  In this paper, we propose a simultaneous transmitting and reflecting
reconfigurable intelligent surface (STAR-RIS) and energy buffer aided
multiple-input single-output (MISO) simultaneous wireless information and power
transfer (SWIPT) non-orthogonal multiple access (NOMA) system, which consists
of a STAR-RIS, an access point (AP), and reflection users and transmission
users with energy buffers. In the proposed system, the multi-antenna AP can
transmit information and energy to several single-antenna reflection and
transmission users simultaneously by the NOMA fashion in the downlink, where
the power transfer and information transmission states of the users are modeled
using Markov chains. The reflection and transmission users harvest and store
the energy in energy buffers as additional power supplies, which are partially
utilized for uplink information transmission. The power outage probability,
information outage probability, sum throughput, and joint outage probability
closed-form expressions of the proposed system are derived over Nakagami-m
fading channels, which are validated via simulations. Results demonstrate that
the proposed system achieves better performance as compared to the proposed
system with discrete phase shifts, the STAR-RIS aided MISO SWIPT-NOMA
buffer-less, conventional RIS and energy buffer aided MISO SWIPT-NOMA, and
STAR-RIS and energy buffer aided MISO SWIPT-time-division multiple access
(TDMA) systems. Furthermore, a particle swarm optimization-based power
allocation (PSO-PA) algorithm is designed to maximize the uplink sum throughput
with a constraint on the uplink joint outage probability and Jain's fairness
index (JFI). Simulation results illustrate that the proposed PSO-PA algorithm
can achieve an improved sum throughput performance of the proposed system.
