Optimal Policies in Energy Harvesting Two-Way Channels with Processing Costs

We consider a two-way communication channel in which both users rely solely on energy harvested from nature. Each user incurs a processing cost per unit time as long as it communicates; that is, each user's energy consumption includes energy spent for transmission and energy spent for processing. We maximize the sum throughput by a given deadline subject to energy causality constraints. We first show that the optimal power policy is bursty; the two users communicate only during a portion of the time that is uniquely determined by their available energies and processing costs. We show that it is optimal for the two users to be fully synchronized; they turn on and exchange data during the same portion of time, and then turn off together. We first solve the single energy arrival case, and then extend it to solve the multiple energy arrival throughput maximization problem. We show that it is optimal for the users to communicate in a deferred fashion; users postpone their energy consumption to utilize later time slots first. We present an algorithm that gives the optimal deferred policy by iteratively applying a modified version of the single energy arrival result in a backward manner.