Cooperative Hierarchical Deep Reinforcement Learning based Joint Sleep, Power, and RIS Control for Energy-Efficient HetNet

Energy efficiency (EE) is one of the most important metrics for 5G and future 6G networks to reduce energy costs and control carbon footprint. Sleep control, as a cost-efficient approach, can significantly lower power consumption by switching off network devices selectively. Meanwhile, reconfigurable intelligent surface (RIS) has emerged as a promising technique to enhance the EE of 5G beyond and 6G networks. In this work, we jointly consider sleep and transmission power control for reconfigurable intelligent surface (RIS)-aided energy-efficient heterogeneous networks (Hetnets). In particular, we first propose a fractional programming (FP) method for RIS phase-shift control, which aims to maximize the sum-rate under given transmission power levels. Then, considering the timescale difference between sleep control and power control, we introduce a cooperative hierarchical deep reinforcement learning (Co-HDRL) algorithm, including a cross-entropy enabled meta-controller for sleep control, and correlated equilibrium-based sub-controllers for power control. Moreover, we proposed a surrogate optimization method as one baseline for RIS control, and conventional HDRL as another baseline for sleep and power control. Finally, simulations show that the RIS-assisted sleep control can achieve more than 16% lower energy consumption and 30% higher energy efficiency than baseline algorithms.