A Probabilistic QoS-Aware User Association in Cell-Free Massive MIMO for Industry 4.0

Industry 4.0 requires wireless solutions to meet the demanding reliability and latency requirements of cyber-physical systems serving many industrial sensors and actuators. The cell-free massive multiple input multiple output (MIMO) paradigm, exploiting both massive MIMO gains and cell-free properties, is expected to play a crucial role in addressing Industry 4.0 communication requirements. However, finding an optimal user association to satisfy the quality of service (QoS) requirements is critical. In this article, we propose a novel centralized probabilistic user association algorithm to identify and maximize the number of served users without relying on short-term channel state information to satisfy the QoS requirements. In larger factories, approximately 90% of the total users are satisfied. However, as the system becomes interference-limited and is expected to meet challenging requirements, the number of served users decreases. Nevertheless, the proposed solution exhibits adaptability in maximizing the number of satisfied users. Simulation results further prove the effectiveness of the proposed solution in terms of achievable spectral efficiency and maximizing the number of satisfied users across varying requirements and factory sizes.