GNSS Research Articles

BAYESIAN ESTIMATE OF TELECOMMUNICATION SYSTEMS PREPAREDNESS

The paper assumes a Bayesian estimate of the telecommunication systems availability ratio. Downtime and uptime are described by gamma distributions with positive integer parameters. Estimates of the distribution parameters are obtained using the maximum likelihood method. For the set samples, the values of the desired probability distribution densities are found and an expression for estimating the availability ratio is derived. Numerical estimates for the standard and assumed estimates are given. For a system with two states, a Bayesian estimate of the availability function with consideration of downtime and serviceable condition takes into account the features of backup equipment and the effect of its failure defined by performance reliability and features that ensure the reliability of information signals. The proposed Bayesian approach has the following advantages: it is possible to conduct quantitative estimates with lack of sufficient statistics on functional use indicators; it takes into account all destabilizing factors of various nature; the presence of a lower mean square error compared to traditional methods. To implement the proposed approach that estimates the availability ratio, confidence probabilities are introduced relative to the indicator of failure flows and equipment recovery. The parameters of the a priori information can be determined by different methods or on the basis of sufficient statistical data. To illustrate the discussed calculation algorithm, a digital data transmission system of a standard satellite navigation system consisting of terminal, radio equipment, and a transponder is considered. To estimate the required values, we used data on interruptions in the operation of equipment due to its malfunction during a conditional year. The frequency of downtime caused by signal propagation conditions and equipment failures was evaluated. It was shown that the gamma distribution is suitable for describing the frequency distribution of downtime. The frequency distribution of the cyclicity coefficient with the condition of the selected time interval was also taken into account. Sample mathematical expectations and mean square deviations of the downtime coefficient were found. As a result, the numerical example shows the correctness of using the Bayesian estimate of weighted equipment preparedness.

Precision and Characteristics Analysis of Precise Satellite Clock Bias Data of BDS

High-precision satellite clock bias (SCB) data is a critical product for satellite navigation systems to realize accurate navigation, positioning and timing. Unlike other satellite navigation systems, the precise SCB data for the BeiDou Navigation Satellite System (BDS) are mainly determined by two methods, the Two-Way Time Transfer (TWTT) method and the Orbit Determination and Time Synchronization (ODTS) method. Awareness of the data variations obtained from different methods can be used to improve clock modeling performance, and be beneficial to higher-rate GNSS positioning and for predictions in real-time applications. We describe a comprehensive method to analyze the systematic and random characteristics of BDS SCB data obtained from TWTT and ODTS and discuss possible causes of observed variations. Some new conclusions are drawn: the data continuity of TWTT is highly related to satellite orbit types; affected by orbit error and other factors, the fitting residuals (RMS) of ODTS is 0.2 ns worse than that of TWTT on average, while the fitting precision of TWTT is 0.49 ns. There are up to 8ns periodic fluctuations in the mutual agreement between TWTT and ODTS data. The stability result shows a remarkable effect of flicker phase modulation (FLPM) noise can be seen in the period of 300-1000 s in TWTT data. All the BDS satellites display more complex, nonpower law behavior due to the effects of periodic clock variations.

Aerospace engineering experience and on-board software projects of satellite navigation systems

The main stages of creating global space navigation systems of the first generation are discussed in the article. The authors give a description of the scope and content of work, stages and timing of this work, and also give the main characteristics of the satellites and on-board software testing processes of these space navigation systems. The list and sequence of technological stages of the on-board software testing process are defined in the description of the methodology for guaranteeing the quality of development and maintenance of the on-board software of communication and navigation satellites.

WITHDRAWN: Implementation of deep learning algorithms for predicting ionospheric total electron content

Abstract Geomagnetic storms affect the ionospheric structure of the earth, leading to concealment in the communication of satellite navigation systems. To not experience the mishappening, we need to make accurate predictions about the atmospheric conditions in the ionospheric layer under extreme space weather conditions. It, being physically challenging to predict such behaviours of geomagnetic storms. In this paper, we are going to predict the upcoming storms depending on the previous data collected and on the Ionospheric total electron content. For this, we intend to use the Matrix laboratory i.e., MATLAB and the deep learning algorithms LSTM (Long Short-Term Memory) and Seq2Seq (Sequence to Sequence). This study brings new perceptions of the algorithms as well as the behavior of the Total Electron Content (TEC) of the ionosphere.

