Int. J. Ad Hoc and Ubiquitous Computing, Vol. 27, No. 4, 2018 295 Alternative forwarding strategies for geographic routing in wireless networks Jung-Tsung Tsai* Department of Computer Science and Information Engineering, National Taiwan Normal University, Taipei 11677, Taiwan Email: jutsai@csie.ntnu.edu.tw *Corresponding author Yunghsiang S. Han Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan Email: yshan@mail.ntust.edu.tw Abstract: Greedy forwarding (GF), the fundamental geographic routing scheme, is locally optimal on advancement distance per hop. Instead, we propose a forwarding scheme outperforming GF on total advancement distance to destination through routing decision made from neighbour positions with one-step forward expectation. We then consider that a wireless network topology consists of two subareas of different node densities and that a packet originated in one subarea is destined for the other. Routing over a least hop count path in such a network reflects the Fermat’s principle. Like refraction of light at the interface between two media of different refractive indices, we derive our Snell’s laws and propose geographic refraction routing (GRR) schemes. Results show that when network settings and source-destination pairs provide for obvious refraction, refraction operation can slightly shorten mean path hop counts for reliable routing but significantly improve routing success probabilities for best-effort one. Keywords: geographic routing; greedy forwarding; refraction routing; Snell’s law; Fermat’s principle; wireless network. Reference to this paper should be made as follows: Tsai, J-T. and Han, Y-H. (2018) ‘Alternative forwarding strategies for geographic routing in wireless networks’, Int. J. Ad Hoc and Ubiquitous Computing, Vol. 27, No. 4, pp.295–307. Biographical notes: Jung-Tsung Tsai received his BS, MS, and PhD from National Tsing-Hua University, National Taiwan University, and the University of California, San Diego, in 1985, 1987, and 1995, respectively, all in electrical engineering. He worked in the Industrial Technology Research Institute (ITRI), Hsinchu, Taiwan as a researcher developing web-based network management tools from 1996 to 1997. He joined the Faculty of National Taiwan Normal University in 1997, where he is currently an Associate Professor in the Department of Computer Science and Information Engineering. His research interests are in the areas of opportunistic scheduling, switching, routing, mobility management, and power control. Yunghsiang S. Han received his PhD from Syracuse University in 1993. He was, from 1993 to 1997, with HuaFan University, with National ChiNan University from 1997 to 2004, and with National Taipei University from 2004 to 2010. From August 2010, he is with National Taiwan University of Science and Technology as a Chair Professor. He has published several highly cited works and serves as the editors of several international journals. He was the winner of the Syracuse University Doctoral Prize and a Fellow of IEEE. One of his papers won the prestigious 2013 ACM CCS Test-of-Time Award in cybersecurity. 1 Introduction The idea of geographic routing is to utilise information on neighbour positions and a packet destination to determine the next relay node to receive the packet. If one neighbour closer to destination than the current node exists, in terms of Euclidian distance here, the one closest to destination is chosen. This method is called greedy forwarding (GF) (Finn, 1987), viewed as a locally optimal strategy (Karp and Kung, 2000a). This procedure is repeated until destination is reached or such a Copyright © 2018 Inderscience Enterprises Ltd.