Joint Long-Term Energy Efficient Scheduling and Beamforming Design for URLLC in Cell-Free MIMO Systems

In this letter, we develop a queue-aware long-term energy-efficient optimization scheme for cell-free multiple-input multiple-output (CF-MIMO) systems in the ultra-reliable and low-latency communication (URLLC) scenario. Considering the coordinated multi-point (CoMP) and hybrid orthogonal scheduling scheme, we formulate a stochastic optimization problem to maximize the long-term utility and to maintain the network stability. By introducing Lyapunov framework, the long-term energy-efficient optimization problem is decomposed into a sequence of subproblems. Then, we propose an energy-efficiency (EE) based beamforming, user association and subcarrier assignment (EE-BUASA) algorithm to achieve the long-term energy-efficient scheduling. The numerical results illustrate that the proposed algorithm outperforms the baseline schemes and can provide a trade-off between utility and stability.