Automatic Neighbor Relation (ANR)

ANR leverages User Equipment (UE) measurement reports to detect missing neighbor cells. When a UE reports a strong Physical Cell Identity (PCI) not in the current Neighbor Relation Table (NRT), the eNB/gNB instructs the UE to read the target cell's E-UTRAN Cell Global Identifier (ECGI) or NR Cell Global Identifier (NCGI). This automated process eliminates manual drive testing and ensures the handover candidate list remains dynamically updated as the network topology changes.

The Neighbor Relation Table (NRT) is the central database managed by ANR containing all established neighbor relationships. Each entry includes:

• Target Cell Identifier (TCI): The unique ECGI/NCGI of the neighbor cell
• No Remove flag: Prevents automatic deletion of critical neighbors
• No HO flag: Allows a neighbor to be listed but blocks handover attempts
• No X2/Xn flag: Prevents automatic X2/Xn interface setup The RIC can enrich these entries with AI-derived performance metrics for intelligent handover decisions.

Upon discovering a new neighbor cell, ANR triggers the automatic establishment of the X2 interface (LTE) or Xn interface (5G NR) between base stations. The serving eNB/gNB uses the discovered target cell's global ID to resolve its IP address via the Transport Network Layer (TNL) address discovery process. This enables direct inter-cell communication for coordinated scheduling, interference management, and seamless handover execution without manual transport network configuration.

ANR continuously monitors for PCI confusion and PCI collision scenarios that cause handover failures. PCI confusion occurs when two neighbor cells share the same PCI, making it impossible to uniquely identify a handover target. PCI collision happens when two overlapping cells use the same PCI. The RIC's ANR function correlates UE measurement reports with global cell identities to detect these conflicts and trigger automated PCI reallocation, ensuring unambiguous cell identification across the network.

Traditional SON-based ANR operates reactively. The RAN Intelligent Controller (RIC) enhances ANR with predictive AI/ML models that:

• Forecast mobility patterns to pre-configure neighbor relations before UEs enter overlapping coverage areas
• Optimize NRT pruning by analyzing historical handover success rates to remove stale or underperforming neighbors
• Correlate ANR events with Mobility Robustness Optimization (MRO) to jointly tune handover trigger thresholds This closed-loop mechanism transforms ANR from a reactive discovery tool into a proactive network optimization function.

The ANR closed-loop mechanism operates through a continuous cycle:

1. Monitor: The RIC ingests UE measurement reports and handover failure statistics via the E2 interface
2. Analyze: AI models detect missing neighbors, PCI conflicts, and stale NRT entries
3. Decide: The xApp/rApp determines optimal neighbor additions, removals, or PCI reassignments
4. Execute: Configuration changes are pushed to the RAN via the O1 or E2 interface
5. Verify: Post-action KPIs confirm improved handover success rates, closing the loop without human intervention.