  Simultaneously transmitting and reflecting reconfigurable intelligent surface
(STAR-RIS) assisted non-orthogonal multiple access (NOMA) communication systems
are investigated in its vicinity, where a STAR-RIS is deployed within a
predefined region for establishing communication links for users. Both
beamformer-based NOMA and cluster-based NOMA schemes are employed at the
multi-antenna base station (BS). For each scheme, the STAR-RIS deployment
location, the passive transmitting and reflecting beamforming (BF) of the
STAR-RIS, and the active BF at the BS are jointly optimized for maximizing the
weighted sum-rate (WSR) of users. To solve the resultant non-convex problems,
an alternating optimization (AO) algorithm is proposed, where successive convex
approximation (SCA) and semi-definite programming (SDP) methods are invoked for
iteratively addressing the non-convexity of each sub-problem. Numerical results
reveal that 1) the WSR performance can be significantly enhanced by optimizing
the specific deployment location of the STAR-RIS; 2) both beamformer-based and
cluster-based NOMA prefer asymmetric STAR-RIS deployment.
