On the Performance of Non-Orthogonal Transmission Enabled Two-Tier CoMP Networks

Non-orthogonal multiple access (NOMA) enables more flexible transmission designs for next generation wireless communication systems. Integrating NOMA with coordinated multi-point transmission (CoMP) can further boost the benefit brought in by joint transmission. In this paper, we investigate the performance of a two-tier CoMP hotspot network with NOMA under Nakagami-m fading environment. In the considered system, a macro base station (MBS) applies zero-forcing beamforming (ZF-BF) to provide multiple interference-free signal streams. The signals of two user equipments (UEs) associated with the MBS and a small-cell base station (SBS), are superimposed in each stream. Cross-tier joint transmission is applied for SBS UEs (SUEs) to efficiently improve received signal quality. Under stochastic geometry framework, we derive the analytical expressions of outage probability and study the influence of key parameter settings. Numerical results show that although a slight degradation can be expected for MBS UEs, NOMA still improves the overall outage performance for the system, especially at high target spectral efficiency region.