Optimal transmission policy for cooperative transmission with energy harvesting and battery operated sensor nodes

In this paper, we consider a scenario where one energy harvesting and one battery operated sensor cooperatively transmit a common message to a distant base station. The goal is to find the jointly optimal transmission (power allocation) policy which maximizes the total throughput for a given deadline. Initially, we address the case in which the storage capacity of the energy harvesting sensor is infinite. In this context, we identify the necessary conditions for such optimal transmission policy. On their basis, we first show that the problem is convex. Then we go one step beyond and prove that (i) the optimal power allocation for the energy harvesting sensor can be computed independently; and (ii) it unequivocally determines (and allows to compute) that of the battery operated one. Finally, we generalize the analysis for the case of finite storage capacity. Performance is assessed by means of computer simulations. Particular attention is paid to the impact of finite storage capacity and long-term battery degradation on the achievable throughput.

• An energy harvesting (EH) and a battery operated (BO) sensor form an antenna array.
• The optimal policy for throughput maximization is identified.
• The optimal policy for the EH sensor can be computed independently from the BO one.
• The optimal policy for the BO sensor can be computed from that of the EH one.
• The impact of finite storage capacity and battery degradation is analyzed.