Simple GNSS Assisted and Trusted Receiver
Background & Objectives
Roads across Europe are becoming more congested and it is widely recognised that the network needs to be more effectively managed. One tool to tackle this challenge is road-user charging (RUC).
RUC has the potential to reduce congestion , lower vehicle emissions and generate revenue streams for infrastructure improvement. It can ensure that revenues are based on actual road usage creating a financial incentive for changing driving behaviour. This might include using private cars less overall and, in particular, reducing peak-times levels of travel in urban areas by effectively spreading out the morning and evening ‘rush hour’.
Charging schemes to date have focused on specific areas (e.g. individual cities), infrastructure (e.g. major motorways, tunnels and bridges) and classes of vehicles (e.g. trucks) using fixed roadside infrastructure. This technology is not feasible for more extensive charging schemes that will need to cover far greater areas, more road types and a great number of vehicles, and which will vary charges depending on location and time of day. More flexible schemes require the positioning element to be onboard the vehicle and GNSS-based devices have been identified as the best option to achieve this. The challenge is to develop and demonstrate GNSS-based solutions which can reliably determine vehicle positions even in the most demanding operating environments.
The SIGNATURE solution includes an assistance service which provides ephemeris data and corrections from EDAS, optimised for the user location. The assistance message can be generated to conform to existing A-GNSS standards but the project will also explore potential benefits of including EGNOS products in the assistance message and will assess the feasibility of a broadcast assistance service.
The onboard unit (OBU) hosts a bespoke receiver which exploits the continuous availability of assistance data and does not attempt to decode navigation data directly from satellite signals. This allows its design to focus on rapid signal acquisition with high sensitivity and to achieve a rapid TTFF, even in areas where conventional receivers struggle. Measurement data from the receiver is then processed with application-specific navigation algorithms on the OBU which aim to improve the integrity of the position solution relative to standard solutions.
The position data from the OBU is assessed by processing it with a map matcher once it has been transferred back to the service centre. This makes it possible to assess whether improvements in the OBU position output are significant in terms of matching the vehicle location successfully and more reliably to road segments, and for more of the journey.
SIGNATURE is prototyping a GNSS-based solution for road applications which will provide a trustworthy solution in a cost-effective and scalable manner. It demonstrates that a robust positioning solution offering high availability and integrity, even in demanding urban environments, can be based upon low-cost GNSS components. Demonstrating the performance of GNSS solutions is critical to support its adoption as the core technology for applications such as congestion management, fair and flexible road pricing, and pay-as-you-drive insurance.
This robust, high-availability, high-integrity solution is delivered firstly through providing reliable assistance (A-GNSS) data from the EGNOS Data Access Service (EDAS) to optimise the receiver acquisition and tracking capabilities, and reducing time to first fix (TTFF), and secondly through the implementation of embedded GNSS reliability algorithms into an onboard terminal, providing assurance of positioning information.
Together these features can lead to improvements in an RUC environment in terms of:
- charging accuracy (correct cost per trip);
- charging integrity (probability and amount of overcharging);
- charging availability (amount of charged usage).
Work performed & results
At the conclusion of the project there will be an end-to-end SIGNATURE prototype solution which has been extensively tested in field trials and which promotes the use of EDAS. Outputs will include hardware, software and algorithms, which can be exploited by developing the whole prototype further or by commercialising specific elements of the solution. For example:
- Assistance server
Using data from EDAS, standard assistance messages or bespoke messages with EGNOS corrections and integrity can be created and transferred to the OBU. EDAS data streams will also be used to provide a GNSS monitoring and prediction service across Europe.
- OBU positioning algorithms
These are algorithms producing OBU locations with a high degree of accuracy, availability and integrity through the exclusion of outlying measurements and provision of quality metrics (e.g. horizontal protection level). Improved data going into map matchers should provide greater assurance and support enforcement.
- OBU test platform
The SIGNATURE prototype OBU is based on a single-board computer offering a high degree of flexibility. It can host alternative receivers and positioning algorithms, and manipulate different assistance data with a high degree of configurability. It is a powerful platform for developing and assessing OBU devices and their component parts.