Signals Of Navigation Systems Research Articles

Principles of construction of nanosatellite radar systems based on global navigation satellite system reflectometry

Objectives. The development of radar remote sensing systems based on the reception of signals of navigation satellite systems reflected from the surface enables a constellation of nanosatellites to be deployed, in order to perform radar surveying of the Earth’s surface. The aim of this work is to develop the principles of construction of onboard bistatic remote sensing systems on nanosatellites, in order to assess the energy potential and possibilities for its increase.Methods. The optimal processing method in onboard bistatic radar systems is a development of known analytical methods of optimal processing in monostatic systems. The calculation of the energy potential is based on the experimental data obtained by other authors.Results. The utilization of signals from navigation satellite systems for surface sensing is a promising and developing area. The USA and China have deployed satellite constellations to perform remote sensing using reflected signals of navigation satellites. An algorithm for optimal processing in such systems, which realizes the principle of aperture synthesis, was developed, and the energy potential of bistatic synthetic aperture radar was calculated. In order to achieve this processing, the proposed scheme uses a standard navigation receiver to form reference signals.Conclusions. The application of optimal processing methods in bistatic radar enables a synthetic aperture based on scattered satellite navigation system signals. In order to improve the accuracy of estimates, the signal-to-noise ratio needs to be increased by combining coherent accumulation (aperture synthesis) and incoherent accumulation (aggregating measurements from different spacecraft). The signal processing methods and receiver structure proposed in this work onboard nanosatellites allow aperture synthesis to be achieved with realizable hardware requirements.

Correction of navigation systems by using satellite navigation system signals and genetic algorithm

A method for algorithmic correction of the inertial navigation system of an aircraft under conditions of autonomous operation of the inertial navigation system is considered. Compensation for navigation system errors is implemented by using a genetic algorithm. To increase the accuracy of building an error model in the genetic algorithm, the «shaking» method is used. The results of mathematical modeling demonstrated the used modification effectiveness of the genetic algorithm for correcting the inertial navigation system. Keywords genetic algorithm, inertial navigation system, prediction, errors, «shaking» method

Robust Autonomous Vehicle Computer-Vision-Based Localization in Challenging Environmental Conditions

In this paper, we present a novel autonomous vehicle (AV) localization design and its implementation, which we recommend to employ in challenging navigation conditions with a poor quality of the satellite navigation system signals and computer vision images. In the case when the GPS signal becomes unstable, other auxiliary navigation systems, such as computer-vision-based positioning, are employed for more accurate localization and mapping. However, the quality of data obtained from AV’s sensors might be deteriorated by the extreme environmental conditions too, which infinitely leads to the decrease in navigation performance. To verify our computer-vision-based localization system design, we considered the Arctic region use case, which poses additional challenges for the AV’s navigation and might employ artificial visual landmarks for improving the localization quality, which we used for the computer vision training. We further enhanced our data by applying affine transformations to increase its diversity. We selected YOLOv4 image detection architecture for our system design, as it demonstrated the highest performance in our experiments. For the computational platform, we employed a Nvidia Jetson AGX Xavier device, as it is well known and widely used in robotic and AV computer vision, as well as deep learning applications. Our empirical study showed that the proposed computer vision system that was further trained on the dataset enhanced by affine transformations became robust regarding image quality degradation caused by extreme environmental conditions. It was effectively able to detect and recognize images of artificial visual landmarks captured in the extreme Arctic region’s conditions. The developed system can be integrated into vehicle navigation facilities to improve their effectiveness and efficiency and to prevent possible navigation performance deterioration.

RESULTS OF SEMI-NATURAL TESTS OF THE AUTONOMOUS DETERMINATION OF THE VEHICLE LONGITUDE AND LATITUDE

Navigation parameters such as vehicle heading, linear speed and latitude and longitude are determined today, as a rule,using satellite navigation systems. However, there is a need for autonomous determination of navigation parameterswhen satellite navigation system signals are unavailable for one reason or another. For example, satellite navigationsystem signals can be jammed by electromagnetic countermeasures.Autonomous systems for determining the vehicle navigation parameters are inertial navigation systems, the basis ofwhich is the double integration of signals from accelerometers, as well as the integration of signals from gyroscopes toform one or another coordinate system, if we are talking about strapdown inertial navigation systems (SINS).Integration of the output signals of accelerometers and gyroscopes, which contain errors, leads to the accumulation ofSINS errors. To increase accuracy, SINS are integrated, for example, with satellite navigation systems. However, suchsystems cease to be completely autonomous.The article uses the method of autonomous determination of vehicle latitude and longitude, which is a new method ininertial navigation. The method is based on the strapdown inertial technology, which, unlike the standard methods usedin SINS, does not use the integration of the output signals of accelerometers and gyroscopes. To determine the angles oflatitude and longitude, the signals of the gyroscopes included in the inertial measurement unite (IMU) are used.As a result of a semi-natural experiment, the efficiency of the method of autonomous determination of latitude andlongitude was verified. Flight data of a small-sized aircraft were used for experimental verification. The data containedinformation about the angles of the heading, pitch, roll of the aircraft, the output signals of three micromechanicalgyroscopes, three micromechanical accelerometers, information about latitude, longitude and altitude measured by thereceiver of the satellite navigation system, as well as information about the horizontal and vertical components of speedand current time. Plots of calculated values of latitude and longitude and values measured using the receiver of thesatellite navigation system are given. From the given plots and tables, it can be seen that from a certain time, thecalculated values coincide with the "reference" ones, which confirms the efficiency of the method of autonomousdetermination of latitude and longitude.

