Joint Subcarrier Pairing and Power Allocation for Cooperative Nonorthogonal Multiple Access

In this correspondence, a downlink cooperative nonorthogonal multiple access transmission scheme is considered in the multicarrier scenario, where the user equipment (UE) with strong channel conditions acts as a relay to help the UE with weak channel conditions. A joint optimization of subcarrier pairing and power allocation is formulated as a mixed-integer nonconvex problem, with the objective to minimize the transmit power of the base station and the relay (strong UE) under the quality of service requirements of both UEs. We first explore the inherent property of power allocation for a single subcarrier pair. Then, in light of the property, we employ the Lagrange dual method and the Hungarian algorithm, in an asymptotically optimal manner, to solve the joint subcarrier pairing and power allocation problem. Numerical results show that our proposed algorithm outperforms other schemes with or without cooperation.