Spaceborne atomic clock performance review of BDS-3 MEO satellites

On June 23, 2020, the final satellite of the third generation Beidou satellite navigation system (BDS-3) was launched, which represents the BDS-3 is fully operational and can provide global services. Due to the fact that BDS-3 constellation mainly consists of Medium Earth Orbit (MEO) satellites, we only discussed the in-orbit atomic clock performance of MEO, and compared to that of the latest generation of GPS as well as Galileo satellites. Based on the precise satellite clock product provided by German Research Center for Geosciences (GFZ), a level of 0.2 ns fitting precision is obtained, and it is better than BDS-2. The periodic terms of satellite clock are analyzed by means of spectrum analysis. Except some mutual periodic terms, several exclusive periodic terms, approximately 8 h, 6 h and 4.8 h harmonics, are found in passive hydrogen masers (PHMs) of BDS-3, and possible reasons are given. Clock systematic characteristics, such as frequency accuracy and drift rate are examined and found that PHMs have better result than rubidium atomic clocks. Finally, frequency stability is evaluated: all BDS-3 satellite clocks can reach the order of 10-15 at the average interval of 86400 s, which is much better than BDS-2 and comparable to the latest type of GPS III as well as Galileo satellites.

On Linear and Circular Approach to GPS Data Processing: Analyses of the Horizontal Positioning Deviations Based on the Adriatic Region IGS Observables

Global and regional positional accuracy assessment is of the highest importance for any satellite navigation system, including the Global Positioning System (GPS). Although positioning error can be expressed as a vector quantity with direction and magnitude, most of the research focuses on error magnitude only. The positional accuracy can be evaluated in terms of navigational quadrants as further refinement of error distribution, as it was shown here. This research was conducted in the wider area of the Northern Adriatic Region, employing the International Global Navigation Satellite Systems (GNSS) Service (IGS) data and products. Similarities of positional accuracy and deviations distributions for Single Point Positioning (SPP) were addressed in terms of magnitudes. Data were analyzed during the 11-day period. Linear and circular statistical methods were used to quantify regional positional accuracy and error behavior. This was conducted in terms of both scalar and vector values, with assessment of the underlying probability distributions. Navigational quadrantal positioning error subset analysis was carried out. Similarity in the positional accuracy and positioning deviations behavior, with uneven positional distribution between quadrants, indicated the directionality of the total positioning error. The underlying distributions for latitude and longitude deviations followed approximately normal distributions, while the radius was approximated by the Rayleigh distribution. The Weibull and gamma distributions were considered, as well. Possible causes of the analyzed positioning deviations were not investigated, but the ultimate positioning products were obtained as in standard, single-frequency positioning scenarios.

Constant Envelope Multiplexing of Multi-Carrier DSSS Signals Considering Sub-Carrier Frequency Constraint

With the development of global navigation satellite systems (GNSS), multiple signals modulated on different sub-carriers are needed to provide various services and to ensure compatibility with previous signals. As an effective method to provide diversified signals without introducing the nonlinear distortion of High Power Amplifier (HPA), the multi-carrier constant envelope multiplexing is widely used in satellite navigation systems. However, the previous method does not consider the influence of sub-carrier frequency constraint on the multiplexing signal, which may lead to signal power leakage. By determining the signal states probability according to the sub-carrier frequency constraint and solving the orthogonal bases according to the homogeneous equations, this article proposed multi-carrier constant envelope multiplexing methods based on probability and homogeneous equations. The analysis results show that the methods can multiplex multi-carrier signals without power leakage, thereby reducing the impact on signal ranging performance. Meanwhile, the methods could reduce the computation complexity. In the case of three different carriers multiplexing, the number of optimization equations is reduced by nearly 66%.

