Coverage Optimization of Hybrid Active-Passive STAR-RIS-Assisted Indoor–Outdoor Communication Under Hardware Impairments and Imperfect CSI

Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) offers a promising solution to conquer the challenge of severe signal attenuation through buildings for seamless indoor-outdoor connectivity in 6G networks. This paper focuses on hybrid active-passive STAR-RIS assisted indoor-outdoor communications and delves into the comparative impact of diverse non-ideal factors on system performance, such as transceiver hardware impairments, imperfect channel state information (CSI), and STAR-RIS phase noise. Under these system imperfections, our objective is to maximize the minimum user rate by optimizing user grouping, non-orthogonal multiple access (NOMA) decoding order, power allocation coefficients, active beamforming, and transmission and reflection beamforming, thereby enhancing system robustness and user fairness. Given the complexity of the formulated problem, characterized by interwoven optimization variables, we propose a collaborative convex optimization iterative (CCOI) algorithm by blending successive convex approximation (SCA), semidefinite relaxation (SDR), Gaussian randomization, and convex upper bound approximation. This methodology is capable of adeptly striking a balance between system performance and computational efficiency. Simulation results demonstrate the significant advantages of our proposed CCOI algorithm and provides guiding insights on system design for various defects. Additionally, the hybrid active-passive STAR-RIS structure offers enhanced flexibility and effectively balances the performance trade-offs between conventional active and passive models.