A Novel MBS-Based Resource Allocation Scheme for Symbiotic Radio Under SWIPT-Enabled Cell-Free Massive MIMO

In this paper, symbiotic radio under simultaneous wireless information and power transfer (SWIPT)-enabled cell-free massive multiple-input multiple-output (CF-mMIMO) is investigated, where multiple access points serve all primary users and backscatter devices (BDs). We derive closed-form expressions for the achievable rates of the primary users and BDs, downlink signal-to-interference-plus-noise-ratio (SINR) and the harvested energy of the primary users. We aim to maximize fairness among BDs through joint optimization of the power splitting factor of SWIPT, uplink and downlink power control and backscatter coefficients of BDs. Being different from traditional low-complexity modified bisection search (MBS) schemes applied in other systems where the non-convex issues of the downlink SINR constraints are not considered, a novel MBS-based resource allocation scheme is proposed for symbiotic radio under SWIPT-enabled CF-mMIMO employing successive convex approximation method to address the non-convex issue and thus enhance the applicability of the MBS scheme. Simulation results show that our proposed scheme can obtain a near-optimal solution with low complexity, which could reduce the processing delay of the central processing unit in CF-mMIMO networks.