For fifth-generation (5G) and 5G-Advanced networks, outage reduction within the context of reliability is a key objective since outage denotes the time period when a user equipment (UE) cannot communicate with the network. Earlier studies have shown that in the experimental high mobility scenario considered, outage is dominated by the interruption time that stems from the random access channel (RACH)-based handover process from the serving cell to the target cell. A handover by itself is a necessary mobility process to prevent mobility failures and their associated outage. This paper proposes a RACH-less handover signaling scheme for the 3rd Generation Partnership Project (3GPP) conditional handover (CHO) mechanism. The proposed scheme exploits the decoupling between the CHO preparation and execution phases to establish initial synchronization between the UE and the target cell through an early acquisition of the timing advance. This significantly curtails the RACH process and therefore the handover interruption time. Results based on a system-level simulation-based mobility study have shown that the proposed scheme significantly reduces the outage and its constituent handover interruption time relatively by 18.7% and 43.2%, respectively.

翻译：在第五代（5G）及5G-Advanced网络中，降低中断时间作为可靠性指标的核心目标至关重要，因为中断时间定义为用户设备（UE）无法与网络通信的时段。已有研究表明，在实验性高移动性场景中，中断主要由从服务小区到目标小区的基于随机接入信道（RACH）切换过程导致的中断时间主导。切换本身是防止移动性失效及其关联中断的必要移动性管理过程。本文针对第三代合作伙伴计划（3GPP）条件切换（CHO）机制，提出一种免RACH切换信令方案。该方案利用CHO准备与执行阶段的解耦特性，通过提前获取定时提前量建立UE与目标小区间的初始同步，从而显著缩短RACH过程及切换中断时间。基于系统级仿真移动性研究的结果表明，所提方案可将中断时间及构成中断的切换中断时间分别降低18.7%和43.2%。