Abstract-We consider an energy harvesting device whose state at a given time is determined by its energy level and an "importance" value, associated to the transmission of a data packet to the receiver at that particular time. We consider policies that, at each time, elect whether to transmit the data packet or not, based on the current energy level and data importance, so as to maximize the long-term average transmitted data importance. Under the assumption of i.i.d. Bernoulli energy arrivals, we show that the sensor should report only data with an importance value above a given threshold, which is a strictly decreasing function of the energy level, and we derive upper and lower bounds on the thresholds for any energy level. Leveraging on these findings, we construct a suboptimal policy that performs very close to the optimal one, at a fraction of the complexity. Finally, we demonstrate that a threshold policy, which on the average transmits with probability equal to the average energy arrival rate is asymptotically optimal as the energy storage capacity grows large. Energy harvesting devices (EHD) collect, or "harvest", energy from the environment in order to perform sensing and data-communication tasks, thus having the ability to operate autonomously for extended periods of time [1] . In contrast to traditional sensors, where the objective is to minimize energy consumption under a performance constraint, e.g., delay [2], in the case of an EHD, the objective is the "management" of the harvested energy. Intuitively, an EHD should judiciously perform its assigned task based on its available energy, becoming more "conservative" as its energy supply runs low to ensure uninterrupted operation, and more "aggressive" when energy is abundant. In this paper, we study the case of an EHD which reports incoming data of different "importance" levels to a receiver (RX), with the overall goal to maximize the long-term average importance of the reported data. A number of practical examples fall under this general model: a temperature-sensing EHD, where the importance is an increasing function of the temperature value, higher temperatures being the indicator of overheating or fire; an EHD which relays different priority packets in a sensor network [3] ; an EHD which adjusts the packet information rate based on the channel condition to the RX, in which case the importance level corresponds to the instantaneous rate and the objective is to maximize the longterm average throughput [4] . We consider a slotted-time system with i.i.d. Bernoulli energy arrivals, and i.i.d. importance values which follow an arbitrary continuous distribution. We show that, for the class of binary (transmit/no transmit) policies, the optimal policy
In REF , the problem of maximizing the long term transmitted data utility at the fusion center of an energy harvesting WSN has been studied.
On optimal transmission policies for energy harvesting devices
2012 Information Theory and Applications Workshop
2012 Information Theory and Applications Workshop
Computer Science