Void Avoidance in Three-Dimensional Mobile Underwater Sensor Networks

Mobile underwater sensor networks are usually featured with three-dimensional topology, high node mobility and long propagation delays. For such networks, geographic routing has been shown to be very suitable. However, routing voids pose great challenges on the greedy policy used in most geographic routing protocols. The problem is more severe for underwater sensor networks because of node mobility and threedimensional topology. In this paper, we propose a void avoidance protocol, called Vector-Based Void Avoidance (VBVA), to address the routing void problem in mobile underwater sensor networks. VBVA adopts two mechanisms, vector-shift and back-pressure, to handle voids. Vector-shift mechanism is used to route data packets along the boundary of a void. Back-pressure mechanism routes data packets backward to bypass a concave void. VBVA handles the routing void problem on demand and thus does not need to know network topology and void information in advance. Therefore, it is very robust to cope with mobile voids in mobile networks. To the best of our knowledge, VBVA is the first void avoidance protocol to address the three-dimensional and mobile void problems in underwater sensor networks. Our simulation results show that VBVAworks effectively and efficiently in mobile underwater sensor networks.