  We consider the combination of uplink code-domain non-orthogonal multiple
access (NOMA) with massive multiple-input multiple-output (MIMO) and
reconfigurable intelligent surfaces (RISs). We assume a setup in which the base
station (BS) is capable of forming beams towards the RISs under line-of-sight
conditions, and where each RIS is covering a cluster of users. In order to
support multi-user transmissions within a cluster, code-domain NOMA via
spreading is utilized. We investigate the optimization of the RIS weights such
that a large number of users is supported. As it turns out, it is a coupled
optimization problem that depends on the detection order under interference
cancellation and the applied filtering at the BS. We propose to decouple those
variables by using sum-rate optimized weights as the initial solution, allowing
us to obtain a decoupled estimate of those variables. Then, in order to
determine the final weights, the problem is relaxed into a semidefinite program
that can be solved efficiently via convex optimization algorithms. Simulation
results show the effectiveness of our approach in improving the detectability
of the users.
