A Statistical Analysis of RF-Energy Harvesting in Wireless Networks

The ability of wireless terminals to harvest energy from Radio Frequency (RF) signals is gaining tremendous momentum as a mean to prolong the lifetime of these terminals and to recycle the radiated energy. This article gives a much needed statistical analysis for the amount of harvested energy over a period of time T. By studying the input/output characteristics of a typical harvesting circuit, we show that i) the amount of harvested energy over a period of T seconds, denoted by ψ_out, is a stochastic process, and ii) that it can be written as a scaled version of the amount of incoming energy, ψ_in, over the same period of time, i.e., ψ_out = ε̂ψ_in, where ε̂ ∈ [0, 1] is the harvesting efficiency. We also unveil the dependence of ψ_out on the sensitivity of the harvesting circuit which is captured using a Signal to Noise Ratio (SNR) threshold, γ_th.