Performance Evaluation of Different GNSS Positioning Modes

This paper gives a comparison of different GPS positioning modes using RTKLIB which is free and open-source software. The modes tested in this work are Single point positioning (SPP), precise point positioning (PPP), Satellite-based augmentation system (SBAS), Differential GPS (DGPS), and Real-Time Kinematic (RTK). The data for tests were obtained from NetR9 receivers, these types of receivers are multi-frequencies and multi-constellation receivers that provide carrier and phase measurements. The SPP mode is the very simplest mode, it can be used for applications where accuracy is not less than 5m, and it can be improved to achieve 1m by using SBAS corrections but only in the coverage area of the system. The DGPS can also provide 1m accuracy using a second receiver as a base station which can increase the cost of the operation. For applications that need very high accuracy, RTK and PPP can be used to reach centimeter-level accuracy. RTK needs a base station in addition to the rover receiver used for the positioning; PPP uses precise orbital and clock solutions which are not available in real time for all users

Positioning in urban environments

This thesis will try to further increase the accuracy of a mixed GNSS and inertial solution for navigation in urban areas. The mix will represent a set of low cost sensors to mea-sure their performance. The objectives will be the implementation of a multi-constellation GNSS receiver, and the research and test of modelling techniques for GNSS measure-ments based on carrier-to-noise ratio. Any other technique that allows for an increase in the accuracy will also be used and tested. The laboratory work for this thesis will be done at l'Ecole Nationale de l'Aviation Civile as part of an exchange program. First of all the theoretical studies will be carried out, first of stand-alone GNSS and INS navigation and then on their integration. This integration will consist on the use of a Kalman Filter algorithm, and therefore additional theory on the implementation of this filter will be necessary. Then the current algorithm developed by ENAC is analysed, together with the hardware connection requested with the different equipment. A measurement campaign was done to collect new samples from ENAC at the outskirts of Toulouse to the city center. Data was then post process several times to obtain the most optimal configuration for the receiver in urban and suburban environments. The re-sults showed that the implementation of GLONASS together with the suggested weighting modelling based on carrier-to-noise level measurements allowed an increase of almost 50% in the accuracy of the position and the estimation of the yaw

Airborne Wireless Communication Modeling and Analysis with MATLAB

Over the past decade, there has been a dramatic increase in the use of unmanned aerial vehicles (UAV) for military, commercial, and private applications. Critical to maintaining control and a use for these systems is the development of wireless networking systems [1]. Computer simulation has increasingly become a key player in airborne networking developments though the accuracy and credibility of network simulations has become a topic of increasing scrutiny [2-5]. Much of the inaccuracies seen in simulation are due to inaccurate modeling of the physical layer of the communication system. This research develops a physical layer model that combines antenna modeling using computational electromagnetics and the two-ray propagation model to predict the received signal strength. The antenna is modeled with triangular patches and analyzed by extending the antenna modeling algorithm by Sergey Makarov, which employs Rao-Wilton-Glisson basis functions. The two-ray model consists of a line-of-sight ray and a reflected ray that is modeled as a lossless ground reflection. Comparison with a UAV data collection shows that the developed physical layer model improves over a simpler model that was only dependent on distance. The resulting two-ray model provides a more accurate networking model framework for future wireless network simulations

Aiding GPS with Additional Satellite Navigation Services

In modern warfare navigation services are very important. GPS is currently providing service for accurate navigation, except in some areas, especially urban areas, where GPS signals cannot always be tracked by users. In these cases some additional navigation support could be provided by other global navigation satellite systems. If GPS is combined with other navigation systems than the navigation gap will be minor. In this thesis, the effect of combining GPS with other satellite navigation systems, specifically GLONASS, Galileo and Compass, is evaluated in terms of availability and position dilution of precision (PDOP) values. First, satellite constellations are simulated in Satellite Tool Kit (STK) to generate ephemeris data. A street scenario is then established for simulating different elevation mask angles to represent urban and mountainous areas. The performance of the combined system is also evaluated as a function of the uncertainty in the time offset between systems. Combined GPS/GLONASS and GPS/Compass solutions showed little improvement for low elevation mask angles, however they provided some enhancement for higher elevation angles. Combined GPS/Galileo performance was improved for all elevation angles compared to only GPS, GPS/GLONASS, and GPS/Compass. The best results for availability and PDOP were obtained from combining all four systems. Although using satellites from other constellations enhances availability and decreases errors. It also brings dependency on other systems other than GPS. Adding two satellites from only the Galileo constellation to GPS is shown to be a configuration with a good compromise between dependency and performance

