Energy Minimization for NOMA Cellular Networks With Two-Dimensional Resource Allocation

In this paper, we investigate the energy minimization for the cellular networks with non-orthogonal multiple access (NOMA). Different from most of existing studies in NOMA networks that considered the resource allocation in only frequency domain or time domain, we discuss the two-dimensional time-frequency communication resource allocation. We formulate the considered problem as a mixed integer non-linear programming (MINLP), and decompose it into three nested subproblems: transmit power optimization, communication resource allocation, and NOMA group partition. Then, we solve them iteratively. For the transmit power optimization subproblem, we first propose a transmit power iteration (TPI) algorithm, after the simplification of the rate requirement constraint, to obtain the transmit powers of cellular users (CUs) in the special case such that a group of CUs only occupies the communication resource in one sub-channel, and prove its optimality and convergence theoretically. Then, a rate requirement allocation based TPI (RRA-TPI) algorithm is further proposed to obtain the transmit powers of CUs in the general cases. For the communication resource allocation and NOMA group partition subproblems, a two-dimensional resource allocation (TDRA) algorithm and a coalition game (CG) algorithm are proposed to solve them, respectively. Simulation results show that via two-dimensional time-frequency resource allocation, we can achieve a significant system energy reduction.