The goal of this paper is to demonstrate the capability of the 1U CubeSat to study the radiation spectra on LEO. The research was realized by the Lucky-7 mission with the primary goal of testing electronics such as a power supply, piNAV L1 GPS receiver, UHF communication system, and other subsystems in the natural space environment, and the secondary goal of testing the possibility of using 1U CubSat class satellites for scientific tasks. The satellite is equipped with a piNAV GPS receiver and piDOSE radiation detector, silicon diode radiation spectrometer, camera, and other sensors. The on-board computer enables storage of 34 h of measurements of the radiation spectrum. These measurements can be downloaded by the UHF communication system during four satellite passes over the monitoring ground station. We successfully verified all necessary instruments and their cooperation and measurement procedure. The UHF communication was identified as the most critical subsystem because of its low capacity, which slowed down the satellite operation. We needed four zenith passes to upload 34 h of measurement.
Highly Efficient Portable Lightning Strike Counter - Case Study of Its Implementation and Testing
Safely conducting flowing lightning current into the grounding system via air-terminals and down-conductors constitutes a key method of protecting objects being struck by lightning discharge. At present, there is no other safer method of protection than capturing and conducting lightning current and its dispersion in the ground. By having to conduct powerful lightning current, the protection systems are exposed to excessive thermic and electrical stress. When such protection systems are correctly designed, installed and regularly checked, the threat to objects is considerably reduced as the systems are dimensioned for such purposes. An opposite case occurs when a protection system is damaged, most frequently due to the thermic effects of lightning current. Then, there are only two possibilities of detecting damage: either by providing regular and timely inspections or by means of controls based on the information supplied by a lightning strike counter. The key requirement of the first method is that the relevant object has not been repeatedly struck by lightning current during a period of at least 5 years. The other method provides instant information, in real time, and inspection of the protection system may be carried out immediately. Hence, sooner than another lightning stroke discharge could be repeated. This paper examines the method of detecting lightning current in down-conductor and the possibility of providing real-time information.
Methodology and Detection of Lightning Strikes in Down-conductors via Sigfox Network
Lightning poses a risk to buildings, people, and technical facilities. The lightning air-terminal and down-conductor are the basic protection against direct lightning discharge. In terms of the reliable functioning of the lightning conductor, the key is to monitor the passage of the lightning current through the lightning conductors and to brief the facility manager in real time of the need to carry out appropriate checks. We hereby present a system for contactless monitoring of lightning attacks, and experimental results of testing by means of a lightning impulse current generator (LICG). Finally, we introduce an IoT system for large-scale monitoring.
Study of the Two-Line Element Accuracy by 1U CubeSat with a GPS Receiver
There is a common practice to calculate orbital trajectories of space objects like satellites and space debris using Two-Line Element Sets (TLEs). However, TLEs provide rather coarse parameters for fine orbit computation and their precision varies with age of their issue and position of the satellite. The paper evaluates such induced position determination error using the comparison of a position calculated from TLE data for a small CubeSat class satellite and a position obtained from the on-board custom GPS receiver that is a part of such satellite payload. The analyses of the impact of satellite position at the orbit, i.e., a dependency of position error on satellite geographical latitude, and impact of the ageing of TLE data in frame of position and velocity vector were made. There was shown that use of TLE data can bring some significant errors in calculation of predicted satellite position which can affect performance and efficiency of some related tasks like steering the ground station antenna for communication with the satellite or planning the satellites operations namely for the classes of small and amateur satellites.
CubeSat Observation of the Radiation Field of the South Atlantic Anomaly
The movement of the South Atlantic Anomaly has been observed since the end of the last century by many spacecrafts equipped with various types of radiation detectors. All satellites that have observed the drift of the South Atlantic Anomaly have been exclusively large missions with heavy payload equipment. With the recent rapid progression of CubeSats, it can be expected that the routine monitoring of the South Atlantic Anomaly will be taken over by CubeSats in the future. We present one-and-a-half years of observations of the South Atlantic Anomaly radiation field measured by a CubeSat in polar orbit with an elevation of 540 km. The position is calculated by an improved centroid method that takes into account the area of the grid. The dataset consists of eight campaigns measured at different times, each with a length of 22 orbits (~2000 min). The radiation data were combined with GPS position data. We detected westward movement at 0.33°/year and southward movement at 0.25°/year. The position of the fluence maximum featured higher scatter than the centroid position.
PDOP parameters improvement using multi-GNSS and signal re-transmission at lunar distances
Precise navigation for satellites of any kind is the key to future cost-effective Lunar missions. The usability of Global Navigation Satellite Systems (GNSS) for such high-altitude applications is still challenging due to reduced signal power levels, satellites visibility or signal processing complexity with all that resulting in a low position, velocity and time (PVT) accuracy, which is typically expressed by geometric dilution of precision (GDOP) parameters. This paper proposes a navigation method based on re-transmission combined with multi-GNSS concept, specifically signal reception from GPS, Galileo, Glonass, BeiDou and SBAS satellites’ antenna pattern main-lobes and side-lobes. Those signals are re-transmitted from the user satellite at the Lunar distance to the Earth, where all the signal processing is assumed to be performed. Based on the results from the tests of the of modelled scenario, the method presents an improvement of the position dilution of precision (PDOP, a subset of GDOP) parameters for the missions at the Lunar distance.
VHF/UHF Transceiver with Digital Signal Processing
The innovative approach in designing the radio part of the professional VHF/UHF (narrow-band) transceivers based on the application of the digital intermediate frequency stages known from the wide-band systems is presented. The main problem is the dynamic range of the analog to digital converter, which is the weakest part of the concept. The combination of the presented common analog RF front end and digital implementation of the further receiver stages improves production repeatability and reduces production and setup costs and the final size of the transceiver in comparison to pure analog design. We presented the parameters of the key blocks, which are RF filters and Digital Down Converter including analog to digital converter, that substantially contribute to the complete design. The proper selection and design of such parts show the valuable impact to the proposed approach of digital signal processing based transceiver.
