Final commissioning of the PRISMA GPS navigation system

A method is presented to synchronize and aid the absolute navigation solutions of the members of a swarm by means of relative inter-swarm measurements. Moreover, the operational benefits thereof are discussed. Collaborative operation of vehicles, especially of unmanned aerial vehicles in close formation, requires accurate relative and absolute navigation. A novel method for collaborative multi-sensors fusion of relative and absolute navigation information is presented designed to cope with GNSS-denied environment. Relative inter-swarm measurements and absolute navigation means cannot be fused straight away as they are defined in fundamental different frames. Moreover, the sensor fusion has to fulfill two objectives – firstly, restoring the relative geometry of the swarm, and secondly, determining the absolute positions of each vehicle in an optimal way for the overall swarm. Key for collaborative navigation is to establish a common knowledge within the swarm which is achieved by exchanging the absolute state estimations, the state uncertainties and the relative measurements. Based on the common knowledge the “Consistent INS Drift Algorithm” computes for each vehicle a new position which is statistically optimal for the overall swarm. Simultaneously, these new positions represent the actual geometry of the swarm by essentially resampling the relative measurements. By fusing these new positions the navigation filters are synchronized and the relative measurements are implicitly used to aid the absolute navigation solutions. This reveals several operational benefits: the absolute navigation solutions are consistent – the whole swarm drifts consistently as only the Inertial Navigation Systems (INS) may remain as absolute navigation means, and hence, the naming “Consistent INS Drift Algorithm”. Moreover, the drift is statistically slower than the best individual INS. Having at least one vehicle equipped with a drift-free navigation mean such as Terrain Referenced Navigation stops the swarm to drift. Therefore, heterogeneous navigation systems are natively supported enabling true collaboration.

Providing high accuracy of the coordinates and trajectories of objects by measurements conducted in navigation systems and complexes is an urgent task, which improves safety and efficiency of different modes of transport. However difficult environmental conditions, where vehicles are commonly used, stipulate influence of different factors on performance of onboard satellite navigation receivers, which are used as basic navigation devices for ground vehicle nowadays. Setting on cars used for common purposes additional navigation devices, which provide better performance, in most cases is economically unreasonable. Economically reasonable ways to improve onboard navigation complexes of vehicles, which are used for common purposes, are examined in this article. Functional diagram and principles of work of navigational complex, which uses the satellite navigation receiver and simplified variant of inertial navigation system is pointed as well. Also, the justification of methods for minimizing the error formats of coordinates and trajectories of moving objects based on information processing in multipositional, in particular satellite-inertial navigation systems and complexes, is presented. The obtained research results give an opportunity to develop an algorithm for coordinate refinement, which can be implemented in the improved on-board navigational complex of vehicle. KEY WORDS: NAVIGATION SYSTEMS AND COMPLEXES, INERTIAL SENSORS, NAVIGATION DEFINITIONS, ACCURACY AND RELIABILITY OF COORDINATES AND TRAJECTORIES OF MOVING OBJECTS, ELLIPS OF ERRORS, PROBABILISTIC-GEOMETRIC METHODS.

This paper describes a process by which Global Navigation Satellite System (GNSS) nominal statistics and fault rates can be assessed with high confidence. The use of a GNSS in Advanced Receiver Autonomous Integrity Monitoring (ARAIM) requires knowledge of the level of performance of the signal-in-space (SIS) user range error (URE) in both nominal and faulty conditions. The performance characterization is done through a careful analysis of historical data, from which a determination of whether or not it meets the performance commitments of the constellation service provider (CSP) can be made. Typically, this analysis is carried out though a comparison of the broadcast navigation messages with post-processed precise estimates of the satellite clock and orbit states. This paper highlights the issues with such an approach as well as mitigation strategies to those issues. The issues primarily impact the estimates of fault rates rather than nominal statistics, as the number of faults is small compared to the overall amount of nominal data. In particular, methods of ensuring integrity in the logged broadcast navigation messages and precise clock and orbit products used in the analysis are described. In order to verify precise clock and orbit products, a Kalman filter (KF) to produce independent GNSS clock bias estimates has been developed and tested. The KF leverages the International GNSS Service (IGS) receiver network to produce estimates of GNSS clock biases given precisely known positions of the receivers as well as precise satellite orbit products. The KF serves multiple purposes in detecting and verifying faults. First, when only low rate (5 or 15 minute) clock products are available, higher rate products can be produced to detect short faults. Second, when precise clock products are available, the KF serves as a secondary check to protect against erroneous external precise products, which have been observed. Initial testing of the filter has shown an RMS error of under 20 centimeters for a five day run of GPS clock bias estimates, which is sufficient performance for precise product verification and fault detection.

