Satellite Radio Navigation Systems Research Articles

MATHEMATICAL MODELING OF THE CONTROLLED MOTION OF THE WHEELED MACHINE-TRACTOR UNIT

A brief review of the systems of precise farming is given, problems of scientific and practical research are formulated to create a domestic system of accurate farming using autopilotation. The analysis of applied software used in the development and approbation of algorithms for controlling the movement of wheeled agricultural machines is carried out. The ideology of the development of mechatronic systems using the CAMeL-View application package is presented, a mechanical-mathematical model of the machine-tractor unit consisting of a wheeled tractor and a semi-mounted plow is described. The results of mathematical modeling of the movement of a machine-tractor unit at a speed of 2.5 m / s are presented using control based on the basic maneuvers of wheeled vehicles when the soil is processed to a depth of 0.24 m. The required slope angle of the tractor frame is defined as a linear combination of dependencies for changing the curvature of the trajectory, the direction of motion, the lateral displacement and the initial angle of rotation of the steered wheels. The analysis of the results allows to draw a conclusion about the rather good quality of the working movement of the arable unit, which indicates the efficiency of the proposed control algorithm. The program implementation of the control algorithm is proposed in the wheeled agricultural machines developed with the participation of authors of the electromechanical control system for the movement using satellite radio navigation systems GLONASS and GPS. With a real control of the movement of a wheeled agricultural machine, a significant deterioration in the quality of motion is caused by inaccurate determination of its current coordinates when using satellite GPS and GLONASS radio navigation systems. Accordingly, the level of lateral deviations of the working mechanisms of the agricultural machine will be higher than the motion obtained from the modeling results, using the proposed control algorithm. The final conclusion about the limits of applicability of the proposed control for various fieldwork will be made based on the results of field tests of the control system.

Correlation functions of complete CBOC signals derived as the inverse Fourier transform of energy spectra

For the complete composite binary offset carrier (CBOC) signals of new-generation global satellite radio-navigation satellite systems (SRNSs), analytical expressions for correlating functions (CFs) characterizing the single components of the modulating function are derived in terms of the inverse Fourier transform (IFT) of energy spectra at different fractional coefficients. The CF calculation technique is based on the energy spectra of complete CBOC signals represented as a partial sum of the series of cosines of the angles that are multiples of the angle γCBOC = ωτM2, where τM2 is the meander-pulse duration of the subcarrier oscillation of binary offset carrier (BOC) signals with BOC(6,1) modulation. In a number of cases, the IFT of energy spectra applied to calculating the CFs of complete CBOC signals is preferable (in particular, from the viewpoint of labor intensiveness) to the procedures by which CFs are obtained using the general definition. The CFs graphs constructed with the help of complete CBOC signals employed in the E1 band of the Galileo SRNS are presented.

Singular Spectral Analysis in Filtration of Noisecontaminated Signals of Pseudolite Navigation

Background: The relevance of this research is determined by the necessity to evaluate precision specifications of ground equipment for satellite radio navigation system consumers, in particular regarding signal filtration and recovery tasks with view to the type of signal and nature of interferences. Method: A Pseudolite signal filtration and recovery algorithm has been developed, using singular spectral analysis, which allows for successful Pseudolite signal processing in noisecontaminated conditions and may be considered as an effective program implementation of a filtering unit as a part of the receiving equipment. Findings: Comparative analysis of noise components of signals used in Pseudolite navigation has been done, possibilities for enhancing interference immunity of Pseudolite systems, based on filtering such signals, have been discussed in this research. Numerical experiments were conducted to prove that the presented algorithm allows for successful Pseudolite signal processing in noise-contaminated conditions and may be considered as an effective program implementation of a filtering unit being a part of the receiving equipment. Applications/Improvements: Materials of this research may be useful for satellite radio navigation system consumers, while enhancing accuracy of attitude sensing of various mobile objects.

