Hybrid Energy Harvesting Wireless Systems: Performance Evaluation and Benchmarking

Energy harvesting (EH) is an attractive and green solution to the problem of limited lifetime of wireless sensor networks (WSNs). Unlike a conventional node that dies once it runs out of energy, an EH node harvests energy from the environment and replenishes its rechargeable battery. We investigate a new class of hybrid networks that comprise both EH and conventional nodes and differ from conventional and all-EH WSNs. We propose two new and insightful performance criteria called k-outage duration and n-transmission duration to evaluate these networks. They overcome the pitfalls associated with defining lifetime, which arise because the EH nodes never die but can occasionally run out of energy, and capture the dynamic time evolution, which occurs because the conventional nodes irreversibly drain their batteries. They also account for the inability of the nodes to transmit data due to insufficient battery energy and channel fading. We prove two computationally efficient novel bounds for evaluating these criteria. Our results characterize the effect of the number of EH and conventional nodes and channel fading statistics on these criteria. Further, given a total cost constraint, we determine the conventional and EH node mixture in the network that optimizes these criteria.