Successful Handover Report

Description

The Successful Handover Report (SHR) is a key enabler for advanced mobility management and Self-Organizing Network (SON) functionalities in 5G NR and evolved LTE networks. It is a structured message generated by the target node (gNB or eNB) upon the successful completion of a handover and sent back to the source node. Unlike basic handover completion signals, the SHR contains a rich set of contextual data about the radio conditions and configuration at the moment of handover execution. This report is defined within the context of the Xn Application Protocol (XnAP) and NG Application Protocol (NGAP) for inter-gNB and inter-system communication, as referenced in specifications like TS 38.423 and TS 38.413.

The report's content is comprehensive. It typically includes the Cell Radio Network Temporary Identifier (C-RNTI) assigned to the User Equipment (UE) in the target cell, detailed measurement results reported by the UE just before the handover (e.g., Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ)), and the specific configuration of the radio bearers that were successfully established. Furthermore, it can contain timestamps and identifiers for the specific handover command. This granular data allows the source node to build a historical record of handover outcomes correlated with the radio conditions that triggered the handover decision.

Architecturally, the SHR flows over the Xn interface between gNBs or the NG interface between an eNB and a 5GC. Its generation and consumption are integral to Mobility Robustness Optimization (MRO) algorithms. By analyzing sequences of SHRs (and their counterpart, the Handover Failure Report), the network can detect issues like too-early, too-late, or handovers to wrong cells. The source node can then adjust its handover control parameters, such as hysteresis margins, time-to-trigger, or cell individual offsets, in an automated or semi-automated manner. This closed-loop optimization is vital for maintaining seamless mobility in dense, heterogeneous 5G deployments with complex interference scenarios.

Purpose & Motivation

The SHR was introduced to address the limitations of earlier mobility management systems, which often relied on simplistic success/failure indicators or required extensive drive testing and manual analysis to optimize handover parameters. In 4G LTE, SON features began automating optimization, but the data exchange was often less detailed. The advent of 5G, with its use of higher frequencies (mmWave), ultra-dense networks, and demanding use cases like ultra-reliable low-latency communication (URLLC), created a pressing need for more intelligent and data-driven mobility management.

The primary problem SHR solves is the lack of visibility for the source node into the *result* of its handover decision. Before SHR, a source node would command a handover and might receive an acknowledgment of completion, but not the detailed context of *why* it succeeded under those specific radio conditions. This made troubleshooting suboptimal handovers and fine-tuning algorithms inefficient. The SHR provides this crucial feedback, enabling the source node to learn from every handover event. Its creation was motivated by the desire to enhance SON capabilities, reduce operational expenditure (OPEX) by minimizing manual optimization, and fundamentally improve mobility robustness—a critical factor for user experience and network performance in advanced 5G systems.