Energy Efficiency of Ultra-Dense Small Cell Radio Access Networks for 5G and Beyond

Small cell base station (BS) densification in the radio access network (RAN) is an effective solution to improve the RAN capacity. However, small cell BS densification by adding more non-zero energy-consuming BSs increases energy consumption, compromising energy efficiency, which can be mitigated by adopting sleep mode. A comprehensive evaluation framework is applied in this research to analyse the capacity, energy consumption, and energy efficiency performance of the ultra-dense small cell RANs as a complete energy efficiency assessment, which is lacking in the literature. The impact of advanced techniques millimetre wave (mmWave), antenna array beamforming, and integrated access and backhaul (IAB) on RAN energy efficiency are also investigated. MATLAB- based simulation results show that the ultra-dense small cell RANs, where the number of BSs greatly exceeds the number of active user equipment (UEs), can only be energy efficient if all the empty cells without UE association are turned off completely. Energy efficiency enhancement comes from capacity improvement and energy consumption constraint. Specifically, the ultra-dense small cell RANs can achieve maximum performance improvement of 7.56-fold and 2.35-fold regarding capacity, 3780.11-fold and 32.38-fold regarding energy consumption using the current power model, and 28591.53-fold and 75.97-fold regarding energy efficiency in homogeneous and heterogeneous infrastructures, respectively, comparing the cases with and without the sleep mode. In addition, mmWave and IAB trade energy consumption and energy efficiency for capacity improvement and backhaul cost reduction. With mmWave and IAB, dense small cell RAN can achieve a maximum of 2.55-fold and 1.70-fold for capacity improvement, 2.46-fold and 2.89-fold for energy consumption reduction using the current power model, and 6.27-fold and 8.34-fold energy efficiency enhancement for UE densities of 900 and 300 UEs/km2, respectively, comparing the cases with and without the sleep mode.