Bounded-Latency Alerts in Vehicular Networks

Vehicle-to-vehicle communication protocols may be broadly classified into in three categories; bounded-delay safety alerts, persistent traffic warnings and streaming media for telematics applications. We focus on the first category of time-critical messaging as is it of greatest value to the driver and passengers. Safety alerts are transmitted from a vehicle during events such as loss of traction, sudden braking and airbag deployment. The objective for a safety protocol is to relay messages across multiple vehicles within a 1.5-2 km distance to alert approaching vehicles within a bounded end-to-end delay (e.g. 1.5 sec). Due to high mobility and ephemeral connectivity we must employ broadcast protocols, as well as mitigation strategies to curtail inherent issues associated with broadcast protocols, such as broadcast storm problem. In this paper, we present a location division multiple access (LDMA) scheme to suppress the broadcast storm problem and ensure bounded end-to-end delay across multiple hops. This scheme requires participating vehicles to time synchronize with the GPS time and receive the regional map definitions consisting of spatial cell resolutions and temporal slot schedules via an out-of-band FM/RDBS control channel. We use the GrooveNet vehicular network virtualization platform with realistic mobility, car-following and congestion models to evaluate the performance of LDMA in simulation and on the road.