Interference management for active RIS-aided symbiotic radio networks

Symbiotic radio (SR) is a technology that facilitates mutually beneficial sharing of spectrum and energy between primary and secondary systems. In SR networks, utilizing active reconfigurable intelligent surface (RIS) as the secondary transmitter (STx) enhances this mutual benefit compared to passive RIS. This paper addresses the interference management challenges that inevitably arise from employing active RIS. We consider a common SR network consisting of three types of users: SR users, non-SR users, and eavesdroppers. Additionally, each SR user has their own unique cellular services. We propose minimizing the total power consumption while satisfying a sufficiently large signal-to-interference-plus-noise ratio (SINR) for SR users, a small enough SINR for eavesdroppers, and a small enough interference temperature for non-SR users. The alternative optimization (AO) method is used for decoupling multi-variables. The non-convex constraints are relaxed as convex ones through first-order Taylor approximation, and the bounded channel state information (CSI) error model is handled using the S-procedure. Simulations validate the superiority of the proposed algorithm and demonstrate that the total power consumption is minimized while meeting performance thresholds. Additionally, the results offer valuable insights for SR network deployment.