Undervolting in WSNs: Theory and Practice

Adapting the voltage level of a processing unit to the actual system load leads to an increased energy efficiency. The aim is to extend the battery lifetime, but existing voltage scaling approaches still act with reserve. To reduce the energy consumption even further, it is possible to power the electric circuits below the specified voltage levels. Considering the processing unit of wireless sensor nodes, this “undervolting” saves up to 42% of energy per clock cycle, and hence would lead to a significant longer lifetime of nodes and networks. Contrariwise, operating processors or nodes outside their specifications add some extra incertitude to the system. In this paper, we analyze the effects of undervolting for a typical wireless sensor node in theory and practice. Moreover, we give a detailed insight into the dependencies and used a prototype implementation to characterize the influence of lower than recommended voltage levels on the microcontroller unit (MCU). In addition, the impact of different temperatures is considered as well as the behavior of an undervolted transceiver unit and, therefore, the effects on the wireless communication. While classical computer applications may contain too many hazards to outweigh the improved energy consumption when using undervolting, we show that it is particularly suitable for wireless sensor networks (WSNs) with a huge potential of saving energy and the opportunity of novel power management approaches on every layer.