Active STAR-RIS-Assisted Symbiotic Radio Communications Under Hardware Impairments

In this letter, we study an active simultaneously transmitting and reflecting reconfigurable intelligent surface (aSTAR-RIS) assisted symbiotic radio system under hardware impairments (HIs). The aSTAR-RIS is adopted to not only assist in transmitting primary signals from a base station (BS) to a primary user (PU), but also as a secondary transmitter to deliver secondary signals to secondary users (SUs). We aim to minimize the system power consumption by optimizing the transmit beamforming vector at the BS, the coefficients matrices and amplification matrix at the aSTAR-RIS. Specifically, we present the feasibility condition for the formulated problem and propose an alternating optimization (AO) algorithm to find its near-optimal solution. Numerical results show the effectiveness of the proposed algorithm as compared to various benchmark schemes.