NEAL: Neighbor Management to Exploit Asymmetric Links in Wireless Sensor Networks

While asymmetric links in wireless sensor networks can be useful, it is difficult to exploit them efficiently. Factors that contribute to the difficulties include the inherent one-way communication with asymmetric link that complicates asymmetric link discovery, changes in link quality over time, and a small neighbor table size that can be less than the number of neighboring nodes. In order to address these challenges, we propose NEAL, a neighbor management scheme that is designed to exploit asymmetric links. In particular, NEAL is made up of components to efficiently discover asymmetric links, monitor their status and manage the (small) neighbor table. We implement NEAL in TinyOS and evaluate its performance using TOSSIM. Simulation results show that more than 80% of asymmetric links can be discovered and maintained with minimum overhead. Using a collection tree application and ETX as the routing metric, the average path ETX can be reduced by up to 20%.