Single point positioning with vertical total electron content estimation based on single-epoch data

Abstract. This paper proposes a new mathematical method of ionospheric delay estimation in single point positioning (SPP) using a single-frequency receiver. The proposed approach focuses on the Δ vertical total electron content (VTEC) component estimation (MSPPwithdVTEC) with the assumption of an initial and constant value equal to 5 TECU in any observed epoch. The principal purpose of the study is to examine the reliability of this approach to become independent from the external data in the ionospheric correction calculation process. To verify the MSPPwithdVTEC, the SPP with the Klobuchar algorithm was employed as a reference model, utilizing the coefficients from the navigation message. Moreover, to specify the level of precision of the MSPPwithdVTEC, the SPP with the International Global Navigation Satellite Systems (GNSS) Service (IGS) TEC map was adopted for comparison as the high-quality product in the ionospheric delay determination. To perform the computational tests, real code data were involved from three different localizations in Scandinavia using two parallel days. The criterion was the ionospheric changes depending on geodetic latitude. Referring to the Klobuchar model, the MSPPwithdVTEC obtained a significant improvement of 15 %–25 % in the final SPP solutions. For the SPP approach employing the IGS TEC map and for the MSPPwithdVTEC, the difference in error reduction was not significant, and it did not exceed 1.0 % for the IGS TEC map. Therefore, the MSPPwithdVTEC can be assessed as an accurate SPP method based on error reduction value, close to the SPP approach with the IGS TEC map. The main advantage of the proposed approach is that it does not need external data.

A Study on the Analysis of Crust Deformation on the Korean Peninsula after the Tohoku Earthquake using GNSS Observation

A Study on the Analysis of Crust Deformation on the Korean Peninsula after the Tohoku Earthquake using GNSS Observation

Investigation of the positioning accuracy for the integrated navigation system at the measurement signals interruption

An integrated navigation system as part of an inertial navigation system corrected by signals from a satellite navigation system is researched. The integrated navigation system is installed on a mobile carrier is arranged. The organization of the experimental study, the design of the stand used to install the equipment on a mobile carrier, and the measurement processing technique are considered. When the signals of the satellite system disappear, signal prediction algorithms are used. The results of assessing the positioning accuracy of the integrated navigation system in case of discontinuities in the reception of navigation signals, assessing the forecast accuracy by using the presented algorithms and conclusions drawn from the analysis of the results are presented. Keywords inertial navigation system; satellite navigation system; predictive model; positioning accuracy; trends; self-organization; identification

О возможности детектирования локальных особенностей зоны главного ионосферного провала по данным навигационных спутниковых систем

О возможности детектирования локальных особенностей зоны главного ионосферного провала по данным навигационных спутниковых систем

УПРАВЛЕНИЕ ДВИЖЕНИЕМ НАЗЕМНОГО МОБИЛЬНОГО РОБОТА ПРИ НАРУШЕНИИ ЦЕЛОСТНОСТИ НАВИГАЦИОННЫХ ДАННЫХ СПУТНИКОВОЙ НАВИГАЦИОННОЙ СИСТЕМЫ

The article discusses the determination of navigational data corruption, which received by the satellite navigation system as well as traffic control of ground mobile robots. It also specifies the movement features of ground robots, which affect the data integrity monitoring. It proposes an algorithm of control to implement the methods of autonomous onboard monitoring of the navigational data integrity. The algorithm is based on the equations of signal correspondence in various parts of the control system. It is designed to determine the inoperability of the satellite navigation system that implies the loss of signal and failure in the navigation problem solution. The algorithm takes into account the non-deterministic nature of moving ground robot with possible stops in the process of following the trajectory. The article considers the implementation variants of algorithm to assess reliability for the control system containing additional sensors of the robot’s displacement and for the hardware-redundant system containing no additional sensors. The results of modeling the movement of a ground mobile robot along an arbitrary trajectory in case of navigational data corruption are presented. The features of algorithm based on the simulation results are described in the article. The authors considered variants of robot control in case of navigational data corruption. The structure of the system and a method for controlling a mobile robot in case of satellite navigation system failures are also proposed. The method is based on the control mode in the system, according to the measured data of the position of the robot in the case of navigational data corruption or otherwise according to the data calculated from the robot model. The implementation of the method makes it possible to avoid significant deviations of the robot from a given trajectory of movement at intervals of signal loss of the satellite navigation system.

