Integrity Complemeting High Accuracy Service via EGNSS
Background & Objectives
With the advent of new positioning based applications, and most importantly, new safety-critical and precise positioning applications (like autonomous transport), the European Commission is assessing the possible evolutions of the EGNSS to introduce new services. One of these evolutions could be an integrity service complementing the EGNSS High Accuracy in the 2030+ timeframe to meet the needs (e.g. integrity, precision, , availability and continuity) in autonomous transport.
EGNOS and Galileo are today the main components of the European GNSS environment.
EGNOS is the European SBAS that provides corrections and integrity information to GPS L1 C/A civilian signals for safety-of-life users over Europe. In particular, integrity information is provided as part of the EGNOS Safety of Life (SoL) service to meet the demands of safety-critical applications in the civil aviation sector (e.g. landing procedures) requiring enhanced and guaranteed performance to GPS standalone positioning solutions. The next generation of EGNOS, EGNOS V3, will augment GPS and Galileo constellations in the L1 and L5 bands and extend the service area to the entire landmasses of EU member states.
Galileo is the European Union’s Global Navigation Satellite System (GNSS), providing an accurate, guaranteed global positioning service under civilian control. It is operational since the Initial Service declaration at the end of 2016. Galileo will be the first Core constellation to broadcast global (and then enhanced regional) high accuracy corrections through its High Accuracy Service (HAS).
Autonomous transportation applications drive the need for enhanced precision, high availability and continuity, low Time To First Fix, low Latency, and most importantly, reliability and integrity for SoL.
How shall this EGNSS environment evolve to answer the needs of these applications?
The ICHASE project will assess feasibility and added-value for EGNSS systems and services evolutions to meet the target performances for autonomous vehicles, leveraging on:
- GNSS as a source for absolute positioning, obviously complemented by other non-GNSS technologies
- The Galileo foreseen HAS service, over the E6 band, as a precise positioning service,
- The EGNOS SoL ready infrastructure, as an enabler for the introduction of a new integrity service complementing high accuracy for SoL applications,
- Non GNSS
- Additional enabling technologies for positioning in harsh environments (like non-GNSS positioning sensors, threats detection and mitigation technologies, in addition to GNSS positioning).
The foreseen developments target a twofold objective:
- Definition of an integrity concept customised to an autonomous vehicle for road, particularly considering the various constrained environments applicable to these applications (e.g. urban environments).
- Definition of EGNSS service(s) in the 2030+ timeframe, which will efficiently support these applications, providing the necessary commitments on EGNOS (and Galileo) new messages used in such an integrity concept.
All of the ICHASE developments build on a fully established fact, where no single solution or positioning source can answer all of the needs raised by autonomous vehicles.
Work performed & results
ICHASE addressed the challenging objective of computing a highly precise and reliable positioning for Autonomous Driving Level 4 and 5.
Why is positioning for AD applications challenging?
When compared with other transports mode (like aviation, rail or road), the autonomous driving needs are more challenging. They combine the need for high accuracy, and continuity, with harsh and diverse operational domains. On top of this, safety is of utmost importance when it comes to such safety critical applications.
This means that, having technology ready for autonomous driving is not enough. One of the biggest drivers for a scaled adoption is the users acceptance, which is driven by Safety.
To this end, ICHASE developed a user centric End to End integrity concept that relies on two main parts:
- A user integrity concept building on sensor fusion architecture,
- A high precision and integrity service to be delivered by the EGNSS infrastructure.
In this case, the EGNSS systems provides monitoring of the GNSS based high precision service and related integrity data, and the user unit embeds the needed tools for local feared events monitoring and mitigation and thus computes the protection level of the high precision position.
Figure 1. End to End Integrity concept to monitor local, regional & global Feared Events
Please note that, throughout this document, by On Board Unit (OBU) it is referred to the positioning module of the OBU.
The starting point for ICHASE was the user needs evaluated through several Key Performance Indicators (KPI), as captured in the next table. These user needs were based on state of the art review, as well as interviews of stakeholders from the Autonomous Driving value chain, and were finally validated by the experts reviewing the outputs of the ICHASE project.
As shown in Table 1, the user TTA must be less than 1 second. To comply with this requirement, either the system or the user must be able to transmit alarms in case an integrity problem is detected. However, the system supported TTA is not enough for the user. Therefore, the user shall have his own integrity detection (using non GNSS sensors) to be able to react in less than the system TTA, by implementing a coasting mechanism.
ICHASE then proposed an OBU positioning module architecture to meet these needs, building on a consistency check approach. This module leverages on a separation between two independent sub-modules, “doer” and “checker”, to compute a final accurate navigation solution and provides the corresponding integrity indicator.
