Multiplexing of short real-time messages for road transport informatics systems

Avoiding traffic collapses requires intelligent and integrated traffic systems, all of which rely on communication systems. For future dedicated short range communication systems (SRC), a 1 GHz band between 63 and 64 GHz has been assigned, integrating all kinds of road transport and traffic telematics (RTTT) services. This system will support both communication between vehicles and infrastructure (via beacons) as well as inter-vehicle communication. The data to be transmitted will consist mainly of short messages, either broadcasted to all receiving neighbour stations (cooperative driving, route guidance) or exchanged in handshake protocols in a point-to-point dialogue (road pricing, parking management). A crucial point for system performance will therefore be the multiplexing and blocking unit, which has to combine these short, variable length messages into transmission packets, taking into account their respective real-time constraints. The complexity of this task is increased by the fact that all SRC systems are based on time division multiplexing (TDM) techniques, so after each transmission a reaccess delay has to be met. We present a new type of integrated blocking/multiplexing unit particularly suited for inter-vehicle communication systems. It aims to minimise the age of received information concerning the redundancy in cooperative driving messages that are repeated frequently (⩽20 Hz). The simulation results show the improvement over well-known strategies like head of the line (HOL)