A Hybrid Routing Protocol for 3-D Vehicular Ad Hoc Networks

In Vehicular Ad hoc NETworks (VANETs), traditional routing protocols are mainly based on planar scenarios. However, the actual application environments of VANETs are three-dimensional (3-D). For example, an important way to fully utilize the city space is the elevated overpass which is popular in most big cities. In this paper, we investigate the routing issues in 3-D scenarios of VANETs. We first analyze the characteristics of a 3-D city road network and present the key design points of 3-D routing protocols in VANETs. Afterward, we propose our hybrid improved 3-D scenario oriented routing (ITSR) which consists of two parts. The first is the routing strategy simple ITSR (S-ITSR) addressing the issue in the simple 3-D city scenario. In S-ITSR, we design intralayer greedy forwarding, interlayer greedy forwarding, and interlayer recovery strategy in combination with the degradation of the transmission range. The second is the routing strategy complex ITSR based on the complex 3-D city scenario. In this protocol, we introduce the concept of virtual neighbor node and the complete process of neighbor list considering the feature of the fluctuant transmission range. Finally, we conduct simulations to evaluate the network performance. Simulation results show that ITSR can achieve enhanced performance in terms of the packet delivery ratio, hop count, and end-to-end delay.