Relative Positioning for Collision Avoidance Systems
Increasing road safety is one of the EU's priorities of the European Commission; the REPOSIT project was commissioned to address the situation of technology being used only to mitigate the effects of accidents once the vehicle has collided (structural design of car bodies, airbags, etc.) or to try to increase the performance and reliability of the systems controlling the dynamics of the car just before a potential collision (ADAS - advanced driver assistance systems such as ABS, ESP, etc.).
REPOSIT was therefore conceived as a system to improve road safety by increasing the awareness of drivers regarding the position of the other cars on the road and how they are moving.
The use of positioning devices (GPS) is very widespread nowadays for navigation purposes, but another possible application (less well used) is to combine the information from two devices in order to obtain a much more precise relative positioning between the units. This is one of the main concepts that make REPOSIT possible.
In order to be able to obtain a relative positioning, we need two units to share their information and that can be achieved thanks to a set of emerging technologies related to inter-vehicular communications. Nowadays, vehicles are isolated entities on the road, but in the near future they will be exchanging information with other vehicles to provide in-vehicle entertainment, safety solutions and so on.
The REPOSIT concept goes further than just vehicle positioning (relative to other vehicles: 'Relative GPS') in that it can alert the user of potentially dangerous situations. If a potential collision is predicted, an alarm is raised in order to warn the driver in advance and reduce his reaction time.
There are studies that suggest that the reaction time is a very significant factor in road accidents as the driver does not have enough time to make a decision in order to avoid a collision. REPOSIT tries to decrease that reaction time in order to avoid the collision or at least allow enough time to the car to reduce its energy before the crash.
REPOSIT aimed to address the use of Relative GPS and wireless vehicle-to-vehicle (V2V) communications integrated with existing Collision Avoidance Systems (CAS).
The final goal of REPOSIT, from the scientific and technological point of view, was to be able to prove how the use of Relative GPS combined with wireless vehicle-to-vehicle communications is feasible and makes sense in the context of Collision Avoidance Systems and, in particular, for the case of longitudinal and intersection collisions.
Identified tasks deployed for reaching project objectives were:
- implementation of Relative GPS algorithms applicable to longitudinal and intersection CAS;
- modelling and characterisation of wireless vehicle-to-vehicle communications applicable to longitudinal and intersection CAS;
- implementation of longitudinal and intersection CAS integrating Relative GPS and V2V communications;
- simulation of the implemented longitudinal and intersection CAS integrating Relative GPS and vehicle-to-vehicle communications, and addressing major results.
The main steps were:
- define REPOSIT components - RGNSS Module, V2V Module and CAS Module;
- develop and tune each single module;
- study obtained test results;
- analysis of future enhancements for REPOSIT.
Complementary activities were:
- analysis and results of the in-vehicle integration case;
- analysis and results from the Standardisation and Certification viewpoint.
- studied user needs and application requirements, producing a 'System Requirements' deliverable;
- developed algorithms and produced an integrated simulator for V2V communications, RGNSS positioning and CAS warnings;
- run simulations on the scenarios that were defined (72 tests on each software version);
- analysed the feasibility of in-vehicle integration, including the deliverable 'REPOSIT In vehicle integration';
- established a certification and standardisation policy, including a business plan and a CEN Workshop Agreement (CWA).
A key achievement was the software development and the final results extracted from the simulation phase. The software modules were developed to simulate each technology involved in REPOSIT (Relative GNSS positioning, V2V communications and CAS) and a mainstream code comprises the required function calls and synchronism among modules, tying the overall REPOSIT simulator as a whole. Therefore every simulated vehicle inherits a standard logical architecture and all vehicles are properly synchronised to the millisecond level thanks to the PPS pulse signal received from the GNSS receiver, and they interchange data through the communication module.
The vehicle-to-vehicle/vehicle-to-infrastructure (V2V/V2I) communication module developed allows inter-vehicular communications providing the required data transfer capabilities for a relative positioning algorithm that works in real-time. The data types devised to be interchanged among vehicles are GNSS raw data of approximately 1kb length per vehicle at 1Hz to compute GNSS relative algorithms, and Alarm data warning in advance to all nearby vehicles after a critical red alarm is detected.
A RGNSS (Relative Global Navigation Satellite System) module takes and processes as input the raw data provided by the GNSS receiver on-board a vehicle and the raw data received from other vehicles in real-time through the communication channel.
The trialled system was found to have sufficient accuracy for lane detection (across-carriageway) and properly detects the collision time instant (along the carriageway).
A Collision Avoidance System (CAS) Module was developed, which takes the relative positioning information provided by the RGNSS module as inputs, as well as the information received from other vehicles through the V2V communication link. With this information it predicts the relative dynamics of the vehicles on the road, and it also can adva
REPOSIT was a concept and feasibility activity, so Certification needs to be achieved prior to any use for road traffic. Therefore feasibility of standards approval and of Certification according to well defined, institutionally accepted rules, is a condition for REPOSIT feasibility.
REPOSIT has demonstrated its potential on highways and linear scenarios, but it is still a challenge for it to be effective on continuously changing roads. The system has to count on additional future information to anticipate the changing conditions or increase the monitoring frequency to minimise error peaks, and both initiatives are affordable at low cost by using available maps for such extrapolation and low cost GNSS receivers. So the system has to evolve to face these new challenges using cooperative systems, and remaining a cost effective product. Also, it has to wait until V2V becomes a reality to prove its value in different environments. However, PEPOSIT is still feasible and will potentially show how GNSS systems can tell us more than just our location.
The REPOSIT system is analogous with a current navigation system within a vehicle but with a V2V communication and additional software running at the background, so it is mainly software, and due to this, cost effective. Perhaps the most expensive part would be the wholly in-vehicle REPOSIT installation linked with the dashboard HMI, so a strategy could be to leave REPOSIT to be also installed externally, thus making it affordable.
Recommended future work is the development of a demonstrator system using real vehicles, in order to prove simulations against real world situations. This demonstrator needs final V2V standard hardware for communications, further integration of digital maps and in-vehicle sensors for the CAS algorithm, and final definition of HMI system for in-vehicle usage.
The REPOSIT Roadmap identifies roles for industry developers (to build an integrated prototype), regulators (standardisation), car manufacturers (implementation once demonstrations have proved successful), end users (in terms of awareness) and public authorities/agencies (for eSafety funding). Low-cost solutions are a key to success – or in other words, 'cost-affordable', i.e. 'when the end-user perceives the product services as clearly beneficial.'
REPOSIT also needs, from a very high penetration rate, to work properly as a collision warning system. Until this is reached, REPOSIT services include simple GNSS navigation and V2I (Vehicle-to-Infrastructure) facilities.