Delay-aware relay selection with heterogeneous communication range in VANETs

Vehicular ad hoc networks have been used for improving driving experiences by providing safety, efficiency and infotainment applications. Due to high mobility of vehicles, network topology changes frequently, and highly dynamic topology results in lost connection. The geographic routing protocol is used since it does not rely on the establishment of topology. With the popularity of heterogeneous wireless network links, heterogeneous communication range should be taken into consideration when selecting relay from candidate set. The greedy geographic routing protocol with the principle of selecting nearest node to destination may not ensure high packet delivery ratio and low end-to-end delay in this situation. This paper proposes a GPSR-based routing protocol called ETD-GPSR which incorporates the metric expected transmission delay (ETD) for data dissemination with heterogeneous communication range in VANETs. The neighbor table with asymmetric wireless links is established with the help of acknowledgement lists and intermediate nodes. Thus, potential good forward links overshadowed by poor reverse links can be found during the periodic beacon message exchange. Attaching each link with expected transmission delay which takes link quality, link delay and communication range into consideration, the vehicle with the minimum ETD is selected as next hop. Simulation results show that in urban environment with heterogeneous communication range, using the metric ETD has increased the packet delivery ratio and decreased the end-to-end delay.