Exploiting opportunities in V2V transmissions with RSU-assisted backward delivery

The vehicle-to-vehicle (V2V) data transmissions in Vehicular Ad-hoc Networks (VANETs) have been applied in many areas including the Internet of Vehicles, mobile data offloading, and mobile crowdsensing. The V2V-based data delivery that is opposite to the direction of a vehicle is called a backward delivery against the traffic flow, and it is blocked by an existing problem: a traffic hole. Under the backward delivery with a traffic hole problem, there are no available vehicles that can move the data to its destination using the movement-assisted routing protocol; the data move in the direction opposite to that of the vehicle's motion. In this paper, we investigate backward data delivery under the traffic hole problem in order to provide more opportunities for V2V data transmissions. To mitigate the impact of the traffic hole on the backward data delivery, we propose an RSU-Assisted Backward Delivery scheme (RABD) which employs the roadside units (RSUs) as low-cost relays instead of traditional access points. RABD combines two methods of data delivery: one based on backward data forwarding among vehicles and another which is forwarded by the RSU. To reduce resource consumption, we investigate the single-copy scheme and consider the tradeoffs of both methods. Our extensional simulations verify the effectiveness of our proposed schemes.