ground machines commonly integrating commercial automatic navigation systems. Farm equipment manufacturers and satellite-based navigation system providers, in a joint effort, have pushed this technology to unprecedented heights; yet there are many unresolved issues and an unlimited potential still to uncover. The complexity inherent to intelligent vehicles is rooted in the selection and coordination of the optimum sensors, the computer reasoning techniques to process the acquired data, and the resulting control strategies for automatic actuators. The advantageous design of the network of onboard sensors is necessary for the future deployment of advanced agricultural vehicles. This article analyzes a variety of typical environments and situations encountered in agricultural fields, and proposes a sensor architecture especially adapted to cope with them. The strategy proposed groups sensors into four specific subsystems: global localization, feedback control and vehicle pose, non-visual monitoring, and local perception. The designed architecture responds to vital vehicle tasks classified within three layers devoted to safety, operative information, and automatic actuation. The success of this architecture, implemented and tested in various agricultural vehicles over the last decade, rests on its capacity to integrate redundancy and incorporate new technologies in a practical way.

English

The use of global positioning system (GPS) for precision guidance of weapons is being questioned due to its vulnerability of jamming and spoofing for non-military code users. In this paper a novel approach is proposed for guidance of weapons where use of GPS or other civilian Satellite-based navigation system is threatened. The proposed approach is modelled and simulated using SIMULINK for realistic trajectories and scenario. The results of simulation are validated with the actual GPS data.

Optimum parameter for estimating phase fluctuations on transionospheric signals at high latitudes

Transionospheric radio signals may experience fluctuations in their amplitude and phase due to irregularity in the spatial electron density distribution, referred to as scintillation. Ionospheric scintillation is responsible for transionospheric signal degradation that can affect the performance of satellite based navigation systems. Usually, the scintillation activity is measured by means of indices such as the normalised standard deviation of the received intensity S 4 and the standard deviation of the received phase σ ϕ typically calculated over 1 min of data. Data from a GPS scintillation monitor based on 50 Hz measurements recorded at Dirigibile Italia Station (Ny-Alesund, Svalbard), in the frame of the ISACCO project ( De Franceschi et al., 2006) are used to investigate possible adoption of an alternative parameter for the estimate of phase fluctuations: i.e., the standard deviation of the phase rate of change S ϕ . This parameter is shown to better correlate with S 4 being much less detrending dependent than σ ϕ . The couple ( S 4, S ϕ ) should be then considered a more physical proxy of radio scintillation than the couple ( S 4, σ ϕ ).

New Approach for Calculating Position Domain Integrity Risk for Cycle Resolution in Carrier Phase Navigation Systems

A new theoretical approach is described to quantify position-domain integrity risk for cycle ambiguity resolution problems in satellite-based navigation systems. It is typically conservatively assumed that all incorrectly fixed cycle ambiguities cause hazardously large position errors. While simple and practical, this conservative assumption can unnecessarily limit navigation availability for applications with stringent requirements for accuracy and integrity. In response, a new method for calculating the integrity risk for carrier phase navigation algorithms is developed. In this method we evaluate the impact of incorrect fixes in the position domain and define tight upper bounds on the resulting navigation integrity risk. Furthermore, a mechanism to implement this method with partially-fixed cycle ambiguity vectors is also derived. The improvement in navigation availability using the new method is quantified through covariance analysis performed over a range of error model parameters.

Scintillations effects on satellite to Earth links for telecommunication and navigation purposes

Radio wave scintillations are rapid fluctuations in both amplitude and phase of signals propagating through the atmosphere. GPS signals can be affected by these disturbances which can lead to a complete loss of lock when the electron density strongly fluctuates around the background ionization level at small spatial scales. This paper will present recent improvements to the theoretical Global Ionospheric Scintillation Model (GISM), particularly tailored for satellite based navigation systems such GPS coupled with Satellite Based Augmentation System (SBAS). This model has been improved in order to take into account GPS constellation, signals, and receiver response to ionospheric scintillation environments. A new modelling technique, able to describe the scintillation derived modifications of transionospheric propagating fields is shown. Results from GPS derived experimental measurements performed at high and low magnetic latitudes will show preliminary assessments of the scintillation impact on real receivers and system operations. Nevertheless, comparisons between theoretical scintillation models, such as WBMOD and GISM, with GPS derived experimental data will be shown.

