Dynamic user association for energy minimization in macro-relay network

In this paper, an energy minimization problem for users with heterogeneous locations and rate requirements in the macro-relay network is considered, in which the rate requirements of all users are strictly guaranteed and meanwhile the total energy consumption of the network is minimized. First, the energy minimization problem is formulated as an integer optimization problem, which is similar to the well-known knapsack problem and has been proven to be NP-hard. Then the complexity of the optimal exhaustive search method is analyzed and a practical and effective algorithm, macro and relay selection for energy minimization (MRSEM), is proposed. The proposed MRSEM algorithm dynamically associates users to macro or relay station according to both the radio frequency energy and circuit energy, thus to minimize the total energy consumption of the system. Extensive simulations are conducted and the results show that, the proposed MRSEM algorithm can significantly reduce the total energy consumption compared with existing schemes, while it almost achieves the optimal solution of the exhaustive search method.