Background In designing communication protocols for use in wireless sensor networks, one must consider the limitations of wireless systems in general: limited reliability and finite energy capacity. In the case of a data gathering sensor network (many-to-one), we see that these limitations are closely correlated because link loses are caused by exhausted nodes. Single-route routing protocols select an optimal path from the source to the destination and continue to use it until the path is exhausted. This design subjects the network to branch connectivity losses due to the loss of critical nodes. To mitigate the effects of critical nodes, multi-path routing can be used. Transmission along multiple paths effectively increases reliability in approximate proportion to the number of paths used. However, the use of multiple paths increases energy consumption and therefore decreases overall network lifetime. Youngest Path Routing In order to avoid branch failures in sensor networks, we propose Youngest Path Routing, a routing algorithm that leverages the advantages of multi- path routing, but does not expend extra energy via redundant transmission. In this scheme, each node maintains a list of possible parents and the “ages” corresponding to the paths from these parents. The “age” is an aggregation of the battery level of each node along the optimal path. age(n) = min{ batt_lvl(n), max{ age(parents_of_n)}} Using this metric, a larger age value corresponds to a younger path. Packets are routed to the youngest path only and age values are updated via the acknowledgement packets, which follow the reverse path of the original packet. Youngest Path Routing encourages uniform network energy dissipation, which, in turn, maximizes overall network lifetime. Simulation 100 node wireless sensor network, arranged in a 50x50 square grid pattern, each node 5ft away from the other, with base station at center, was simulated using java. Radios are assumed to be calibrated so that transmissions have a radial “reach” of 30ft. MAC layer was abstracted away to show advantages of routing protocol only. Each node is initialized with 1mAh battery level. Transmission of a single packet uses ~27mAs of energy. Reception of a single packet uses ~22mAs of energy. Power consumption of idling node considered negligible. A packet is sent every 10 seconds from each node to the base station and the number of exhausted nodes is recorded. A node “death” is defined as a node with 0 energy or a node with no route to destination. Results are compared against energy consumption of routing protocol, which uses a particular path until exhaustion, then reinitializes a new path. This alternative protocol simulates a single-route routing protocol which refreshes its routes upon detection of a dropped packet (or lost ACK). References V. Raghunathan, C. Schurgers, S. Park, and M. Srivastava, “Energy-Aware Wireless Microsensor Networks,” IEEE Signal Processing Magazine, pp , March E. Biagioni, S. Chen, “A Reliability Layer for Ad-Hoc Wireless Sensor Network Routing,” Proceedings of the 37 th Hawaii International Conference on System Sciences, J. Lee, B. Krishnamachari, and C. Kuo, “Impact of Energy Depletion and Reliability on Wireless Sensor Network Connectivity,” November 18, 2004 Youngest Path Many-to-One Routing* Karric Kwong Advisor: Ruzena Bajcsy Values within the circles represent the age of the path from that node to the base station. Example of a transmission and acknowledgement along a chosen path to base station A. Note the change in path preference after the age updates via the ACK packet. (Nodes D and B are not shown) Results show that the use of Youth Routing lengthens the time until the death of the first node in the network. It can also be seen that Youth Routing causes a more uniform network death while the alternative method exhibits a gradual network degradation. *This work is supported by the National Science Foundation under grant NSF-CCR