The paper summarizes the experiences with the operation of the piNAV GPS receiver in a 1U unstabilized CubeSat operated on LEO orbit. piNAV L1 is a GPS receiver developed by an author for small satellite missions. The receiver is equipped with the 15 GPS L1 C/A channels and acquisition accelerator that shortens the cold start of the receiver on LEO to 65 s. The typical power consumption is 120 mW. Lucky-7 is a private 1U technological CubeSat with power budget 1 W that operates on the quasisynchronous polar orbit at altitude 520 km. One of its scientific missions is to test the operation of GPS. The space experiments proved the successful operation of the GPS receiver. The position information was available for approximately 80% of the time, where the position outage was caused by a satellite rotation and relatively long navigation signal reacquisition. The experimental data proved that the position availability can be improved by a higher-performance signal acquisition engine.
Measurement of cosmic radiation in LEO by 1U CubeSat
CubeSats are inexpensive tools for studying cosmic radiation. The paper presents an architecture and measurement of Lucky 7 1U CubeSat, which was launched to the quasi-synchronous polar orbit with an altitude of 520 km on June 27, 2019. The satellite is equipped with a scintillator detector whose luminescence emission is measured by a PIN diode and a space GPS receiver that labels the radiation measurement with a precise time and position. The cosmic radiation data were collected since summer 2019. The obtained measurement results are in good conformity with model calculations of the fluxes of the radiation components in Low Earth Orbit (LEO). During the performed pilot experiment, the objectives are to test a simple and inexpensive system providing input data for numerical models together with precise time and position data; and measure count rate data, which are compared with the models.
New Accuracy Testing of the Lightning VHF Interferometer by an Artificial Intercloud Pulse Generator
The authors have rearranged an optimal method for signal processing of interferometric measurements, based on the angle-of-arrival estimation approach, and have analyzed errors of estimating the direction of arrival of intercloud pulse signals. The method was then implemented in the performance of optimized interferometer hardware. This article presents application of an array of plate antennas matched by the 50 omega parallel resistor that are directly connected to 50-omega high-frequency low-noise amplifiers for each channel. The important contribution of the authors is to cover the plate antenna capacitance to the input bandpass filter. The proposed compensation enables to reduce linear distortion of the received signal, which is one of the main sources of errors of the time-of-arrival estimation, and to optimize the antenna impulse response. The novelty of this article can be seen in the application of the artificial intercloud pulse generator for testing, precision calibration of the proposed system, and fixing of potential imperfections and losses in both hardware and processing software. The practical application of the proposed interferometer is demonstrated on the processing of real lightning events. As the interferometer operates in the frequency bands that are dedicated to other radio communication services, this article provides results for measurements of interference that were realized with the aim of finding an optimal installation location.
Radiation Data Acquisition with Research Stratospheric Balloon Incorporating IoT Telemetry System
he paper presents a radiation data measured in the atmosphere during the flight of a stratospheric balloon. The balloon carries the third version of the gondola with custom-developed electronic device integrating GPS, IoT, data storage and gamma radiationsensors. The radiation is measured by a miniature low-power silicon detector equipped with the plastic scintillator. The gondola enables to track the balloon during the whole stratospheric flight. The IoT network simplifies reception of the telemetry dataon the ground.
The cold start of the space GPS receiver, i.e. the start without any information about the receiver position, satellite constellation, and time, is complicated by a large Doppler shift of a navigation signal caused by the satellite movement on the Earth orbit. That increases about five times the search space of the navigation signals compared to the standard GPS receiver. The paper investigates a method of the acceleration of the GPS receiver cold start time designed for the pico- and femto-satellites. The proposed method is based on a combination of the parallel search in Doppler frequency and PRN codes and the serial search in code phase delay. It can shorten the cold start time of the GPS receiver operating on LEO orbit from about 300 to 60 seconds while keeping the simplicity of FPGA signal processor and low power consumption. The developed algorithm was successfully implemented and tested in the piNAV GPS receiver. The energy required for the obtaining of the position fix was reduced five times from 36 on to 7.7 Joules. This improvement enables applications of such receiver for the position determination in smaller satellites like Pocket Cube or femto-satellites with a lower energy budget than the Cube Satellite.
Testing Signal Processing Techniques for Digital VHF/UHF Transceiver in High-level SDR Programming Environment
Nowadays, due to cost savings, flexibility or improvement of service quality, modern communication devices solely rely on the digital domain when it comes to signal processing. The paper presents a comfortable, fast and straightforward approach of testing and verifying developed digital signal processing techniques before their implementation into a digital mobile transceiver. The approach benefits from the concept of an Software-defined radio (SDR) by employing a high-level programming environment capable of direct analog radio frequency (RF) front end control in real-time via a user defined software.
CALIBRATION OF THE VHF LIGHTNING INTERFEROMETER TRIGGERING UNIT USING A LIGHTNING CURRENT GENERATOR
VHF interferometer serves for the registration and localization of lightning radio pulses for further analyses of the inter-cloud processes that are connected with charge transfer and emission of radio pulses. As the bandwidth, of the VHF interferometer, is very wide due to the precise measurement of the time difference of arrival, the interferometer generates a large volume of data that must be processed and stored. The triggering system of the VHF lightning interferometer enables to select scientifically valuable data from the data stream. The ideal triggering unit synchronizes data acquisition with the return stroke event. The basic requirements placed on the triggering circuits are a low false alarm rate and a high probability of lightning discharge detection. The unit consists of a whip antenna that is sensitive in the electrical field, an amplifier and a matched filter that is tuned to the return stroke wave. The usage of the correctly designed matched filter increases detection probability of the lightning discharge and reduces false alarm rate. The key problem is laboratory testing of the triggering unit in a near-realistic environment. The paper proposes a method based on the generation of the return stroke wave by a lightning current generator. As the gain of the common electrically short whip antenna cannot be determined with sufficient precision, the electric field of the generator is properly calibrated by an electromagnetic field probe based on a plate radiator. This approach facilitates accurate control of the amplitude of the return stroke radio wave and study of the sensitivity of the triggering circuits on nonstandard waves.
