Lyapunov-Optimized Two-Way Relay Networks With Stochastic Energy Harvesting

Energy harvesting wireless cooperative communications have become more and more popular in recent years. In this paper, we consider a two-way relay cooperative network, where the relay is an energy harvesting node and uses decode-and-forward (DF) or amplify-and-forward (AF) cooperation protocol. We formulate the energy management problem in such a network as an optimization problem, which minimizes the long-term average outages with a long-term average battery constraint. We then apply Lyapunov optimization to transform the long-term optimization problem into the drift-plus-penalty. We also conduct theoretic analysis of the proposed energy management strategy. Specifically, we prove that the long-term average battery constraint can be guaranteed with the proposed strategy and derive an upper bound of the average outages with the proposed strategy. Furthermore, we analyze theoretically the diversity order and energy harvesting gain of the proposed strategy with the DF and AF protocols. Finally, simulation results using real-solar irradiance data measured by the solar site in Elizabeth City University show that the outage performance and the diversity order of our algorithms are better than the existing MDP-based method.