Dissertations / Theses on the topic 'GPS receivers'

A new, open-access Global Positioning System (GPS) signal, known as L1C, is the most recent of several modernized Global Positioning System (GPS) signals. The first launch of a GPS satellite with this signal is expected to occur within a few years. One of the interesting features of modern Global Navigation Satellite System (GNSS) signals, including GPS L1C, is the presence of data and pilot components. The pilot component is a carrier with a deterministic overlay code but no data symbols; whereas, the data component carries the navigation data symbols used in the receiver processing. A unique aspect of GPS L1C is the asymmetrical power split between the two components, 75% of the power is used for the pilot and the remaining power, or 25%, for the data. In addition, the pilot and the data components are transmitted in phase with orthogonal spreading codes. Unassisted acquisition of GNSS spread spectrum signals requires a two-dimensional search for the spreading code delay and Doppler frequency. For modern two-component GNSS signals, conventional GNSS acquisition schemes may be used on either component, correlating the received signal with either the pilot or the data spreading code. One obvious disadvantage of this approach is the wasting of power; hence, new techniques for combining, or joint acquisition of the pilot and the data components, have been proposed. In this dissertation, acquisition of GPS L1C is analyzed and receiver techniques are proposed for improving acquisition sensitivity. Optimal detectors for GPS L1C acquisition in additive white Gaussian noise are derived, based on various scenarios for a GPS receiver. Monte Carlo simulations are used to determine the performance of these optimal detectors, based on detection and false alarm probabilities. After investigating the optimal detectors for GPS L1C acquisition, various sub-optimal detectors that are more efficient to implement are thoroughly investigated and compared. Finally, schemes for joint acquisition of L1C and the legacy GPS C/A code signal are proposed and analyzed.

The atmosphere in low latitude regions is of particular interest to GPS researchers because the propagation of GPS signals becomes significantly delayed compared with other regions of the world. Hence this limits GPS positioning accuracy in equatorial regions. Although the atmospheric delay can be modelled, a residual component will still remain. Reducing, or mitigating the effect of residual atmospheric delay is of great interest, and remains a challenge, especially in equatorial regions. Analysis of relative positioning accuracy of GPS baselines has confirmed that the residual atmospheric delay is distance-dependent, even in low latitude areas. Residual ionospheric delay is the largest component in terms of both absolute magnitude and variability. However it can be largely eliminated by forming the ionosphere-free combination of measurements made on two frequencies. The residual tropospheric delay is smaller in magnitude but rather problematic due to strong spatio-temporal variations of its wet component. Introducing additional troposphere ???scale factors??? in the least squares estimation of relative position can reduce the effect of the residual. In a local GPS network, the distance-dependent errors can be spatially modelled by network-based positioning. The network-based technique generates a network ???correction??? for user positioning. The strategy is to partition this network correction into dispersive and non-dispersive components. The latter can be smoothed in order to enhance the ionosphere-free combination, and can be of benefit to ambiguity resolution. After this step, both the dispersive and non-dispersive correction components can be used in the final positioning step. Additional investigations are conducted for stochastic modelling of network-based positioning. Based on the least squares residuals, the variance-covariance estimation technique can be adapted to static network-based positioning. Moreover, a two-step procedure can be employed to deal with the temporal correlation in the measurements. Test results on GPS networks in low latitude and mid-latitude areas have demonstrated that the proposed network-based positioning strategy works reasonably well in resolving the ambiguities, assisting the ambiguity validation process and in computing the user???s position. Furthermore, test results of stochastic modelling in various GPS networks suggests that there are improvements in validating the ambiguity resolution results and handling the temporal correlation, although the positioning result do not differ compared to using the simple stochastic model typically used in standard baseline processing.

The majority of navigation satellite receivers operate on a single frequency and experience an error due to the ionospheric delay. They compensate for the ionospheric delay using an ionospheric model which typically only corrects for 50% of the delay. An alternative approach is to map the ionosphere with a network of real-time measurements, with either a thin shell approximation or a full 3D map. Here, a time-dependent 3D tomographic imaging technique is used to map the free electron density over the full-height of the ionosphere during solar maximum. The navigation solutions computed using corrections based upon models and thin-shell and full-height maps are compared in this project. The models and maps are used to calculate the excess propagation delay on the L1 frequency experienced by GPS receivers at selected locations across Europe and North America. The excess delay is applied to correct the pseudo-range single frequency observations at each location and the improvements to the resulting positioning are calculated. It is shown that the thin-shell and full-height maps perform almost as well as a dual-frequency carrier-smoothed benchmark and for most receivers better than the unfiltered dual-frequency benchmark. It is also shown that the unfiltered dual-frequency method is not reliable, which is of concern as it is a proposed upgrade to current positioning systems. The improvements in positioning accuracy vary from day to day depending on ionospheric conditions but can be up to 25m during mid-day at solar maximum conditions at European mid-latitudes. The full-height corrections perform well under all geomagnetic conditions and are considerably better than thin-shell corrections under extreme storm conditions. The transmission of the navigation correction requires a forecast, an image compression and a system of distribution across a local region. The feasibility of this is demonstrated for regions of land and near-land coastal regions across Europe.

Since its introduction in the early 1980??s, the Global Positioning System (GPS) has become an important worldwide resource. Although the primary use of GPS is for position location, the inherent timing accuracy built into the system has allowed it become an important synchronisation resource for other systems. In most cases the GPS end user only requires a position estimate without awareness of the timing and synchronisation aspects of the system. A low accuracy position (at the several-metre level) with a low update rate of about 1Hz is often acceptable. However, obtaining more accurate position estimates (at the sub-metre level) at higher update rates requires the use of differential correction signals (DGPS) and greater processing power in the receiver. Furthermore, some extra challenges arise when simultaneously gathering information from a group of independently moving remote GPS receivers (rovers) at increased sampling rates (10Hz). This creates the need for a high bandwidth telemetry system and techniques to synchronise the position measurements for tracking each rover. This thesis investigates and develops an overall solution to these problems using GPS for both position location and synchronisation. A system is designed to generate relative position information from 30 or more rovers in real-time. The important contributions of this research are as follows: a) A GPS synchronised telemetry system is developed to transport GPS data from each rover. Proof of concept experiments show why a conventional RF Local Area Network (LAN) is not suitable for this application. The new telemetry system is developed using Field Programmable Gate Array (FPGA) devices to embed both the synchronising logic and the central processor. b) A new system architecture is developed to reduce the processing load of the GPS receiver. Furthermore, the need to transfer the DGPS correction data to the rover is eliminated. Instead, the receiver raw data is processed in a centralised Kalman filter to produce multiple position estimates in real-time. c) Steps are taken to optimise the telemetry data stream by using only the bare essential data from each rover. A custom protocol is developed to deliver the GPS receiver raw data to the central point with minimal latency. The central software is designed to extract and manage common elements such as satellite ephemeris data from the central reference receiver only. d) Methods are developed to make the overall system more robust by identifying and understanding the points of failure, providing fallback options to allow recovery with minimal impact. Based on the above a system is designed and integrated using a mixture of custom hardware, custom software and off-the-shelf hardware. Overall tests show that efforts to minimise latency, minimise power requirements and improve reliability have delivered good results.

The Global Positioning System (GPS) of navigation satellites was first developed for global navigation and position determination purposes. Signals from satellites are delayed by the Earths neutral atmosphere on propagating to ground-based receivers, termed the tropospheric delay. Although an unwanted term for precise positioning, the tropospheric delay may be converted to atmospheric water vapour, which is a vital parameter for weather forecasting.This research investigates the optimum GPS processing strategy to estimate atmospheric water vapour derived from ground-based GPS receivers particularly in the Australian region. For this purpose, GPS data observations from GPS permanent stations across Australia, mainly from the Australian Regional GPS Network, will be processed using scientific GPS software in post-processed mode and near real-time mode.This research shows that by applying high accuracy GPS data processing, the tropospheric delay could be estimated precisely. The quality of GPS data processing is indicated by the station coordinates repeatability since the coordinates can gauge at least a coarse assessment of the ability of the processing method to estimate the tropospheric delay.The precipitable water can be estimated from the wet component after separating the tropospheric delay into dry and wet components. High accuracy GPS data processing is dependent on the best choice of processing strategies, and the correct application of error-correction models and a priori constraints. This research finds that the GPS- PW estimation agrees with Radiosonde-PW estimation with an average of standard deviation at 2.5mm level for post-processed strategy and 2.8mm for near real-time strategy. The standard deviation of tropospheric parameter estimates is 1.1mm for post-processed strategy and 1.5mm for near real-time strategy.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California
For the final evaluation of a GPS attitude determination algorithm, it was determined its true performance in terms of accuracy, reliability and dynamic response. To accomplish that, a flight test campaign was carried out to validate the attitude determination algorithm. In this phase, the measured aircraft attitude was compared to a reference attitude, to allow the determination of the errors. The system was built using non-dedicated airborne GPS receivers, and a complete Flight Tests Instrumentation (FTI) System. The flight test campaign was carried out at the Brazilian’s Flight Test Group T-25C 1956 Basic Trainer aircraft. The performance and accuracy of the system is demonstrated under static and dynamics tests profiles, which are fully compliant with the Federal Aviation Administration (FAA) Advisory Circular (AC) 25-7A. Dynamic response of the system is evaluated.