Digital Up and Down Converter for High Performance VHF and UHF transceiver
The Digital Up and Down Converter (DUC/DDC) is a basic building part of the professional digital mobile transceiver. The paper presents DDC/DDS for dual mode professional VHF/UHF transceiver developed for railway radio. The transceiver complies ETSI standards for NFM and Digital Mobile Radio (DMR). The DUC/DDC is featured with the channel selectivity exceeding 70 dB and dynamic range more than 90 dB. The implementation of the other standards that use constant envelope modulation like small satellite UHF communication links is also possible.
V čase rozšiřování využívání GNSS systémů v široké oblasti aplikací a to i v rámci strategické infrastruktury vyvstává potřeba systému detekujícího případné rušení tohoto signálu za účelem snížení provozuschopnosti dané infrastruktury. Příspěvek popisuje systém detektoru rušení GNSS signálu GIDeLoc (GNSS Interference Detector and Localizer), jeho funkce a složení. Současně popisuje proceduru zastaničení, která slouží pro inicializaci systému před jeho nasazením, způsob synchronizace mezi jednotlivými měřicími stanovišti a postupy výpočtů relevantních k požadovaným výstupům ze systému.
High Performance SDR for Monitoring System for GNSS Jamming Localization
This paper presents a basic description of a monitoring system which is designed for the GNSS jamming detection and localization as well as giving the theoretical issue together with specific consequences. The usage of that system is targeted to an aviation safety and space together with general transportation. The system is an extensive project, and this document is mainly about measuring station as an essential part of it. The paper presents specific localization techniques which will be used in digital signal processing. Several tests of the functionality of the measuring station have been made and presented in this paper. The result of the paper comes from the basic test of the measuring station. In that test, functionality - clock synchronization, mutual phase of an antenna array, software-defined radio was proved. The monitoring system is still developing and other important results will be described in the future.
Modernized solar radio spectrograph in the L band based on software defined radio
The paper presents the concept, implementation, and test operation of a modernized solar radio spectrograph for an investigation of the solar emission and solar bursts in radio frequency bands. Besides having a strong diagnostic significance for studying the flare energy release, the solar radio bursts can also cause strong interference for radio communication and navigation systems. The current spectrograph for the Ondrejov observatory (Astronomical Institute of Czech Academy of Sciences) was modernized by using a direct-conversion receiver connected to a field-programmable gate array (FPGA) for the fast Fourier transform (FFT) spectrum estimation and put into the test operation. The higher time and frequency resolution and lower noise in comparison with the existing analog instrument were reached by the implementation of the latest optimal signal processing methods. To reduce the costs for such modernization, the operating frequency range was divided into four sub-bands of bandwidth 250 MHz, which brings another benefit of greater scalability. The first observations obtained by the new spectrograph and their comparison with the analog device are presented in the paper with future steps to put the spectrograph into the regular operation.
GNSS systems are susceptible to radio interference despite then operating in a spread spectrum. The commerce jammers power up to 2 watts that can block the receiver function at a distance of up to 15 kilometers in free space.
HIGH ALTITUDE BALLOON TEST FLIGHT OF MINIATURE LOW POWER DOSIMETER FOR SMALL SATELLITES
A miniature low power dosimetry system based on silicon photodiode and scintillation crystal was tested aboard high altitude balloon test flight. Results captured during climbing and descent confirmed the usability of the system aboard small satellite in comparison with thestandard Geiger tube solution.
Systém pro odhalování nezákonného rušení GNSS sign álu
V čase stálého rozšiřování využívání GNSS systémů v široké oblasti aplikací, a to i v rámci strategické infrastruktury vyvstává potřeba systému detekujícího případné rušení GNSS signálu ohrožující provozuschopnost dané infrastruktury. Tento příspěvek popisuje systém, který je schopen odhalovat takovéto rušení typu „jamming“ a „spoofing“. Systém poskytuje uživateli informaci o spolehlivosti a integritě GNSS signálu a lokalizaci zdroje rušení. Zamezí tak případným nehodám či hrozbám vedoucím ke snížení bezpečnosti provozu infrastruktury, která využívá informace o poloze a času získané z GNSS.
Telemetry System of FIK III. Stratospheric Balloon
The paper presents design and application of a telemetry system for stratospheric balloon based on Internet of Things System of SigFox. The purpose of the telemetry system is balloon tracking during the stratospheric flight. It was tested on experimental flight of FIK III stratospheric balloon equipped with SigFox as main transmitter and UHF transmitter for backup. The payload consisted of ADS-B receiver, and two independent dosimeters for radiation measurement. The paper presents verification of operation of telemetry system on results obtained during experiment. The end of paper covers also some considerations about advantages and drawbacks of such solution.
Testing of the Interference Immunity of the GNSS Receiver for UAVs and Drones
GNSS systems are susceptible to the radio interference despite they operate in a spread spectrum. This problem becomes critical in the field of general aviation, UAV, and drones. In addition, there is a wide range of commerce of jammers of power up to 2 watts that can block the receiver function at a distance of up to 15 kilometers in free space. The paper presents two original methods developed for testing of the GNSS
receiver behavior and interference immunity. The first methodology is based on a usage of a GNSS simulator for generation of the satellite signals and a vector signal RF generator for generating different types of interference signals. The second software radio methodology is based on a software GNSS simulator and a signal processing in Matlab. The signal samples from the software GNSS simulator is combined with the
interference generated in Matlab and the resulting signal is replayed by a software radio. In the frame of the research, two GNSS receivers suitable for UAV and drone navigation was tested for various jamming signals and scenarios. The results are not so optimistic as the jammer signal is propagated by the line of sight in most cases. The commercial jammer can block tested receivers on to the distance from kilometers to tens of kilometers.
Experimental SDR receiver for monitoring and processing of solar radio bursts
The paper introduces a design of radio spectrography receiver that shall serve as equipment for reception, monitoring, and processing of solar radio bursts. These burst can affect operation of many radio communication and navigation services as is presented on example of GPS satellites signal degradation. The concept and design of the spectrography receiver is presented together with discussion of hardware requirements and proposed solution.
piNAV L1 is a GPS L1 receiver for position determination of the small satellites at LEO orbits. The receiver was tested by the ReGen software GPS simulator for static and dynamic scenarios. The typical horizontal position error for static scenario is 2.5 m (95%). The position errors for dynamic scenarios are affected by the dynamic stress errors.
