Two-Stage Power Allocation for Dual-Hop Relaying Systems With Non-Orthogonal Multiple Access

To improve the sum-rate (SR) and the outage probability of the dual-hop relay system, a novel two-stage power allocation scheme with non-orthogonal multiple access is proposed. In this scheme, after the reception of the superposition coded symbol with a power allocation from the source, the relay decodes-and-forwards a new superposition coded symbol with another power allocation to the destination. By employing a simple linear combination, the destination jointly decodes the information symbols from the received signals from the source and the relay. Assuming Rayleigh fading channels, the ergodic SR and the outage performance of the system are investigated. In addition, a suboptimal power allocation strategy with closed form of the power allocation factors is also designed, which is close to the optimal one. Through numerical results, it is shown that the performance of the proposed scheme is significantly improved compared with the existing works.