Vehicle to Vehicle module
The vehicle-to-vehicle module enables the inter-vehicular communications that provide the required data transfer capabilities for a real-time working relative positioning algorithm.
It is of utmost importance that it works under low delay constraints in order to provide the best accuracy for all the vehicles without a noticeable lag.
It is based on the IEEE 802.11 protocol family. While 802.11p (the standard that is being worked on for these inter-vehicular applications) the simulations have been carried on with the well known 802.11a that should approximate quite well the worst case situation for 802.11p.
The system works by broadcasting the information in the channel following an exponential backoff collision avoidance algorithm. That means that if a vehicle tries to transmit and detects someone else is transmitting it will wait a longer random time before trying again. This time is in the range of milliseconds, because new data arrives every second and it is not worth trying to transmit old information when you have fresh one waiting to be sent. In a regular data system we are used to value a lot recovering all the pieces of information, but in a real-time system such as REPOSIT it is more important to share as soon as possible the latest available information.
The above scenario as taken from the Car-To-Car consortium website, shows vehicles talking to each other.
Nowadays, current technology makes possible to establish radio links among vehicles that are a few hundred meters apart. That is enough to warn the drivers that cruise at the maximum legal speed with at least 5 seconds in advance if the trajectory prediction is accurate.
