Optimal user association and resource allocation for device-to-device communications underlaying cellular networks

We study a joint user association and resource allocation problem for device-to-device communications underlaying cellular networks. In particular, the problem formulation is to maximize the sum rate across cellular users (CUs) and device-to-device users (DUs) under the constraints of the minimum data rate requirements of individual users. To solve the problem, we decompose such optimization problem into two subproblems: the resource allocation subproblem for any pair of DU and CU, and the user association subproblem. Due to the convex nature of the resource allocation subproblem, we derive the optimal solution in the closed-form expression. We further relax the user association subproblem, although as an integer programming, to a linear programming, and then obtain its optimal solution via interior-point methods. Our analysis shows that the proposed algorithm has low overhead signaling during its implementation, and our simulation results further show that the proposed algorithm can guarantee the maximum system sum rate.