This research demonstrates the potential of novel technology for space-based remote sensing of the topside ionosphere-plasmasphere, supported by ionospheric imaging, which can augment and enhance our current understanding of the Earth’s plasmasphere. The research was conducted in two phases. The first was the development of a technology demonstrator ‘TOPCAT’ that installed a dual-frequency GPS receiver dedicated for topside ionosphere-plasmasphere imaging into a Low Earth Orbit (LEO). The novelties of TOPCAT were that it was designed from commercial-off-the-shelf (COTS) components and was installed on-board the CubeSat ‘UKube-1’, greatly reducing development and launch costs of the instrument. The successful launch of TOPCAT for space-borne remote sensing of the topside ionosphere and plasmasphere could provide the necessary proof of concept for the installation of a constellation of CubeSats – a possible next phase that may be implemented in the future. Thus, in its first stage, the thesis discusses the development of TOPCAT, together with design challenges encountered from constraints imposed by CubeSat technology. The discussion also includes the series of qualification tests performed to successfully qualify TOPCAT as a space-worthy payload design that can remotely image regions beyond the ionosphere. The second phase of research was the validation of the Multi-Instrument Data Analysis System (MIDAS) for the topside ionosphere and plasmasphere. A tomography algorithm originally developed for the ionosphere, MIDAS uses total electron content (TEC) measurements from differential phase of GPS signals, and inverts them to derive the electron density of the region. The thesis investigates the extension of MIDAS to image regions beyond the ionosphere by validating the algorithm for the topside ionosphere and plasmasphere. The process was carried out by first reconstructing a simulation by Gallagher et al. [1988] to verify the quality of the images. This was followed by the use of real GPS phase data from the COSMIC constellation to reconstruct the topside ionosphere-plasmasphere, and the qualitative comparison of the images with previous independent observations obtained through COSMIC and Jason-1 missions. Results showed that MIDAS can successfully reconstruct the undisturbed (quiet) topside ionosphere-plasmasphere using COSMIC data. However, imaging the storm-time topside ionosphere-plasmasphere requires better data coverage (i.e. more receivers) as the resolution offered by COSMIC was not sufficient to reconstruct fast-evolving structures – thereby emphasising the need for more data sources providing high resolution global coverage, such as a constellation of CubeSats with LEO-based GPS receivers.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California
The embedded system related hardware technology has experienced rapid development, and it provided the software technology with a huge space for growth. Therefore using software approaches to perform GPS receiver functions in a powerful and generic hardware platform is becoming more feasible. In this paper, the software GPS receiver technology and the design basics of the software receiver are discussed. Further in the Matlab simulation environment, the implementation of a software receiver for replacing the processing functions of ASIC in traditional GPS receivers, i.e. RF front end and multi-channel correlator, is presented. Some simulation results and implementation details are included.

The Global Positioning System (GPS) of navigation satellites was first developed for global navigation and position determination purposes. Signals from satellites are delayed by the Earths neutral atmosphere on propagating to ground-based receivers, termed the tropospheric delay. Although an unwanted term for precise positioning, the tropospheric delay may be converted to atmospheric water vapour, which is a vital parameter for weather forecasting.This research investigates the optimum GPS processing strategy to estimate atmospheric water vapour derived from ground-based GPS receivers particularly in the Australian region. For this purpose, GPS data observations from GPS permanent stations across Australia, mainly from the Australian Regional GPS Network, will be processed using scientific GPS software in post-processed mode and near real-time mode.This research shows that by applying high accuracy GPS data processing, the tropospheric delay could be estimated precisely. The quality of GPS data processing is indicated by the station coordinates repeatability since the coordinates can gauge at least a coarse assessment of the ability of the processing method to estimate the tropospheric delay.The precipitable water can be estimated from the wet component after separating the tropospheric delay into dry and wet components. High accuracy GPS data processing is dependent on the best choice of processing strategies, and the correct application of error-correction models and a priori constraints. This research finds that the GPS- PW estimation agrees with Radiosonde-PW estimation with an average of standard deviation at 2.5mm level for post-processed strategy and 2.8mm for near real-time strategy. The standard deviation of tropospheric parameter estimates is 1.1mm for post-processed strategy and 1.5mm for near real-time strategy.

Thesis submitted in partial fulfilment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2015
Space-borne GPS receivers designed for nano-satellites are faced with various challenges. This research is undertaken to address the problems of inefficiency and high-costs associated with space-borne GPS receivers. The problem of inefficiency relates to poor performances of the GPS receiver in terms of the algorithmic models, execution speed, memory usage and errors proness. The problem of high-costs relates to the spacegrade hardware cost, implementation complexity, development time, as well as the manufacturing, production and the testing processes involved. The research objectives are to i) establish an efficient high-dynamics software-defined GPS receiver, ii) demonstrate a firmware approach and then iii) postulate a low-cost hardware implementation roadmap. The research methodology employed to address the problems and to attain the objectives is based-on using Matlab computing platform to i) implement a software-defined GPS receiver using free open-source GPS receiver algorithms, ii) further develop the software GPS receiver and lastly iii) convert the improved GPS receiver algorithms to firmware. The GPS receiver was successfully implemented in Matlab floating-point algorithms with a ±100kHz Doppler search bins and was used to post-process a pre-captured real GPS L1 C/A signal dataset. The pre-captured GPS signal was acquired, tracked, decoded and post-processed to extract the navigation message; use to compute the GPS receiver position, UTC date and time. Attempt to convert the entire Matlab floating-point GPS receiver algorithms to equivalent VHDL implementations failed; however, three of the Matlab floating-point algorithms (check_t.m, deg2dms.m and findUtmZone.m), were successfully converted to equivalent fixed-point formats in Matlab, Simulink and finally VHDL. These three algorithms, now created and optimised to fixed-point formats (efficient and enable implementation unto a low-cost microcontroller), set the basis for the firmware implementation. They were simulated and verified in Matlab, Simulink and VHDL using the Matlab HDL Coder workflow. Altera Quartus II software was then used to compile (synthesise, place & route and generate programming files) the three converted generic VHDL algorithms to embedded firmware, suitable for a FPGA programming. The Matlab HDL Coder workflow used in this research is feasible and can be used to accurately design and implement an improved GPS receiver and furthermore achieve it in three equivalent algorithms. This conclusion was drawn and the proposed recommendations are to address the conversion issues in the other Matlab floating-point GPS receiver algorithms that failed in the conversion process and to further develop and implement the GPS receiver as a fully functional unit, based-on the Xilinx space-grade, radiation hardened and low-cost Virtex 5QV FPGA.

Vertical reference for hydrographic survey can be provided in two ways: through the use of an expensive and very accurate GPS-aided INS system, or through the classical method of compensating for heave motion measured on board the vessel and tide data taken from a nearby tide gauge. Whilst the GPS-aided INS approach offers significant advantages in terms of accuracy their high cost has prohibited their widespread use within the hydrographic survey industry and the classical method is still prevalent. Heave motion of a survey vessel has traditionally been measured using inertial technologies, which can be expensive and have problems with usability and instability, resulting in higher survey costs and a significant hydrographer input burden. Heave can also be measured through the use GPS receivers by the differencing of measured carrier phase pseudo-range from adjacent epochs and the recent introduction by U-Blox of the Antaris AEK-4T, an off the shelf low cost GPS receiver capable of measuring and recording the carrier phase pseudo-range observable, has allowed the exploration of a novel method of measuring and compensating for vessel heave using off the shelf low cost GPS receivers. The work presented in this thesis details a method of compensating for vessel heave motion in bathymetry data that has been developed specifically for use with the U-Blox Antaris receiver. The technique is based on the production of highly accurate velocity estimates using the carrier phase observable. Carrier phase measurements are differenced across adjacent epochs to give relative delta range estimates between receiver and satellite along the direct line of sight, which are then processed to calculate an accurate estimate of receiver delta position across the epoch, a measurement analogous to receiver velocity. This technique has been termed Temporal Double Differencing (TDD). Integrated vertical velocity estimates produce the relative vertical displacement of the vessel over time. Because of bias errors in the velocity estimates from TDD, this vertical displacement is subject to drift. The drift is removed by passing the data through a high-pass filter designed to stop the drift frequencies yet pass the required frequencies of vertical vessel motion. An obvious advantage of this technique over conventional technologies is cost. Instruments currently on the market are centred on inertial sensors and generally have prices ranging from £12,000 to £25,000. Low cost GPS receivers are priced at around £200 and so this technique can have sizeable cost implications for the hydrographic survey industry. In addition the nature of the TDD algorithm results in a heave sensing technology that is not subject to turn induced heave which can affect inertial based sensors, and also imposes no requirement on the user to account for parameters such as vessel heave characteristics and current heave state. A further advantage over interferometric GPS heave compensation techniques is that the TDD algorithm is stand-alone and requires no reference receiver. Two trials have been undertaken to test the ability of the low cost U-Blox receiver to record accurate phase pseudo-range observables and subsequently produce a heave estimate: a Spirent GPS hardware simulator trial, and a sea trial. The simulator trial has been the first to quantify the errors associated with the measurement of carrier phase pseudo-range observables using low cost commercially available receivers. The trial used three separate receivers: a Novatel OEM4, a Leica 530 and a low cost U-Blox Antaris. Three scenarios were programmed into the simulator to rigorously test the effects of receiver quality and receiver dynamics on the resulting velocity estimates using the TDD algorithm. The sea trial involved fitting various sensors to the vessel including a Honeywell HG1700 IMU, an Applanix POS-RS GPS-aided INS system and the same three GPS receivers as used in the simulator trial. The POS-RS system and the inertial based heave sensor were used to provide a reference against which the novel low cost heave output could be compared. The comprehensive nature of the sea trial makes it the first work to compare the results from the TDD heave algorithm using varying grades of receiver, and against truth data from both an inertial based heave system and a GPS-aided INS. The results of the simulator trial have shown that under static conditions the TDD velocity estimation using the U-Blox Antaris is of comparable quality to that produced using both the Novatel OEM4 and the Leica 530. Under dynamic conditions the performance of the U-Blox Antaris is greatly degraded when undergoing large accelerations, an artefact of the inferior componentry used in the signal tracking loops. The sea trial has demonstrated the ability of the TDD heave algorithm developed for use with commercially available low cost GPS receivers to measure vessel heave to a similar standard as inertial based technologies at a fraction of the cost and with greatly reduced instability and usability issues that are traditionally associated with inertial based heave sensors.

