Three-dimensional geographic routing in wireless mobile ad hoc and sensor networks

Geographic routing has been considered as an attractive approach for wireless mobile ad hoc and sensor networks due to its effectiveness and scalability. Over the past few decades, numerous geographic routing protocols have been proposed extensively in 2D space. However, these protocols are no longer valid if ad hoc or sensor networks are distributed in 3D environments, such as space, atmosphere, and ocean. Because of the surprisingly difficulty of designing geographic routing protocols for 3D networks compared to 2D networks, only a few prior studies have focused on 3D geographic routing specifically designed for ad hoc and sensor networks. In this article, we first illustrate the principles of 3D geographic routing, and categorize current research work based on different criteria. Then we compare the 3DGR protocols under study through comprehensive analysis. Finally, we point out the open issues and opportunities for further research.