Data offloading with renewable energy powered base station connected to a microgrid

This paper proposes a general model for offloading to an access point (AP) to minimize energy cost in a heterogeneous network with a renewable-energy powered base station (BS) that is connected to a microgrid. We consider the setting where both the BS and the AP can buy energy from the grid to satisfy their requirements, but the BS can sell back any excess renewable energy to the grid. The downlink scenario is considered whereby the BS and the AP cooperate to serve a set of users, and the problem is to determine the user assignment to the BS or the AP. In the specific case of time division multiple access, we show that the optimal user assignment problem is NP Hard. We propose a sub-optimal, low complexity algorithm for this setting and obtain an approximation guarantee to the worst case sub-optimality of our algorithm. Simulations show that our algorithm performs well, with only a small gap to the optimal exhaustive search method over the set of users.