Remote sensing has been demonstrated an important tool in agricultural and natural resource management and research applications, however there are limitations that exist with traditional platforms (i.e., hand held sensors, linear moves, vehicle mounted, airplanes, remotely piloted vehicles (RPVs), unmanned aerial vehicles (UAVs) and satellites). Rapid technological advances in electronics, computers, software applications, and the aerospace industry have dramatically reduced the cost and increased the availability of remote sensing technologies.Remote sensing imagery vary in spectral, spatial, and temporal resolutions and are available from numerous providers. Appendix A presented results of a test project that acquired high-resolution aerial photography with a RPV to map the boundary of a 0.42 km2 fire area. The project mapped the boundaries of the fire area from a mosaic of the aerial images collected and compared this with ground-based measurements. The project achieved a 92.4% correlation between the aerial assessment and the ground truth data.Appendix B used multi-objective analysis to quantitatively assess the tradeoffs between different sensor platform attributes to identify the best overall technology. Experts were surveyed to identify the best overall technology at three different pixel sizes.Appendix C evaluated the positional accuracy of a relatively low cost UAV designed for high resolution remote sensing of small areas in order to determine the positional accuracy of sensor readings. The study evaluated the accuracy and uncertainty of a UAV flight route with respect to the programmed waypoints and of the UAV's GPS position, respectively. In addition, the potential displacement of sensor data was evaluated based on (1) GPS measurements on board the aircraft and (2) the autopilot's circuit board with 3-axis gyros and accelerometers (i.e., roll, pitch, and yaw). The accuracies were estimated based on a 95% confidence interval or similar methods. The accuracy achieved in the second and third manuscripts demonstrates that reasonably priced, high resolution remote sensing via RPVs and UAVs is practical for agriculture and natural resource professionals.

The rapid evolution of current and upcoming high speed and complex communications networks often necessitates flawless time synchronization among the network nodes in order to guarantee performance. GPS based synchronizers have long been used for synchronizing telecommunications equipment, currently providing an accuracy of up to 10ns. Such high accuracy demands excellent operation from GPS timing receivers. Interference is an important threat to GPS performance. Any degradation in performance, due to the introduction of interference, can cause these receivers to provide a low quality timing solution, or to lose lock with incoming GPS signals altogether. This consideration motivates the study of the performance of GPS timing receivers in the presence of harmful interference. This work is devoted to the theoretical and practical investigations of the effects of RF interference on GPS-based synchronizers and their impacts on communications networks. Contributions made during this work include: a) Identification of the processes and the parameters involved in producing a timing solution which are vulnerable to interference; b) experimentbased confirmation of a hypothesis about the effects of interference on GPS timing receivers; c) identification of the effects of degraded synchronization on the performance of communications networks, especially CDMA and GSM cellular networks, which rely upon GPS based synchronizers; and d) proposal of a method to predict and avoid communications network performance degradation.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada
The four-quadrant frequency discriminator (FQFD) plays an important role in GPS receivers for carrier synchronization. This paper presents a detailed study of the operating principle of the FQFD, and the acquisition performance degradation due to the gain fluctuation of the FQFD is discussed. A modified FQFD called the enveloped-four-quadrant frequency discriminator (Enveloped-FQFD) is proposed, which introduces an envelope calculator on the basis of the FQFD. Performance comparison of the FQFD and the Enveloped-FQFD is given through theoretical analysis and computer simulation. Simulation results show that by employing the Enveloped-FQFD, a quicker pull-in process and a wider threshold than the FQFD can be achieved, while the additional hardware costs are trivial.

When a radio signal traverses the atmosphere it will be delayed by not only thedistance between transmitter and receiver, but also the atmosphere. Given knowl-edge of the characteristics of the sent signal the effect of the atmosphere can beobtained from the received signal. This concept is called radio occultation. Radiooccultation can provide high accuracy profiles of temperature, pressure and watervapour troughout the atmosphere.This report aims to present the work and results from a thesis performed atRUAG Space in Göteborg. The purpose of the thesis was to implement a simulatorwhich with high accuracy could generate a signal as it would have been receivedhad it propagated through the atmosphere.We will show that the generated signal passes the requirements that have beenset.
När en radiovåg passerar genom atmosfären kommer den att fördröjas, inte bara avavståndet mellan sändare och mottagare utan också av atmosfären. Givet kunskapom karaktäristiken hos den sända signalen kan atmosfärens effekt erhållas från denmottagna signalen. Detta koncept kallas för radio-ockultation. Radio-ockultationkan med hög noggrannhet ge profiler för temperatur, tryck och vattenånga genomatmosfären.Denna rapport ämnar presentera det jobb och de resultat som uppnåtts genomett examensarbete genomfört på RUAG Space i Göteborg. Examensarbetets syftevar att implementera en simulator som med hög noggrannhet kan generera ensignal så som den hade sett ut då den propagerat genom atmosfären.Vi kommer att visa att den genererade signalen uppnår de krav som ställts.

Total electron content (TEC) data measured from ground-based GPS receivers is compared to HF backscatter from ionospheric irregularities obtained by Super Dual Auroral Radar Network (SuperDARN) radars.  We present the first observations of a recurrent region of anomalous enhanced TEC at mid-latitudes over North America and attempt to characterize its frequency of occurrence.  Next, we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization (TOI) from mid-latitude plumes of storm enhanced density (SED) during a geomagnetic storm on 26 September 2011.  A channel of high density F region plasma was transported from the dayside ionosphere and into the polar cap by enhanced convection electric fields extending to mid-latitudes.  After the solar wind IMF conditions quieted and the dayside convection electric fields retreated to higher latitudes, an SED was observed extending to, but not entering, the dayside cusp region.  The source mechanism (enhanced electric fields) previously drawing the plasma from mid-latitudes and into the polar cap was no longer active, resulting in a fossil feature which persisted for several hours as it elongated in magnetic local time. Finally, we discuss ground surface effects on the HF backscatter observed by four SuperDARN radars. Monthly ground scatter occurrence rates are calculated for comparison with Arctic sea ice boundaries derived from satellite observations, showing reduced backscatter from regions covered by ice.
Master of Science

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California
NASA Marshall Space Flight Center’s Bantam Robust Guidance Navigation & Control Project is investigating off the shelf navigation sensors that may be inexpensively combined into Kalman filters specifically tuned for launch and orbital vehicles. For this purpose, Marshall has purchased several GPS receivers and is evaluating them for these applications. The paper will discuss the receiver selection criteria and the test equipment used for evaluation. An overview of the analysis will be presented including the evaluation used to determine their success or failure. It will conclude with goals of the program and a recommendation for all GPS users.

It has been shown in ionospheric research that modelling total electron content (TEC) during storm conditions is a big challenge. In this study, mathematical equations were developed to estimate TEC over Sutherland (32.38⁰S, 20.81⁰E), during storm conditions, using the Empirical Orthogonal Function (EOF) analysis, combined with regression analysis. TEC was derived from GPS observations and a geomagnetic storm was defined for Dst ≤ -50 nT. The inputs for the model were chosen based on the factors that influence TEC variation, such as diurnal, seasonal, solar and geomagnetic activity variation, and these were represented by hour of the day, day number of the year, F10.7 and A index respectively. The EOF model was developed using GPS TEC data from 1999 to 2013 and tested on different storms. For the model validation (interpolation), three storms were chosen in 2000 (solar maximum period) and three others in 2006 (solar minimum period), while for extrapolation six storms including three in 2014 and three in 2015 were chosen. Before building the model, TEC values for the selected 2000 and 2006 storms were removed from the dataset used to construct the model in order to make the model validation independent on data. A comparison of the observed and modelled TEC showed that the EOF model works well for storms with non-significant ionospheric TEC response and storms that occurred during periods of low solar activity. High correlation coefficients between the observed and modelled TEC were obtained showing that the model covers most of the information contained in the observed TEC. Furthermore, it has been shown that the EOF model developed for a specific station may be used to estimate TEC over other locations within a latitudinal and longitudinal coverage of 8.7⁰ and 10.6⁰ respectively. This is an important result as it reduces the data dimensionality problem for computational purposes. It may therefore not be necessary for regional storm-time TEC modelling to compute TEC data for all the closest GPS receiver stations since most of the needed information can be extracted from measurements at one location.

