Collaborative navigation as a solution for PNT applications in GNSS challenged environments: report on field trials of a joint FIG / IAG working group

PNT stands for Positioning, Navigation, and Timing. Space-based PNT refers to the capabilities enabled by GNSS, and enhanced by Ground and Space-based Augmentation Systems (GBAS and SBAS), which provide position, velocity, and timing information to an unlimited number of users around the world, allowing every user to operate in the same reference system and timing standard. Such information has become increasingly critical to the security, safety, prosperity, and overall qualityof-life of many citizens. As a result, space-based PNT is now widely recognized as an essential element of the global information infrastructure. This paper discusses the importance of the availability and continuity of PNT information, whose application, scope and significance have exploded in the past 10–15 years. A paradigm shift in the navigation solution has been observed in recent years. It has been manifested by an evolution from traditional single sensor-based solutions, to multiple sensor-based solutions and ultimately to collaborative navigation and layered sensing, using non-traditional sensors and techniques – so called signals of opportunity. A joint working group under the auspices of the International Federation of Surveyors (FIG) and the International Association of Geodesy (IAG), entitled ‘Ubiquitous Positioning Systems’ investigated the use of Collaborative Positioning (CP) through several field trials over the past four years. In this paper, the concept of CP is discussed in detail and selected results of these experiments are presented. It is demonstrated here, that CP is a viable solution if a ‘network’ or ‘neighbourhood’ of users is to be positioned / navigated together, as it increases the accuracy, integrity, availability, and continuity of the PNT information for all users

An Overview of Distributed Spacecraft Autonomy at NASA Ames

Autonomous decision-making significantly increases mission effectiveness by mitigating the effects of communication constraints, like latency and bandwidth, and mission complexity on multi-spacecraft operations. To advance the state of the art in autonomous Distributed Space Systems (DSS), the Distributed Spacecraft Autonomy (DSA) team at NASA\u27s Ames Research Center is developing within five relevant technical areas: distributed resource and task management, reactive operations, system modeling and simulation, human-swarm interaction, and ad hoc network communications. DSA is maturing these technologies - critical for future large autonomous DSS - from concept to launch via simulation studies and orbital deployments. A 100-node heterogenous Processor-in-the-Loop (PiL) testbed aids distributed autonomy capability development and verification of multi-spacecraft missions. The DSA software payload deployed to the D-Orbit SCV-004 spacecraft demonstrates multi-agent reconfigurability and reliability as part of an ESA-sponsored in-orbit technology demonstration. Finally, DSA\u27s primary flight mission showcases collaborative resource allocation for multipoint science data collection with four small spacecraft as a payload on NASA\u27s Starling 1.0 satellites

EKF Based Trajectory Tracking and Integrity Monitoring of AIS Data

This work presents a novel approach for integrity monitoring of AIS data. Currently, the AIS is a valuable source for maritime traffic situation assessment but not suited for collision avoidance, as it is prone to failures and not capable of indicating the level of data integrity. To tackle this, an EKF was designed to track vessel trajectories, which allows for failure detection based on residual monitoring. For the latter, two methods for hypotheses testing were implemented, namely chi-squared and GLR tests. In addition, the IMM framework was adopted for mixing the state estimates of two different process models, the CV and CTRV. The designed filter will be validated on behalf of simulated and real-world AIS data

