  The reconfigurable intelligent surface (RIS)-assisted sparse code multiple
access (RIS-SCMA) is an attractive scheme for future wireless networks. In this
letter, for the first time, the RIS phase shifts of the uplink RIS-SCMA system
are optimized based on the alternate optimization (AO) technique to improve the
received signal-to-noise ratio (SNR) for a discrete set of RIS phase shifts.
The system model of the uplink RIS-SCMA is formulated to utilize the AO
algorithm. For further reduction in the computational complexity, a
low-complexity AO (LC-AO) algorithm is proposed. The complexity analysis of the
two proposed algorithms is performed. Monte Carlo simulations and complexity
analysis show that the proposed algorithms significantly improve the received
SNR compared to the non-optimized RIS-SCMA scenario. The LC-AO provides the
same received SNR as the AO algorithm, with a significant reduction in
complexity. Moreover, the deployment of RISs for the uplink RIS-SCMA is
investigated.
