  This paper proposes a simultaneous transmitting and reflecting reconfigurable
intelligent surface (STAR-RIS) aided wireless-powered non-orthogonal multiple
access (NOMA) system, which includes an access point (AP), a STAR-RIS, and two
non-orthogonal users located at both sides of the STAR-RIS. In this system, the
users first harvest the radio-frequency energy from the AP in the downlink,
then adopt the harvested energy to transmit information to the AP in the uplink
concurrently. Two policies are considered for the proposed system. The first
one assumes that the time-switching protocol is used in the downlink while the
energy-splitting protocol is adopted in the uplink, named TEP. The second one
assumes that the energy-splitting protocol is utilized in both the downlink and
uplink, named EEP. The outage probability, sum throughput, and average age of
information (AoI) of the proposed system with TEP and EEP are investigated over
Nakagami-m fading channels. In addition, we also analyze the outage
probability, sum throughput, and average AoI of the STAR-RIS aided
wireless-powered time-division-multiple-access (TDMA) system. Simulation and
numerical results show that the proposed system with TEP and EEP outperforms
baseline schemes, and significantly improves sum throughput performance but
reduces outage probability and average AoI performance compared to the STAR-RIS
aided wireless-powered TDMA system. Furthermore, to maximize the sum throughput
and ensure a certain average AoI, we design a genetic-algorithm based time
allocation and power allocation (GA-TAPA) algorithm. Simulation results
demonstrate that the proposed GA-TAPA method can significantly improve the sum
throughput by adaptively adjusting system parameters.
