Ekho: bridging the gap between simulation and reality in tiny energy-harvesting sensors

Harvested energy makes long-term maintenance-free sensor deployments possible; however, as devices shrink in order to accommodate new applications, tightening energy budgets and increasing power supply volatility leaves system designers poorly equipped to predict how their devices will behave when deployed. This paper describes the design and initial FPGA-based implementation of Ekho, a tool that records and emulates energy harvesting conditions, in order to support realistic and repeatable testing and experimentation. Ekho uses the abstraction of I-V curves---curves that describe harvesting current with respect to supply voltage---to accurately represent harvesting conditions, and supports a range of harvesting technologies. An early prototype emulates I-V curves with 0.1mA accuracy, and responds in 4.4μs to changes in energy conditions.