This paper presents experiences with eNav, a smartphone-based vehicular GPS navigation system that has an energy-saving location sensing mode capable of drastically reducing navigation energy needs. Traditional navigation systems sample the phone's GPS at a fixed rate (usually around 1Hz), regardless of factors such as current vehicle speed and distance from the next navigation waypoint. This practice results in a large energy consumption and unnecessarily reduces the attainable length of a navigation session, if the phone is left unplugged. The paper investigates two questions. First, would drivers be willing to sacrifice some of the affordances of modern navigation systems in order to prolong battery life? Second, how much energy could be saved using straightforward alternative localization mechanisms, applied to complement GPS for vehicular navigation? According to a survey we conducted of 500 drivers, as much as 91% of drivers said they would like to have a vehicular navigation application with an energy saving mode. To meet this need, eNav exploits on-board accelerometers for approximate location sensing when the vehicle is sufficiently far from the next navigation waypoint (or is stopped). A user test-study of eNav shows that it results in roughly the same user experience as standard GPS navigation systems, while reducing navigation energy consumption by almost 80%. We conclude that drivers find an energy-saving mode on phone-based vehicular navigation applications desirable, even at the expense of some loss of functionality, and that significant savings can be achieved using straightforward location sensing mechanisms that avoid frequent GPS sampling.

The PPP is a technique being actively researched and developed for estimating the precise position of a stationary point on the surface of the earth. Its particular features are that unlike the relative positioning method, the PPP does not require reference points and it provides the centimeter-level positioning accuracy in real-time using the precise orbit and clock information of the navigation satellites such as the GPS satellites. Lately, the application of the PPP technique to the onboard navigation of the low earth orbit (LEO) satellites is attracting attentions from aerospace researchers and engineers. Such a navigation technique is called the PPP in Space or the Space PPP. As for the existing approaches, the PPP in Space methods using precise LEO satellite dynamics [1] and kinematic PPP which does not use such dynamics [2] [3] were proposed and these results were impressive: the decimeter-level or even the centimeter-level satellite positioning accuracy was confirmed by the offline experiments using actual European LEO satellites dataset. Although these navigation methods are obviously state-of-the-art, this paper takes an another approach that focuses on improving the accuracy of satellite onboard navigation (NAV) using the PPP technique. The methodology presented in this paper is similar to the work [4] that used a reference orbit trajectory for the PPP in Space, that is, the errors of the reference trajectory were estimated using the PPP technique. However, the calculation of their reference trajectories requires the computational time and it can not be performed onboard a satellite. Therefore, we designed our method to work in realtime by using the onboard NAV as the reference trajectory. The performance of the proposed PPP NAV method was evaluated using the actual data of a Japanese earth observation satellite ALOS2 (Advanced Land Observing Satellite) [5].

This paper is devoted to understanding relative navigation models that are used for space vehicles. The relative navigations models and approaches which are based on different systems (Inertial Navigation Systems (INS)&Global Navigation Satellite System (GNSS) , Laser&INS, Vision- Based, etc.) are compared. These models and approaches can be used individually or combined for solving relative navigation problems. Advantages and disadvantages of the models vary according to the usage area, platform type, and environment. Different methods and approaches exist in addition to different estimation and optimization algorithms for adaptation, control, and sensor fusion. Most of the models assume perfect attitude conditions. This study considers satellites' position estimates according to each other within formation on the Low Earth Orbit (LEO). Also, the aim of this article is to understand correlation between the relative navigation systems and the effectiveness of the algorithms which are used for estimating states during constellation or formation flight.