A Portuguese Case Study

There is a high national dependency on Position, Navigation and Timing (PNT) Systems for several individuals, services and organisations that depend on this information on a daily basis. Those who rely on precise, accurate and continuous information need to have resilient systems in order to be highly efficient and reliable. A resilient structure and constantly available systems makes it easier to predict a threat or rapidly recover in a hazardous environment. One of these organisations is the Portuguese Navy, whose main purposes are to combat and maintain maritime safety. In combat, resilient PNT systems are needed for providing robustness in case of any threat or even a simple occasional system failure. In order to guarantee maritime safety, for example in Search and Rescue Missions, the need of PNT information is constant and indispensable for positioning control. The large diversity of PNT-dependent equipment, developed over the last two decades, is a valid showcase for the high GPS dependency that is seen nowadays – which is vulnerable to various factors like interference, jamming, spoofing and ionospheric conditions. The recent interest over integrated PNT system resolutions is related to the search for redundancy, accuracy, precision, availability, low cost, coverage, reliability and continuity. This study aimed to build a current PNT Portuguese picture based on Stakeholder Analysis and Interviews; assess the vulnerability of those who depend mainly on GPS for PNT information and, find out what the next steps should be in order to create a National PNT Strategy.Existe uma elevada dependência nacional em sistemas de Posição, Navegação e Tempo (PNT) por parte de diversos indivíduos, serviços e organizações que dependem desta informação no seu dia-a-dia. Todos os que dependem de informação precisa, exata e contínua, necessitam de ter sistemas resilientes para que sejam altamente eficientes e fiáveis. Uma estrutura resiliente e sistemas continuamente disponíveis facilitam a previsão de possíveis ameaças ou a expedita recuperação da funcionalidade, em ambientes hostis. Uma destas organizações é a Marinha Portuguesa cujas funções principais são o combate, a salvaguarda da vida humana no mar e a segurança marítima e da navegação. Para o combate, são necessários sistemas PNT, resilientes, que ofereçam robustez em caso de uma simples ameaça ou falha temporária dos sistemas. Por forma a ser possível cumprir a missão, a necessidade de ter informação PNT, fidedigna e atualizada, é constante e indispensável para o controlo preciso e exato da posição. Uma unidade naval, por forma a permanecer continuamente no mar, manter a sua prontidão, treinar a sua guarnição ou ser empenhada num cenário de guerra, necessita de saber, com confiança e sem erros, a sua posição e referência de tempo. A grande diversidade de sistemas dependentes de informação PNT, desenvolveu-se em larga escala nas últimas duas décadas e sustenta cada vez mais a alta dependência do GPS, que é vulnerável a diversas fontes de erro, tais como interferência, empastelamento, mistificação e condições ionosféricas. Atualmente, o elevado interesse na criação de sistemas PNT integrados está associado à procura da redundância, exatidão, precisão, disponibilidade, baixo custo, cobertura, fiabilidade e continuidade. Este estudo teve como objetivos construir o panorama atual, em Portugal, ao nível dos Sistemas PNT, baseando-se numa análise de Stakeholders e entrevistas; avaliar a vulnerabilidade de organizações e serviços que dependam exclusivamente do GPS como fonte de informação PNT; e propor um possível caminho para que seja possível criar uma Estratégia PNT Naciona

Availability of Maritime Radio Beacon Signals for R-Mode in the Southern Baltic Sea

This paper presents an overview of the development of a terrestrial positioning system called Ranging Mode (R-Mode) in the Southern Baltic Sea region which utilizes already existing maritime radio infrastructure. Here, an R-Mode testbed is planned to be set up until 2020 that meets maritime user needs for resilient PNT. First measurements of radio beacon signals on-board a vessel sailing in the Southern Baltic Sea show the good availability of beacon signals in this region. A comparison of received signals with a coverage prediction based on the nominal range of radio beacons shows the shortcoming of this approach and emphasizes the need for more elaborated coverage predictions which consider all effects of medium frequency wave propagation at day and night. In the measurements results the skywave has a major impact on the beacon signal stability in the night. The time stability of the signal amplitude seems to be a good indicator for disturbed reception conditions

Methodology for optimizing a Constellation of a Lunar Global Navigation System with a multi-objective optimization algorithm

