User Association Coalition Games with Zero-Forcing Beamforming and NOMA

In future fifth generation (5G) and beyond wireless technologies, ultra-dense networks (UDNs) will be employed to serve a massive amount of devices with mobile access. One of the major challenges in UDNs is user association, which is essential for dealing with intra- and inter-cell interference. In this paper, a user association problem is formulated and solved via a game theoretical approach. Specifically, in an effort to mitigate interference and maximize the sum-rate of the system, a coalition game is employed which exploits the cooperation among the small base stations (SBSs). Two algorithms are proposed, one where zero-forcing (ZF) or regularized ZF (RZF) beamforming is applied and another where ZF and non-orthogonal multiple access (NOMA) are jointly considered. Simulation results show that the proposed algorithms can significantly improve the overall sum-rate, providing near-optimal solutions while keeping the complexity low.