Pseudolite Architecture and Performance Analysis for the FAA\u27s NextGen Airspace

By 2025 the FAA plans to have fully implemented its NextGen Airspace design. NextGen takes advantage of modern positioning technologies as well as automation, data sharing, and display technologies that will allow more efficient use of our ever busier National Airspace (NAS). A key element of NextGen is the transition from surveillance RADAR providing aircraft separation and navigation to the use of the GPS and Automatic Dependent Surveillance Broadcast (ADS-B). ADS-B couples the precision of the GPS with networked ground and airborne receivers to provide precise situational awareness to pilots and controllers. The result is increased safety, capacity, and access with reduced reliance on an outdated and costly existing infrastructure. Reliance on the vulnerable GPS requires a backup system with higher positioning accuracy than those that are in place today. The USAF 746th Test Squadron at Holloman AFB, in partnership with Locata Corp., has demonstrated an Ultra High Accuracy Reference System (UHARS) over the Holloman Range composed of pseudolites (ground based satellites) transmitting GPS like signals. This study evaluates the suitability of the UHARS when applied on a national scale to meet Alternate Precision Navigation and Timing (APNT) requirements. From a systems architecture perspective UHARS is evaluated against APNT CONOPs stated Operational Improvements and Scenarios. From a signal architecture perspective the UHARS is evaluated against frequency and bandwidth constraints, service volume requirements and positioning accuracy determined by NextGen Airspace aircraft separation criteria

Scoping Study on Pseudolites

Pseudolites or pseudo-satellites are an emerging technology with the potential of enabling satellite navigation indoors. This technology found several applications that are not limited to indoor navigation. Precise landing, emergency services in difficult environments and precise positioning and machine control are few examples where pseudolite technology can be employed. Despite the great potential of this technology, severe interference problems with existing GNSS services can arise. The problem can be particularly severe when considering non-participating receivers, i.e., legacy devices not designed for pseudolite signals. The design of pseudolite signals is thus a complex problem that has to account for market requirements (modifications of existing receivers for enabling the use of pseudolite signals, measurement accuracy, target application), regulatory aspects (frequency bands to be allocated for pseudoliteservices) and interference problems. The main aspects for the design of a pseudolite signal standard minimizing the interference problem without compromising the location capabilities of the system are considered. The focus is on the signal characteristics and topics relevant for the signal design. A literature review on the different pseudolite applications, prototypes and solutions adopted for minimizing the interference problem is first conducted. Recommendations on the aspects that should be further investigated are then provided.JRC.DG.G.6-Security technology assessmen

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

Development and Pseudolite Applications in Positioning and Navigation

Iako su Globalni navigacijski satelitski sustavi (GNSS) uveli revolucionarne promjene na području pozicioniranja i navigacije, poznato je da preciznost, pouzdanost, dostupnost i cjelovitost rezultata dobivenih tom tehnologijom značajno ovisi o broju i geometrijskom rasporedu vidljivih satelita. To je osobito izraženo u područjima s ograničenom vidljivošću satelita, kao što su gradska područja, doline, otvorena rudnička okna, velika gradilišta. Osim toga, u zatvorenim prostorima ili ispod zemlje, npr. tvorničke hale, unutrašnjost zgrada, tuneli, pozicioniranje je potpuno onemogućeno zbog nedostupnosti satelitskih signala. Ti nedostaci mogu se otkloniti uključivanjem dodatnih izvora signala koje odašilju pseudoliti (naziv izveden od pseudo-sateliti), terestrički generatori i odašiljači signala sličnih satelitskim, za primjenu u lokalnom području. Pseudoliti se mogu koristiti kao nadopuna GNSS-a u slučaju nedovoljnog broja vidljivih satelita ili za poboljšanje geometrije te kao samostalan mjerni sustav koji može u potpunosti zamijeniti konstelaciju GNSS satelita, u zatvorenim prostorima, ispod zemlje ili na drugim planetima. Iako to može izgledati kao nova mjerna tehnologija, koncept terestričkih odašiljača datira još iz vremena početaka razvoja GPS-a, kada su pseudoliti osmišljeni za testiranje GPS korisničke opreme. Od tada, uvidjevši da se pseudoliti mogu vrlo uspješno koristiti i u druge svrhe, istraživački timovi širom svijeta neprekidno usavršavaju i razvijaju nove konstrukcije pseudolita nastojeći ih prilagoditi zahtjevima pojedinih primjena. U članku se prikazuju teorijske osnove, prednosti i nedostaci, razvoj tehnologije pseudolita, daljnja istraživanja i nove konstrukcije te primjena pseudolita u nekim područjima pozicioniranja i navigacije.Although the Global navigation satellite systems (GNSS) introduced a revolutionary change in the areas of positioning and navigation, it is well known that the precision, reliability, availability and integrity of the results obtained by this technology, heavily depend on the number and geometric distribution of the satellites being tracked. This is especially problem in areas with limited sky visibility, such as urban canyons, valleys, deep open-pit mines, larges construction sites. Furthermore, indoors, or underground, such as factory halls, inside buildings, tunnels, positioning is totally disabled due to unavailability of satellite signals. These limitations can be overcome by including additional ranging signals transmitted from pseudolites (the term derived from the pseudo-satellite), ground-based generators and transmitters of GPS-like signals, for use in the local area. Pseudolites can be used to augment the GNSS satellite constellation in case of inadequate satellites coverage and to improve the geometry, and as an independent measurement system that can completely replace the GNSS, such as indoors, underground or on the surface of other planets. While this may seem like a new measurement technology, the concept of ground-based transmitters can be tracked back to the early development of GPS, when the pseudolites been designed to test the GPS user equipment. Since than, seeing that the pseudolites can be successfully used for other purposes, researches teams around the world continuously improve and develop new pseudolite concepts and hardware, trying to adapt them to the requirements of certain applications. This paper presents the theoretical basis, advantages and disadvantages, technology development of pseudolites, further research, and new construction, and application of pseudolites in some areas of positioning and navigation

