Arbutus: Network-Layer Load Balancing for Wireless Sensor Networks

The hot spot problem is a typical byproduct of the many-to-one traffic pattern that characterizes most wireless sensor networks: the nodes with the best channel to the sink are overloaded with traffic from the rest of the network and experience a faster energy depletion rate than their peers. Routing protocols for sensor networks typically use a reliability metric to avoid lossy links and thus directly exacerbate the problem. Significant advantages can be obtained by embedding a load balancing scheme at the network layer, as we show with the design and implementation of Arbutus, a novel routing protocol for wireless sensor networks with a built-in load balancing scheme. By imposing a special structure on the collection tree, privileging longer hops, and accounting for network load in the route selection process, Arbutus reduces the impact of hot spots on network lifetime without a deterioration of the end-to-end reliability performance. An implementation of Arbutus on Berkeley motes and the MoteLab testbed shows a 30% reduction in the network traffic load needed to achieve the same packet delivery rate as an existing mote-oriented protocol. This provides key benefits such as a significant lifetime gain and increased fault tolerance.