Global Navigation Satellite Systems (GNSS) are not only used in terrestrial applications, but also in Low-Earth orbit satellites and in higher altitude missions. NASA’s Magnetospheric Multiscale (MMS) mission has demonstrated the capabilities of existing GNSS systems to provide positioning, navigation, and timing (PNT) services in the Cis-lunar space.The resurgence in plans by national space agencies for Lunar exploration presents a need for accurate, precise, and reliable navigation systems to ensure the safety and success of future missions.Moreover, the increased amount of Moon missions over recent years, shows the requirement of navigation capabilities for Low Lunar orbiters, Moon landers, Moon rovers, and manned missions.The success of Global Navigation Satellite Systems (GNSS) on Earth, presents an opportunity for the study of a potential design requirements and expected performance of a Lunar GNSS constellation.We have approached this problem through the methodology of multi-objective optimization; numerically simulating the orbits, and using the Position Delution of Precision (PDoP) as the figure of merit to optimise a set of 200 constellation designs and improving them gradually over 1864 generations. Over 12,000 unique constellation designs were generated with the best 10 constellations presented in this paper for consideration and further study. Compared to the literature, these 10 constellations achieved a 44% improvement in PDoP (2.73) using the same number of satellites in each constellation, and meeting the performance requirements of planned Lunar missions

EXPLORING THE USE OF HUMAN RELIABILITY AND ACCIDENT INVESTIGATION METHODS TO INFLUENCE DESIGN REQUIREMENTS FOR NAVAL SYSTEMS

This thesis explores whether established methods from human reliability analysis and accident investigation can be applied early in system development to identify the design vulnerabilities that increase risk of system failure. Human reliability analyses evaluate performance shaping factors to quantify the likelihood of human failure before an accident occurs. Mishap investigations performed after an accident identify both human contributions to the system's failure and recommendations to avoid human failures in the future. This thesis proposes a method to evaluate system resiliency to variations in human performance and estimate the likelihood of human error. This method begins with functional analysis and failure mode analysis for a system concept, and then proposes two questionnaires based on human reliability and accident investigation criteria. This method is intended for the requirements development phase before system requirements are finalized and system design prototypes are completed. A demonstration of this method evaluates the human role using the electronic chart display and information system. Results from the demonstration reveal the two dominant factors that increase human error probability. The thesis concludes with an examination of the method's performance and results in support of validation of the method. Follow-on work is proposed to conduct a human subjects experiment for further validation and verification of the method.Civilian, Department of the NavyApproved for public release. distribution is unlimite

An Impulse Detection Methodology and System with Emphasis on Weapon Fire Detection

This dissertation proposes a methodology for detecting impulse signatures. An algorithm with specific emphasis on weapon fire detection is proposed. Multiple systems in which the detection algorithm can operate, are proposed. In order for detection systems to be used in practical application, they must have high detection performance, minimizing false alarms, be cost effective, and utilize available hardware. Most applications require real time processing and increased range performance, and some applications require detection from mobile platforms. This dissertation intends to provide a methodology for impulse detection, demonstrated for the specific application case of weapon fire detection, that is intended for real world application, taking into account acceptable algorithm performance, feasible system design, and practical implementation. The proposed detection algorithm is implemented with multiple sensors, allowing spectral waveband versatility in system design. The proposed algorithm is also shown to operate at a variety of video frame rates, allowing for practical design using available common, commercial off the shelf hardware. Detection, false alarm, and classification performance are provided, given the use of different sensors and associated wavebands. The false alarms are further mitigated through use of an adaptive, multi-layer classification scheme, leading to potential on-the-move application. The algorithm is shown to work in real time. The proposed system, including algorithm and hardware, is provided. Additional systems are proposed which attempt to complement the strengths and alleviate the weaknesses of the hardware and algorithm. Systems are proposed to mitigate saturation clutter signals and increase detection of saturated targets through the use of position, navigation, and timing sensors, acoustic sensors, and imaging sensors. Furthermore, systems are provided which increase target detection and provide increased functionality, improving the cost effectiveness of the system. The resulting algorithm is shown to enable detection of weapon fire targets, while minimizing false alarms, for real-world, fieldable applications. The work presented demonstrates the complexity of detection algorithm and system design for practical applications in complex environments and also emphasizes the complex interactions and considerations when designing a practical system, where system design is the intersection of algorithm performance and design, hardware performance and design, and size, weight, power, cost, and processing