Relative Navigation for Satellite Formation Flying based on Radio Frequency Metrology

When a person is concurrently interacting with different systems, the amount of cognitive resources required (cognitive load) could be too high and might prevent some tasks from being completed. When such human multitasking involves safety-critical tasks, for example in an airplane, a spacecraft, or a car, failure to devote sufficient attention to the different tasks could have serious consequences. To study this problem, we define an executable formal model of human attention and multitasking in Real-Time Maude. It includes a description of the human working memory and the cognitive processes involved in the interaction with a device. Our framework enables us to analyze human multitasking through simulation, reachability analysis, and LTL and timed CTL model checking, and we show how a number of prototypical multitasking problems can be analyzed in Real-Time Maude. We illustrate our modeling and analysis framework by studying the interaction with a GPS navigation system while driving, and apply model checking to show that in some cases the cognitive load of the navigation system could cause the driver to keep the focus away from driving for too long.

Popular navigation services are used by drivers both to plan out routes and to optimally navigate real time road congestion in internet of vehicles (IoV). However, the navigation system (such as GPS navigation system) and apps (such as Waze) may not be possible for each individual user to avoid traffic without creating congestion on the clearer roads, and it might even be that such a recommendation leads to longer aggregate routes. To solve this dispersion, in this paper, we first apply a concept of virtual vehicle in IoV, which is an image of driver and vehicle. Then, we study a setting of non-atomic routing in a network of m parallel links with symmetry of information. While a virtual vehicle knows the cost function associated with links, they are known to the individual virtual vehicles choosing the link. The virtual vehicles adapt the cooperation approach via strategic concession game, trying to minimize the individual and total travel time. How much benefit of travel time by the virtual vehicles cooperating when vehicles follow the cooperation decisions? We study the concession ratio: the ratio between the concession equilibrium obtained from an individual optimum and the social optimum. We find that cooperation approach can reduce the efficiency loss compared to the non-cooperative Nash equilibrium. In particular, in the case of two links with affine cost functions, the concession ratio is at most 3/2. For general non-decrease cost functions, the concession ratio is at most 2. For the strategic concession game, the concession ratio can approach to 1 which is a significant improvement over the unbounded price of anarchy.

Within the PROBA-2 microsatellite mission, a miniaturized single-frequency GPS receiver based on commercial-off-the-shelf (COTS) technology is employed for onboard navigation and timing. A rapid electronic fuse protects against destructive single-event latch-ups (SEL) and enables a quasi-continuous receiver operation despite the inherent sensitivity to space radiation. While limited to single-frequency C/A-code tracking with a narrow-band frontend, the receiver is able to provide precision navigation services through processing of raw GPS measurements on ground as well as a built-in real-time navigation system. In both cases, ionospheric path delays are eliminated through a combination of L1 pseudorange and carrier phase measurements, which also offers a factor-of-two noise reduction relative to code-only processing. By comparison with satellite laser ranging (SLR) measurements, a 0.3-m (3D rms) accuracy is demonstrated for the PROBA-2 reduced dynamic orbit determinations using post-processed GPS orbit and clock products. Furthermore, the experimental onboard navigation system is shown to provide real-time position information with a 3D rms accuracy of about 1 m, which notably outperforms the specification of the Standard Positioning Service (SPS). In view of their lower hardware complexity, mass budget and power requirements as well as the reduced interference susceptibility, legacy C/A-code receivers can thus provide an attractive alternative to dual-frequency receivers even for demanding navigation applications in low Earth orbit.

