Device-to-device (D2D) communication was proposed to enhance the coverage of cellular base stations. In a D2D enabled non-standalone fifth generation cellular network (NSA), service demand of a user equipment (UE) may be served in four \emph{modes}: through LTE only, through NR only, through LTE via D2D and through NR via D2D. Such mode selection should consider the service requirements of the UEs (e.g., high data rate, low latency, ultra-reliability, etc.) and the overhead incurred by handovers. In existing mode selection approaches for D2D enabled NSA, the service requirements of the UEs have been largely ignored. To address this, in this paper, we propose a mode selection algorithm for D2D enabled NSA based on a two-level Analytic Hierarchy Process (AHP). The proposed AHP-based mechanism considers the service requirements of the UEs in level 1; and mode selection options (i.e., LTE only, NR only, LTE via D2D and NR via D2D) in level 2. Thereafter, a novel mode selection algorithm is proposed by combining the static ranking computed by the proposed two-level AHP and the variation of Reference Signal Received Power (RSRP) in different modes, thus capturing the impact of UE mobility and reducing unnecessary handovers. Simulation results show that our proposed algorithm outperforms the best performing related work in terms of the major Key performance indicators (KPIs) for all three slices, i.e., enhanced mobile broadband (eMBB), ultra reliable low latency (uRLLc) and massive machine type communications (mMTc).

翻译：设备到设备（D2D）通信被提出以增强蜂窝基站的覆盖范围。在支持D2D的非独立组网第五代蜂窝网络（NSA）中，用户设备（UE）的服务需求可以通过四种**模式**来满足：仅通过LTE、仅通过NR、通过D2D经由LTE以及通过D2D经由NR。这种模式选择应考虑UE的服务需求（例如，高数据速率、低延迟、超高可靠性等）以及切换所产生的开销。在现有的支持D2D的NSA模式选择方法中，UE的服务需求在很大程度上被忽略了。为了解决这个问题，本文提出了一种基于两级层次分析法（AHP）的支持D2D的NSA模式选择算法。所提出的基于AHP的机制在第一级考虑UE的服务需求；在第二级考虑模式选择选项（即，仅LTE、仅NR、通过D2D的LTE和通过D2D的NR）。此后，通过结合所提出的两级AHP计算的静态排名与不同模式下参考信号接收功率（RSRP）的变化，提出了一种新颖的模式选择算法，从而捕捉UE移动性的影响并减少不必要的切换。仿真结果表明，对于所有三种切片——增强移动宽带（eMBB）、超高可靠低延迟通信（uRLLC）和海量机器类通信（mMTC）的主要关键性能指标（KPI），我们提出的算法均优于性能最佳的相关工作。