Telemetry system for research stratospheric balloon
The paper presents telemetry system for stratospheric balloon mission based on the UHF transceivers designed for Internet of Things. The system operates in 869.5 MHz frequency band. The system uses very short packet without channel coding that can be successfully received and decoded under low signal to noise ratio. The modem sensitivity −124 dBm and the transmission power 25 dBm can ensure reliable communication for distances longer than 100 km with omnidirectional antennas and 200 km with 10 dBi ground station directional antenna. The telemetry system uses GFSK modulation of bit rate 1200 Bd and is designed for a transmission of the balloon position and status.
Družicová navigace. Od teorie k aplikacím v softwarovém přijímači
Kniha shrnuje současné poznatky družicových navigačních systémů a principů jejich funkce a zabývá se aplikací softwarového rádia pro realizaci navigačních přijímačů. Publikace obsahuje původní vědecké a technické výsledky týkající se využití softwarového rádia pro výzkumné a vývojové účely nových a modernizovaných družicových navigačních systémů a signálů. Konkrétně popisuje realizovaný navigační senzor pro malé výzkumné družice a univerzální softwarový přijímač pro výzkum družicových navigačních systémů.
ADS-B Reception at Airport Airside Areas using TDL-based Channel Modeling
In this paper we introduce an approach to reception and processing of the ADS-B extended squitter signals provided by aircrafts and other vehicles on the airport airside area. The paper presents a method for use channel modelling based on TDL model for purposes of ADS-B signal processing enhancement. The model tests are based on real data measurements at Prague airport. The method for application of this approach and verification tests are presented as well.
Bolidozor radio meteor detection network
Kákona, J., Kákona, M., Povišer, M., Milík, J., Dvořák, R., Štrobl, J., doc. Dr. Ing. Pavel Kovář, Szylar, J., Bednář, P., Křivský, L., Chroust, J.
Proceedings of the International Meteor Conference 2015. Mechelen: International Meteor Organization, 2015. pp. 157-160. ISBN 978-2-87355-029-5.
Radio meteor detection networks could improve the knowledge about meteors under daylight or inconvenient weather conditions. We present a new approach to the meteor detection system. The hardware described in this paper has unique features for time synchronization of multiple nodes, therefore meteor trajectory calculation is possible in case of appropriate network deployment.
Estimation of parameters for ground ADS-B radio channel model
We propose the model of radio channel for ADS-B signal reception at the ground area of airport, which is typical by interference caused by multipath propagation. The model is based on a tapped delay line (TDL) model. The source data for model parameters estimation are obtained by measurements at Prague Vaclav Havel airport. We compare simulated results based on proposed model with experimental measurements.
The cold start of the LEO satellite GPS receiver is complicated due to a large Doppler frequency shift, Doppler frequency rate of the navigation signals and a rapid change of the satellite visibility. The cold start time can be shortened by a proper strategy of a selection of the satellites to be searched for. The cold start simulator was developed and used for optimization of the sequence of the satellites search, for development and testing of an advanced satellite selection algorithm that utilizes information on the satellites already detected and for optimization of a frequency search range. The best performance was achieved by using an advanced selection strategy. The strategy is based on the selection of the satellites nearest to the detected satellite, using the average angle between the Earth center (apex) and the satellites. Furthermore, the simulation shows that it is not practical to investigate all frequencies within the range of the maximum possible Doppler frequency shift of the carrier wave of the navigation signal, but investigate approximately +/- 35 kHz range and, if not successful, switch to the next satellite. The simulations proved that a simple GPS receiver with the sequential search algorithms can operate in the LEO orbit.
Empirical Model of the ADS-B Channel for Airport Area
The paper describes approach to processing of the ADS-B extended squitter signals and data provided by targets on the ground area of the airport. These signals are affected by radio channel environment which causes distortion and interference. The paper presents a method for estimation of the channel TDL model based on empirical data processing. This method is applied on measurement and processing campaign with the real signals from MLAT transmitters at the Prague Vaclav Havel airport. The results of channel model parameters are presented here as well.
Distributed Extended Kalman Filter for Position, Velocity, Time Estimation in Satellite Navigation Receivers
Common techniques for position-velocity-time estimation in satellite navigation, iterative least squares and the extended Kalman filter, involve matrix operations. The matrix inversion and inclusion of a matrix library pose requirements on a computational power and operating platform of the navigation processor. In this paper, we introduce a novel distributed algorithm suitable for implementation in simple parallel processing units each for a tracked satellite. Such a unit performs only scalar sum, subtraction, multiplication, and division. The algorithm can be efficiently implemented in hardware logic. Given the fast position-velocitytime estimator, frequent estimates can foster dynamic performance of a vector tracking receiver. The algorithm has been designed from a factor graph representing the extended Kalman filter by splitting vector nodes into scalar ones resulting in a cyclic graph with few iterations needed. Monte Carlo simulations have been conducted to investigate convergence and accuracy. Simulation case studies for a vector tracking architecture and experimental measurements with a real-time software receiver developed at CTU in Prague were conducted. The algorithm offers compromises in stability, accuracy, and complexity depending on the number of iterations. In scenarios with a large number of tracked satellites, it can outperform the traditional methods at low complexity.
Study of the RF Front-end of the Multi-Constellation GNSS Receiver
The paper presents analysis of the requirements on the RF Front-end of the Multi-Constellation GNSS Receiver. One of the main problems of the multi-constellation GNSS receiver is the amplifying ans splitting of signals of partial systems working in different bands.The paper studies a variety of possibilities of the design of the multi-constellation receiver frontend from the noise figure and jamming resistance point of view.