Applying filtering for determining the angular orientation of spinning objects during interference

This article discusses the application of user navigation equipment of satellite radionavigation systems (GLONASS/GPS) for measuring the inclination of the aerial axis of rotation. The authors have demonstrated that the required accuracy of the angular inclination is achieved only in a relative phase mode, which is not always feasible. The application of filtering for measured parameters of navigation equipment has namely been used for planimetric coordinates. Filtering is performed using the second order Kalman filter. It has significant effect; thus, even at a speed of 1 rpm, there is no disruption in the autonomous coded mode; for the relative phase mode, the required accuracy is achieved at 3 rpm.

Synthesis of Optimal Incoherent Subcarrier Tracking of BOC(1,1) Navigation Signals

Navigation receivers of global positioning systems that are operated in complex electromagnetic environment must have an increased noise immunity characteristic. One way of such noise immunity rising is to use incoherent operating mode of navigation receiver. There are known processing algorithms for navigation signals with Binary Phase Shift Keying (BPSK) modulation. But in the near-term outlook Global Navigation Satellite Systems (GLONASS), Global Positioning Systems (GPS) and Galileo known navigation signals with Binary Offset Carrier (BOC) modulation will be radiated. Processing algorithms for such signals are not described in scientific literature. So it is interesting to work out processing algorithms for BOC modulated signals in incoherent operating mode of navigation receiver. The article is devoted to synthesis and analysis of incoherent subcarrier tracking system under receiving BOC (1,1) navigation signals. To synthesize an optimal tracking system, optimal estimation theory and dual estimation method are used that allow taking into account multi-peak a posteriori distribution of delay that caused by the periodic process (digital sinusoid) in the radio signal modulation function. When analyzing the synthesized estimation algorithm, the procedure for describing delay discriminators and dual variable discriminators were used in the form of a statistical equivalent, including discrimination and fluctuation characteristics. New equations have been obtained that describe optimal tracking system for incoherent mode of a navigation receiver. New expressions for delay and dual variable discriminators are derived. The article gives a scheme for these discriminators and formulas for their statistical characteristics. Simulated results are provided that illustrate accuracy characteristics enhancement. The obtained tracking algorithms may be used in the navigation consumer equipment of GLONASS, GPS, Galileo and other radio-navigation satellite systems operating with BOC(1.1) modulated signals.

Correlation functions of BOC and AltBOC signals as the inverse Fourier transforms of energy spectra

The navigation signals with sine binary offset carrier (sinBOC), cosine BOC (cosBOC), and alternative BOC (AltBOC) modulations are discussed. A technique for calculating the correlation functions (CFs) of the single components of modulating functions (MFs) inherent to the given signals, which is based on the inverse Fourier transform (IFT) of energy spectra, is proposed. This technique makes it possible to derive analytical expressions for the CFs characterizing the single components of the MFs of sinBOC and cosBOC signals and complete AltBOC waveforms with a constant envelope at the multiplicity coefficients N m = 2‒4. The graphs of CFs are constructed. Several illustrating examples, in which most attention is paid to sinBOC, cosBOC, and AltBOC signals employed in the Galileo satellite radio-navigation system and the global positioning system, are presented.

Improving capabilities of broadband differential satellite navigation systems via radio occultation technology

The existent satellite system for radio occultation monitoring the Earth’s neutral atmosphere and ionosphere (COSMIC) provides data to consumers in the regions with limited possibilities of constructing dense measurement networks (e.g., in the World Ocean area). A forthcoming increase of LEO small spacecrafts and the deployment of new satellite radio navigation systems will result in a pronounced increase in the efficiency of radio occultation method and its space resolution. As a result, the Space-Based Augmentation Systems (SBAS) broadband differential system will become global, or the quality of corrections delivered to single-frequency consumers of individual systems, e.g., the Augmentation and Monitoring System, will be improved. Therefore, the methods for processing and analyzing obtained radio occultation data should be improved. A simple method to reconstruct the electron density profile at radio occultation points, based on the total electron content measurement on the satellite–satellite path and the IRI-type ionospheric model has been proposed. The method needs initial information, it does not require refraction measurements, and it is free of the assumption that the ionosphere is spherically stratified in the occultation region. Verification of the proposed method based on data for 121 radio occultation cases across Europe in May 2013 demonstrated good agreement with the vertical sounding data.

