A successful transmission probability based AP clustering scheme in user-centric cell-free networks

Cell-free network is a promising architecture with numerous merits in energy efficiency and macro diversity, which is easy and flexible to integrate with other communication technologies. However, its current network topology where access points (APs) are connected to a central processing unit (CPU) to jointly serve the users, causes huge burden to the fronthaul network. To deal with this problem, in this paper, we first combine thoughts in user-centric (UC) network where users are served by selected subset of APs. Then, we propose a successful transmission probability (STP) based AP clustering scheme to reduce the fronthaul capacity requirement (FCR). By using stochastic geometry and proper approximation methods, the approximated STP calculation expression is derived. Numerical simulations demonstrate that the obtained STP expression can provide a tight approximation compared to Monte Carlo simulation results under different system parameters while keeping the computation tractable. Furthermore, the relationship between the FCR and the STP threshold is formulated as a clustering optimization problem, which gives insights on clustering design in UC-CF network systems. We show by simulation results that the proposed scheme requires less fronthaul capacity than the original CF approach while ensuring the STP performance.