Joint Subcarrier Assignment and Downlink-Uplink Time-Power Allocation for Wireless Powered OFDM-NOMA Systems

In this paper, a wireless powered orthogonal frequency division multiplexing (OFDM)-non-orthogonal multiple access (NOMA) system is considered. The subcarrier assignment, energy harvesting/information transmission (EH/IT) time allocation, and downlink -uplink power allocation are jointly optimized to maximize the system sum-throughput while taking user fairness into account. Due to the intractability of the considered problem, we first decompose the original problem into two subproblems, namely, subcarrier assignment subproblem with fairness consideration and joint downlink-uplink time-power allocation subproblem. For subcarrier assignment subproblem, with given joint downlink-uplink time-power allocation, a locally optimal subcarrier assignment algorithm is proposed based on the many-to-many matching theory. Then with given subcarrier assignment, an algorithm based on golden section method, iterative water-filling and projected subgradient method is proposed for achieving the optimal solution to joint downlink-uplink time-power allocation subproblem. An alternate iteration framework is further proposed to jointly optimize two subproblems for maximizing the system sum-throughput. Simulation results validate the effectiveness of the proposed algorithms, i.e., the proposed framework approaches to the joint downlink-uplink time-power allocation optimal solution with less than 5% throughput loss compared to the upper bound and with only about 40% complexity of the interior-point algorithm.