Probability Distribution Functions of the Sum of Squares of Random Variables in the Non-zero Mathematical Expectations

The article concluded probability distribution functions sum of the squares of the random variables in the non-zero expectations. The resulting distribution function is possible to create an efficient single-step phase ambiguity resolution algorithm in determining the spatial orientation of the signals of satellite radio navigation systems. Obtained thresholds at rejecting false solutions, as well as statistical data of the algorithm.

Is It Time for Commercial Weather Satellites? Analyzing the Case of Global Navigation Satellite System Radio Occultation

This article argues that while the creation of a commercial weather satellite sector is neither easy nor assured, the future prospects for commercial weather satellites are good. Global Navigation Satellite System Radio Occultation (GNSS-RO) satellite commercial data buys are poised to be the vanguard in the opening of this new sector. The article discusses the current state of the U.S. weather satellite system and the trends providing the impetus for commercial activity in this area. It identifies the most likely government and commercial actors for GNSS-RO data provision and analyzes the legal, technical, economic, and international relations issues facing these entities. Based on this analysis, the article concludes that the commercial weather satellite sector is poised to begin, with government purchases of commercial GNSS-RO data leading the way. It concludes by discussing critical policy decisions that will affect the success of GNSS-RO companies as well as the implications of success for other areas of the commercial weather satellite sector.

Tracking Algorithm for Estimating the Orientation Angles of the Object Based on the Signals of Satellite Radio Navigation System

In the article, the theory of optimal filtering of information processes is used to synthesize optimal one-stage estimation algorithm for the object orientation angles using the signals of the satellite navigation system. The article also provides equations of optimal filtering, as well as their representation in the form of the tracking system comprising of an orientation angles discriminator and a smoothing filter. The synthesized algorithm has no tracking systems for the phases of the received signals (or phase differences) and the procedures for resolving the ambiguity of phase measurements that enhance its noise immunity while maintaining high precision in estimating the orientation angles. The article provides expressions for the calculation of the Cramer-Rao lower limit for the dispersion errors matrix for estimating object orientation angles when receiving signals of an arbitrary number of navigation satellites. The results of the simulation of the synthesized system are provided in the study.

Complete composite binary offset carrier modulated signals and their correlation function

The formation and structure of complete composite binary offset carrier (CBOC) modulated signals are analyzed as applied to the new-generation satellite radio navigation systems (SRNSs) (in particular, the European Galileo and, presumably, Chinese BeiDou/Compass systems). The block diagram of the CBOC-signal satellite transmitter based on the coherent adaptive subcarrier modulation (CASM) algorithm is discussed. Analytical expressions for the correlation functions (CFs) characterizing the single elements of the modulating function (MF) of CBOC signals are derived at arbitrary fractional coefficients. The CFs of the single elements of the MFs of CBOC signals are represented graphically and their properties are discussed. The Fourier transforms of CFs are used to calculate the energy spectra (power spectral densities) of the single elements of the MFs of CBOC signals. CF features and the energy spectra of CBOC signals are analyzed using signals with CBOC(6, 1, a 2/11) modulation, which are typical of the European Galileo and Chinese BeiDou/Compass systems at the carrier frequency f car = 1575.42 MHz and the fractional coefficient a 2 = 1.

