  The sum-rate performance of simultaneous transmitting and reflecting
reconfigurable intelligent surface (STAR-RIS) assisted full-duplex (FD)
communication systems is investigated. The reflection and transmission
coefficients of STAR-RIS elements are optimized for the energy splitting and
mode switching protocols to maximize the weighted sum rate of the system. The
underlying optimization problems are non-convex, and hence, the successive
convex approximation technique has been employed to develop efficient
algorithms to obtain sub-optimal solutions. Thereby, the maximum average
weighted sum rate and corresponding coefficients at the STAR-RIS subject to
predefined threshold rates and unit-modulus constraints are quantified. The
performance of the proposed system design is compared with the conventional
reflecting/transmitting-only RISs and half-duplex counterparts via simulations
where it is observed that STAR-RIS can boost the performance of FD systems.
