Vehicular and Pedestrian GNSS Integrity Algorithms and Results for Urban and Road Environments Developed After an Extensive Real Data Collection Campaign

Integrity in the domain of Global Navigation Satellite Systems (GNSS) has been understood as the ability of detecting and alerting of incorrect user positions, providing therefore a certain level of reliability or trust in the estimated user location. This concept of integrity was imported from the “safety-critical” aviation services, thus requiring an extremely high level of reliability, and it has been one of the drivers of satellite navigation systems in the past decades. As the use of GNSS has also expanded to mass market users, terrestrial user communities have also shown interest in applications requiring reliable positions. These terrestrial “liability-critical” applications (i.e. initially referred to applications that require a certain level of trust for economical or legal reasons, and later extended to terrestrial applications that require a level of trust for whatever purpose) require a high level of reliability, but somehow lower than in aviation. However, most of these users are located in populated areas and aviation environmental assumptions and algorithms are not fully applicable to them because of local environmental characteristics, which include buildings, trees, etc., increasing the multipath and the Non-Line-of-Sight (NLOS) signals, and dominating the GNSS measurement errors. Also threats like radio frequency (RF) interference and spoofing can deny the positioning service or lead to misleading positions. These local effects, which cannot be corrected by the ground or satellite segments, are very important in urban environments and degrade the signals leading to potentially high positioning errors and therefore may also hinder the provision of a full integrity positioning service. At receiver level, integrity has been mainly provided through Receiver Autonomous Integrity Monitoring (RAIM) algorithms. Based on the redundancy of satellite measurements, receivers were able to detect a satellite failure and exclude a faulty satellite from the navigation solution. In addition, combination of GNSS measurements with different types of external sensors can be used to overcome the impact of local effects. The objective of this paper is to present the results obtained in the research and development of PVT algorithms to mitigate the integrity faults in terrestrial environments (in particular urban and road) for vehicular and pedestrian users, thus improving terrestrial positioning services and enabling many terrestrial “liability-critical” applications. The tested integrity techniques include: - GNSS based PVT integrity techniques for autonomous vehicular navigation, that is, those which do not require information from outside the GNSS receiver to operate. - Hybrid integrity techniques for vehicular users using external sensors in combination with GNSS. - Integrity techniques for pedestrian users. The algorithms have been tested using the data obtained through an extensive collection campaign carried out in urban and road environments for vehicular and pedestrian users, allowing the assessment of high integrity confidence levels. Terrestrial applications are mainly interested in horizontal positions, so the integrity is provided in terms of a horizontal protection level (HPL), associated to the estimated position that should bound the horizontal position error (HPE) with a certain confidence level or target integrity risk (TIR). The results are evaluated in terms of accuracy (HPE), availability (size of HPLs) and integrity. Two applications, Road User Charging (RUC) and E-112, were selected among others for being the most significant in terms of required GNSS integrity. For each application, a set of possible service performance metrics was elaborated and then it was traced, making assumptions, to examples of the navigation and integrity performance metrics that could be required by the application. These sets of navigation and integrity performance metrics were used in the comparison with the results obtained when processing the collected real data. Summarizing, this paper presents the results of vehicular and pedestrian integrity techniques in urban and road environments using an extensive real data set, which allows the assessment of high confident levels, and provides a preliminary insight into the use of these integrity techniques for Road User Charging (RUC) and E-112 applications.