Optimization and testing of the GEMTEC model of total electron content in the ionosphere

A renewed version of the model of the total electron content in the ionosphere, GEMTEC, is presented, aimed at an increase in the accuracy of positioning of single-frequency equipment of satellite radio navigation systems. The results of testing of this model in comparison with the standard method of compensation of the ionospheric delay of radio signals using the Klobuchar model are presented. It is shown that the proposed model is much more accurate than the Klobuchar model.

Recent global warming hiatus dominated by low‐latitude temperature trends in surface and troposphere data

AbstractOver the last 15 years, global mean surface temperatures exhibit only weak trends. Recent studies have attempted to attribute this so called temperature hiatus to several causes, amongst them incomplete sampling of the rapidly warming Arctic region. We here examine zonal mean temperature trends in satellite‐based tropospheric data sets (based on data from (Advanced) Microwave Sounding Unit and Global Navigation Satellite System Radio Occultation instruments) and in global surface temperatures (HadCRUT4). Omission of successively larger polar regions from the global mean temperature calculations, in both tropospheric and surface data sets, shows that data gaps at high latitudes cannot explain the observed differences between the hiatus and the prehiatus period. Instead, the dominating causes of the global temperature hiatus are found at low latitudes. The combined use of several independent data sets, representing completely different measurement techniques and sampling characteristics, strengthens the conclusions.

CHAMP climate data based on the inversion of monthly average bending angles

Abstract. Global Navigation Satellite System Radio Occultation (GNSS-RO) refractivity climatologies for the stratosphere can be obtained from the Abel inversion of monthly average bending-angle profiles. The averaging of large numbers of profiles suppresses random noise and this, in combination with simple exponential extrapolation above an altitude of 80 km, circumvents the need for a "statistical optimization" step in the processing. Using data from the US–Taiwanese COSMIC mission, which provides ~1500–2000 occultations per day, it has been shown that this average-profile inversion (API) technique provides a robust method for generating stratospheric refractivity climatologies. Prior to the launch of COSMIC in mid-2006, the data records rely on data from the CHAMP (CHAllenging Mini-satellite Payload) mission. In order to exploit the full range of available RO data, the usage of CHAMP data is also required. CHAMP only provided ~200 profiles per day, and the measurements were noisier than COSMIC. As a consequence, the main research question in this study was to see if the average bending-angle approach is also applicable to CHAMP data. Different methods for the suppression of random noise – statistical and through data quality prescreening – were tested. The API retrievals were compared with the more conventional approach of averaging individual refractivity profiles, produced with the implementation of statistical optimization used in the EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites) Radio Occultation Meteorology Satellite Application Facility (ROM SAF) operational processing. In this study it is demonstrated that the API retrieval technique works well for CHAMP data, enabling the generation of long-term stratospheric RO climate data records from August 2001 and onward. The resulting CHAMP refractivity climatologies are found to be practically identical to the standard retrieval at the DMI (Danish Meteorological Institute) below altitudes of 35 km. Between 35 and 50 km, the differences between the two retrieval methods started to increase, showing largest differences at high latitudes and high altitudes. Furthermore, in the winter hemisphere high-latitude region, the biases relative to ECMWF (European Centre for Medium-range Weather Forecasts) were generally smaller for the new approach than for the standard retrieval.

Correlation functions of complete AltBOC signals with a constant envelope

The structure of the modulating function (MF) of a complete alternative binary offset carrier modulated signal (AltBOC signal) with a constant envelope (eight-component complete AltBOC signal) is considered. Analytical expressions for the correlation functions (CFs) of single elements of the MFs of complete AltBOC signals with a constant envelope are derived at typical values of multiplicity coefficient Nm of meander pulses (Nm = 2 and 3). Plots of the CFs of single elements of the MFs of complete AltBOC signals with a constant envelope are obtained for Nm = 2 and 3. The properties of these CFs are discussed. With the help of the Fourier transform applied to the CFs, the energy spectra (spectral power densities) of single elements of the MFs of complete AltBOC signals with a constant envelope are calculated at Nm = 2 and 3. In illustrating examples, most attention is focused on complete AltBOC signals with a constant envelope at the carrier frequency fcar = 1191.795 MHz for the AltBOC (15, 10) modulation and the repetition rate of the elements of ranging-code pseudorandom sequences fs = 10fref = 10.23 MHz, where the reference (base) frequency is fref = 1.023 MHz. These signals are applied in the Galileo European satellite radio navigation system (SRNS) and, as is supposed, in the Chinese BeiDou-2/Compass SRNS.