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

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

Closely-coupled integration of Locata and GPS for engineering applications

GPS has become an almost indispensable part of our infrastructure and modern life. Yet because its accuracy, reliability, and integrity depend on the number and geometric distribution of the visible satellites, it is not reliable enough for the safety of life, environmental or economically critical applications. Traditionally, this has been addressed by augmentation from dedicated support systems, or integration with other sensors. However, from an engineering perspective only expensive inertial systems or pseudolites offer the accuracy required. In the case of pseudolites, the equivalent of ground based satellites, geometry constraints, fading multipath, imprecise clocks, the near-far effect, tropospheric delay and legislative obstructions make them difficult to implement. This thesis takes a step forward, by proposing a loosely coupled integration with Locata, a novel, terrestrial positioning technology, based on the pseudolite concept. It avoids the above pitfalls by utilising frequency and spatially separated antennas and a license-free frequency band, though this comes at the cost of in-bound interference. Its ability to provide stand-alone position and network synchronisation at nanosecond level is used commercially in open-cast mining and in military aviation. Discussion of Locata and GPS technology has identified their shortcomings and main limiting factors as well as the advantages of the proposed integration. During the course of this research, tropospheric delay, planar solution and known point initialisation ambiguity resolution methods have been identified as the main limiting factors for Locata. These are analysed in various static and kinematic scenarios. Discussion also includes ambiguity resolution, noise and interference detection and system performance in indoor and outdoor scenarios. The proposed navigation engine uses a closely coupled integration at the measurement level and LAMBDA as the ambiguity resolution method for Locata and GPS. A combined solution is demonstrated to offer a geometrical improvement, especially in the respect of height determination, with centimetre to decimetre accuracy and a minimum requirement of two signals from any component. This study identifies that proper separation and de-correlation of Locata and GPS ambiguities and better tropospheric models are essential to reach centimetre level accuracy. The thesis concludes with examples of system implementation including: seamless navigation, city-wide network deployment, urban canyons, a long term-monitoring scenario and indoor positioning. This demonstrates how the proposed navigation engine can be an advantage in areas such as: civil engineering, GIS, mobile mapping, deformation, machine navigation and control

Optimal Geometric Deployment of a Ground Based Pseudolite Navigation System to Track a Landing Aircraft

With much of the military and civilian communities becoming dependent on GPS technology to navigate it has become imperative that the navigation systems be tested in situations in which GPS does not work. This testing is especially necessary for precise tasks such as landing an aircraft. Currently, research is being conducted into using a pseudolite-based reference system to use as a truth model for the GPS jamming test. Pseudolite systems have been proven to provide sub-centimeter level accuracy in the horizontal plane; however in the vertical plane the position error is still in the decimeter to meter level range. This is largely due to the fact that the geometry of a ground based pseudolite system provides poor slant angles in the vertical plane, which contributes to large positioning errors. The goal of this research is to study the effects of system geometry on the vertical plane solution. The results of this effort show that elevation angles of greater than 20°-30° are necessary to attain reasonably good positioning solutions. Multiple pseudolite deployments, while effective at reducing the geometry errors, are very cost ineffective and the geometries pose significant risks to a landing aircraft. The best geometry involved using an orbiting aircraft, with a pseudolite transmitter and receiver attached, as an elevated pseudolite to create better slant angles and thus better positioning solutions