Two-way and multiple-access energy harvesting systems with energy cooperation

We study the capacity regions of two-way and multiple-access energy harvesting communication systems with one-way wireless energy transfer. In these systems, energy required for data transmission is harvested by the users from nature throughout the communication duration, and there is a separate unit that enables energy transfer from the first user to the second user with an efficiency of α. Energy harvests are known by the transmitters a priori. We first investigate the capacity region of the energy harvesting Gaussian two-way channel (TWC) with one-way energy transfer. We show that the boundary of the capacity region is achieved by a generalized two-dimensional directional water-filling algorithm. Then, we study the capacity region of the energy harvesting Gaussian multiple access channel (MAC) with one-way energy transfer. We show that if the priority of the first user is higher, then energy transfer is not needed. In addition, if the priority of the second user is sufficiently high, then the first user must transfer all of its energy to the second user.