  This letter investigates the bit error rate (BER) performance of simultaneous
transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) in
non-orthogonal multiple access (NOMA) networks. In the investigated network, a
STAR-RIS serves multiple non-orthogonal users located on either side of the
surface by utilizing the mode switching protocol. We derive the closed-form BER
expressions in perfect and imperfect successive interference cancellation
cases. Furthermore, asymptotic analyses are also conducted to provide further
insights into the BER behavior in the high signal-to-noise ratio region.
Finally, the accuracy of our theoretical analysis is validated through Monte
Carlo simulations. The obtained results reveal that the BER performance of
STAR-RIS-NOMA outperforms that of the classical NOMA system, and STAR-RIS might
be a promising NOMA 2.0 solution.