La navigation avec les systèmes de navigation par satellites (GNSS) est un réel défi dans des environnements contraints (semi-urbain, urbain, feuillage dense) à cause des multitrajets et du masquage du signal. Cette thèse propose un nombre de solutions architecturales et algorithmiques pour le récepteur GNSS afin de pallier ces problèmes. Ces solutions se veulent capables d’exploiter les atouts des poursuites scalaire et vectorielle tout en minimisant leurs défauts et de profiter de l’efficacité de certaines techniques de filtrage Bayésien non linéaire quant à aborder la non-Gaussianité et les non-linéarités associées au problème de navigation et de poursuite vectorielle. Une attention particulière est accordée à certains estimateurs Bayésiens qui essaient d’approximer la loi a posteriori sans linéariser le modèle de filtrage, notamment le filtre de Kalman et les méthodes de filtrage particulaire, mais aussi au filtre de Kalman étendu, dont l’estimation de la loi a posteriori est basée sur la linéarisation du modèle de filtrage. En premier lieu, une brève étude bibliographique présentant les fondamentaux des systèmes et des récepteurs GNSS ainsi que les algorithmes de navigation et de poursuite y associés est faite. Ensuite le fonctionnement d’un récepteur GNSS en milieux contraints est investigué. La thèse propose des modèles pour caractériser les erreurs de poursuite induites par les multitrajets dans une boucle de poursuite vectorielle. Ces modèles permettent d’exprimer les erreurs de poursuite en fonction du délai, de la phase et de la fréquence d’évanouissement des multitrajets. En exploitant le fait que la présence des multitrajets se reflète sur la sortie moins des corrélateurs, de nouveaux détecteurs de multitrajets sont formulés. Un détecteur de masquage du signal direct est aussi proposé. L’attention se tourne ensuite vers la conception d’architectures robustes de poursuite et positionnement pour un récepteur GNSS, incorporant les détecteurs proposés et d’autres indicateurs de qualité. Une boucle de poursuite vectorielle capable de détecter et d’exclure des mesures qui ne sont pas saines du calcul de la solution de navigation en utilisant les indicateurs de qualité est proposée. Deux autres boucles de poursuite, la boucle de poursuite adaptative scalaire-vectorielle et la boucle de poursuite conjointe scalaire-vectorielle, avec la même capacité de détection et exclusion de fautes, sont formulées. Elles bénéficient de la robustesse de la poursuite vectorielle en milieux contraints et de la précision de la poursuite scalaire en milieux dégagés. Des résultats expérimentaux montrent que les solutions conçues offrent une meilleure alternative de poursuite et positionnement par rapport aux boucles usuelles de poursuite scalaire et de poursuite vectorielle. Enfin, la thèse présente des approches de filtrage Bayésien non linéaire pour résoudre le problème de navigation et de poursuite vectorielle. Des stratégies de filtrage itératives et adaptatives appliquées au filtre de Kalman sont étudiées. Une nouvelle approche de filtrage particulaire dénommée filtre particulaire itératif et adaptatif (IAUPF) est formulée. Cette approche exploite les propriétés de convergence des méthodes itératives, l’immunité à la divergence dont jouissent les filtres adaptatifs, et la synergie entre les approches de filtrage particulaire et de Kalman. Des simulations de Monte Carlo avec une borne inférieure de Cramér-Rao a posteriori comme référence ainsi que des résultats expérimentaux montrent que l’approche IAUPF a une meilleure performance comparativement aux autres estimateurs Bayésiens présentés
Navigation with Global Navigation Satellite Systems (GNSS) is a real challenge in harsh environments (suburban, urban, heavy foliage) due to multipath and signal blockage. This thesis proposes a number of GNSS receiver architectural and algorithmic solutions to deal with this challenge. These solutions aim at exploiting the strengths of scalar and vector tracking while minimizing their weaknesses and at utilizing the efficiency of some nonlinear Bayesian filtering techniques in addressing the nonlinearities and non-Gaussianities associated with the navigation and vector tracking problem. Attention is given to some Bayesian estimators that approximate the posterior distribution without linearizing the filtering model, namely the unscented Kalman and particle filtering methods, as well as to the extended Kalman filter, whose posterior estimation is grounded on linearization of the filtering model.First, a brief literature review that presents the fundamentals of GNSS and GNSS receivers together with the applied navigation and tracking algorithms is provided. Then an investigation of the GNSS receiver operation in multipath environments is performed. The thesis proposes models for characterizing multipath induced tracking errors in a vector tracking loop. These models make it possible to express the tracking errors with respect to multipath delay, multipath phase and multipath fading frequency. By exploiting the fact that multipath presence is mirrored on the Early-minus-Late correlator output, novel multipath detectors are devised. A correlator-based non-line-of-sight detector is designed as well. Attention is then directed towards the design of robust tracking and positioning GNSS receiver architectures that incorporate the proposed detectors among other signal quality indicators. A vector tracking scheme capable of detecting and excluding unhealthy measurements from position-velocity-time calculation in the navigator using correlator-based signal quality indicators is suggested. Two other novel tracking schemes, the adaptive scalar-vector tracking loop and the conjoint scalar-vector tracking loop, with the same fault detection and exclusion capability, are formulated. They benefit from vector tracking robustness in harsh environments and scalar tracking positioning accuracy in open sky environments. Experimental results show that the proposed solutions have better tracking and positioning performance than the usual scalar and vector tracking loops. Finally, the thesis presents a number of nonlinear Bayesian filtering approaches to solve the navigation and vector tracking problem. Iterative and adaptive strategies as applied to the unscented Kalman filter are studied. A novel unscented particle filter approach, the iterated adaptive unscented particle filter (IAUPF), is proposed. This approach exploits the convergence properties of iterative methods, the divergence suppression benefits of adaptive filters and the synergy of unscented Kalman and particle filtering approaches. Monte-Carlo simulations conducted with a posterior Cramér-Rao lower bound used as benchmarking reference as well as experimental results demonstrate that the IAUPF outperforms the other Bayesian estimators that are presented

International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada
There is an interest in using Global Positioning System (GPS) receivers to find: Time Space Position Information (TSPI), miss distances between a missile and target, and using the data real time as an independent tracking aid for range safety. Ashtech, Inc. has several standalone GPS receivers they believe can work at high g levels. This paper investigates how the Ashtech GPS receivers work under high g loading in one axis. The telemetry system used to collect data from the receivers and the reconstruction of the data will also be discussed. The test was done at SNORT (Supersonic Naval Ordnance Research Track) located at NAWS, China Lake, CA. The g level obtained was about +23 g’s with a deceleration of -15 g’s. The velocity reached was about Mach 2.0. A summary of the errors is included.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada
Since June of 1993, an experimental GPS receiver system has been orbiting the earth aboard a small, low-altitude, polar-orbiting satellite called RADCAL. The purpose of the experiment was to prove the concept of using GPS for satellite navigation. If successful, the system would also provide a backup to the satellite's primary navigation beacon. The goal: provide position and velocity data to an accuracy of three to five meters, and provide attitude data to within a degree. The configuration of the RADCAL GPS experiment precluded realtime feedback loops for navigation; the data was stored and downloaded after a designated collection period. On the ground, a lengthy process was used to yield the position and attitude data days after the collection event. The GPS receivers and ground equipment were configured in several modes; they ultimately yielded a position accuracy of five meters, and attitude of two degrees. This was the original goal, and the experiment was considered successful. However, one of the receivers failed in November 1993, and the other failed in January 1995. The GPS receivers were commercially available and not spaceflight proven; they were suspected of being vulnerable to single-event upsets and latchups. This turned out to be the cause of the failure of both receivers. The interface between the GPS receivers and RADCAL's other subsystems proved to be the area which could not tolerate corrupt data. The single-event latchups problems would ultimately lead to the failure of the receivers. These difficulties, as well as other lesser obstacles, provide a host of lessons learned for future satellite navigation systems.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 19, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. C. Mark Cowell. Includes bibliographical references.

Aquesta tesi gira al voltant del disseny de receptors per a sistemes globals de navegació per satèl·lit (Global Navigation Satellite Systems, GNSS). El terme GNSS fa referència a tots aquells sistemes de navegació basats en una constel·lació de satèl·lits que emeten senyals de navegació útils per a posicionament. El més popular és l'americà GPS, emprat globalment. Els esforços d'Europa per a tenir un sistema similar veuran el seu fruit en un futur proper, el sistema s'anomena Galileo. Altres sistemes globals i regionals existeixen dissenyats per al mateix objectiu: calcular la posició dels receptors. Inicialment la tesi presenta l'estat de l'art en GNSS, a nivell de l'estructura dels actuals senyals de navegació i pel que fa a l'arquitectura dels receptors.

El disseny d'un receptor per a GNSS consta d'un seguit de blocs funcionals. Començant per l'antena receptora fins al càlcul final de la posició del receptor, el disseny proporciona una gran motivació per a la recerca en diversos àmbits. Tot i que la cadena de Radiofreqüència del receptor també és comentada a la tesis, l'objectiu principal de la recerca realitzada recau en els algorismes de processament de senyal emprats un cop realitzada la digitalització del senyal rebut. En un receptor per a GNSS, aquests algorismes es poden dividir en dues classes: els de sincronisme i els de posicionament. Aquesta classificació correspon als dos grans processos que típicament realitza el receptor. Primer, s'estima la distancia relativa entre el receptor i el conjunt de satèl·lits visibles. Aquestes distancies es calculen estimant el retard patit pel senyal des de que és emès pel corresponent satèl·lit fins que és rebut pel receptor. De l'estimació i seguiment del retard se n'encarrega l'algorisme de sincronisme. Un cop calculades la distancies relatives als satèl·lits, multiplicant per la velocitat de la llum el retards estimats, l'algorisme de posicionament pot operar. El posicionament es realitza típicament pel procés de trilateralització: intersecció del conjunt d'esferes centrades als satèl·lits visibles i de radi les distancies estimades relatives al receptor GNSS. Així doncs, sincronització i posicionament es realitzen de forma seqüencial i ininterrompudament. La tesi fa contribucions a ambdues parts, com explicita el subtítol del document.