Development of a differential GPS tracking system for sounding rocket payloads

Thesis (M.S.) University of Alaska Fairbanks, 2001The purpose of this thesis was to develop a system that could track a sounding rocket payload with a commercial GPS receiver. A GPS receiver was chosen that still outputs raw data when the COCOM limits are exceeded. All the hardware to support the OEM GPS receiver in a reverse differential system was designed and built, including both a ground system and two flight systems to support both on-board storage and telemetry. A software program was developed to archive and compute positions from the raw data. The GPS system has been ground tested and flown on an Orion sounding rocket. The testing shows that the system works and the expected accuracy is 10-50 ft. depending on the distance between the ground station and the rocket, satellite geometry and other sources of error

Advanced tracking systems design and analysis

The results of an assessment of several types of high-accuracy tracking systems proposed to track the spacecraft in the National Aeronautics and Space Administration (NASA) Advanced Tracking and Data Relay Satellite System (ATDRSS) are summarized. Tracking systems based on the use of interferometry and ranging are investigated. For each system, the top-level system design and operations concept are provided. A comparative system assessment is presented in terms of orbit determination performance, ATDRSS impacts, life-cycle cost, and technological risk

Continued study of NAVSTAR/GPS for general aviation

A conceptual approach for examining the full potential of Global Positioning Systems (GPS) for the general aviation community is presented. Aspects of an experimental program to demonstrate these concepts are discussed. The report concludes with the observation that the true potential of GPS can only be exploited by utilization in concert with a data link. The capability afforded by the combination of position location and reporting stimulates the concept of GPS providing the auxiliary functions of collision avoidance, and approach and landing guidance. A series of general recommendations for future NASA and civil community efforts in order to continue to support GPS for general aviation are included

Simulation and analysis of differential global positioning system for civil helicopter operations

A Differential Global Positioning System (DGPS) computer simulation was developed, to provide a versatile tool for assessing DGPS referenced civil helicopter navigation. The civil helicopter community will probably be an early user of the GPS capability because of the unique mission requirements which include offshore exploration and low altitude transport into remote areas not currently served by ground based Navaids. The Monte Carlo simulation provided a sufficiently high fidelity dynamic motion and propagation environment to enable accurate comparisons of alternative differential GPS implementations and navigation filter tradeoffs. The analyst has provided the capability to adjust most aspects of the system, the helicopter flight profile, the receiver Kalman filter, and the signal propagation environment to assess differential GPS performance and parameter sensitivities. Preliminary analysis was conducted to evaluate alternative implementations of the differential navigation algorithm in both the position and measurement domain. Results are presented to show that significant performance gains are achieved when compared with conventional GPS but that differences due to DGPS implementation techniques were small. System performance was relatively insensitive to the update rates of the error correction information

Using the GPS to Collect Trajectory Data for Ejection Seat Design, Validation, and Testing

The dynamic characteristics of an aircraft ejection seat are a crucial concern when evaluating aircraft ejection systems and their ability to separate aircrew members safely from disabled aircraft. Every ejection seat model undergoes real-time dynamic tests to determine potential injury to aircrew members during ejection. Ejection seat tests are conducted at high-speed test tracks. The test track facilities provide the required telemetry and high-speed photography to monitor and validate the aircraft escape system performance. Ejection seat test and evaluation requires very accurate position and velocity determination during each test run to determine the relative positions between the aircraft, ejection seat, manikin, and the ground. Current test and evaluation systems rely on expensive video camera systems to determine the position and velocity profiles. This research presents the design and test results from a new GPS-based system capable of monitoring all major ejection-test components. Small, low-power, lightweight GPS receivers, capable of handling high accelerations, are mounted on the manikin and/or ejection seat to obtain the position and velocity during the ejection sequence. The research goal is to augment the camera system with a differential GPS-based measurement system capable of providing accuracy that meets or exceeds the current video systems accuracy

Automated Aerial Refueling Position Estimation Using a Scanning LiDAR

This research examines the application of using a scanning Light Detection and Ranging(LiDAR) to perform Automated Aerial Refueling(AAR). Specifically this thesis presents two algorithms to determine the relative position between the tanker and receiver aircraft. These two algorithms require a model of the tanker aircraft and the relative attitude between the aircraft. The first algorithm fits the measurements to the model of the aircraft using a modified Iterative Closest Point (ICP) algorithm. The second algorithm uses the model to predict LiDAR scans and compare them to actual measurements while perturbing the estimated location of the tanker. Each algorithm was tested with simulated LiDAR data before real data became available from test flights. The data collected from this test ight was used to determine the accuracy of the two algorithms with real LiDAR data. After correcting for modeling errors the accuracy of each algorithm is about a Mean Radial Spherical Error of 40cm