PAGER-M: A Novel Location-based Routing Protocol for Mobile Sensor Networks Le Zou, Mi Lu, Zixiang Xiong Department of Electrical Engineering, Texas A&M University lezou@ee.tamu.edu, mlu@ee.tamu.edu, zx@lena.tamu.edu Abstract In this paper we present a location-based routing protocol called Partial-partition Avoiding Geographic Routing-Mobile (PAGER-M), for mobile sensor networks that consist of frequently moving sensors. The protocol uses the location information of sensors and the base station to assign a cost function to each sensor node, which is close to the Euclidean length of a sensor node’s shortest path to the base station. A packet is forwarded to the base station using greedy forwarding whenever possible. When a packet reaches sensor nodes near local minimums, where greedy forwarding will be impossible after a number of hops, the packet is forwarded following the high-cost-to-low- cost rule. Extensive simulations are used to compare the performance of PAGER-M with Greedy Perimeter Stateless Routing (GPSR) and Ad-hoc On-demand Distance Vector protocol (AODV) in mobile sensor networks. Experimental results show that PAGER-M achieves higher delivery ratio, lower routing overhead and lower energy consumption. 1. Introduction Wireless sensor networks [1] consist of a large number of densely deployed sensors that have wireless communication, computing, and sensing capacities. In some application scenarios, sensor nodes in these networks move frequently either because they have locomotion capacity or because of the instability of the sensing environment. These mobile sensor networks find applications ranging from biology or biocomplexity research [2], search-and-rescue operations, and environment monitoring [3]. They require efficient and reliable routing protocols rather than flooding when the network mobility is not too high to make it the only choice. Many routing protocols [4~20] have been proposed for ad-hoc/sensor networks. Among them, a number of location-based routing protocols [14~20] have been studied. These location-based protocols utilize the location information of sensor nodes to achieve scalability [21] in large-scale sensor networks. Location service systems [22~24] also justify the use of these location-based routing protocols. Among them, stateless routing protocols do not require a node to memorize past traffic/paths, thus maintain almost no state information. Greedy-Face-Greedy (GFG) [17] and Greedy Perimeter Stateless Routing (GPSR) [18] are currently the most popular stateless location-based routing methods in mobile wireless ad-hoc/sensor networks. GFG/GPSR is shown to perform well in considerably dense (average degree > 20) wireless networks with dynamic topologies. However, as shown in this paper, when the density of wireless networks is reduced, the performance of GPSR also begins to decrease. In this paper, we propose a novel location-based routing protocol called PAGER-M for mobile wireless sensor networks. PAGER-M utilizes the location information of sensor nodes and the base station to assign each sensor node a cost, which is close to a sensor’s Euclidean length of the shortest path to the base station. When a sensor node receives a packet, it forwards the packet to the base station using greedy forwarding [14] whenever possible. Greedy forwarding may fail at a concave node (local minimum) that has no closer neighbor to the base station. To avoid this situation, when a packet reaches sensor nodes near a concave node, the packet is forwarded to a neighbor following the high-cost-to- low-cost rule. PAGER-M does not require a node to memorize the past traffic/path; in this sense, it is a stateless location-based routing protocol. In PAGER- M, multiple forwarding choices are provided for a sending node. This path redundancy reduces the transmission failures caused by mobility. The beacon interval is randomized and prolonged to reduce the interference and routing overhead. Extensive simulations are used to compare the performance of PAGER-M with Greedy Perimeter Stateless Routing (GPSR) [18] and AODV [7] in mobile wireless sensor networks with different parameters. Experimental results show that PAGER-M has a higher delivery ratio, lower routing overhead and lower energy consumption.