Performance Analysis of STAR-RIS Assisted NOMA Systems With Hardware Impairments

Unlike conventional reconfigurable intelligent surfaces (RIS), simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) have been used to achieve a more flexible degree of freedom in signal propagation. This paper evaluates the performance of STAR-RIS assisted non-orthogonal multiple access networks under hardware impairments over Nakagami-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading channels. Firstly, we derive exact analytical expressions for the probability density function and cumulative distribution function of the sum of cascaded channels using Fox’s <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i>-function. Furthermore, we conduct performance analysis including the outage probability, diversity orders, and average achievable rate for a pair of users. Finally, Simulation results validate the analytical expressions and demonstrate that the outage performance improves with increasing the number of STAR-RIS elements <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i>, hardware impairments degrade overall network performance.