Joint User Association and Power Allocation for Hybrid Half-Duplex/Full-Duplex Relaying in Cellular Networks

For hybrid half-duplex/full-duplex relaying in a relay-aided cellular network, a joint user association, relay mode selection, and power allocation scheme is proposed to maximize the energy efficiency under the minimum spectral efficiency requirement and transmission power constraints. This combinatorial optimization problem is a mixed-integer nonconvex one, which is difficult to be solved in its original form. To circumvent this issue, the problem is first transformed into an equivalent one whose objective function is in a parametric subtractive form. Then, the equivalent problem is reformulated as a convex one by relaxing index variables, converting the nonconvexity by the successive convex approximation, and constructing auxiliary variables. In this way, the equivalent nonconvex problem is approximated by a convex one in each iteration, and the dual decomposition technique is employed to solve the convex one. An iterative algorithm is further developed to reach the solution to the primal problem. Simulation results show that the performance of the iterative algorithm can be very close to the optimal solution obtained by the exclusive searching within only a few number of iterations. Moreover, the proposed scheme outperforms existing ones, which only adhere to either the user association or the relay mode selection but not both.