Data retrieval time for energy harvesting wireless sensor networks

TL;DR

This paper models and analyzes the retrieval time in energy harvesting wireless sensor networks, revealing how energy harvesting and broadcasting rates impact performance.

Contribution

It introduces a phase-type distribution model for sensor broadcast times and derives the retrieval time distribution, including asymptotic expressions for large battery capacity and harvesting rates.

Findings

Retrieval time depends mainly on energy harvesting and broadcasting rates.

Large sensor batteries do not significantly reduce retrieval time.

Analytical expressions for retrieval time distribution are provided.

Abstract

We consider the problem of retrieving a reliable estimate of an attribute monitored by a wireless sensor network, where the sensors harvest energy from the environment independently, at random. Each sensor stores the harvested energy in batteries of limited capacity. Moreover, provided they have sufficient energy, the sensors broadcast their measurements in a decentralized fashion. Clients arrive at the sensor network according to a Poisson process and are interested in retrieving a fixed number of sensor measurements, based on which a reliable estimate is computed. We show that the time until an arbitrary sensor broadcasts has a phase-type distribution. Based on this result and the theory of order statistics of phase-type distributions, we determine the probability distribution of the time needed for a client to retrieve a reliable estimate of an attribute monitored by the sensor network. We also provide closed-form expression for the retrieval time of a reliable estimate when the capacity of the sensor battery or the rate at which energy is harvested is asymptotically large. In addition, we analyze numerically the retrieval time of a reliable estimate for various sizes of the sensor network, maximum capacity of the sensor batteries and rate at which energy is harvested. These results show that the energy harvesting rate and the broadcasting rate are the main parameters that influence the retrieval time of a reliable estimate, while deploying sensors with large batteries does not significantly reduce the retrieval time.