“Positioning and telecommunications” in the world

Among the numerous technical solutions to positioning, Global Navigation Satellite Systems (GNSS) have a special place. This is mainly due to the fact that they have brought such simplicity of use and low cost that many applications and domains have taken advantage of positioning; for example, civil engineering, the tracking of animals and, of course, car navigation and Location-Based Services (LBS) intended to provide geo-based applications to users. Initially designed for military purposes, the American Global Positioning System (GPS) has found a large public use, both for professional and mass market applications. This success largely exceeded the hopes of its designers and was mainly due to the incredible performances provided to users. Positioning rapidly became a new way to carry out many tasks that demanded considerably more effort than previously. This success, especially for GPS, has led to a strategic problem: if one imagines the deployment of positioning in domains such as transportation, telecommunications or safety, then it is of vital importance to share the management of a global positioning system. This was indeed the problem of the European Union: the decision to launch Galileo, the future European constellation, was closely related to strategic options. This was also the case for GLONASS, the Russian constellation launched in the 1980s, and for COMPASS, the future Chinese satellite-based navigation system. The original goal of GPS was to allow positioning in environments with no local or regional ground infrastructure or where the deployment of an infrastructure would be difficult, e.g., at sea or in the desert. Of course, the problem of positioning did not start with satellites and many previous techniques were used. The success of GPS in many applications, mainly transportation, means that satellite-based navigation has entered the public mind, although it still has many limitations. Some limitations, such as coverage, availability or even integrity are being largely dealt with in the scientific and industrial GNSS communities.

A Bayesian Approach to Multipath Mitigation in GNSS Receivers

Multipath is known to be one of the most dominant sources of accuracy degradation in satellite-based navigation systems. Multipath may cause biased position estimates that could jeopardize high-precision applications. This paper considers the problem of tracking the time-variant synchronization parameters of both the line-of-sight signal (LOSS) and its multipath replicas. In particular, the proposed algorithm tracks time-delays, amplitudes, phases and proposes a procedure to extract Doppler shifts from complex amplitudes. However, the interest is focused on LOSS time-delay estimates, since those provide the means to compute user's position. The undertaken Bayesian approach is implemented by a particle filter. The selection of the importance density function, from which particles are generated, is performed using a Gaussian approximation of the posterior function. This selection provides a particle generating function close to the optimal, which yields to an efficient usage of particles. The complex-linear part of the model, i.e., complex amplitudes, is tackled by a Rao-Blackwellization procedure that implements a complex Kalman filter for each generated particle, thus reducing the computational load. Computer simulation results are compared to other Bayesian filtering alternatives (namely, the extended Kalman filter, the unscented Kalman filter and the sequential importance resampling algorithms) and the posterior Cramer-Rao bound.

