  This manuscript presents an energy-efficient alternating optimization
framework based on intelligent reflective surfaces (IRS) aided non-orthogonal
multiple access beamforming (NOMA-BF) system for 6G wireless communications.
Specifically, this work proposes a centralized IRS-enabled design for the
NOMA-BF system to optimize the active beamforming and power allocation
coefficient (PAC) of users at the transmitter in the first stage and passive
beamforming at IRS in the 2nd stage to maximize the energy efficiency (EE) of
the network. However, an increment in the number of supportable users with the
NOMA-BF system will lead to NOMA user interference and inter-cluster
interference (ICI). To mitigate the effect of ICI, first zero-forcing
beamforming along with efficient user clustering algorithm is exploited and
then NOMA user interference is tackled efficiently through a proposed iterative
algorithm that computes PAC of NOMA user through simplified closed-form
expression under the required system constraints. In the 2nd stage, the problem
of passive beamforming is solved through a technique based on
difference-of-convex (DC) programming and successive convex approximation
(SCA). Simulation results demonstrate that the proposed alternating framework
for energy-efficient IRS-assisted NOMA-BF system can achieve convergence within
a few iterations and provide efficient performance in terms of EE of the system
with low complexity.
