Inter-gNB Handover via L2 U2N Relay RRC State Coordination
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Solution Overview
Problem
Current wireless communication technologies do not support inter-gNB path switching, particularly from direct to indirect paths or vice versa, due to a lack of knowledge about the radio resource control (RRC) state of candidate relay UEs under the target gNB, leading to inefficiencies and potential handover failures.
Innovation Solution
A base station processor is configured to receive measurement reports from UEs, select target relay UEs, and perform handover preparations by determining the RRC state of candidate relay UEs, either through direct selection or querying the target gNB for state information, ensuring appropriate handover procedures are initiated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inter-gNB path switching is not supported, then handover failures and latency occur, but implementing it requires knowledge of RRC state of candidate relay UEs which increases system complexity
Solution Approach 1:
The source gNB performs preliminary actions by querying the target gNB for RRC state information of candidate relay UEs before making handover decisions. This preliminary knowledge acquisition enables informed handover decisions without increasing operational complexity during the actual handover execution.
Solution Approach 2:
The target gNB acts as an intermediary that provides RRC state information about candidate relay UEs to the source gNB. This intermediary mechanism allows the source gNB to make informed handover decisions without directly managing the complexity of tracking RRC states of all UEs across multiple gNBs.
2Measurement precision
If the source gNB queries the target gNB for RRC state information, then handover decisions are informed and accurate, but signaling overhead and processing time increase
Solution Approach 1:
The RRC state information query is performed as a preliminary action during handover preparation, allowing the source gNB to make informed decisions without delaying the actual handover execution. The query is integrated into the existing handover preparation messaging流程, minimizing additional time overhead.
3Productivity
If the source gNB selects target relay UE without knowing RRC state, then handover can proceed quickly, but handover failures occur due to incompatible RRC states
Solution Approach 1:
The source gNB performs preliminary querying of the target gNB for RRC state information before selecting the target relay UE. This preliminary knowledge enables the source gNB to select compatible relay UEs that can successfully support the handover, preventing failures while maintaining efficient handover speed.
Solution Approach 2:
The target gNB provides feedback regarding the RRC state of candidate relay UEs to the source gNB. This feedback mechanism enables the source gNB to make informed selections of target relay UEs that are compatible with the handover requirements, thereby improving success rates without significantly impacting handover speed.
Data Source
AI summary
A base station is configured to receive a measurement report from a first user equipment (UE) including channel measurement results for a sidelink channel with at least a second UE available as a candidate relay UE for a layer 2 (L2) UE-to-network (U2N) relay, the measurement report further including a relay identifier and serving cell information for a serving cell of the second UE, select the second UE as a target relay UE for the first UE regardless of a current radio resource control (RRC) state of the second UE with the serving cell of the second UE and transmit a handover preparation message to the serving cell of the target relay UE, wherein the serving cell of the target relay UE is a target cell for handover of the first UE, the handover preparation message including the relay identifier of the target relay UE.