Global positioning: technologies and performance

Foreword. Acknowledgements. Preface. Chapter 1. A brief history of navigation and positioning. 1.1 The first age of navigation. 1.2 The age of the great navigators. 1.3 Cartography, lighthouses and astronomical positioning. 1.4 The radio age. 1.5 The first terrestrial positioning systems. 1.6 The era of artificial satellites. 1.7 Real-time satellite navigation constellations today. 1.8 Exercises. Bibliography. Chapter 2. A brief explanation of the early techniques of positioning. 2.1 Discovering the world. 2.2 The first age of navigation and the longitude problem. 2.3 The first optical based calculation techniques. 2.4 The first terrestrial radio based systems. 2.5 The first navigation satellite systems: TRANSIT and PARUS/TSIKADA. 2.6 The second generation of navigation satellite systems: GPS, GLONASS and Galileo. 2.7 The forthcoming third generation of navigation satellite systems: QZSS and COMPASS. 2.8 Representing the world. 2.9 Exercises. Bibliography Chapter 3. Development, deployment and current status of satellite based navigation systems. 3.1 Strategic, economical and political aspects. 3.2 The global positioning satellite systems: GPS, GLONASS and Galileo. 3.2.1 The Global Positioning System : GPS. 3.2.2 The GLONASS. 3.2.3 Galileo. 3.3 The GNSS1: EGNOS, WAAS and MSAS. 3.4 The other satellite based systems. 3.5 Differential satellite based commercial services. 3.6 Exercises. Bibliography. Chapter 4. Non-GNSS positioning systems and techniques for outdoors. 4.1 Introduction (large area without contact or wireless systems). 4.2 The optical systems. 4.3 The terrestrial radio systems. 4.4 The satellite radio systems. 4.5 Non-radio based systems. 4.6 Exercises. Bibliography. Chapter 5. GNSS system descriptions. 5.1 System description. 5.2 Summary and comparison of the three systems. 5.3 Basics of GNSS positioning parameters. 5.4 Introduction to error sources. 5.5 Concepts of differential approaches. 5.6 SBAS system description (WAAS and EGNOS). 5.7 Exercises. Bibliography. Chapter 6. GNSS navigation signals: description and details. 6.1 Navigation signal structures and modulations for GPS, GLONASS and Galileo. 6.2 Some explanations of the concepts and details of the codes. 6.3 Mathematical formulation of the signals. 6.4 Summary and comparison of the 3 systems. 6.5 Developments. 6.6 Error sources. 6.7 Time reference systems. 6.8 Exercises. Bibliography. Chapter 7. Acquisition and tracking of GNSS signals. 7.1 Transmission part. 7.2 Receiver architectures. 7.3 Measurement techniques. 7.4 Exercises. Bibliography. Chapter 8. Techniques for calculating positions. 8.1 Calculating the PVT solution. 8.2 Satellite's position computations. 8.3 Quantified estimation of errors. 8.4 Impact of pseudo range errors on the computed positioning. 8.5 Impact of geometrical distribution of satellites and receiver (notion of DOP). 8.6 Benefits of augmentation systems. 8.7 Discussion on interoperability and integrity. 8.8 Effect of multipath on the navigation solution. 8.9 Exercises. Bibliography. Chapter 9. Indoor positioning problem and main techniques (Non-GNSS). 9.1 General introduction to indoor positioning. 9.2 A brief review of possible techniques. 9.3 Network of sensors. 9.4 Local area telecommunication systems. 9.5 Wide-area telecommunication systems. 9.6 Inertial systems. 9.7 Recap tables and global comparisons. 9.8 Exercises. Bibliography. Chapter 10. GNSS-based indoor positioning and a summary of indoor techniques. 10.1 HS-GNSS. 10.2 A-GNSS. 10.3 Hybridization. 10.4 Pseudolites. 10.5 Repeaters. 10.6 Recap tables and comparisons. 10.7 Possible evolutions with availability of the future signals. 10.8 Exercises. Bibliography. Chapter 11. Applications of modern geographical positioning systems. 11.1 Introduction. 11.2 A chronological review of the past evolution of applications. 11.3 Individual applications. 11.4 Scientific applications. 11.5 Applications for public regulatory forces. 11.6 Systems under development. 11.7 Classifications of applications. 11.8 Privacy issues. 11.9 Current receivers and systems. 11.10 Conclusion and discussion. 11.11 Exercises. Bibliography. Chapter 12. The forthcoming revolution. 12.1 Time and space. 12.2 Development of current applications. 12.3 The possible revolution of everybody's daily life. 12.4 Possible technical positioning approaches and methods for the future. 12.5 Conclusion. 12.6 Exercises. Bibliography. Index.

Space Weather and the Global Positioning System

Space Weather and the Global Positioning System

Statistical Comparison of Various Interpolation Algorithms for Grid-Based Single Shell Ionospheric Model Over Indian Region

Future Satellite Based Navigation Systems based on GPS, like US Wide Area Augmentation Sysytem (WAAS), are of global interest to the scientific community. Precise estimation of ionospheric delay is most crucial for successful implementation of the systems. Due to the complex ionospheric structure and large variation of Total Electron Content (TEC) in low latitudes, it is necessary to compare and validate the efficiency of the existing algorithms in this region. In this study, performances of the various interpolation algorithms for TEC calculation at ionospheric grid point (IGP) and user position for gridbased Single Shell Model have been tested for 72 test days of 2005. Based on the results obtained from this analysis, it has been found that, for the Indian region, it would be more suitable to use Ordinary Kriging in place of Planar Fit to estimate delay at an IGP (as used by US WAAS). It has also been found that Ordinary Kriging performs better than the Bilinear Interpolation technique at the user end.

New Algorithm and Results of WAAS Ionospheric Delay Correction

电离层介质的色散性是影响电磁波信号进行卫星导航定位精度的重要因素之一.配合北斗二代分系绩研制任务,提出了一种新的电离层折射校正算法,并利用2000年7月1日到3日的双频GPS观测数据对6个用户站进行试算,进一步将试算所得均方根误差和电离层网格算法得到的误差进行比较.结果表明,对于中纬区域的用户站,估算的TEC误差约为0.5 m左右;而低纬用户误差相对增大,为1 m左右.文中给出的算法与电离层网格模型所提供的精度相差不多,在未来中国自主的卫星增强系统中采用新方法进行电离层进行修正是可行的及有效的.

A Difference Test Method for Early Detection of Slowly Growing Errors in GNSS Positioning

Satellite based navigation system integrity monitoring is essential both for liability and safety critical services. The threats to system integrity are the potential failure modes that could occur at system, operational and user sensor levels. Research on identification, characterisation and modelling of such failure modes, suggests that failures that grow slowly over time (e.g. ramp error less than 2 m/s), also referred to as slowly growing errors (SGE) are the most difficult to detect early. Conventional snapshot algorithms detect SGEs when the test statistic crosses the threshold usually after relatively long periods of time. A recent concept based on the average of residuals over time has been found to have a significant weakness. This paper proposes a “difference test” algorithm capable of detecting SGEs early. In this method, the test statistic is the difference between the norm of current residuals and the norm of the residuals at a previous epoch. The distribution of the test statistic is over-bounded by a normal distribution whose parameters are derived from two Chi-distributions. Results show that the new algorithm results in a significant reduction in detection time compared to conventional methods.

