A sensor node with energy harvesting

Abstract

Introduction Applications including remote sensing, embedded sensing (e.g. in bridges or buildings), or sensors for public safety require that sensing and transmission take place with minimal human intervention and no direct connection to the power mains. Ideally, sensing nodes should be autonomous and able to harvest ambient energy from vibrations, light, electromagnetic radiation, or heat. Thus energy harvesting nodes for wireless communications [5, 1] are of great interest. Here we study nodes that have packet buffers and energy storage buffers (e.g. capacitors or batteries) and we use the Energy Packet(EP) [2, 3] abstraction so that one EP is the amount of energy needed to transmit a Data Packet (DP). Ideally the energy flow into the device, expressed as EPs per unit time, should balance the flow of DPs that are assembled for transmission so that DPs are not held up. However we show that if EP and DP flows are exactly balanced, the system exhibits an unstable behaviour so that both the backlog of packets and the amount of stored energy saturate their respective storage, and derive results concerning the performance of the system when the energy and work flows are unbalanced. The study can be generalised to the multihop case. Consider a system that at stime t contains K(t) DPs to transmit and M(t) EPs in storage. Let the data buffer capacity be B DPs, while the energy storage device can store up to E EPs. The state of the system is then the pair (K(t),M(t)) and are interested in its probability distribution p(n,m, t) = Pr[K(t) = n,M(t) = m). Arrival of DPs to the data buffer follows a Poisson process of rate λ, while the EPs arrive into the energy buffer as a Poisson process of rate Λ corresponding to some rate of a joules/second, where a is the energy required to transmit one packet. We assume that the rates at which energy is harvested and data collected is slow as compared to the rate at which DPs are transmitted by the device, e.g. it may take many milliseconds to get enough energy from the harvester while it may