D2D Communications Strategy for Optimizing Energy Efficiency in Ultra-Dense Networks

The integration of Device-to-Device Communications (D2D) and millimeter wave band (mmW) within Ultra-Dense Networks (UDN) plays a crucial role in the context of the Fifth Generations (5G) networks, as it effectively addresses the substantial demands for high-volume traffic. Therefore, in UDN high-density indoor locations, internet service providers and end-users would deploy numerous Small Base Stations (SBSs) to meet the substantial User Equipment (UE) demands. The cumulative energy consumption of all SBSs is expected to be significant despite their tiny size and lower power requirements, resulting in notable environmental and economic consequences. Disabling the underutilized SBSs within current cellular networks presents an effective strategy for conserving energy without compromising the Quality of Service (QoS) experienced by UEs. This paper primarily concerns Energy Efficiency (EE) in UDN with many SBSs. It proposes a centralized awake/sleep control mechanism for SBSs in the mmW band to reduce network power consumption without compromising the network efficacy of UE. D2D communication assisted in optimizing the user's association with the grouping UEs approach. It can minimize the limited communication range in mmW bands and reduce SBSs in awake mode. Based on the evaluation results presented, with the proposed UEs association optimization and SBS awake/sleep mechanism, effectiveness in EE improvements and network efficiency can be guaranteed.