Implementation of a Vector-based Tracking Loop Receiver in a Pseudolite Navigation System

We propose a vector tracking loop (VTL) algorithm for an asynchronous pseudolite navigation system. It was implemented in a software receiver and experiments in an indoor navigation system were conducted. Test results show that the VTL successfully tracks signals against the near–far problem, one of the major limitations in pseudolite navigation systems, and could improve positioning availability by extending pseudolite navigation coverage

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

Mass-Market Receiver for Static Positioning: Tests and Statistical Analyses

Nowadays, there are several low cost GPS receivers able to provide both pseudorange and carrier phase measurements in the L1band, that allow to have good realtime performances in outdoor condition. The present paper describes a set of dedicated tests in order to evaluate the positioning accuracy in static conditions. The quality of the pseudorange and the carrier phase measurements let hope for interesting results. The use of such kind of receiver could be extended to a large number of professional applications, like engineering fields: survey, georeferencing, monitoring, cadastral mapping and cadastral road. In this work, the receivers performance is verified considering a single frequency solution trying to fix the phase ambiguity, when possible. Different solutions are defined: code, float and fix solutions. In order to solve the phase ambiguities different methods are considered. Each test performed is statistically analyzed, highlighting the effects of different factors on precision and accurac

Estimation and Mitigation of Unmodeled Errors for a Pseudolite Based Reference System

Current flight reference systems rely heavily on the Global Positioning System (GPS), causing susceptibility to GPS jamming. Additionally, an increasing number of tests involve jamming the GPS signal. A need exists to develop a system capable of GPS-level accuracy during these outages. One promising solution is a ground-based pseudolite system capable of delivering sub-centimeter level accuracy, yet operating at non-GPS frequencies. This thesis attempts to determine the unknown errors in the Locata system, one such pseudolite-based system, to achieve the accuracy required. The development of a measurement simulation tool along with a Kalman filter algorithm provides confirmation of filter performance as well as the ability to process real data measurements and evaluate simulated versus real data comparatively. The simulation tool creates various types of measurements with induced noise, tropospheric delays, pseudolite position errors, and tropospheric scale-factor errors. In turn, the Kalman filter resolves these errors, along with position, velocity, and acceleration for both simulated and real data measurements, enabling error analysis to pinpoint both expected and unexpected error sources

Review of Unbiased FIR Filters, Smoothers, and Predictors for Polynomial Signals

Extracting an estimate of a slowly varying signal corrupted by noise is a common task. Examples can be found in industrial, scientific and biomedical instrumentation. Depending on the nature of the application the signal estimate is allowed to be a delayed estimate of the original signal or, in the other extreme, no delay is tolerated. These cases are commonly referred to as filtering, prediction, and smoothing depending on the amount of advance or lag between the input data set and the output data set. In this review paper we provide a comprehensive set of design and analysis tools for designing unbiased FIR filters, predictors, and smoothers for slowly varying signals, i.e. signals that can be modeled by low order polynomials. Explicit expressions of parameters needed in practical implementations are given. Real life examples are provided including cases where the method is extended to signals that are piecewise slowly varying. A critical view on recursive implementations of the algorithms is provided

An Assessment of Indoor Geolocation Systems

Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance

Indoor Positioning with GNSS-Like Local Signal Transmitters

Not all the techniques proposed have, of course, been based on radio techniques, but they are the most important ones for two main reasons: their level of development and maturity on the one hand and their ability to "cross" or to "get around" obstacles such as walls, furniture or people on the other hand. Optical based techniques, like laser based distance measurements or vision based (camera) scene analysis systems present some real advantages in terms of measurement accuracy (a few millimetres for the former) or orientation determination (very useful for any guidance system, available for the latter). Unfortunately, the foreseen use of positioning devices being mainly dedicated to pedestrians in urban environments, optical obstacles are numerous. These latter techniques are then considered as potential hybridisation candidates. Many types of sensors have also been studied for positioning, such as infrared or ultrasound. Once again, although accuracy can reach centimetre values, the environmental constraints are not compatible with the ubiquitous systems being sought. Another category is, of course, inertial systems which could be a valuable alternative to radio systems: time and distance associated position drifts are not yet sufficiently mastered and the given positioning is relative , which means the need for "something else" in order to provide the user with an absolute location. The object of this section is to focus on radio based approaches

