A delay-sensitive vehicular routing protocol using Ant Colony Optimization

Vehicular Ad hoc Networks (VANETs) are confronted with numerous difficulties and challenges, such as scalability issues, rapid changes of network topology and channel capacity restriction, which can induce communication deterioration. In this paper, we propose a delay-sensitive vehicular routing protocol, which uses the intersections as anchors to establish optimal delay routing paths consisting of a list of intersections. The main feature of our protocol is the periodic estimation of the road segment delay expressed in the combination of average delay and delay variance using multi-hop vehicle relaying. As this estimation is local to road segments, we make use of ACO (Ant Colony Optimization) concept to discover end-to-end best delay paths from source to target intersection which is closest to the destination. Route setup process is achieved by reactive forward ants and backward ants, which are in charge of network exploration and pheromone dissemination respectively. Routing selection is implemented at each intersection to opportunistically choose best next intersection based on a pheromone routing table. A proactive route maintenance is initiated by source to update, expand and improve the routing information during data transmission period using periodic proactive ants sampling. In addition, we make use of simple carry and/or greedy forwarding technique to relay packets between adjacent intersections. The simulation results indicate that our protocol shows better communication performance compared with a basic geographical routing protocol (GPSR) and a min-delay routing protocol (CAR) in regard to delivery ratio, average end-to-end delay and overhead.