Role switching and power allocation technique for mobile users in non-orthogonal multiple access

In this paper, role switching and power allocation schemes are proposed to tackle user mobility in non-orthogonal multiple access (NOMA) systems. A downlink transmission scenario is considered, where two highly mobile users, a cell center user and a cell edge user, are paired/served over the same channel resource using NOMA. In such high mobility scenarios, when these users come very close to, or even cross, each other, their channel gains may become similar or even violate the initial channel ordering when they were paired. This article refers to such condition as NOMA principle violation problem (NPVP). To solve this NPVP, optimized power role switching-NOMA (OPRS-NOMA) technique is proposed. Role switching technique is used to switch the roles of mobile users on the basis of their dynamic channel ordering. Furthermore, a power allocation scheme based on bisection search power optimization is presented to maximize the average sum capacity of mobile NOMA users. Random way point mobility model is considered for user mobility , where individual and sum capacity are used for performance evaluation. Simulation results show that OPRS-NOMA outperforms the conventional NOMA and orthogonal multiple access schemes.