Dual-frequency Tracking of Compass Signals: Compass Implementation to the Witch Navigator Receiver
The paper describes the implementation of the Compass signal processing for the Witch Navigator receiver - an experimental GNSS software receiver for research and education purposes which has been developing at CTU in Prague. The description is shown in comparison with the implementation of the legacy signal processing: GPS L1 C/A and GLONASS L1. It is practically verified that the Compass signal has great compatibility with GPS/GLONASS signals, which results in simplification of multi-system receiver. The implemented Compass receiver can process signals in B1 (E2) and B2 (E5b) bands simultaneously. Due to rapid deployment of the Compass constellation it is now possible to perform real-time and dual-frequency measurement in geographical location of the Czech Republic, Prague. All three satellite types are visible in Prague: GEO, IGSO and MEO. Paper shows measurement results and is focused on signal characteristics and their quality.
The Galileo system introduces an extremely wideband civil E5 signal for high precision navigation. The structure of the receiver for the E5 signal is complicated due to the signal complexity and the large bandwidth. It is possible to process the whole E5 signal or process separately E5a and E5b parts combining obtained results afterwards (we call here such method as piece-wise processing). The second procedure has three times worse standard deviation of the pseudorange then first one. The main goal of the paper is to present a design of an E5 receiver which we will call the economic E5 receiver (ecoE5). It is built from jointly controlled correlators for the processing of the E5a and E5b signals which are parts of the E5 signal. Control of these partial E5a and E5b correlators is realized by only one delay and one phase lock loops. The performance, i.e. the pseudorange noise and multipath errors, of the receiver equipped with the ecoE5, is only slightly worse (the standard deviation of the pseudorange noise is 10 - 20% larger) than the performance of the optimal E5 receiver and it is much better than the performance of the receiver combining the piecewise (E5a and E5b) measurements. The ecoE5 receiver hardware demands are about one quarter of the hardware demands of the classical E5 receiver.
In the paper, the study of the applicability of the GPU approach in GNSS signal acquisition is studied. Two methods, PCSS and DBZP, have been investigated with discussed implementation in C and CUDA languages.
Ranging Property of the Dual-Band Band Limited Signal (DBBLS)
The Dual-Band Band Limited Signal (DBBLS) is a signal with its power spectral density consisting of two separate lobes. Signals that can be considered as DBBLS are for example signals with BOC, AltBOC modulation, signals modulated on two close carriers and many other signals, which are used in modern satellite navigation systems. This signal advantage is its excellent ranging property. The parted power spectral density enables processing the DBBLS as a single wideband signal in single-channel receiver or as two narrow band signals in two-channel receiver. The signal processing of the ranging signals is based on the calculation of the cross-correlation function, which can be calculated from the signal measured by the two-channel receiver by the derived method more efficiently than from the whole signal. The two-channel processing has nearly optimal performance, but the hardware and computation complexity is much lower. The developed method can by applied, for instance, for the processing of the Galileo E5 signal or pair of the Compass L1 signals.
Universality and Realistic Extensions to the Semi-Analytic Simulation Principle in GNSS Signal Processing
Semi-analytic simulation principle in GNSS signal processing bypasses the bit-true operations at high sampling frequency. Instead, signals at the output branches of the integrate&dump blocks are successfully modeled, thus making extensive Monte Carlo simulations feasible. Methods for simulations of code and carrier tracking loops with BPSK, BOC signals have been introduced in the literature. Matlab toolboxes were designed and published. In this paper, we further extend the applicability of the approach. Firstly, we describe any GNSS signal as a special instance of linear multi-dimensional modulation. Thereby, we state universal framework for classification of differently modulated signals. Using such description, we derive the semi-analytic models generally. Secondly, we extend the model for realistic scenarios including delay in the feed back, slowly fading multipath effects, finite bandwidth, phase noise, and a combination of these. Finally, a discussion on connection of this semi-analytic model and position-velocity-time estimator is delivered, as well as comparison of theoretical and simulated characteristics, produced by a prototype simulator developed at CTU in Prague.
Interoperable GPS, GLONASS and Galileo Software Receiver
The new and modernized GNSS navigation systems will provide various navigation services and signals for civil user. The system operators work on basic interoperability agreements which simplify multi-system navigation receiver architecture and reduce its cost. The most current GNSS signals can be processed by one or several classical E-L correlators with a look up table PRN generator of a length of 10,230 chips. Most signals are processed optimally, but for some signals, like Galileo E1b and E1c or GPS L1C, this signal processor does not utilize all signal components and properties. The proposed E-L correlator was implemented to the FPGA of the experimental software GNSS receiver and was tested on the Galileo E1b, E1c, and E5a signals. The target multi-system GNSS receiver architecture based on an ExpressCard peripheral card for the standard PC computer or notebook is described herein. Up to one hundred universal correlators and signal snapshot capture unit ...
Interoperable GPS, GLONASS and GALILEO Software Receiver
The new and modernized GNSS navigation systems will provide various navigation services and signals for civil user. The system operators work on basic interoperability agreements which simplify multisystem navigation receiver architecture and reduce its cost. The most current GNSS signals of GPS, GLONASS and GALILEO can be processed by one or several classical EL correlators with a look up table PRN generator of length 10230 chips. Most signals are processed optimally, but for some signals, like Galileo E1b and E1c or GPS L1C, this signal processor does not utilize all signal components and properties. The proposed EL correlator was implemented to the FPGA of the experimental software GNSS receiver and was tested on the GALILEO E1b, E1c and E5a signals. The target multisystem GNSS receiver architecture based on an ExpressCard peripheral card for the standard PC computer or notebook is described in the paper. Up to hundred universal correlators and also signal snapshot capture unit..
Reduced-complexity GNSS Software Simulator Based on Correlator Output Signal Modeling
This article presents an algorithm for reducing complexity of GNSS tracking simulators. The existing simulators, known
as bit true, are solely based on generation and processing of IF samples. The introduced simulator generates the signals at
the output branches of the correlators, hence lowers the sampling rate from tens of Megahertz down to units of kilohertz.
The user further does not need to enter the spreading codes, but their correlation functions. This approach limits
the algorithms to be tested under high dynamics, fadings and interference. However, fast initial design can be carried out
hereby. A prototype simulator has been developed and tested under the Matlab environment.
The Implementation of the Dual Frequency GLONASS Receiver to the Witch Navigator
The paper discusses the implementation of the dual frequency GLONASS receiver to the Witch Navigator software receiver. The Witch Navigator is an open source software receiver designed for study and research purposes. We review the Witch Navigator software and hardware concepts as well as their mutual interactions. Focus is placed on the GLONASS specific code with the utilization of either frequency. Finally, results of the so far implemented software blocks are presented.