Development and Application of Big Data in the Field of Satellite Navigation

Based on the characteristics of big data, the meaning of fog computing, and the spatiotemporal data characteristics of satellite navigation systems, the concept, connotation, and characteristics of Beidou big data were put forward. The Beidou big data processing process was sorted out, the preliminary architecture of the Beidou big data system with fog computing function was built, and finally the fog computing based Beidou big data system was proposed. Big data research content provides technical support for further tapping the value of Beidou satellite navigation system data and realizing the incremental development of satellite navigation systems.

Acquisition of Positional Accuracy with Comparative Analysis of GPS and EGNOS in Urban Constituency

Over the years, precise positioning has been the ultimate goal for Satellite Navigation Systems. The American Global Navigation Satellite System deliver the position and time information intended for various sectors such as vehicle tracking, oil exploration, atmospheric studies, astronomical telescope pointing, airport and harbor security tracking etc. Corresponding technological competitors such as Russian Global Navigation Satellite System (GLONASS), European Union’s GALILEO, China’s BeiDou and Japanese Quasi Zenith Satellite System (QZSS) are few other versions of Satellite based Augmentation Systems. Nevertheless, stern security measures, geographical statistics and stimulation of diverse Electronic Gadgets at indoor/outdoor surroundings make it critical to acquire data about any vicinity with seamless accessibility, accuracy and integrity with satellite links. In this paper, positional accuracy has been tested with analysis of EGNOS, EDAS and simple GPS receiver models at Rome City, Italy. To support results, various real time experiments/tests has been performed with GPS Receiver SIRF Demo software. The test was conducted on-board a car by installing a laptop equipped with GPS Receiver plus supportive SBAS (EGNOS particularly) through three diverse bus routes of locality and outcomes of few tested samples inside the Rome City center are specified to check the availability of desired satellite signals. Subsequently, comparative analysis has been executed between the simple GPS data received and GPS + EGNOS data collected during daytime traffic. The strength of test signals reveals accuracy of EGNOS in open terrain area with less congestion. Furthermore, Asian and European Advanced GPS systems are compared in terms of performance as well as feasibility of authentic, accurate and swift satellite navigation systems.

Life Prediction Method of On-board Hydrogen Clock under Multiple Mechanisms

As the on-board time reference of the navigation system ranging, the on-board hydrogen clock is the core part of the payload of the satellite navigation system, and its lifetime directly determines the duration of the navigation satellite mission. In order to meet the demand for life prediction of on-board hydrogen clocks, this paper expounds the composing and design of the hydrogen clock and focuses on the factors affecting the lifetime. In general, the factors include: the hydrogen supply period of the hydrogen component in the vacuum module, the period of the vacuum system to maintain a specific vacuum degree, the degradation speed of the bulb coating, the atomic preparation ability including the ionization device of the ionization bulb and the ionization circuit, the performance of the magnetic shielding and other key factors. In addition, the key performance indicators are also considered. The telemetry data and the test data of the key components on the ground are comprehensively utilized to evaluate the lifetime at which the relevant performance parameters reach the threshold. Based on the random failure, degradation, consumption and the key performance indicators of the hydrogen clock, a multi-mechanical and competitive life prediction method is proposed. The case study shows that the new method can be used to get the more dependable results of life prediction.

Development control system robotic platform for horticulture

The article presents a control system for a robotic platform for horticulture. The electronic control system consists of a running engine control unit, a stepper motor steering unit, an electronic differential control unit, a power plant automatic on / off control unit, and battery charging balancing. The developed control system of the robotic vehicle contains a central computer that collects information from sensors and sensors, processes it and transmits control signals to the drives of the machine movement. The movement of the robotic platform is carried out both by a radio signal with a remote control, and in offline mode on a pre-set map of the area according to data from the GLONASS/GPS differential receiver of the satellite navigation system. It is also possible to independently control the movement of a robotic platform using a vision system. The autonomy of the robotic platform provides 10 hours of continuous operation in low-light conditions in various weather conditions.