The position fixing capability of the Loran system has been well recognized for use in transport aircraft as a navigation system monitor. The role of Loran-C as a navigation and control system has not been recognized, however, primarily because of the unwieldly time difference coordinates of the system. With the successful development of cockpit operable auto-track receivers and proof of the feasibility of automatic coordinate conversion, it now becomes possible to discuss the potential of Loran-C as a system capable of providing navigation control in the horizontal plane. To this end, three separate tracks across the North Atlantic area are analyzed to show the accuracy of positional, track and steering information that is available from the proper processing of Loran-C signals. From the analysis, it is evident that within its coverage area the system is capable of being used as a primary navigation system or, on a supersonic transport, it can be used in conjunction with an inertial navigator to obtain dual operational redundancy of the navigation systems.

This paper presents a narrow band frequency reconfigurable antenna for global navigation systems. Proposed frequency tunable antenna operates for GLONASS (1.601 GHz), GPS (1.575 GHz) and COMPASS (1.561 GHz) navigational systems. Antenna design consists of rectangular patches, two pin-diode switches, feed network, biasing circuitry and supply lines to make antenna operational for three frequency bands. Antenna is simulated and optimized using CST—Computer simulation technology and is fabricated on Roger RO4350b substrate. The demonstrated antenna along with being frequency agile possess essential performance characteristics like high gain, stable radiation patterns and good radiation efficiency for all three frequency bands, making it prospective choice for wireless navigational systems.

This paper describes our latest efforts in building a speech recognizer for operating a navigation system through speech instead of typed input. Compared to conventional speech recognition for navigation systems, where the input is usually restricted to a fixed set of keywords and keyword phrases, complete spontaneous sentences are allowed as speech input. We will present the interaction of speech input, parsing and the necessary reactions to the requested queries. Our system has been trained on German spontaneous speech data and has been adapted to navigation queries using MLLR. As the system is not restricted to command word input, a parser is necessary to further process the recognized utterance. We show that within a lab environment our system is able to handle arbitrary spontaneous sentences as input to a navigation system successfully. The performance of the recognizer measured in word error rate gives a result of 18%. The parser has also been evaluated and yields an error rate of 20%.

Real-time precise orbit and clock products are crucial for real-time high-precision precise point positioning (PPP). The key for precise orbit prediction is to precisely determine the initial conditions (satellite position, velocity at the initial epoch) and the solar radiation pressure (SRP) parameters using an arc of known precise orbits. The optimal arc length will be investigated for precise orbit prediction, with which the high-accuracy satellite clocks can be estimated. The orbit prediction accuracies with different arc lengths and conditions over time are also investigated. The results indicate that the predicted orbit accuracy is governed by the SRP parameters. In addition, the predicted orbits and estimated clocks are evaluated quantitatively with respect to PPP solutions during in and out of eclipses seasons, based on which the optimal arc length is identified. The numerical results show that high-accuracy orbital prediction can be achieved using an arc length between 36 and 48 h and generally an arc length of 42 h is considered to be optimal. With this optimal arc length, the estimated clock accuracy is 0.048 and 0.122 ns for a prediction interval of 6 and 24 h, respectively. The average PPP ambiguity fix-rates with a prediction interval of 6 h are 80.2 and 84.7 % over an observation period of 30 min and 1 h, respectively.

Abstract. The PERIGEO R&D project aims at developing, testing and validating algorithms and/or methods for space missions in various field of research. This paper focuses in one of the scenarios considered in PERIGEO: navigation for atmospheric flights. Space missions heavily rely on navigation to reach success, and autonomy of on-board navigation systems and sensors is desired to reach new frontiers of space exploration. From the technology side, optical frame cameras, LiDAR and inertial technologies are selected to cover the requirements of such missions. From the processing side, image processing techniques are developed for vision-based relative and absolute navigation, based on point extraction and matching from camera images, and crater detection and matching in camera and LiDAR images. The current paper addresses the challenges of space navigation, presents the current developments and preliminary results, and describes payload elements to be integrated in an Unmanned Aerial Vehicle (UAV) for in-flight testing of systems and algorithms. Again, UAVs are key enablers of scientific capabilities, in this case, to bridge the gap between laboratory simulation and expensive, real space missions.