  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.
