Cognitive RF–FSO Fronthaul Assignment in Cell-Free and User-Centric mMIMO Networks

Cell-free massive MIMO (CF-mMIMO) network and its user-centric (UC) version are considered as promising techniques for the next generations of wireless networks. However, fronthaul backhaul assignments challenging issues in these In this paper, energy efficiencies uplink transmission CF- UC-mMIMO networks studied, wherein access points (APs) connected to aggregation nodes (ANs) through radio frequency (RF) and/or free-space optic (FSO) fronthauls, ANs a central processing unit via fiber backhauls. The achievable data rates derived by taking into account effects hardware non-ideality at APs ANs, FSO alignment weather conditions. To have robust energy-efficient network, especially presence misalignment adverse conditions, first, cognitive RF–FSO assignment algorithm is proposed cost sharing available RF bandwidth between links. Then, optimal power allocations users investigated, two analytical approaches solve non-convex optimization problem. Through numerical results, we discussed how utilizing achieves higher efficiency compared that FSO-only, RF-only, or simultaneously using links, e.g., achieving up $198\%$ under unfavorable Moreover, misalignment, on networks’ performances discussed.