On the Achievable Sum-Rate of NOMA-Based Diamond Relay Networks

Non-orthogonal multiple access (NOMA) is an effective solution to improve spectral efficiency since it oversteps the limit of the orthogonality imposed on the transmitted data flows. In this paper, a NOMA-based dual-hop diamond relay network where a source communicates with a destination via two decode-and-forward (DF) relays is considered. It is assumed that either the statistical channel state information (S-CSI) or instantaneous channel state information (I-CSI) is acquired to the network. Specifically, first, for the S-CSI assumption, closed-form expression of the achievable sum-rate in the high signal-to-noise ratio region is derived, and two effective power allocation schemes are proposed accordingly; second, for the I-CSI assumption, the achievable sum-rate is analyzed and the dynamic power allocation scheme is proposed; third, a promising hybrid power allocation (HPA) scheme that resorts to both S-CSI and I-CSI is proposed to improve the performance under the S-CSI assumption and to reduce the computational complexity and feedback overhead under the I-CSI assumption. Simulation results demonstrate that, first, NOMA is superior to the conventional schemes in terms of achievable sum-rate, especially for the case that the near-far effect is severe and, second, the HPA strategy can be an effective solution with moderate computational complexity and superior performance.