Relaying and stability in energy harvesting simple networks

Wireless systems of rechargeable nodes have extended lifetime and are self-sufficient. The transmission policies in these systems need to adapt to the harvested energy availability. In this work, we investigate the interaction between relaying, energy harvesting, and stability. We introduce the problem of general relaying cost minimization for cooperative energy harvesting networks. We consider a simple network in which a source transmits to a destination through network-level cooperation with a number of relay nodes. The source and the relays have energy harvesting capability. To adapt the relaying process to the available harvested energy, we exploit partial relay cooperation in which the flows through the relays are controlled. The relaying cost minimization problem is feasible when the data queues of the source and the relays are stable. The stability conditions of the data queues are derived. Then, we introduce the energy consumption as a cost criterion for the optimization problem to find an energy-efficient partial relaying protocol. We assess the effect of partial relay cooperation compared to the cases of no cooperation and full relay cooperation.