RIS-Assisted Safe Sleeping for Coverage and Energy Efficiency in Dense Small Cell Networks
The increasing density of 5G and beyond networks has greatly increased energy demands, making energy efficiency an essential objective for next-generation systems. While cell sleeping is a well-known technique used to reduce consumption, most existing schemes fall short in maintaining service continuity and fail to address the long delays introduced by hardware reactivation. These limitations can severely affect the Quality of Service (QoS), especially for applications requiring low latency and high reliability. This study introduces RIS-Assisted Safe Sleeping (RASS), a unified framework that enables dense small cell deployments to save energy without sacrificing user experience. RASS integrates three complementary mechanisms, namely a coverage-safety certificate that verifies robust SINR before deactivation, RIS resource slicing that allocates reflection elements for both coverage support and wake-up signalling, and an RIS-assisted paging channel that reduces the visible effect of hardware wake-up delay. Through systematic sensitivity analysis, we identify that RASS performs best with a slicing factor of α = 0.7 and moderate coverage thresholds between -6 and -4 dB. Simulation results demonstrate significant benefits over conventional schemes: the safe-sleep ratio rises substantially, blocking probability falls by as much as 40%, and energy efficiency improves by more than 20%. The results show that integrating coverage validation, RIS resource allocation, and wakeup delay mitigation enables RASS to balance energy efficiency while ensuring service is available. Overall, RASS provides an efficient framework for improving energy efficiency in ultra-dense 5G and beyond networks while maintaining a reliable user experience.