Пространство аномалийсигналов ГЛОНАСС L1/L2OF и L1/L3OC согласно модели аномалий ИКАО

Determining the GLONASS signal threat space is necessary for the operation of the signal quality monitor, which is a part of the station that generates differential corrections for these signals. To account for the threat effects on the signal, known as the Evil Waveform (EWF), a model recommended by ICAO is used. The thresholds for the EWF detection are determined according to the established limiting errors of differential measurements. The measuring path of the navigation receiver of the station is represented by a serial connection of a pre-correlation filter, including an antenna, and a tracking loop correlator, the discriminator of which is used to estimate the EWF error. Four types of filters with their numerical parameters and several values of the discrimination S-curve width are considered, which made it possible to obtain the results of the EWF impact for 84 variants of the path configuration for each signal. The maximum range of change in the values ??of the model parameters among all options, when the error exceeded the threshold, determined the desired threat space for each signal. It is concluded that the wider the signal spectrum, the smaller is its threat space. The presented way of determining the threat space is applicable to other signals of navigation systems.

Компенсация погрешностей интегрированной навигационной системы с использованием искусственных нейронных сетей

The paper presents a new method for improving the accuracy of an integrated navigation system in terms of coordinate and velocity when there is no signal received from the global navigation satellite system. We used artificial neural networks to simulate the error occurring in an integrated navigation system in the absence of the satellite navigation system signal. We propose a method for selecting the inputs for the artificial neural networks based on the mutual information (MI) criterion and lag-space estimation. The artificial neural network employed is a non-linear autoregressive neural network with external inputs. We estimated the efficiency of using our method to solve the problem of compensating for the error in an integrated navigation system in the absence of the satellite navigation system signal

Vector network analyzer usage at calibration of delay in satellite radio navigation system signal simulators

This article presents a method of vector network analyzer application at the task of global navigation system simulator calibration. Calibrated parameter is internal delay of the radiofrequency signal in simulator. Attention is payed to reducing of calibration uncertainty by means of taking into account the part, which is caused by impedance of simulator and other equipment mismatches. The goal of research is to estimate the non-excluded uncertainty after vector network analyzer measurements’ usage for correction calculation. Measured parameters are the group delay, reflection and transmission coefficients of cable with connectors, and reflection coefficients of simulator and oscilloscope. The goal has been achieved by means of simulation modelling. The main parts of modelling were simulation of vector network analyzer measurements’ and calculation the statistics of the non-excluded uncertainty. As the result, was shown, that if to use vector network analyzer for global navigation system simulator calibration, the part of uncertainty, caused by impedance mismatch, can be reduced in a several times.

Selected Aspects of Using the Telemetry Method in Synthesis of RelNav System for Air Traffic Control.

Accuracy is an important factor in air traffic management which is why high requirements are necessary for each navigation system. The aim of this article is to describe the principles of the RelNav system and telemetry and their accuracy. We present the algorithms of the relative navigation system, which could be used for air traffic control in the case of the unavailability of satellite navigation system signals. This article sums up the different positioning methods, and deals with the accuracy of the relative navigation system (RelNav). Furthermore, the article considers the factors that influence the positioning accuracy. For this task, a computer simulation was created to evaluate the accuracy of the telemetric method. Next, we discuss the principles of telemetry and algorithms for calculating the position of the flying object (FO).

Acquisition and Tracking Performance of Satellite Navigation System Signal using Tiered Differential Polyphase Code

Abstract In this paper, we analyze the acquisition and tracking performance of signal using a tiered differential polyphase code as the secondary code. The Zadoff-Chu sequence is known to have a CAZAC (Constant Amplitude Zero Auto-Correlation) characteristics. The secondary code generated by differential encoding of the Zadoff-Chu sequence also has the same characteristics as the Zadoff-Chu sequence. Therefore, long integration will give better correlation results. We compare signal acquisition and tracking performance when using the NH sequence and Zadoff-Chu sequence as the secondary code. Monte-carlo simulation is performed using MATLAB. We use the probability of detection and the mean acquisition time for signal acquisition performance and tracking jitter for signal tracking performance.