Satellite clock time offset prediction in global navigation satellite systems

In an operational sense, satellite clock time offset prediction (SCTOP) is a fundamental requirement in global navigation satellite systems (GNSS) tech- nology. SCTOP uncertainty is a significant component of the uncertainty budget of the basic GNSS pseudorange measurements used in standard (i.e not high-precision), single-receiver applications. In real-time, this prediction uncertainty contributes directly to GNSS-based positioning, navigation and timing (PNT) uncertainty. In short, GNSS performance in intrinsically linked to satellite clock predictability. Now, satellite clock predictability is affected by two factors: (i) the clock itself (i.e. the oscillator, the frequency standard etc.) and (ii) the prediction algorithm. This research focuses on aspects of the latter. Using satellite clock data—spanning across several years, corresponding to multiple systems (GPS and GLONASS) and derived from real measurements— this thesis first presents the results of a detailed study into the characteristics of GNSS satellite clocks. This leads onto the development of strategies for modelling and estimating the time-offset of those clocks from system time better, with the final aim of predicting those offsets better. The satellite clock prediction scheme of the International GNSS Service (IGS) is analysed, and the results of this prediction scheme are used to evaluate the performance of new methods developed herein. The research presented in this thesis makes a contribution to knowledge in each of the areas of characterisation, modelling and prediction of GNSS satellite clocks. Regarding characterisation of GNSS satellite clocks, the space-borne clocks of GPS and GLONASS are studied. In terms of frequency stability—and thus predictability—it is generally the case that the GPS clocks out-perform GLONASS clocks at prediction lengths ranging from several minutes up to one day ahead. There are three features in the GPS clocks—linear frequency drift, periodic signals and and complex underlying noise processes—that are not observable in the GLONASS clocks. The standard clock model does not capture these features. This study shows that better prediction accuracy can be obtained by an extension to the standard clock model. The results of the characterisation and modelling study are combined in a Kalman filter framework, set up to output satellite clock predictions at a range of prediction intervals. In this part of the study, only GPS satellite clocks are considered. In most, but not all cases, the developed prediction method out- performs the IGS prediction scheme, by between 10% to 30%. The magnitude of the improvement is mainly dependent upon clock type

GNSS integrity assessment of an Integrated PNT-Unit in a signal degraded inland water environment

Within the framework of the project “Precise and Integer Localisation and Navigation in Rail and Inland water Traffic” (PiLoNav) an integrated Position, Navigation and Timing (PNT) Unit for inland waterways has been developed and implemented through the combination of Global Navigation Satellite Systems (GNSS) receivers and an inertial measurement unit (IMU), where the IMU is used for short-term stabilization and to assure continuous PNT solution in GNSS signal blockage areas. The aim of this integrated navigation system is to provide precise navigation capability with defined levels of accuracy, integrity and continuity. Integrity in GNSS stands for the evaluation of the trust that can be placed in the correctness of the information supplied by a navigation system with or without augmentations. This trust can be increased by using only non-faulty GNSS signals for positioning estimation. GNSS integrity monitoring should on one hand perform self-consistency checks on redundant measurements, and on the other hand, trigger timely and valid warnings to users when it must not be used for the intended operation. Therefore, the implementation of a Receiver Autonomous Integrity Monitoring (RAIM) algorithm as a part of the PNT-Unit assures GNSS integrity. RAIM was first introduced in the aviation sector for only using reliable satellites during safety critical landing approaches. The need of RAIM in the maritime sector emerges from the requirements for maritime radio navigation systems as specified by the International Maritime Organization (IMO). Due to the limited manoeuver space on inland waterways, the requirement on positioning accuracy and integrity is very demanding. This work summarizes the difficulties of a classical snapshot-RAIM algorithm for a non- augmented GPS-based navigation system in operational degraded signal environments. Such environments include inland waterways with bridges, locks and other natural and artificial obstacles that cause GPS signal blockage and multipath. As the RAIM algorithm is based on pseudorange redundancy, the number of visible satellites is crucial for the availability of integrity information. It will be shown that the environment described above often compromises RAIM availability and performance. First results, based on several hours of collected GPS-data during a measurement campaign which took place at the river Moselle in Koblenz in August 2012, are given