Abstract
Energy-neutral operation (ENO) is a major concern for Internet of things (IoT) sensor systems. Animals can be tagged with IoT sensors to monitor their movement and behavior. These sensors wirelessly upload collected data and can receive parameters to change their operation. Typically, the behavior monitors are powered by a battery where the system relies upon harvesting solar radiation for sustainable operation. Solar panels typically are used as the harvesting mechanism and can have a level of uncertainty regarding consistent energy delivery due to factors such as adverse weather, foliage, time of day, and individual animal behavior. The variability of available energy inevitably creates a trade-off in the rate at which data can be collected with respect to incoming and stored energy. The objective of this research was to investigate and simulate methods and parameters that can control the data collection rate of an IoT behavior monitor to achieve sustained operation with unknown and random energy harvesting. Analysis and development of a control system were performed by creating a software model of energy consumption and then simulating using different initial conditions and random energy harvesting rates for evaluation. The contribution of this effort was the exploration into the usage of a discrete-time gain scheduled Proportional–Integral–Derivative (PID) that was tuned to a specific device configuration, using battery state of charge as an input, and found to maintain a battery level set-point, reject small solar harvesting energy disturbances, and maintain a consistent data collection rate throughout the day.
Highlights
Wireless embedded systems or mobile devices in the form of Internet of things (IoT) systems have become ubiquitous in our daily lives
Energy usage of a wildlife behavior monitoring device manufactured by Cellular Track Technologies (CTT) shown in Figure 1, was measured in a fixed setting using a programmable power supply to mimic solar energy in order to illustrate the problem with a fixed data collection rate that exceeds the harvested energy
The CTT-1000a wildlife behavior monitor consists of an MSP430 microcontroller, a GPS receiver, a real-time clock, FLASH data storage, a Li-ion battery, a Global System for Mobile Communications (GSM) cellular modem, and solar panel tightly integrated into a single system
Summary
Wireless embedded systems or mobile devices in the form of Internet of things (IoT) systems have become ubiquitous in our daily lives. Battery-powered IoT devices must either rely on a stored charge or harvest energy to continue operation. Deployed IoT devices, in the form of geo-location solar powered animal behavior monitors, are a candidate for examining the impact of a proportional data collection rate on the stored charge and harvestable energy. Conservative fixed data collection rates for animal behavior monitors best address the unpredictable nature of solar energy harvesting by attempting to operate with excess stored energy [1]. The opposite would be aggressive fix rates that would most certainly drain the battery and be unable to continuously collect data. In order to continually collect data, ENO controllers able to vary data collection rates proportional to the amount of energy harvested were sought for an IoT animal behavior monitoring device
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