The Witch Navigator -- A Software GNSS Receiver Built on Real-Time Linux
The Witch Navigator (WNav) is an open source project of GNSS (Global Navigation Satellite System)
receiver whose hardware is implemented as an ExpressCard hosted in PC with Linux OS.
The paper describes the whole conception of WNav with focus on the kernel part (device driver) and
the real-time user space process, provides information about the processes synchronization and presents
the achieved performance.
The first obvious milestone is to develop the fully functional GPS L1 C/A receiver which justifies
the selected conception. The achieved results and experience with this legacy signal are presented in the
paper, as well.
Witch Navigator - a Low Cost Software Receiver for Education and Research
The Witch Navigator is a low cost software receiver developed at the Czech Technical University for education and research purposes. The receiver is designed universally for various missions from simple single frequency GPS L1 C/A receivers to complex multi-GNSS-system, multi-frequency and multi-antenna receiver. The Witch Navigator receiver is designed as an ExpessCard periphery for a notebook or a PC. The cards can be mutually interconnected to the large system. The Witch Navigator is equipped with a powerful FPGA capable to run GNSS correlators (traditional receiver concept) or to send GNSS signal samples to the PC for entire processing.
Witch Navigator -- a software GNSS receiver for education and research
The paper introduces the Witch Navigator, which is an ExpressCard form factor software GNSS receiver for a notebook or a personal computer, developed for educational and research purposes. The signal processing runs on a FPGA and a PC processor, the mutual communication is realized via a PCI Express bus. The receiver is equipped with two reconfigurable front ends. The complex multi-antenna, multi-frequency and multi-constellation GNSS system can be built by interconnecting several receiver cards by a special connector.
Witch Navigator -- softwarový GNSS přijímač pro výzkum a vývoj
The paper deals with an optimal processing of a Galileo E5 signal. A proposed correlator structure was developed on a base of a deep study of an E5 signal cross correlation function. Due to the non linearity of the E5 AltBOC modulation the proposed correlator calculates the cross correlation function between a received signal and a signal replica for all possible hypotheses of the navigation message bits. A correct peak tracking verification is realized by implementation of a single side band correlator, which also serves for course signal acquisition and secondary ranging code synchronization. The signal processing was verified on the Galileo Giove A and Giove B satellites with very positive preliminary results.
Interoperable GPS, GLONASS and Galileo Software Receiver
The recent development of the GNSS systems and international cooperation resulted in important technical problems of the GNSS systems which are an interoperability and compatibility. In the interoperable receivers the most expensive parts - front ends - can be shared for signals reception of different systems. The unification of the signal processor is also possible with some small performance deterioration but the hardware complexity reduction is considerable. The paper analyses applicability of a classical E-L correlator for processing of various GNSS signals and compare its performance with optimal method. The low complex interoperable processor of software receiver based on a FPGA for the GPS, Galileo and GLONASS systems is proposed. The results of testing on the Galileo E1 and E5 signals are presented. The last part of the paper proposes architecture of a low cost multi system GNSS receiver based on mass market components.
Opisyvaetsâ arhitektura mul´tisistemnogo priemnika GNSS, postroennogo na baze periferijnoj platy ExpressCard dlâ standartnogo personal´nogo komp´ûtera ili noutbuka. V PPVM priemnika realizuetsâ do sta universal´nyh korrelâtorov i vypolnâetsâ zahvat i cifrovaâ obrabotka signalov. Privoditsâ obzor harakteristik nastoâŝih i perspektivnyh signalov sistem GPS, GLONASS i GALILEO dlâ graždanskih potrebitelej. Predlagaetsâ prostaâ struktura E-L-korrelâtora GNSS i opisyvaûtsâ vozmožnosti ego ispol´zovaniâ dlâ obrabotki časti signalov GNSS. Privodâtsâ rezul´taty ispytanij korrelâtora s signalami E1 i E5a sistemy GALILEO, vyvody.
The developement of advanced GNSS signal processing algorithms such as multi-constellation, multi-frequency and multi-antenna navigation requires an easily reprogrammable software defined radio solution. Various receiver architectures for this purpose have been introduced. RF front-end with FPGA universal correlators on ExpressCard connected directly to PC was selected and manufactured. Such a~unique hardware combination provides the GNSS researchers and engineers with a~great convenience of writing the signal processing algorithms including tracking, acquisition and positioning in the Linux application programming interface and enables them to reconfigure the RF front-end easily by the PC program. With more of these ExpressCards connected to the PC, the number of the RF channels, correlators or antennas can be increased to further boost the computational power. This paper reveals the implementation aspects of the receiver, named the Witch Navigator, and~gives the key test results.
Galileo AltBOC E5 Signal Characteristics for Optimal Tracking Algorithms
The paper compares various signal processing methods of the E5 signal from a simple one based on the separate signal component processing to an optimal one based on the processing of the whole signal power. The philosophy of the optimal processing method is firstly described on a simple example which is QPSK modulated navigation signal by the pilot and data signal. The correlator for QPSK modulation usually processes these two orthogonal components separately but the simultaneous processing of such signal is also possible. The problem of the second approach is signal replica generation because of its dependency on the navigation message.
The paper deals with the design of the high performance front end for GNSS software receiver. The various front end architectures are analyzed. The design of the complete analogue signal processing chain i.e. multi frequency antenna LNA, RF filters and configurable receiver for civil GPS and open Galileo signals are presented in the paper. The front end is based on the direct conversion receiver architecture. The frequency range of developed front end covers all L band GNSS signals. The bandwidth is controlled in range 8 - 66 MHz.
Jubilee 15th Saint Petersburg International Conference on Integrated Navigation Systems. St. Petersburg: State Research Center of Russia Elektropribor, 2008. pp. 357-362. ISBN 978-5-900780-80-1.
High demands on mobile user positioning cannot be satisfied by single navigation system. The paper proposes multi system solution which utilizes navigation and communication systems and signals. The experimental software receiver is described as development tool of such combined system.