Обнаружение радиосигналов спутниковых навигационных систем бескодовым методом

Обнаружение радиосигналов спутниковых навигационных систем бескодовым методом

Підвищення ефективності навігації літального апарату під час посадки за допомогою супутникової навігаційної системи

У цій статті представлено два алгоритми, що дозволяють підвищити ефективність навігації повітряного судна під час заходу на посадку за сигналами супутникової навігаційної системи. Перший алгоритм описує створення в просторі віртуальних опорних площин за координатами чотирьох точок на злітно-посадковій смузі та подальше обчислення горизонтального та вертикального кутового відхилення літального апарату від них. Другий алгоритм описує автономний контроль цілісності навігаційного поля в районі аеродрому за наявності в зоні видимості чотирьох супутників однієї системи. Методи дослідження: Використовувались методи планування експерименту, методи аналітичної геометрії та лінійної алгебри. Результати: Отримано нові експериментальні дані. Обговорення: Результати експериментального дослідження першого алгоритму показали принципову можливість обчислення відхилень літального апарату вказаним способом. Показано, що впровадження запропонованої технології дозволить підвищити ефективність навігації повітряних суден малої авіації під час посадки на аеродромах, які наразі не обладнані радіонавігаційними засобами для інструментальної посадки. Дослідження другого алгоритму показало, що зазначеним способом можливо зменшити кількість відмов супутникової навігаційної системи, що також позитивно впливає на ефективність навігації. Ці результати можуть бути використані у авіакосмічній галузі для зменшення кількості нельотних періодів повітряних суден малої авіації.

Использование виртуальной глиссады для вычисления отклонений летательного аппарата на конечном участке посадки

Objective: The development of a calculation method of aircraft guidance parameters (linear and angular deflection from a synthetic glide path) by means of global satellite navigation system signals. As opposed to the existing methods, it is suggested to use an inclined plane, containing a glide slope line, as a base surface for vertical guidance. Methods: An experimental research was carried out, based on the suggested method of deflections’ calculation, as well as the comparison of results was fulfilled with identification of guidance parameters’ data by means of the existing methods. Results: It is shown that the results of calculating deflections from a glide path by means of the developed method and those methods, which are currently applied in transport planes landing, are practically the same. Practical importance: Application of the given method of calculating aircraft deflections from a glide path will make it possible to simplify significantly the deployment of the ground segment of landing system in airports, which in its turn will give the opportunity to equip regional airdromes of the third and the forth class, which are currently equipped with imprecise approach systems (compass locators or, the so-called, VOR) or have no radio-navigation aids, with satellite systems of precision approach. Satellite landing system implementation will allow aircraft crews, provided with proper airborne equipment, to pass, in case of need, from a contact fly to an instrumental fly conducted under flight rules. The above mentioned will reduce airdromes meteorological minimum, which in its turn will cause the decrease in the number of non-flying days and increase the efficiency of airdromes and fleet exploitation. One more advantage of satellite landing system application is the fact that it allows students to work out the procedure of approach on instrument landing system.

The use of Galileo signals for time transfer metrology

AbstractWe briefly summarise the planned Galileo navigation system signals and their potential application in time and frequency metrology.

The investigation of the ionospheric variability by the radiotranslucence method

To provide a continuous single-point sounding of a large-scale region of the ionosphere the translucence method of studying the ionosphere utilizing satellite navigation system signals has been used. Simultaneous receiving the signals of GPS Navstar and GLONASS from different azimuths gives information on variations of the ionosphere in almost real time. Using measured data the reconstruction of the electron density profiles in the regions of intersection of a sounding ray with the ionosphere has been carried out. The translucence method was used to investigate the ionosphere effects of a partial solar eclipse (PSE) that occurred on 11.08 1999 by probing of the ionosphere with different GPS system signals in the Zwenigorod region.

Hydrogen Maser Wall Shift Experiments and Determination of the Unperturbed Hyperfine Frequency of the Ground State of the Hydrogen Atom

The principal accuracy limitation of a hydrogen maser is the uncertainty in the determination of the hydrogen maser wail shift. In this paper, we describe in detail the experiments on hydrogen maser wall shift and introduce briefly works on hydrogen masers in the Shanghai Bureau of Metrology. In experiments, we changed five different size storage bulbs by. turns. These bulbs were all coated in the same way with a locally made F4 coating. Results of the experiments are K(40°C) = -293 ± 17 mHzcm and a(40°C) = (-17 ± 2) × 10-30C-1. The unperturbed hyperfine frequency of the ground state of the hydrogen atomf0-0 was obtained by comparing five hydrogen masers to Loran C navigation system signals for one month. The average value in respect to TAI isf0-0 = 1420 405 751.768 ± 0.002 Hz. This value is closely in agreement with values of f0-0, which have been published by other authors since 1970.