Energy harvesting self-powered and self-healing topology using LoRa




Dominguez, Ruben

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In order to prolong the operating lifetime, designs and optimization over the Low-Power Wide-Area Networks (LPWAN) in IoT applications are gaining a lot of attention as a choice for communications in future real-time monitoring systems due to the low-power, long-range, and low-cost features. For traditional battery-powered edge devices, the main research/design focus is on reducing energy consumption and improving energy efficiency in general. These conventional low-power techniques employed in new communications protocols are gaining a lot of attention. In orthogonal, there are simultaneously emerging self-sustaining energy harvesting systems for energy extraction and conservation to alternatively prolong node lifetime. With considerations such as cost, longevity, and potential environmental hazards, energy harvesting has been gaining a lot of popularity for addressing the high costs, limited sustainability, and environmental concerns as one of the best battery substitutes. Since energy harvesters can extract various kinds of energy from ambient energy sources such as solar, wind, and kinetic, battery-less operations of many small wireless sensors are enabled. Consequently, energy harvesters are becoming increasingly popular as power sources for IoT edge devices. However, due to the unpredictability of the duty cycle caused by the unstable power supply, ongoing communication can be interrupted resulting in data corruption and inevitable re-transmission. Additionally, It can take a huge amount of time and energy for two devices to establish a connection with the list of probable discrepancies in communication like risking the loss of integrity from collisions of packets in overlapping periods of active radios in the same channel, periods of overhearing, periods of over-broadcasting, etc. With energy harvesting systems’ already limited energy, these problems make the rising hardware solutions for power conservation useless without efficient design for minimizing the possibilities of energy-waste periods. What’s even more challenging is that even after the initial connection, the volatile time data of the clock modules on embedded IoT devices can be drifted with the passage of time by the unstable power supply or be corrupted completely by frequent power outages. As a result, the embedded IoT devices will lose synchronization with each other. Since a synchronized timeline is required so that both transmitter and receiver can turn on their radio simultaneously for communication. After losing time synchronization, both the transmitter and receiver need a huge amount of time and energy to build a wireless connection for transmitting data under energy-harvesting scenarios. Such efforts can be more tremendous when considering receivers such as network gateway need to hop around different channels to collect data based on the schedule. Those challenges render existing communication protocols ineffective. In order to design sustainable systems operating with limited and unstable supply power constraints, appropriate protocols must be designed for efficient energy usage to retain the scarce energy as much as possible. This thesis proposes algorithms for a rapid-healing topology using LoRa for adapting into energy harvesting scenarios from minimizing collisions through unique multi-spreading factors and multi-frequency channel allocations. The algorithm further minimizes over-broadcasting from EH nodes through designated scheduled communications with the gateway and reduces energy consumed from recovering nodes requesting to heal back to the network through consistent in-duty-cycle periods of time for heal-listening in the initialization and healing channel. This approach essentially also provides a lot of time for transmitter nodes to harvest more energy through longer deep-sleep states in idle unscheduled communication while providing rapid healing. Operating under the LoRaWAN, experimentation will be conducted with a testbed consisting of each embedded LoRa node being managed by a central gateway for network configuration and data communication. A series of experiments will be conducted to evaluate the proposed initialization and healing algorithms in terms of time and energy consumption at different run-time phases. This is done to assist in deriving a mathematical model to describe the relationship for required capacitance for an energy harvesting LoRa node to confidently initialize and stay in scheduled sustaining sleeping and sensing routine cycles as well as to support the necessary network healing process.



IOT, LoRa, power harvesting, self-healing



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