Geographic routing has gained much attention as a basic routing primitive inwireless sensor networks due to its memory-less, scalability, efficiency and low overheadfeatures. Greedy forwarding is the simplest geographic routing scheme, it uses the distanceas a forwarding criterion. Nevertheless, it may suffer from communication holes, whereno next hop candidate is closer to the destination than the node currently holding thepacket. For this purpose, a void handling technique is needed to recover from the voidproblem and successfully deliver data packets if a path does exist between source anddestination nodes. Many approaches have been reported to solve this issue at the expenseof extra processing and or overhead. This paper proposes GRACO, an efficient geographicrouting protocol with a novel void recovery strategy based on ant colony optimization(ACO). GRACO is able to adaptively adjust the forwarding mechanism to avoid theblocking situation and effectively deliver data packets. Compared to GFG, one of the bestperforming geographic routing protocols, simulation results demonstrate that GRACOcan successfully find shorter routing paths with higher delivery rate, less control packetoverhead and shorter end-to-end delay
