Using batteries wisely
The energy efficiency of WSN’s is typically evaluated in terms of total energy consumption, which is treated as a proxy for battery lifetime. This is true not only for simulations but also for on-device methods that are based on operation counting or coulomb counting.
All of these techniques estimate the amount of charge drawn from the battery, without considering its electrochemical properties. But the way that charge is drawn from the battery affects how much can be extracted before the cut-off voltage is reached.
Modeling and optimization of battery discharge patternsis an active area of research for high-end, rechargeable batteries, such as electric vehicles and mobile devices. How ever, very few studies of the low-end batteries commonly used in WSN scenarios have been published.
Here we describe our study of the discharge behavior of cheap, non-rechargeable batteries operating with low duty cycles, timing intervals of10-1000’s of milliseconds, and loads up to 10’s of mA.
Our goal is to characterize the battery and investigate the feasibility of designing WSN applications that take battery internals into consideration. For example,consider a (trivial) device that schedules two periodic operations: Should it schedule them sequentially, maximizing the rest time between loads, or should it separate them, minimizing the continuous load on the battery?
Our first exploratory results suggest that battery effects may indeed be significant in the sensor network regime. However, further experimental work is needed to form strong quantitative conclusions.
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