The topic of the paper is to describe influences of the difficult environment to the GNSS and SBAS signals and consequences for signal processing. The satellite line of sight shadowing influence to signal reception is discussed for various environments together with proposed shadowing model.
The model is derived from two state Markov model. The experimental measurements of mobile reception of EGNOS signal has shown the need of supporting SBAS signals in several environment by complementary transmission. Such concept of supporting system with data transmitted by separate channel is discussed
in the paper both for DGNSS and SBAS case.
The possibility and analysis of use of Internet for real time distribution of augmentation data is presented in the paper, namely questions of data latency and augmentation influence to user position in difficult environment.
This paper deals with an alternative navigation method based on DVB-T signal ranging. The proposed signal processing is based on correlation reception using the continual
carrier part of the DVB-T signal. The ranging properties of the proposed signal processing will be derived and verified by simulation and experiments with software DVB-T receiver.
Monitoring station with experimental GNSS receiver provides more information about GPS and EGNOS systems signals. Monitored data are stored in PC workstation in raw form to keep available all information for measurement analyses.
The monitoring station provides monitoring all in view GPS, EGNOS, and Galileo satellites on L1 frequency. The monitored data are stored in raw form. Data are also transformed to the standard format and analyzed.
The paper deals with second order signals characteristics
for satellite navigation systems. The main goal of the paper is to
simplify and clarify signals analysis task by introducing a system
of signals characteristics and their mutual relations. The conception
of the system is based on the fact that the structure of navigation
signals is partially given since the signals should ensure reliable
pseudorange estimations. The proposed conception is then applied on
the tiered code construction employed in Galileo system. Finally it
is shown that the results of the tiered code analysis can be used
in case of the power spectra estimation of BOC modulated signals.
The paper deals with possibility of integration of GNSS as a source of position information into the railway signalling system. It is focused on the use at secondary rail roads where it should substitute conventional ETCS signalling system. The description of the use of GNSS for safety critical applications is presented in the first part of the paper concerning possible influence of GNSS to the failures of the system and its investigation with the use of information or system redundancy. Design of a suitable GNSS receiver based on Software Defined Radio Concept (SDR) was realized in the frame of the project of the Czech Ministry of Transport. The various possible realizations of SDR and aspects of their use are analyzed. The design of the SDR based GNSS receiver for railway applications developed at the Czech Technical University is presented in the end of the paper.
Implementation of the Advanced Signal Processing into the FPGA Based GNSS Software Receiver
This paper deals with an implementation of the high performance GPS/GNSS frequency domain acquisition unit into the FPGA based GNSS software receiver. The coherent acquisition unit with 5 ms integration of the received signal is capable to detect signal of signal to noise ratio 35 dBc/Hz and higher. The significant improvement of the processing gain can be achieved by the additional non-coherent integration. One second non-coherent integration enables to determine acquisition parameters for signal of signal to noise ratio 20 dBc/Hz, which is sufficient for indoor navigation.
The paper deals with the reception, processing, statistical evaluation and archiving of EGNOS (European Geostationary
Navigation Overlay Service) signals together with data of present and future GNSS (GPS, GLONASS, and Galileo).
We describe the software GNSS receiver, its schema, implementation into a computer, results of tests and application for railway, municipal transportation and for shipping of dangerous matters. The receiver, originally for the Galileo system, is on a printed board which is the size of a Euro Card (160x100 mm). Because the Galileo signal is not in the air, it was modified for the GPS and GLONASS systems. Experimental GNSS receiver (EGR) was used as a tool for its development and it is also described. Even if we use the receiver which is able to process signals of all three systems, it is impossible to ensure reception of GNSS signals in adverse conditions (under leaves canopy, in urban canyons, in hollow tracks, etc.). Therefore we have studied the possibilities of communication systems which will use modern signals known from satellite navigation and we have obtained very interesting results when we used DVB-T transmitters as beacons.
We describe the software GNSS receiver, its schema, implementation into a computer, results of tests and application for railway, municipal transportation and for shipping of dangerous matters. The receiver, originally for the Galileo system, is on a printed board which is the size of a Euro Card (160?100 mm). Because the Galileo signal is not in the air, it was modified for the GPS and GLONASS systems. Experimental GNSS receiver (EGR) was used as a tool for its development and it is also described. Even if we use the receiver which is able to process signals of all three systems, it is impossible to ensure reception of GNSS signals in adverse conditions (under leaves canopy, in urban canyons, in hollow tracks, etc.). Therefore we have studied the possibilities of communication systems which will use modern signals known from satellite navigation and we have obtained very interesting results when we used DVB-T transmitters as beacons.
We describe the software GNSS receiver, its schema, implementation into a computer, results of tests and application for railway, municipal transportation and for shipping of dangerous matters. The receiver, originally for the Galileo system, is on a printed board which is the size of a Euro Card (160? 100 mm). Because the Galileo signal is not in the air, it was modified for the GPS and GLONASS systems. Experimental GNSS receiver (EGR) was used as a tool for its development and it is also described. Even if we use the receiver which is able to process signals of all three systems, it is impossible to ensure reception of GNSS signals in adverse conditions (under leaves canopy, in urban canyons, in hollow tracks, etc.). Therefore we have studied the possibilities of communication systems which will use modern signals known from satellite navigation and we have obtained very interesting results when we used DVB-T transmitters as beacons.
Proceedings of the 7th International Navigational Symposium on Marine Navigation and Safety of Sea Transportation. Gdynia/Jurata: Gdynia Maritime University, Faculty of Marine Electrical Engineering, 2007.
We describe the software GNSS receiver, its schema, implementation into a computer, results of tests and application for railway, municipal transportation and for shipping of dangerous matters. The receiver, originally for the Galileo system, is on a printed board which is the size of a Euro Card (160Í100 mm). Because the Galileo signal is not in the air, it was modified for the GPS and GLONASS systems. Experimental GNSS receiver (EGR) was used as a tool for its development and it is also described. Even if we use the receiver which is able to process signals of all three systems, it is impossible to ensure reception of GNSS signals in adverse conditions (under leaves canopy, in urban canyons, in hollow tracks, etc.). Therefore we have studied the possibilities of communication systems which will use modern signals known from satellite navigation and we have obtained very interesting results when we used DVB-T transmitters as beacons.
