A Game Theoretical Approach to D2D Underlaying Downlink NOMA Networks

Spectrum efficiency and users throughput are two major challenges for the 5th generation (5G) wireless mobile systems. Non-orthogonal multiple access (NOMA) and device-to-device (D2D) communications have been recognized as promising techniques to address these challenges, and improve the overall 5G networks performance. In this paper, adopting a game theoretical approach, we propose an analysis framework to help users with poor channel conditions increase their downlink transmission rates. Users (players) choosing between two strategies-namely, connect directly to a NOMA base station; or use the D2D link and rely on the other users to get the service-try to maximize their throughput (payoff) in a game-like context. We define the Nash equilibrium conditions for this game, and we simulate the behaviors of users based on the channel conditions of the different links. The results show a significant rate increase for the users with poor channels, especially when paired with users experiencing better link conditions.