Cost minimization for fading channels with energy harvesting and conventional energy

In this paper, we investigate resource allocation strategies for a point-to-point wireless communications system with hybrid energy sources consisting of an energy harvester and a conventional energy source. By assuming that the non-causal information of the energy arrivals and the channel power gains is known, a mixed integer programming problem is formulated to minimize the total energy cost of such a system over N fading slots under the energy harvesting constraints and a proposed outage constraint. The outage constraint requires that a minimum fraction of slots to be reliably decoded. This constraint is useful if, for example, an outer code is used to recover that all data bits. Optimal linear time algorithms are obtained for two extreme cases: when the number of outage slots is 1 or N -1. For the general case, a lower bound based on linear programming relaxation, and two suboptimal algorithms are proposed. Numerical simulations indicate that the proposed suboptimal algorithms exhibit only a small gap from the lower bound for a wide range of given parameters.