Per una banda, la tesi investiga l'ús del filtrat Bayesià en el seguiment dels paràmetres de sincronisme (retards, desviaments Doppler i phases de portadora) del senyal rebut. Una de les fonts de degradació de la precisió en receptors GNSS és la presència de repliques del senyal directe, degudes a rebots en obstacles propers. És per això que els algorismes proposats en aquesta part de la tesi tenen com a objectiu la mitigació de l'efecte multicamí. La dissertació realitza una introducció dels fonaments teòrics del filtrat Bayesià, incloent un recull dels algorismes més populars. En particular, el Filtrat de Partícules (Particle Filter, PF) s'estudia com una de les alternatives més interessants actualment per a enfrontar-se a sistemes no-lineals i/o no-Gaussians. Els PF són mètodes basats en el mètode de Monte Carlo que realitzen una caracterització discreta de la funció de probabilitat a posteriori del sistema. Al contrari d'altres mètodes basats en simulacions, els PF tenen resultats de convergència que els fan especialment atractius en casos on la solució òptima no es pot trobar. En aquest sentit es proposa un PF que incorpora un seguit de característiques que el fan assolir millors prestacions i robustesa que altres algorismes, amb un nombre de partícules reduït. Per una banda, es fa un seguiment dels estats lineals del sistema mitjançant un Filtre de Kalman (KF), procediment conegut com a Rao-Blackwellization. Aquest fet provoca que la variància de les partícules decreixi i que un menor nombre d'elles siguin necessàries per a assolir una certa precisió en l'estimació de la distribució a posteriori. D'altra banda, un dels punts crítics en el disseny de PF és el disseny d'una funció d'importància (emprada per a generar les partícules) similar a l'òptima, que resulta ésser el posterior. Aquesta funció òptima no està disponible en general. En aquesta tesi, es proposa una aproximació de la funció d'importància òptima basada en el mètode de Laplace. Paral·lelament es proposen algorismes com l'Extended Kalman Filter (EKF) i l'Unscented Kalman Filter (UKF), comparant-los amb el PF proposat mitjançant simulacions numèriques.

Per altra banda, la presentació d'un nou enfocament al problema del posicionament és una de les aportacions originals de la tesi. Si habitualment els receptors operen en dos passos (sincronització i posicionament), la proposta de la tesi rau en l'Estimació Directa de la Posició (Direct Position Estimation, DPE) a partir del senyal digital. Tenint en compte la novetat del mètode, es proporcionen motivacions qualitatives i quantitatives per a l'ús de DPE enfront al mètode convencional de posicionament. Se n'ha estudiat l'estimador de màxima versemblança (Maximum Likelihood, ML) i un algorisme per a la seva implementació pràctica basat en l'algorisme Accelerated Random Search (ARS). Els resultats de les simulacions numèriques mostren la robustesa de DPE a escenaris on el mètode convencional es veu degradat, com per exemple el cas d'escenaris rics en multicamí. Una de les reflexions fruit dels resultats és que l'ús conjunt dels senyals provinents dels satèl·lits visibles proporciona millores en l'estimació de la posició, doncs cada senyal està afectada per un canal de propagació independent. La tesi també presenta l'extensió de DPE dins el marc Bayesià: Bayesian DPE (BDPE). BDPE manté la filosofia de DPE, tot incloent-hi possibles fonts d'informació a priori referents al moviment del receptor. Es comenten algunes de les opcions com l'ús de sistemes de navegació inercials o la inclusió d'informació atmosfèrica. Tot i així, cal tenir en compte que la llista només està limitada per la imaginació i l'aplicació concreta on el marc BDPE s'implementi.

Finalment, la tesi els límits teòrics en la precisió dels receptors GNSS. Alguns d'aquests límits teòrics eren ja coneguts, d'altres veuen ara la llum. El límit de Cramér-Rao (Cramér-Rao Bound, CRB) ens prediu la mínima variància que es pot obtenir en estimar un paràmetre mitjançant un estimador no esbiaixat. La tesi recorda el CRB dels paràmetres de sincronisme, resultat ja conegut. Una de les aportacions és la derivació del CRB de l'estimador de la posició pel cas convencional i seguint la metodologia DPE. Aquests resultats proporcionen una comparativa asimptòtica dels dos procediments pel posicionament de receptors GNSS. D'aquesta manera, el CRB de sincronisme pel cas Bayesià (Posterior Cramér-Rao Bound, PCRB) es presenta, com a límit teòric dels filtres Bayesians proposats en la tesi.
This dissertation deals with the design of satellite-based navigation receivers. The term Global Navigation Satellite Systems (GNSS) refers to those navigation systems based on a constellation of satellites, which emit ranging signals useful for positioning. Although the american GPS is probably the most popular, the european contribution (Galileo) will be operative soon. Other global and regional systems exist, all with the same objective: aid user's positioning. Initially, the thesis provides the state-of-the-art in GNSS: navigation signals structure and receiver architecture. The design of a GNSS receiver consists of a number of functional blocks. From the antenna to the final position calculation, the design poses challenges in many research areas. Although the Radio Frequency chain of the receiver is commented in the thesis, the main objective of the dissertation is on the signal processing algorithms applied after signal digitation. These algorithms can be divided into two: synchronization and positioning. This classification corresponds to the two main processes typically performed by a GNSS receiver. First, the relative distance between the receiver and the set of visible satellites is estimated. These distances are calculated after estimating the delay suffered by the signal traveling from its emission at the corresponding satellite to its reception at the receiver's antenna. Estimation and tracking of these parameters is performed by the synchronization algorithm. After the relative distances to the satellites are estimated, the positioning algorithm starts its operation. Positioning is typically performed by a process referred to as trilateration: intersection of a set of spheres centered at the visible satellites and with radii the corresponding relative distances. Therefore, synchronization and positioning are processes performed sequentially and in parallel. The thesis contributes to both topics, as expressed by the subtitle of the dissertation.

On the one hand, the thesis delves into the use of Bayesian filtering for the tracking of synchronization parameters (time-delays, Doppler-shifts and carrier-phases) of the received signal. One of the main sources of error in high precision GNSS receivers is the presence of multipath replicas apart from the line-of-sight signal (LOSS). Wherefore the algorithms proposed in this part of the thesis aim at mitigating the multipath effect on synchronization estimates. The dissertation provides an introduction to the basics of Bayesian filtering, including a compendium of the most popular algorithms. Particularly, Particle Filters (PF) are studied as one of the promising alternatives to deal with nonlinear/nonGaussian systems. PF are a set of simulation-based algorithms, based on Monte-Carlo methods. PF provide a discrete characterization of the posterior distribution of the system. Conversely to other simulation-based methods, PF are supported by convergence results which make them attractive in cases where the optimal solution cannot be analytically found. In that vein, a PF that incorporates a set of features to enhance its performance and robustness with a reduced number of particles is proposed. First, the linear part of the system is optimally handled by a Kalman Filter (KF), procedure referred to as Rao-Blackwellization. The latter causes a reduction on the variance of the particles and, thus, a reduction on the number of required particles to attain a given accuracy when characterizing the posterior distribution. A second feature is the design of an importance density function (from which particles are generated) close to the optimal, not available in general. The selection of this function is typically a key issue in PF designs. The dissertation proposes an approximation of the optimal importance function using Laplace's method. In parallel, Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) algorithms are considered, comparing these algorithms with the proposed PF by computer simulations.

On the other hand, a novel point of view in the positioning problem constitutes one of the original contributions of the thesis. Whereas conventional receivers operate in a two-steps procedure (synchronization and positioning), the proposal of the thesis is a Direct Position Estimation (DPE) from the digitized signal. Considering the novelty of the approach, the dissertation provides both qualitative and quantitative motivations for the use of DPE instead of the conventional two-steps approach. DPE is studied following the Maximum Likelihood (ML) principle and an algorithm based on the Accelerated Random Search (ARS) is considered for a practical implementation of the derived estimator. Computer simulation results carried show the robustness of DPE in scenarios where the conventional approach fails, for instance in multipath-rich scenarios. One of the conclusions of the thesis is that joint processing of satellite's signals provides enhance positioning performances, due to the independent propagation channels between satellite links. The dissertation also presents the extension of DPE to the Bayesian framework: Bayesian DPE (BDPE). BDPE maintains DPE's philosophy, including the possibility of accounting for sources of side/prior information. Some examples are given, such as the use of Inertial Measurement Systems and atmospheric models. Nevertheless, we have to keep in mind that the list is only limited by imagination and the particular applications were BDPE is implemented. Finally, the dissertation studied the theoretical lower bounds of accuracy of GNSS receivers. Some of those limits were already known, others see the light as a result of the research reported in the dissertation. The Cramér-Rao Bound (CRB) is the theoretical lower bound of accuracy of any unbiased estimator of a parameter. The dissertation recalls the CRB of synchronization parameters, result already known. A novel contribution of
the thesis is the derivation of the CRB of the position estimator for either conventional and DPE approaches. These results provide an asymptotical comparison of both GNSS positioning approaches. Similarly, the CRB of synchronization parameters for the Bayesian case (Posterior Cramér-Rao Bound, PCRB) is given, used as a fundamental limit of the Bayesian filters proposed in the thesis.

