  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.
First, 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.
