15.5.2.7 Successful HO

One of the functions of Mobility Robustness Optimization is to detect a sub-optimal successful handover event. The aim is to identify underlying conditions during successful ordinary handovers, successful LTM cell switches, successful DAPS handovers, successful Conditional handovers, successful LTM Cell switch or successful CHO with candidate SCG(s).

For analysis of successful handover or LTM cell switch, the UE may collect Successful Handover Report (SHR) based on configuration by network, if stored, and makes the SHR available to the network as specified in TS 38.331 [12]. The UE stores the SHR until it is fetched by the network or for 48 hours after the SHR is recorded.

For SHR collected during intra-NR handover, if the target NR node fetches the SHR from the UE and the trigger of SHR is T310/T312, it may forward the information to the source NR node, i.e. the node handling the cell reported as source cell in this SHR, by using the ACCESS AND MOBILITY INDICATION message over Xn or by means of the Uplink RAN configuration transfer procedure and Downlink RAN configuration transfer procedure over NG.

If the NG-RAN node that fetches the SHR from the UE is neither the source node nor the target node of the handover or LTM cell switch, it forwards the information to the node(s) which configured the SHR trigger causing the SHR to be generated, by using the ACCESS AND MOBILITY INDICATION message over Xn or by means of the Uplink RAN configuration transfer procedure and Downlink RAN configuration transfer procedure over NG.

In case of failure shortly after successful Handover or LTM cell switch, the same mobility event may generate both a SHR and a RLF report. In this case, the node(s), which configured the SHR trigger causing the SHR, may take the duplication into account e.g. ignore the SHR.

Upon retrieval of an SHR, the receiving node may analyse whether its mobility configuration needs adjustment.

The SHR can be used to detect one case of Intra-system Too Late Handover, namely when DAPS HO is configured but an RLF is detected in the source cell during a successful DAPS HO.

The SHR can be collected for intra-NR handover or LTM cell switch, and for handover from NR to E-UTRA.