This paper presents an overview of aspects that have to be taken into account in use of GNSS receivers for positioning in the difficult environment, for example indoors. The performing position determination and navigation tasks in such environments come nowadays more and more in the focus of the GNSS community. The GNSS signal indoor reception is affected by strong attenuation and due to the nature of the environment by strong multipath. The paper discusses both of them and their possible impact to the navigation tasks. The effect of the user movement is discussed and the experimental measurements are presented. The measurements were realized with use of experimental GNSS software receiver, described in the paper as well.
Availability of the EGNOS Service for a Land Mobile User
The aim of this study is an analysis of the availability of the EGNOS service for a land mobile user, which is limited by the shadowing of the EGNOS satellites by the various obstacles. The shadowing process is modeled by the Markov process with model parameters determined for various environments by the mobile experimental measurements. The relevance of the model was also tested experimentally and the adequate conformity was observed. The availability of the EGNOS message reception in various environments was experimentally investigated and the statistics were calculated.
Design methods for RF part of GNSS software receivers
The paper deals with the experimental GNSS receiver built at the Czech Technical University for experiments with the real GNSS signal. The receiver is based on software defined radio architecture. Receiver consists of the RF front end and a digital processor based on programmable logic. Receiver RF front end supports GPS L1, L2, L5, WAAS/EGNOS, GALILEO L1, E5A, E5B signals as well as GLONASS L1 and L2 signals. The experimental receiver is also used in GNSS monitoring station, which is independent monitoring facility providing also raw monitoring data of the GPS, EGNOS and Galileo systems via internet.
Assessment of the EGNOS Signal Availability for Land Mobile User
The EGNOS land mobile channel is analyzed in the paper. The shadowing of the EGNOS signal is modelled by two-state Markov process. The results of experimental mesurements of signal reception and model validation fro various enviroments is presented in the paper.
EGNOS Signal Availability Measurements for a Land Mobile User
Comparison of theoretical models and prectical field tests of availability of EGNOS signal for land mobile user. The mathematical model of the satellite signal shadowing based on Markov process was developed and compared with results from experimantal measurements.
The aim of the contribution is to study signal processing methods including multi frequency code and carrier phase tracking methods and compare them whit the classical approach. Research is also focused on reception of a signal in hard conditions. Special attention is given to the methods of multi frequency signal processing.
The Galileo Receiver is investigated in the frame of the GARDA project. The Galileo code and carrier tracking subtask of the Galileo Receiver Core Technologies is carried out at the Czech Technical University. The problem was analysed and split to the particular tasks. The aim of this paper is focused on BOC correlator architecture.
GPS usability and reliability in transport telematics applications are limited due to difficult signal propagation mainly in hilly terrain or in urban areas. Therefore, methods for GPS support by local infrastructure are developed. Integration of GPS with European system Galileo in near future may reduce the limitation significantly, but it brings several new problems, which may be solved efficiently by adequate local augmentation systems. The GSM-GPRS data channel is suitable for interconnecting of mobile telematics environment with a central point and for distribution of GPS/Galileo ephemeris and other supporting information as well. The Experimental Galileo receiver, which is developed at department of Radioelectronics, is suitable experimental platform for development and testing of GPS/Galileo augmentation techniques.
Overview of the Experimental GNSS Software Receiver Design Issues
SDR concept is prospective approach to signal processing in radio systems, including navigation systems. The advantage of software oriented approach resides in easy configuration and modification of signal processing algorithms.
The GNSS position determination is based on the satellite-to-user distance measurement. GNSS satellites transmit the specially designed signal with spread spectrum modulation. The signal propagation delay is measured to obtain the distance information. Because the satellite orbital parameters are known, position and velocity of users receiver equipment is computed consecutively.
The new form of spread spectrum modulation BOC is intended for modernized GPS and Galileo satellites. Correlation feature of the BOC signal requires modification of current signal processing algorithms in GNSS receivers.
Availability of the EGNOS System for a Land Mobile User
GPS indoor applications need powerful DSP techniques for processing of very weak signal. High parallel processing techniques are used for these purposes. This paper describes the effective GPS weak signal-searching algorithm designed for DSP implementation on FPGA.
Implementation of the GLONASS Signal-Processing Algorithm to the Experimental GNSS Receiver
This paper deals with estimation of appropriate channel model for indoor GPS navigation. The need and purpose of such model is discussed. The su_cient information for channel description is channel time variant impulse response. Our estimation of channel impulse response is based on two antennas simultaneous signal measuring. The theoretical model of measurement is proposed and justified. Then the MVUB estimator of channel impulse response is derived from this model.
Návrh algoritmů zpracovnání signálů v hradlovém poli softvérového přijímače
The contribution gives an overview of present and future navigation systems and their augmentations as GPS, GLONASS, GALILEO, WAAS, EGNOS, MSAT, QZSS, BEIDOU, GAGAN. Performance of systems depends on technical parameters and we will try to evaluate it and to present our opinion on advantages of them for different applications and in various situations (reception of week signals suffering from great attenuation under vegetation canopy, in urban canyons, influence of reflections and multipath). The last part of contribution deals an application of software radio technology for user receiver design and results obtained from experiments with different algorithms of processing of satellite navigation systems signals.
Reception of Signals of GLONASS System by Experimental GNSS Receiver
The paper deals with the Software Radio and its applications in processing of signals of satellite navigation systems. Modern Software Defined Radio (SDR) technology enables to digitalize and process radio signals in programmable digital circuits. The high power programmable DSP and FPGA are implemented. The benefit of discussed architecture is in a software definition of the function and parameters of radio electronic systems. This architecture can be used in GNSS for software implementation of processing procedures of new GNSS signals, like GPS L2 C/A, GPS L5 or Galileo.
International-Symposium of European Radio Navigation Networks Integration of GPS, EGNOS, Galileo and LORAN-C/EUROFIX Proceedings. Bonn: Deutsche Gesellschaft für Ortnung und Navigation (DGON), 2003.