GPS has become very popular in recent years. It is used in wide range of applications including aircraft navigation, search and rescue, space borne attitude and position determination and cellular network synchronization. Each application places demands on GPS for various levels of accuracy, integrity, system availability and continuity of service. Radio frequency interference (RFI) which results from many sources such as TV/FM harmonics, radar or mobile satellite systems, presents a challenge to the use of GPS. It can affect all the service performance indices mentioned above. To improve the accuracy of GPS positioning, a continuously operating reference station (CORS) network can be used. A CORS network provides all the enabled GPS users in an area with corrections to the fundamental measurements, producing more precise positioning. A threat to these networks is a threat to all high-accuracy GPS users. It is therefore necessary to monitor the quality of the received signal with the objective of promptly detecting the presence of RFI and providing a timely warning of the degradation of system accuracy, thereby boosting the integrity of GPS. This research was focused on four main tasks: a) Detection. The focus here is on a power spectral density fluctuation detection technique, in which statistical inference is used to detect narrowband continuous-wave (CW) interference in the GPS signal band after being captured by the RF front-end. An optimal detector algorithm is proposed. At this optimal point, for a fixed Detection Threshold (DT), probability of false alarm becomes minimal and for a fixed probability of false alarm, we can achieve the minimum value for the detection threshold. Experiments show that at this point we have the minimum computational load. This theoretical result is supported by real experiments. Finally this algorithm is employed to detect a real GPS interference signal generated by a TV transmitter in Sydney. b) Characterization. In the characterization section, using the GNSS signal structure and the baseband signal processing inside the GNSS receiver, a closed formula is derived for the received signal quality in terms of effective carrier to noise ratio ( ). This formula is tested and proved by calculating the C/No using the I and Q data from a software GPS receiver. For pulsed CW, a similar analysis is done to characterize the effect of parameters such as pulse repetition period (PRP) and also duty cycle on the received signal quality. Considering this characterization and the commonality between the GPS C/A code and Galileo signal as a basis to build up a common term for satellite availability, the probability of satellite availability in the presence of CW interference is defined and for the two currently available satellite navigation systems (GPS L1 signal and Galileo signal (GIOVE-A BOC(1, 1) in the E1/L1 band)) it is shown that they can be considered as alternatives to each other in the presence of different RFI frequencies as their availability in the presence of CW RFI is different in terms of RFI frequency. c) Mitigation. The last section of the research presents a new concept of ?Satellite Exclusion Zone?. In this technique, using our previously developed characterization techniques, and considering the fact that RFI has different effects on different satellite signals at different times depending on satellite Doppler frequency, the idea of excluding the most vulnerable satellite signal from positioning calculations is proposed. Using real data and real interference, the effectiveness of this technique is proven and its performance analyzed. d) Hardware implementation. The above detection technique is implemented using the UNSW FPGA receiver board called NAMURU.

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O Sistema de Posicionamento Global (GPS – Global Positioning System) permite o conhecimento da posição, via satélite, de localidades específicas como um ponto topográfico, um carro em movimento ou de uma pessoa caminhando. A precisão do posicionamento pode variar, já que ela está diretamente relacionada ao tipo de receptor utilizado e aos objetivos em questão. Os receptores de navegação, por apresentarem menos precisão, são normalmente utilizados na obtenção de dados aproximados, que não exigem a mesma acurácia dos receptores topográficos ou geodésicos. No entanto, diante da existência de diferentes elipsóides para diferentes regiões do globo terrestre, admitiu-se a hipótese de que a configuração de um elipsóide inadequado para nossas condições poderia provocar erros ainda maiores na determinação de um posicionamento. Neste contexto, foi desenvolvido o presente trabalho, tendo como principais objetivos avaliar, comparar e analisar o desempenho de seis receptores GPS de navegação idênticos com respeito ao cálculo de áreas, perímetros e afastamentos horizontais. Em função dos resultados obtidos, nas condições em que o trabalho foi conduzido, conclui-se que a utilização de receptor GPS de navegação sem conhecimento de suas limitações e configurações básicas, pode levar o usuário a considerar direções e distâncias incompatíveis com o trajeto pretendido ou demarcado. O usuário comum deve saber, no mínimo, que elipsóide está considerando. Quando comparados com o posicionamento real da área (receptor geodésico configurado para SAD 69), a utilização de receptor de navegação configurado para os elipsóides SAD 69, WGS 84 e Córrego Alegre apresentam deslocamento da área no sentido médio de 224º54’43”, 225º10’51” e 206º04’24”, respectivamente, com distância média de 67,49 m; 129,67 m e 90,57 m, respectivamente...
The Global Positioning System allows the knowledge of the position, through satellite, of specific places as a topographical point, a car in movement or of a person walking. The precision of the positioning may vary, because it is directly related to the type of used receiver and to the objectives in subject. The navigation receivers, for present less precision, are usually used in the obtaining of approximate data, that don't demand accuracy compared to the topographical or geodesic receivers. However, in function of the existence of different ellipsoids for different regions of the earth, the hypothesis admitted was that the configuration of an inadequate ellipsoid for our conditions could still provoke big mistakes in the determination of a positioning. In this context, the present work was developed, having as main objectives to evaluate, to compare and to analyze the performance of six identical navigation GPS receivers with regard to the calculation of areas, perimeters and horizontal removals. In function of the obtained results, in the conditions in that the work was developed, it is ended that the use of navigation GPS receivers without knowledge of its limitations and basic configurations, it can take the user to consider directions and incompatible distances with the intended itinerary or demarcated. The common user should know, at least, what ellipsoid is considering. When compared with the real positioning of the area (geodesic receiver configured for SAD 69), the use of navigation receiver configured for the ellipsoids SAD 69, WGS 84 and Córrego Alegre present displacement of the area on the average sense of 224º54'43, 225º10'51 and 206º04'24, respectively, with on the average distance of 67,49 m; 129,67 m and 90,57 m, respectively. The area and perimeters values obtained by navigation GPS receivers, when compared to the area and perimeter obtained by geodesic...(Complete abstract, click electronic access below)

Orientador: Lincoln Gering Cardoso
Banca: Zacarias Xavier de Barros
Banca: Vilmar Antonio Rodrigues
Resumo: O Sistema de Posicionamento Global (GPS - Global Positioning System) permite o conhecimento da posição, via satélite, de localidades específicas como um ponto topográfico, um carro em movimento ou de uma pessoa caminhando. A precisão do posicionamento pode variar, já que ela está diretamente relacionada ao tipo de receptor utilizado e aos objetivos em questão. Os receptores de navegação, por apresentarem menos precisão, são normalmente utilizados na obtenção de dados aproximados, que não exigem a mesma acurácia dos receptores topográficos ou geodésicos. No entanto, diante da existência de diferentes elipsóides para diferentes regiões do globo terrestre, admitiu-se a hipótese de que a configuração de um elipsóide inadequado para nossas condições poderia provocar erros ainda maiores na determinação de um posicionamento. Neste contexto, foi desenvolvido o presente trabalho, tendo como principais objetivos avaliar, comparar e analisar o desempenho de seis receptores GPS de navegação idênticos com respeito ao cálculo de áreas, perímetros e afastamentos horizontais. Em função dos resultados obtidos, nas condições em que o trabalho foi conduzido, conclui-se que a utilização de receptor GPS de navegação sem conhecimento de suas limitações e configurações básicas, pode levar o usuário a considerar direções e distâncias incompatíveis com o trajeto pretendido ou demarcado. O usuário comum deve saber, no mínimo, que elipsóide está considerando. Quando comparados com o posicionamento real da área (receptor geodésico configurado para SAD 69), a utilização de receptor de navegação configurado para os elipsóides SAD 69, WGS 84 e Córrego Alegre apresentam deslocamento da área no sentido médio de 224º54'43", 225º10'51" e 206º04'24", respectivamente, com distância média de 67,49 m; 129,67 m e 90,57 m, respectivamente...(Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The Global Positioning System allows the knowledge of the position, through satellite, of specific places as a topographical point, a car in movement or of a person walking. The precision of the positioning may vary, because it is directly related to the type of used receiver and to the objectives in subject. The navigation receivers, for present less precision, are usually used in the obtaining of approximate data, that don't demand accuracy compared to the topographical or geodesic receivers. However, in function of the existence of different ellipsoids for different regions of the earth, the hypothesis admitted was that the configuration of an inadequate ellipsoid for our conditions could still provoke big mistakes in the determination of a positioning. In this context, the present work was developed, having as main objectives to evaluate, to compare and to analyze the performance of six identical navigation GPS receivers with regard to the calculation of areas, perimeters and horizontal removals. In function of the obtained results, in the conditions in that the work was developed, it is ended that the use of navigation GPS receivers without knowledge of its limitations and basic configurations, it can take the user to consider directions and incompatible distances with the intended itinerary or demarcated. The common user should know, at least, what ellipsoid is considering. When compared with the real positioning of the area (geodesic receiver configured for SAD 69), the use of navigation receiver configured for the ellipsoids SAD 69, WGS 84 and Córrego Alegre present displacement of the area on the average sense of 224º54'43", 225º10'51" and 206º04'24", respectively, with on the average distance of 67,49 m; 129,67 m and 90,57 m, respectively. The area and perimeters values obtained by navigation GPS receivers, when compared to the area and perimeter obtained by geodesic...(Complete abstract, click electronic access below)
Mestre

