Has green energy arrived? Delay analysis for energy harvesting communication systems

Energy harvesting communication systems provide a “green” solution by obtaining energy from ambient sources, such as sunlight or vibrations. This energy is stored for transmission of data packets which arrive at the link layer of an energy harvesting transmitter. Since the data and energy arrival processes are independent and random, the data packets wait in a queue for the accumulation of sufficient amount of energy and for service completion of previously arrived packets. Thus, the energy arrival process and the data service process jointly impact the data queue dynamics. This makes the queueing analysis of an energy harvesting communication system challenging. In this paper, we formulate a two stage virtual queueing system which decouples the wait stages for the energy arrival process and the service process. This virtual queueing system leads to closed-form expressions for the average packet delay and the probability of data packet loss due to buffer overflow. We assume that the data and energy arrivals are independent Poisson processes and the service time for data packets may have any general distribution. The expressions for the average packet delay and the probability of buffer overflow are shown to be exact when the service time becomes negligible, and the packet delay gets dominated by data packets waiting for arrival of sufficient energy. These expressions are compared with Monte Carlo simulations and are shown to be robust even when the service time is increased up to sixty percent of the average packet delay.