Energy Profiling in Practical Sensor Networks: Identifying Hidden Consumers

Reducing energy consumption of wireless sensor nodes extends battery life and/or enables the use of energy harvesting and thus makes feasible many applications that might otherwise be impossible, too costly or require constant maintenance. However, theoretical approaches proposed to date that minimize Wireless Sensor Network energy needs generally lead to less than expected savings in practice. We examine the experiences of tuning the energy profile for two near-production wireless sensor systems and demonstrate the need for: microbenchmark-based energy consumption profiling; examining start-up costs; and monitoring the nodes during long-term deployments. The tuning exercise resulted in reductions in energy consumption of: 93% for a multihop Telos-based system (average power 0.029 mW); 94.7% for a single hop Ti-8051-based system during startup; and 39% for a Ti-8051 system post start-up. This paper shows that reducing the energy consumption of a node requires a whole system view, not just measurement of a typical sensing cycle. We give both generic lessons and specific application examples that provide guidance for practical WSN design and deployment.