  Reconfigurable intelligent surfaces (RISs) bring great potential to the
advancement of 6G and beyond wireless communication technologies. RISs
introduce a great degree of flexibility, allowing some sort of virtual control
over the wireless channel. Exploiting the flexibility introduced by RISs, we
propose a novel RIS-enabled downlink (DL) non-orthogonal multiple access (NOMA)
scheme where NOMA is enabled over-the-air rather than at the base station (BS)
or the receiver (Rx). Here, the RIS is partitioned into distinctive groups
where each part of the RIS serves a different user equipment (UE) to perform
multiple accessing. The BS transmits an unmodulated signal to the RIS, and each
partition modulates the impinging signal over-the-air by introducing a phase
shift according to the incoming information bits to serve the corresponding UE.
First, the end-to-end system model for the proposed system is presented.
Furthermore, outage probability calculations, theoretical error probability
analysis, and bit error rate (BER) derivations are discussed and reinforced
with comprehensive computer simulation results.
