Diversity analysis of an outage minimizing energy harvesting wireless protocol in Rayleigh fading

In a recent paper, the authors introduced the save-then-transmit (ST) protocol, designed for a wireless link with an energy harvesting transmitter. The outage minimizing ST protocol computes the fraction of each frame to reserve for energy harvesting by the main energy storage device (ESD); the rest of the frame is used concurrently for message transmission and for charging of the secondary ESD. In this paper, we study the performance loss due to the randomness of energy availability at the transmitter, compared to a conventional system with a deterministic supply of power, through a derivation of the outage probability expression under certain special conditions. It will be shown that this performance loss is dependent on the distribution assumed for the energy harvesting rate, X. Different parameter settings for a Gamma-distributed X lead to performance gaps ranging from 1 to 10 dB. These results confirm that the performance loss incurred by using an unreliable energy source is heavily dependent on the variability of the source.