Control Plane Initial Synchronization Optimization for Ultra-Dense Cell-Free Massive MIMO

Ultra-dense cell-free Massive MIMO (CF-MM) is a promising technology for future 6 G networks. Unlike previous research, we focus on the challenges of CF-MM in the control plane. Specifically, we investigate the initial synchronization processing for CF-MM, which is fundamental for user equipment (UE) to access the wireless network. Regardless of whether LTE- or New Radio (NR)-based synchronization signals are used, the existing initial access procedures are incompatible with CF-MM, leading to severe interference on the broadcast channel and thus a high initial access failure rate. To address this issue, we design a new synchronization scheme for CF-MM based on the latest NR standard. With this new scheme, the initial synchronization interference problem is then transformed into a transmission and reception points (TRP) ID partition problem. To solve problem, we then propose an approach that combines the latest multiple operator heuristic (MOH) method with a parameterized local search(PLS) method. Simulation results show that the proposed method can achieve the optimal solution for scenarios with a low number of TRPs. Furthermore, the gap between the proposed method and the optimal solution is less than 2% for high number TRPs cases, demonstrating its effectiveness.