Зенитная тропосферная задержка по данным GPS наблюдений и измерений радиометром водяного пара в пункте Badg (Бадары, Республика Бурятия)

A comparison was carried out of the values of the total zenith tropospheric delay (ZTD) revealed from the observations of the GPS satellite navigation system and measurements by a microwave radiometer of water vapor (MRWV) at the BADG permanent measurement point located on the territory of the “Badary” Observatory of the Institute of Applied Astronomy of the Russian Academy of Sciences. GPS antenna, MRWV device and meteorological station are located in close proximity to each other. This significantly affected the accuracy of the processed data. The differences in the values of the total zenith tropospheric delay obtained from GPS observations and measurements with a microwave radiometer of water vapor are analyzed in terms of mean and standard deviations and the coefficient of cross-correlation. Comparison of the results for 2020 year showed very good agreement. In summer, the BIAS of the difference between the ZTD data from GPS and MRWV observations is about 0.63% of the average summer ZTD value, the cross-correlation coefficient between the data is K = 0.85. In winter, the BIAS of the difference was about 0.21% of the average winter value of ZTD, the cross-correlation coefficient between the data is about K = 0.93. A high degree of reliability of data on ZTD and tropospheric moisture content obtained by continuous GPS measurements is shown.

Distance Measuring Equipment Pulse Interference Suppression Based on Wavelet Packet Analysis

As an indispensable part of global satellite navigation system, the frequency band of DME will overlap with that of the navigation signal, which will cause the signal from the DME platform to be accepted by the Global Navigation Satellite System receiver and form interference. Therefore, it is of great significance to study an effective algorithm to suppress DME pulse interference. This paper has the following research on this problem. In this paper, wavelet packet transform is used to solve for the suppression of DME pulse interference method, wavelet packet analysis belongs to the linear time-frequency analysis method, it has good time-frequency localization characteristics and the signal adaptive ability, due to the function of wavelet packet and parameter selection of DME will affect the ability of interference suppression, combining with the theory of wavelet threshold, function type and decomposition series are discussed to prove the validity of the selected parameters on the pulse interference suppression.

BOC signals processing by two traditional correlator channels

Problem statement. With the development of satellite navigation systems, new navigation BOC signals are being introduced. Since the structure of BOC signals differs from traditional BPSK signals, this complicates their processing, which may require hardware changes and often leads to the need to develop new ones. Objective. Synthesis and analysis of the BOC signal processing algorithm using two BPSK correlators, comparable in accuracy to the direct method. Results. The synthesis and analysis of the BOC signal delay tracking system using two correlators, originally designed to receive only BPSK-conducting signals, are carried out. The statistical characteristics of the delay discriminator are obtained. It is shown how the accuracy and sensitivity of the obtained delay tracking algorithm are correlated with respect to the reference algorithm, which assumes the use of a signal with a digital subcarrier in the reference signal of the correlator. The pull-in characteristic are obtained. Practical relevance. The processing algorithm BOC signals that doesn't require modification of the traditional correlators of the navigation receiver is presented. This algorithm is of great practical importance, since it allows for high-precision reception of modern BOC and AltBOC signals, despite the limitations characteristic of modern navigation equipment. For example, this algorithm allows to receive Galileo E5 signals using the popular NTLab NT1065 chip. A new signal pull-in algorithm is proposed. This algorithm allows to avoid abnormal tracking errors caused by the operation of the tracking system in the side zones of the s-curve. The pull-in characteristics for various receive conditions are given.

Marine Cold Chain Transportation Monitoring and Route Scheduling Optimization Based on IoV-BDS

Recently, the research of the internet of vessels system is a hotspot in the marine engineering area. In this article, the Internet of Vessels based on Beidou satellite navigation system (IoV-BDS) architecture is proposed for marine cold chain transportation monitoring and scheduling. An improved communication method using Beidou short-message communication (SMC) is designed to ensure the reliability of ship-shore data transmission. Additionally, based on the IoV-BDS, we proposed a novel route scheduling optimization model which considers the key costs for marine cold chain transportation, such as fuel, catches damage, and refrigeration energy consumption, and designed a speed selection mechanism. Furthermore, an improved ant colony optimization (IACO) algorithm was utilized to optimize the whole fleet transportation routes, which takes advantage of the A-star algorithm to speed up the convergence of ant colony algorithm (ACO), a novel state transition rule was used to prevent falling into a locally optimal solution. The applicability of IoV-BDS was verified by the shipboard data acquisition and Beidou SMC experiments. The performance evaluation and analysis of route optimization schemes were presented by simulations and comparison with other schemes. The results demonstrated the benefit of our proposed schemes, in terms of solution quality and convergence of the algorithm.