Les systèmes de navigation par satellites GNSS ne cessent d’évoluer et ils sont déjà utilisés dans de nombreuses applications. Avec la venue des nouveaux systèmes Galileo et BeiDou ainsi que la modernisation des systèmes GPS et GLONASS, de nouveaux satellites ainsi que de nombreuses nouvelles fréquences et de nouveaux signaux feront leur apparition dans les prochaines années et qui vont encore ouvrir la porte à d’innombrables nouvelles applications. L’évolution rapide de la téléphonie mobile nécessite une meilleure exploitation des systèmes de navigation et de positionnement dans les environnements urbains.Jusqu'à maintenant, les signaux de navigation GPS ne peuvent pas être bien captés dans les environnements urbains. Les niveaux des signaux y sont très faibles et il est presque impossible d’acquérir et de poursuivre les signaux de façon autonome à cause de l'importance des obstacles. De plus, le positionnement à l’intérieur et dans les environnements urbains sont aussi soumis aux problèmes de multi-trajets, de masquage, d’interférences et de brouillages. Dans ces conditions, il faut pouvoir traiter des signaux très dégradés ou très courts qui ne permettent pas au récepteur d’effectuer le processus de poursuite. Ainsi, cela nous conduit à la nécessité de repenser l'architecture du récepteur GNSS pour les applications modernes.Ce projet de thèse consiste à développer de nouvelles méthodes et architectures de récepteur GNSS de haute sensibilité et robuste aux dégradations des signaux tout en concevant de nouveaux algorithmes intégrés dans un récepteur GNSS hybride capable de fonctionner dans les environnements urbains profonds ou « intérieurs ».La méthodologie prévoit l’utilisation de la nouvelle approche de « détection collective (CD) » ou « acquisition collaborative ». L'approche collaborative qui traite tous les signaux multi-satellites ouvre une solution intéressante. De nombreuses techniques existent dans la littérature pour résoudre les problèmes de positionnement dans les environnements urbains, mais nous proposons la nouvelle approche de détection collective en raison de sa performance en tant que méthode de positionnement direct et méthode d'acquisition de haute sensibilité, par l'application de la détection vectorielle de tous les satellites visibles. En effet, la bonne combinaison des valeurs de corrélation de plusieurs satellites peut réduire le niveau de C/N0 requis des signaux satellites par les algorithmes standards de traitement (acquisition et poursuite) qui ne peuvent pas être acquis individuellement mais permettent de contribuer de manière constructive à une solution collective de positionnement pour chaque utilisateur. L’objectif est de détecter collaborativement les satellites. La combinaison de différents signaux GNSS peut considérablement augmenter la sensibilité d'acquisition du récepteur. Malgré les avantages de cette approche, elle présente également des inconvénients tels que la charge de calcul élevée en raison du grand nombre de points candidats dans le domaine position/biais d’horloge. Ainsi, le travail proposé dans cette thèse consiste à réduire la complexité du CD en optimisant la recherche de points candidats dans le domaine position/biais d’horloge. Enfin, l'objectif est d'appliquer l'approche de détection collective au positionnement GNSS coopératif pour la navigation moderne dans des environnements difficiles. Pour cela, des algorithmes d'exploitation optimale des ressources du récepteur en sélectionnant les meilleurs satellites ou la station de référence seront développés selon certains critères tels que le niveau du rapport signal sur bruit (C/N_0), l’angle d’élévation des satellites ainsi que la configuration géométrique des satellites visibles. L’objectif final est de proposer une nouvelle architecture de récepteur cognitif de haute sensibilité permettant de recevoir de façon optimale les nouveaux signaux GNSS
GNSS satellite navigation systems are constantly evolving and have been already used in many applications. With the advent of the new systems Galileo and BeiDou as well as the modernization of GPS and GLONASS systems, new satellites and numerous new frequencies and signals will appear in the coming years and will open door to countless new applications that are currently impossible. The rapid evolution of mobile telephony and personal navigation devices (PND) requires better use of navigation systems in non-ideal environments, especially the need for positioning in deep urban area. On the one hand, users are waiting for a high positioning accuracy, because of the proximity to various points of interest. On the other hand, urban environment brings specific difficulties in receiving GNSS signals.GNSS navigation signals cannot be properly captured in urban and "indoor" environments. Signal levels are very low and it is almost impossible to acquire and track signals autonomously because of the strong attenuation of signals due to obstacles. In addition, indoor and urban positioning are also subject to multipath problems, masking, interference and jamming. Under these conditions, we must be able to process highly degraded or very short signals that do not allow the receiver to go through the tracking process. Thus, this leads us to the need to rethink the architecture of GNSS receiver for modern applications.This thesis project consists of developing new GNSS methods and architectures of high sensitivity and robustness to signal degradations and designing new algorithms integrated into a hybrid GNSS receiver capable of operating in deep urban environments.The methodology involves the use of the new concept of “Collective Detection (CD)”, also called “collaborative acquisition”. The collaborative approach that treats multi-satellite signals all together opens an interesting solution. Many techniques exist in the literature to solve the problems of positioning in urban environments, but we propose the new Collective Detection approach because of its performance as both a Direct Positioning method, providing a coarse position/clock-bias solution directly from acquisition, and High-Sensitivity acquisition method, by application of vector detection of all satellites in view. Indeed, the correct combination of the correlation values of several satellites can reduce the required Carrier-to-Noise Ratio (C/N_0) level of the satellite signals which cannot be acquired individually by standard signal processing (acquisition and tracking) but make it possible to use them constructively to a positioning solution. The combination of different GNSS signals can considerably increase the acquisition sensitivity of the receiver. Despite the advantages of this approach, it also has drawbacks such as the high computational burden because of the large number of candidate points in the position/clock-bias domain. Thus, the work proposed in this thesis consists of reducing the complexity of the CD by optimizing the search for candidate points in position/clock-bias domain. Finally, the goal is to apply the CD approach to Cooperative GNSS Positioning for modern navigation in harsh environments. For that, algorithms for optimally exploiting receiver resources by selecting the best satellites or the reference station will be developed according to certain criteria such as the C/N_0 level, the elevation angle, and the geometric configuration of the visible satellites. The ultimate goal is to propose a design of a new smart receiver “High Sensitivity Cognitive GNSS Receiver (HS-CGR)” to optimally receive and process GNSS signals

The purpose of this application is to serve the end user of an Android Smart phone, with reliable, instantaneous and location based information on places of interest such as restaurants, gas stations, hotels, movie theaters, and the like by using the phones' built-in GPS. The basic information includes viewing the map and address of the place of interest and getting the directions to a particular place in addition to having some extra features. Contains computer source code.

The University of Canberra (UC) has been involved in GPS processing since the late 1980s. This processing commenced with the GOTEX 1988 campaign and progressed through a series of project specific regional campaigns to the current daily processing of a distributed set of continuously operating sites for the determination of precise GPS station positions for user applications. Most of these earlier campaigns covered only short periods of time, ranging from a few weeks to multiple occupations of a few days to a time over one to two years. With software developments, these multiple occupations were able to be combined to produce results from which crustal motion velocities could be extracted. This first became feasible with the processing of the Australian National Network (ANN), which yielded realistic tectonic velocities from two occupations (1992 and 1993) of sites 12 months apart. Subsequently, this was successfully extended by a further 12 months, with re-occupation of certain sites for a third time in 1994. Analysis of the results indicated that the accuracy of determining the earth signals improved as the time span from first to last observation was increased. The same was true also for the determination of the position of global references sites. However, by current standards the results achieved were poor. Consequently, the process was extended to combine the results of subsequent campaigns with the original ANN data set. From 1995 to 1999, campaigns were conducted across Australia, covering many State and tide gauge sites included in the original ANN solution. These provided additional multiple occupations to improve the determinations for both position and velocity. UC has maintained a data set of the global IGS sites, commencing with the IGS pilot campaign of 1992. Daily data sets for those global sites, which contained days common to the regional campaigns, were processed to produce our own independent global orbit and reference frame connection. The motivation for doing so was fourfold. �Firstly, to see if historic data could be reprocessed using current modern software and thus be able to be incorporated in this and other analysts research programs. �Secondly, to compare the results of the reprocessing of the original data set using modern software with the original ANN solution and then validate both the solutions. �Thirdly, to extend the timespan of observations processed to include more recent campaigns on as many original sites as possible. This to achieve a stronger solution upon which to base the determination of an Australian tectonic plate velocity model and provide quality assurance on the solution comparisons with re-observed sites. �Fourthly, to develop a set of transformation parameters between current coordinate systems and the GDA94 system so as to be able to incorporate new results into the previous system. The final selection of regional and global sessions, spanning from mid 1992 to late 2002, contained almost 1000 individual daily solutions. From this 10 year data span a well determined rigid plate tectonic motion model was produced for Australia. This site velocity model was needed to develop a transformation between the thesis solution in ITRF00 an the GDA94 solution in ITRF92. The significant advantage of the plate velocity model is that all Australian sites can now have computed a realistic velocity, rather than being given a value which has been interpolated between sites whose velocities had been determined over a one or two year span. This plate velocity model is compared with the current tectonic motion NNR-NUVEL-1A model and other recently published models. To perform the comparison between the thesis solution in ITRF00 and the GDA solution in ITRF92 a transformation was developed between the two reference systems. This set of transformation parameters, in conjunction with the plate velocity model developed, enables site solutions at any epoch in the current ITRF00 to be converted onto the GDA94, and vice versa, with a simple, non-varying seven parameter transformation. The comparisons between the solutions are analysed for both horizontal position and height consistency. There were 77 sites whose differences were compared. The horizontal consistency was within estimated precisions for 75 of the 77 sites. However, the vertical comparisons revealed many of the single epoch sites, especially in 1992, have inconsistent results between the two solutions. The heights from this thesis for some West Australian sites were compared with analysis done by DOLA and the height recoveries are very similar, indicating a weakness in the GDA94 solution for some of the single epoch sites. Some of these differences have been resolved but others are still under investigation. This thesis describes the repocessing of the original ANN data set, the addition of later data sets, the results obtained, and the validation comparisons of the old and new solutions. As well as the plate velocity model, transformation is provided which enables the user to compute between the GDA94 system, and any epoch result in ITRF00. Recommendations are made as to which sites need additional work. This includes sites which only need further analysis or investigation and those which require further observations to achieve a result which will have acceptable accuracy and reliability.