Secular resonances as a source of dynamic chaoticity in the long-term orbital evolution of uncontrolled satellites

We present the results of MEGNO analysis of the long-term orbital evolution of uncontrolled objects of satellite radio navigation systems in medium Earth orbits and geostationary orbits. It is shown that secular resonances affecting these objects may give rise to dynamic randomness in their long-term orbital evolution.

Test signals with multilevel subcarriers as applied to satellite radio-navigation systems

Noise-like meander signals are proposed to generate on the basis of multilevel pseudorandom sequences making it possible to include multilevel subcarriers. It is demonstrated that such signals are characterized by the pronounced central region of the principal peak of the real part of their complex autocorrelation function and its other values remain almost identical in the time interval corresponding to the principal correlation peak. They are several times less than those of binary offset carrier modulated signals. It is established that the selection of a subcarrier phase structure makes it possible to more flexibly control the shape of the power spectral density of signals and its arrangement on the frequency in comparison with BOC signals.

The correlation functions of single elements of the modulating functions of double complex meander noise-like navigation signals (alternative binary offset carrier modulated signals)

The correlation characteristics of elements of complex meander pseudo-random sequences (PRSs) are analyzed. These sequences are the basis for forming double complex meander (DCM) noise-like signals (alternative binary offset carrier modulated signals—AltBOC signals) applied in new-generation satellite radio navigation systems (in particular, the European Galileo and Chinese Bei-Dou/Compass systems). Analytical expressions are obtained for the correlation functions (CFs) of single complex meander symbols (MSs) and for the cross CFs (CCFs) of the sine and cosine components of complex MSs. Formulas for the CFs of single elements of the modulating functions (MFs) of an elementary (two-component) AltBOC signal and a four-component AltBOC signal are derived for typical values of multiplicity coefficient Nm (Nm = 2 and 3). Plots of CFs and CCFs are depicted, and the properties of these functions are discussed. The Fourier transform is applied to obtain the energy spectra of single MSs of an elementary AltBOC signal and a complete four-component AltBOC signal. In the examples, the attention is focused on AltBOC signals with the AltBOC (15, 10) modulation and the repetition rate of PRS elements fs = 10 fref = 10.23 MHz, where the reference frequency is fref = 1.023 MHz.

Use of global navigation satellite systems for monitoring deformations of water-development works

The feasibility of using global radio-navigation satellite systems (GNSS) to improve functional safety of high-liability water-development works - dams at hydroelectric power plants, and, consequently, the safety of the population in the surrounding areas is examined on the basis of analysis of modern publications. Characteristics for determination of displacements and deformations with use of GNSS, and also in a complex with other types of measurements, are compared. It is demonstrated that combined monitoring of deformations of the ground surface of the region, and engineering and technical structures is required to ensure the functional safety of HPP, and reliable metrologic assurance of measurements is also required to obtain actual characteristics of the accuracy and effectiveness of GNSS observations.

Miniature Filters, Diplexers and Antennas of L-Band Used in Receivers of Satellite Radionavigation System

New min iature filters, d iplexers, based on low and h igh pass filter, and antennas for satellite radio navigation system based on low and high pass filter are presented. These devises are manufactured on ceramic substrates with different thickness and e =40, 80, 120 by using thick-film technology where topology is formed with silver conductors by laser.In the article simulated and experimental filters, d iplexers and antennas main characteristics are pres ented as well as a topology