Figure 2. Proposal 2: High level consistency-check architecture
This architecture was proved to be both “safe” and viable, through an extensive safety assessment on one side and a comprehensive decision criteria analysis on the other side.
- The safety assessment set the safety arguments to be fulfilled in order to reach the objective set in terms of number of fatal accidents per mile, and the associated verification methods, including a complete Failure Mode and Effect Analysis (FMEA) analysis. This safety assessment, has led to the allocation of a Target Integrity Risk of 5.10-3/h, and an ASIL A safety level to the GNSS + HAIS service. This is a very important conclusion which reduces the constraints / costs / certification and planning for the development of the system which would provide the HAIS service. The Top Down Safety analysis was completed by a Bottom-Up integrity tree, in order to assess the feasibility of the proposed approach based on known performances of each of the sensors used for the final fused solution. Further, the Doer hybridised architecture embeds an Advanced Receiver Autonomous Integrity Monitoring (ARAIM) inspired solution separation or majority vote based architecture which ensures both higher robustness and higher continuity of the solution, while keeping the computational load at acceptable levels.
- The main outcomes of the decision criteria analysis, also based on quantitative assessments and validation with key experts, highlighted the need for a timely implementation of the service, and the need for exploiting synergies with other applications thus ensuring wider adoption.
The Doer branch of this architecture, relies amongst others on the use of a Galileo High Accuracy Service augmented with Integrity data. This new HAIS service shall be compliant with the KPIs provided in Table 2 below.
Table 2. HAIS Service Performance Requirements
It is important to highlight that the HAIS data message will include also time-correlation parameters for non-snapshot PVT computation algorithms.
For the generation of the HAIS data, a hybrid architecture is proposed. Based on this architecture, the HAIS uses the HAS corrections and stations measurements to compute the integrity data and its own corrections as well. It broadcasts the Galileo HAS corrections in nominal cases, and may also compute its own corrections in contingency cases.
As for the dissemination of the HAIS service, it is naturally assumed that hybrid terrestrial and satellite communication networks and road-side units, and GNSS and non-GNSS dissemination means are needed in order to ensure compliance to the target service availability and continuity requirements. An E5b centred SiS is proposed for the dissemination of the HAIS service when disseminated through EGNOS GEOs (and potentially future IGSO / HEO satellites). ITS-G5 and 5G based telecom networks are proposed for terrestrial dissemination means. LEO constellations are proposed as an option. Road-side units part of C-ITS (Cooperative-Intelligent Transport Systems) infrastructures are also considered. Please note that the EGNOS Next (evolution of the EGNOS infrastructure as being studied in H2020-45 study with ESA) infrastructure is considered as a relevant option to host the generation and/or dissemination of the HAIS service.
Figure 4. HAIS service provision scheme
For the deployment of the HAIS service, the proposed roadmap addresses both service level and system level activities, as long as related standardisation and certification processes. It is pointed out that this roadmap shall start by a first analysis step leveraging on synergies with other transport applications, namely rail and maritime, but also drones. This roadmap leads to first demonstration of service by 2025, declaration of Initial Services by 2027, and Full Operational Capabilities service by 2030. An important element of this roadmap on the system level is the coupling of the new uplink station (and more globally new HAIS infrastructure) with that of the EGNOS system.
Figure 5. EGNSS HAIS major activities timeline
The ICHASE consortium has conducted interactions with experts covering the Autonomous Driving value chain, in coincidence with three important phases of the project: for the formulation of the autonomous vehicle for road user needs/requirements, for the definition of the future HA with integrity service concepts/features and service provision, and for the elaboration of the associated roadmap. The results reported here are those consolidated and validated by these experts.
ICHASE final report is available here.
A reliable and precise European positioning service, a trustable and highly accurate user solution, and millions of new opportunities and applications for European citizens are the major axes of the expected impact for the outputs of ICHASE.
The GNSS, as an absolute positioning system, plays an important role in various positioning applications, especially when combined to a multitude of other relative positioning methods. On top of this, the use of an integrity service complementing EGNSS High Accuracy in the 2030+ could result in the provision of an accurate and reliable positioning solution, which will be a key enabler for numerous safety-critical applications, such as autonomous vehicles.
Furthermore, although ICHASE is focused on autonomous vehicles for road applications, the possible link with other safety critical applications such as autonomous transport for rail and maritime will also be addressed.
Disclaimer: The project results represent the views of the consortium. They do not necessarily represent the views of the European Commission and they do not commit the Commission to implementing the results.