A Joint AP Selection and Power Control Scheme for D2D Communications and Cell-Free Massive MIMO Coexistence

Coexistence of device-to-device (D2D) communication and cell-free massive multiple-input multiple-output (CF-mMIM O) is a promising technology for future wireless systems. It is expected to enhance the spectral efficiency (SE), as well as reduce the transmission delay for user equipments. In this paper, we propose a joint access point (AP) selection and power control scheme to maximize the sum SE, oppositing to the existing paper which performs the power control based on the AP selection and the AP selection is performed by the heuristic algorithm, leading to the performance is limited. To address the non-convex optimization problem, the original problem is decomposed into two subproblems: AP selection and power control, both are all resolved by sequential convex approximation (SCA) method. Furthermore, the penalty method is applied in the AP selection, alleviating the narrowing of feasible region brought by the SCA which results in the feasible solution of the original problem unattainable. At the same time, the convergence prove of corresponding algorithm is presented. Numerical results demonstrate the superior performance compared to the existing scheme in terms of improving the performance of the system.