Modeling and Simulating GNSS Signal Structures and Receivers

In this thesis an end-to-end simulation was implemented encompassing the important effects from the user segments point of view. The modeling and implementation aimed to take all the relevant features into account that have a direct and significant impact on the performance of a GNSS receiver. In particular, emphasis was on the effects that are hard to formulate and treat theoretically, such as non-linearities, stochastic processes and the highly complex boundary conditions generated by the interaction of the signal with the environment. The three most important parts of the model development are the signal model, the signal propagation model and the receiver model. The signal model is an extension of the well-known signal modeling used to describe GPS signals. The present model was extended to include any sort of signal structure The most important part of the signal propagation model is essentially a ray-tracing algorithm together with the application of the Fresnel equations. This is a 3-D exact specular ray-tracing, which was derived and implemented during the work accompanying this thesis. Beside the signal model the receiver model constitutes a major part of this work. Essentially, it is a dynamic modeling of the tracking process (DLL and PLL). As the model is based on continuous calculus it was a challenge to incorporate the effects of the noise processes. However, this was solved by using the Îto calculus to extend the ordinary differential equations to stochastic differential equations. The implementation was verified by comparing the results to known theoretical expressions and an indirect experimental verification was performed in the sense that some of the theoretical formulas have been compared with experimental data.In dieser Artbeit wurde ein end-to-end Simulator entwickelt, der die wichtigsten Effekte aus der Sicht des Empfängernutzers berücksichtigt. Bei der Modellierung und der Implementierung wurde versucht die Faktoren zu berücksichtigen, die einen wesentlichen Einfluss auf die Performance eines GNSS Empfängers haben. Die drei wichtigsten Modellkomponenten sind das Signalmodell, das Signalausbreitungsmodell und das Empfängermodell. Das Signalmodell ist eine Verallgemeinerung des bekannten Signalmodells, das für die Modellierung von GPS C/A-code Signalen verwendet wird. Dieses Modell wurde für beliebige Signalstrukturen erweitert. Der Kern des Signalausbreitungsmodells ist ein Ray-tracing Algorithmus zusammen mit der Anwendung der Fresnel Gleichungen. Dabei handelt es sich um ein exaktes, dreidimensionales Ray-tracing Modell, das während der Arbeit entwickelt und implementiert wurde. Das Empfängermodell stellt ebenfalls einen wichtigen Teil der Arbeit dar. Im Wesentlichen werden die Regelkreise (DLL und PLL) als dynamischer Prozess modelliert. Das Modell basiert auf einem kontinuierlichen Ansatz, was die Einbindung von Rauschprozessen erschwerte. Durch die Interpretation der gewöhnlichen Differentialgleichungen als stochastiche Differentialgleichungen und Verwendung des Îto Kalküls konnten verrauschte Signale berücksichtigt werden. Die Implementierung wurde durch den Vergleich bekannter theoretischer Ergebnisse verifiziert. Da die meisten theoretischen Ausdrücke schon mit Experimenten verglichen worden sind, kann dies als indirekter Vergleich mit Experimenten gesehen werden

Initial Implementation and Testing of a Tightly-Coupled IMU/Pseudolite System

Currently, the 746th Test Squadrons (746th TS) Central Inertial and GPS Test Facility (CIGTF) operates one of the most accurate truth reference systems, called the CIGTF Reference System (CRS). CIGTF will be replacing the CRS with a new references system called UHARS (Ultra High Accuracy Reference System). UHARS will differ from CRS by adding the ability to use a non-GPS pseudolite system, as a new measurement source. This research effort describes the design of the extended Kalman filter which is developed in AFIT\u27s SPIDER filter framework which implements a tightly-coupled pseudolite/INS filter

Use of Navigation Beacons to Support Lunar Vehicle Operations

To support a wide variety of lunar missions in a condensed regime, solutions are needed outside of the use of Earth-based orbit determination. This research presents an alternate approach to in-situ navigation through the use of beacons, similar to that used on Earth as well as under technology development efforts. An overview of the current state of navigation aids included as well as discussion of the Lunar Node 1 payload being built at NASA/Marshall Space Flight Center. Expected navigation results of this beacon payload for planned operation from the lunar surface are provided. Applications of navigation beacons to multiple stages of the proposed human lunar landing architecture are given, with initial analysis showing performance gains from the use of this technology. This work provides a starting point for continued analysis and design, laying out the foundation of how navigation beacons can be incorporated into the architecture to enable continued analysis, design, and future expanded capability