Ao longo dos anos, o posicionamento por satélites artificiais através da geotecnologia Global Navigation Satellite System (GNSS) e, principalmente, por meio do sistema americano Global Positioning System (GPS), ganhou importante espaço na área de Geomática. A qualidade das soluções está diretamente relacionada, entre outros fatores, ao tipo de receptor utilizado no trabalho: dispositivos mais caros (geodésicos), capazes de gerar as portadoras L1 e L2 ou L1, L2 e L5, produzem os melhores resultados; por outro lado, receptores topográficos que rastreiam apenas a frequência L1 são mais baratos, mas tornam o processamento dos dados dependente de um modelo ionosférico para reduzir parcialmente os efeitos dessa origem. Visando melhorar as soluções de posicionamento com dispositivos de baixo custo e evitar despesas adicionais do usuário que, eventualmente, necessitaria de utilizar aparelhos mais onerosos, este trabalho tem como objetivo principal propor a implementação de uma Rede Neural Artificial (RNA) para estimar as observações da portadora L2 do sistema GPS com base nas observáveis da L1, buscando-se também aprimorar o método de predição destes dados elaborado em outras pesquisas. Para tanto, selecionou-se um modelo de rede através da técnica de Validação Cruzada (CV), estimaram-se as observações a partir das rastreadas tanto em um receptor geodésico como em um smartphone Android, e comparou-se a acurácia das soluções que foram processadas com e sem as observáveis artificiais criadas pela RNA. A técnica CV demonstrou que uma Multilayer Perceptron (MLP) de quatro camadas escondidas e outra de uma camada intermediária são as configurações mais apropriadas para estimação das observáveis do código e da fase da portadora L2, respectivamente. O tempo de aprendizagem em todos os experimentos não ultrapassou poucos segundos e o processamento dos arquivos RINEX de dupla frequência, criados neste trabalho, revelou melhorias significativas das soluções de posicionamento na maioria dos testes, reduzindo os desvios planos e espaciais em torno de 40 a 50% em relação aos resultados atingidos com apenas os dados originais da portadora L1, sendo que em alguns experimentos foi possível realizar a combinação iono-free (L3) e em outros atender a normativa de georreferenciamento de imóveis rurais do Instituto Nacional de Colonização e Reforma Agrária (INCRA). Os resultados apontam, portanto, que a proposta metodológica da presente investigação atua de forma bastante promissora e como uma alternativa ao uso de receptores mais caros.
Over the years, positioning by artificial satellites through the Global Navigation Satellite System (GNSS) and, mainly, through the American Global Positioning System (GPS), has become increasingly important in Geomatics. The quality of the solutions is directly related, among other factors, to the receiver type used in the work: more expensive (geodetic) devices, capable of generating the carriers L1 and L2 or L1, L2 and L5, produce the best results; conversely, topographic receivers which only trace the L1 frequency are cheaper, but make data processing dependent on an ionospheric model to partially reduce the effects of that source. In order to improve the positioning solutions with low cost devices and avoid additional financial costs to the user who would ultimately need to use more expensive devices, the main objective of this work is to propose the implementation of an Artificial Neural Network (ANN) to estimate the GPS L2 observations from the L1 observables, aiming also to improve the prediction method elaborated in other research. This was done by using the Cross-Validation (CV) technique to select a network model. The observations were estimated from observables tracked on both a geodetic receiver and an Android smartphone, and we compared the accuracy of the solutions that were processed with and without the artificial observations created by the ANN. The CV technique demonstrated that a Multilayer Perceptron (MLP) of four hidden layers and another of an intermediate layer are the most appropriate configurations for the estimation of the L2 code and phase observables, respectively. The learning time in all the tests did not exceed a few seconds and the processing of the dual frequency RINEX files, which were created in this work, revealed significant improvements in the positioning solutions in all the experiments. The plane and spatial deviations were reduced by around 40% to 50% in relation to the results obtained with only the original L1 carrier data. In some tests it was possible to perform the iono-free combination (L3) and in others to meet the georeferencing regulations for rural properties of the National Institute of Colonization and Agrarian Reform (INCRA). The results indicate, therefore, that the methodological proposal of the present investigation acts in a very promising way and as an alternative to the use of more expensive receivers.

Navigation can be described as the art of finding the way from one location to another. Clearly navigation is something that we perform in our every day lives and the role of navigation can not be underestimated. There exist many technologies that implement various navigation systems to aid in this process. The most popular navigation system is the Global Positioning System (GPS) owned and operated by the United States of America Government. GPS is a space-based radio navigation system. Initially GPS was primarily intended for military use but the civilian community has found increasing use of GPS. The main reasons why GPS has become such a success is that users anywhere in the world can obtain accurate position, velocity and time measurements free of charge. GPS receivers have significantly come down in price since the inception of the system and today can be considered inexpensive – as little as 1000 SEK or 125 € for a 12 channel hand held unit. The civilian use of GPS is expected increase even further and new applications of GPS will emerge. GPS is targeted for a modernization process where new civilian signals will be added to provide more accurate and reliable measurements. The European Union is planning a new space-based navigation system, Galileo, which when operational will provide the civilian community with an alternative or complement to GPS. It is of great interest to develop flexible GPS receivers that can easily be adapted to new applications and various user scenarios. New receivers must also be developed for the modernized GPS and the upcoming Galileo system. Another area of navigation interest is the integration of GPS and inertial sensor measurements. Inertial sensors can be found in another type of navigation system, namely Inertial Navigation System (INS). Integration of GPS and INS provide a more reliable and accurate navigation system. The evolution of low cost Micro Micro Electro Mechanical Systems (MEMS) inertial sensors has dramatically decreased the cost of INS. Hence applications of integrated GPS/INS systems will find new markets that have not been considered before because of the high cost associated with inertial sensors. In this thesis Programmable Logic Devices (PLDs) are used in combination with GPS software receivers. This has enabled the rapid development of flexible GPS architectures ideal for adaptation to various user scenarios and applications. It is also show that this combination of PLDs and software can provide a prototyping environment for inclusion of new GPS or Galileo signals with great flexibility. Furthermore a platform for the integration of GPS/INS is proposed. The main idea is that data processing should be implemented in a single processor. This alleviates one obstacle commonly found in other GPS/INS integration implementations, which is the limited observability of measurements from both GPS and INS. With the new platform full observability of all measurements is obtained. The proposed platform also provides synchronization of GPS and INS data streams at the lowest possible level. Exact synchronization of measurements is essential to provide an accurate implementation of data fusion algorithms.
Godkänd; 2003; 20061022 (ysko)

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: The purpose of this study was to develop a Global Positioning System (GPS) receiver for use on a Low-Earth Orbit (LEO) satellite. The study includes an examination of some of the fundamental GPS theory and how the LEO environment affects the operation of a GPS receiver. The hardware and software that was selected for the implementation are discussed. The reasons for porting the software to a new hardware platform and methods employed in the port are given. Thereafter the process of adapting the receiver software for use in space is given. To verify the operation in space, the receiver was subjected to LEO simulations using a GPS signal simulator. These results are shown and discussed. The tests indicated that the adaptations were successful and that the receiver will function on a LEO satellite.
AFRIKAANSE OPSOMMING: Die doel van die tesis was om ’n Globale Posisionerings Stelsel (GPS) ontvanger to ontwikkel vir gebruik op ’n lae-wentelbaan satelliet. Die studie begin met fundamentele GPS teorie en hoe die funksionering van die ontvanger be¨ınvloed word deur die wentelbaan van ’n satelliet. Die hardeware en sagteware vir die implementasie word bespreek. Die rede en metodes om die sagteware aan te pas om te werk op nuwe hardeware word gegee. Daarna word die proses om die sagteware aan te pas vir ruimtegebruik gegee. Om the verifieer dat die ontvanger wel sal kan werk op ’n satelliet was dit getoets in ’n gesimuleerde ruimte-omgewing met ’n GPS seinsimulator. Hierdie resultate word gegee en bespreek. Die toetse het gewys dat die aanpassings suksesvol was en dat die ontvanger in die ruimte sal funksioneer.

A field campaign was conducted during September 2019 on Monte Avena, south-eastern Italian Alps, to assess the feasibility and quality of an innovative measurement technique for the study of thermal structures in the atmospheric boundary layer over mountains. Paragliders were equipped with non-conventional instruments for airborne measurements of meteorological variables, such as air temperature, relative humidity, atmospheric pressure, and wind intensity and direction. The work aims at testing to what extent the instrumented paraglider can represent a valid method for acquiring physical information on thermal structures. The paraglider presents a combination of properties that make it extremely useful for the detection of thermals, compared to other flying vehicles adopted for airborne measurements such as aeroplanes and gliders. A new method for identifying thermals, based on the engine-free property of the paraglider, is proposed and the results suggest its reliability. Measurements have been analysed by means of vertical profiles and horizontal and vertical maps of temperature, virtual potential temperature, water vapour mixing ratio and vertical wind speed. Agreement was found between in-flight measurements and data from soundings and local surface weather stations. Even though the adopted instruments have shown several issues in measuring the atmospheric variables, the new method of collecting atmospheric data by means of an instrumented paraglider has turned out to be promising, both for the identification and characterisation of thermal structures in the mountain boundary layer, and for the study of the basic state of the atmosphere.

Today, GNSS measurements play an important role in the surveying industry, and their use is ever increasing. Many different GNSS receivers and antenna manufacturers are on the market with new ones appearing. The purpose of this study is to investigate the level of measurement uncertainty of three different GNSS receivers: Leica GS15, Sokkia GCX2 and Satlab SL300. The method in this study is based mainly on the method proposed by HMK - Geodatakvalitet 2015 (Manual in measurement and map issues – Geographic data quality 2015 [author’s translation]) by Swedish Lantmäteriet for "Evaluation of measurement uncertainty in Network RTK [author’s translation]”. Some corrections and additions are made to this method but the basis of the method is retrieved from there. Formulas are used to calculate radial deviation and limit requirements for these. Even standard deviations and radial mean deviations as well as tolerances for these are calculated. The field measurements are made on two RIX 95-points. This is done repeatedly to get up to 20 measurements. The GNSS receivers are mounted on a tripod with a tribrach that is centered over the known points. The main finding from this study is that all investigated receivers, apart from four overriding values ​​for the Leica GS15, perform better than specified by their manufacturers. However, Sokkia GCX2 and Satlab SL300 are approved with uncertainties within the calculated tolerances. The Leica GS15 instrument is very close to meeting the demands but does not reach all the way. A committed error during the performed measurements with the Satlab SL300 makes its evaluation based on 19 instead of 20 measurements. Still, calculations are performed on the collected data that resulted in low measurement uncertainties well below the manufacturer's specified uncertainty. The study was conducted during five weeks in May and June 2017.