User association for minimum energy consumption with macro-relay interference

In this paper, by adjusting user-cell association, we investigate an energy minimization problem in the macro-relay network where the rate requirements of all users are strictly guaranteed. We consider the interference between the macro and relay stations and capture the strength of the interference by the interference factor. Firstly, an integer optimization problem is formulated that is NP-hard. Then we propose a practical algorithm, i.e., macro relay selection with interference for energy minimization (MRSIEM), which dynamically selects the macro or relay station for the users according to the locations of the users, their rate requirements and the interference from the macro or relay station. Extensive simulation results show that, compared with existing user association schemes, the proposed MRSIEM algorithm results in significant energy reduction. Furthermore, it achieves the performance of the exhaustive search method in most scenarios.