  In this letter, role switching and power allocation schemes are proposed to
tackle user mobility in non-orthogonal multiple access (NOMA) systems. When
cell center user (CCU) and cell edge user (CEU) come very close or even cross
each other in NOMA pairing, channel gains of paired users violate the basic
NOMA conditions. 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 where roles of mobile users are switched on the basis of their channel
gains. 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.
Individual and sum capacity are used for performance evaluation. Simulation
results show that OPRS-NOMA outperforms the conventional NOMA and orthogonal
multiple access (OMA).
