IAB-Node Group Handover for Inter-CU Migration
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Solution Overview
Problem
Current 3GPP Rel-16 specifications only standardize intra-CU migration for IAB nodes, lacking a specified group handover procedure for inter-CU migration, leading to unclear handling of handover commands for IAB-MTs and UEs during IAB-node migration, especially when the migrating node is not a leaf node, resulting in potential service interruptions and increased signaling load.
Innovation Solution
A method for IAB-node handover involving a target donor CU that performs admission control for UEs and IAB nodes, generates a group handover command containing individual handover commands for all UEs and MTs, and sends a handover acknowledge message with admitted and not admitted PDU session resources, ensuring coordinated handover across multiple CU domains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individual handover commands are sent to each UE and IAB-MT during inter-CU migration, then handover completeness is ensured, but signaling load increases significantly
Solution Approach 1:
The patent merges individual handover commands for multiple UEs and IAB-MTs into a single group handover command. This group command contains handover information for all affected nodes, allowing simultaneous handover execution without requiring separate signaling exchanges for each node, thus reducing overall signaling load while maintaining complete handover coverage.
Solution Approach 2:
The group handover command serves multiple functions simultaneously: it acts as a handover command for the IAB-MT, contains embedded handover commands for all child UEs, and provides coordination information for inter-CU migration. This multi-functionality eliminates the need for separate signaling messages for each function.
2Adaptability or versatility
If traditional handover procedures are used during inter-CU migration, then existing protocol compatibility is maintained, but service interruptions increase
Solution Approach 1:
The group handover command is prepared and transmitted to the IAB-MT in advance, containing all necessary handover information for the IAB-MT and its child UEs. This preliminary action allows the IAB-MT to execute handover for all nodes simultaneously without sequential processing delays, reducing service interruption time while maintaining protocol compatibility through the use of standard RRCReconfiguration messages.
3Reliability
If security key changes are performed for all UEs and IAB nodes during migration, then security is maintained, but handover complexity increases
Solution Approach 1:
Security key change information for multiple UEs and IAB nodes is merged into the single group handover command. The command contains security parameter updates that apply to all affected nodes, allowing simultaneous security reconfiguration without requiring separate key management procedures for each node, thus maintaining security while reducing handover complexity.
Data Source
AI summary
A method by a network node, operating as a target donor CU in an IAB network serving as a candidate donor node for a migrating IAB node and providing connectivity for a UE. A message for IAB handover including contexts of the migrating IAB node and UEs and IAB nodes directly or indirectly served by the migrating IAB node is received. Admission control is performed for the UEs and IAB nodes. A handover command to a mobile termination, MT, of the migrating IAB node, and each UE and MT of the IAB nodes is prepared. A group handover command that recursively contains handover commands of all the UEs and MTs is generated. A handover acknowledge message including a list of admitted and not admitted PDU session resources and containing the group handover command is sent. A RRC Reconfiguration Complete message is received.