An Improved Version of the Fluxgate Compass Module

Satellite based navigation systems (GPS) are widely used for ground, air and marine navigation. In the case of a malfunction or satellite signal inaccessibility, some back-up navigation system is needed. An electronic compass can provide this function. The compass module described in this paper is designed for precise navigation purposes. The compass module is equipped with electronic tilt error compensation, and includes everything in one package – electronics with digital output, sensors. A typical application of this compass is in underground drilling. A critical parameter in this application is heading accuracy. A reading error of 1 degree can cause a displacement of 1.8 metres in the target area (length of tunnel 100 m). This is not acceptable in an urban conglomeration, and therefore a more accurate heading sensing device must be used. An improved version of this electronic compass is being finished.

ATTITUDE & ORBIT CONTROL SYSTEM FOR GALILEO IOV

The Galileo In Orbit Verification (IOV) program, consisting of 4 spacecrafts, is the first step towards an European satellite-based navigation system. The main objective of the IOV phase is to verify the proper functioning of the overall system before starting the next step - Galileo Full Operational Capability (FOC) - where the full deployment of 30 Galileo satellites will be performed. This paper gives an overview of the Galileo IOV Attitude and Orbit Control (AOC) function with the focus being put on the spacecraft attitude control. The AOC is a part of the Avionics subsystem, manufacturing of which has been subcontracted to Astrium. The article also describes the overall requirements on the control system, the AOC hardware and operational architecture as well as selected details on the AOC algorithms with corresponding test results.

Multicomponent receiver architectures for GPS interference suppression

The global positioning system (GPS) is a one-way satellite-based navigation system employing spread-spectrum techniques that is widely used for commercial and military applications. Although the very low signal-to-noise ratio (SNR) is handled by the large spreading gain, GPS is susceptible to high-power interference signals and various types of jammers. We propose multicomponent receiver architectures for GPS interference suppression. A conventional antenna system is first considered which utilizes a minimum-variance distortionless-response (MVDR) beam former and assumes that the GPS signal angle of arrival (AOA) and the antenna model are known at the receiver. However, this receiver is sensitive to AOA estimation errors and can have a high computational complexity. This sensitivity problem is eliminated by a multicomponent system based on a multistage matched filter (MF). Since this MF receiver also has a high computational complexity because the jammer AOAs must be estimated, we introduce a blind interference canceler based on the constant modulus (CM) array that is insensitive to AOA estimation errors and has a low computational complexity. Computer simulations are provided to illustrate the performance of the various systems for interference suppression in example signal scenarios.

Fail-Safe Seaway를 위한 GPS 수신기의 다중비트처리기법 연구

It is necessary that Fail-Safe Seaway technology providing a continuous navigation solution though fault of navigation system is occurred in sea. This paper focus on signal processing of GPS receiver, one of receivers using the software radio technology to implement a integrated radio navigation system including satellite-based and ground-based navigation systems. It is difficult to implement the software GPS receivers using a commercial processor because of the heavy computational burden for processing the GPS signals in real time. This paper proposes an efficient multi-bit GPS signal processing scheme to reduce the computational burden for processing the GPS signals in the software GPS receiver. The proposed scheme uses a compression concept of the multi-bit replica signals and patterned look-up table method to generate the correlation value between the GPS signals and the replica signals.

Status and development of GLONASS

This chapter focuses on various satellite-based navigation systems. The most well-known and widespread system currently used for localization of a radio-receiving terminal is the global positioning system (GPS). All GPS satellites share the same frequency bands, making use of the code division multiple access (CDMA) technique. The transmitted signal on each sub-band is a low-rate binary phase shift keying (BPSK) digital signal containing the so-called navigation (NAV) data that are used by the receiver to perform ranging. Galileo is the European Global navigation satellite systems (GNSSs) providing a global positioning service under civilian control. It has to be interoperable with GPS and GLONASS, the American and Russian GNSSs, respectively. Like GPS and Galileo, GLONASS is based on several ground stations that monitor and control the satellites and their signals. The GPS and Galileo stations are spread on the globe, to guarantee a better control of the constellation and its signals. Differential GPS (DGPS) is an enhancement to GPS that uses a network of fixed, ground-based reference stations to broadcast the difference between the position of a receiver located at each station, as derived instant by instant using the GNSS, and the known fixed positions of the stations themselves.