L1/L2 Mobility Handover Control in Disaggregated 5G Networks
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Solution Overview
Problem
Current wireless communication systems face challenges in managing L1/L2 mobility, particularly in disaggregated architectures where the CU is not involved in UE mobility within or between DUs, requiring efficient L1-based handover mechanisms for UE-initiated measurement reporting.
Innovation Solution
The implementation of a method and apparatus that allow UE to send Buffer Status Reports (BSR) or uplink MAC-Control Elements (MAC-CE) to initiate L1-based handovers, using L1/L2 mobility configurations and CSI reports to identify target cells or beams, and trigger dedicated scheduling requests for pending CSI reports, enabling CU and DU to perform L1/L2 handovers based on UE-initiated measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If L1-based handover mechanism is implemented in disaggregated architecture, then handover latency is reduced and mobility efficiency is improved, but device complexity and signaling overhead increase
Solution Approach 1:
The patent segments the handover control functionality by separating L1/L2 mobility management (handled by DU) from L3 mobility management (handled by CU). This segmentation allows L1-based handover to occur independently at the DU level without requiring L3 intervention, thereby reducing handover latency while maintaining architectural complexity through functional separation.
Solution Approach 2:
The patent implements preliminary action by having the UE perform measurement reporting and trigger handover decisions at L1/L2 layer before L3 processing is required. The DU can initiate handover based on L1 measurement reports and L2 MAC-CE signals, preparing and executing handover before higher-layer protocols would normally process it, thus reducing overall handover time.
2Productivity
If UE-initiated measurement reporting is enabled, then mobility responsiveness is improved, but uplink signaling overhead and network processing load increase
Solution Approach 1:
The patent makes the uplink signaling structures universal by using existing BSR and MAC-CE formats for dual purposes: traditional buffer/status reporting and L1 measurement reporting for mobility. This multi-functionality allows the same uplink resources and signaling structures to carry both data status information and mobility measurement information, reducing overall signaling overhead while improving mobility responsiveness.
Solution Approach 2:
The patent merges L1 measurement reporting with existing uplink control structures (BSR and MAC-CE). By combining mobility measurement information with buffer status reporting in the same uplink transmission, the patent reduces the number of separate signaling messages required, thereby decreasing uplink signaling overhead while maintaining high mobility responsiveness.
3Measurement precision
If L1 CSI reports are used for handover triggering, then measurement precision is improved, but uplink resource requirements and scheduling complexity increase
Solution Approach 1:
The patent implements self-service by enabling the UE to autonomously generate and transmit L1 CSI reports when mobility-triggering events occur, without requiring explicit network scheduling requests. The UE independently determines when measurements should be reported based on configured event criteria, and the network simply receives and processes these self-initiated reports, thereby reducing scheduling complexity while maintaining high measurement precision.
Data Source
AI summary
A method for a network element, NE, is proposed, which comprises receiving from a user equipment, UE, at least one of a BSR or an uplink MAC-CE; determining to perform an L1 based handover for the UE; and sending an L1 based handover command to the UE. Another method for a UE is proposed, which comprises receiving an L1/L2 mobility configuration; deciding that there is an L1 CSI report to send; determining whether the UE has an UL grant; if it is determined that the UE has an UL grant, the method further comprises: sending at least one of a BSR or an UL MAC-CE to a NE; if it is determined that the UE does not have an UL grant, the method further comprises: sending a dedicated SR to a NE indicating that an L1 CSI report is pending; receiving a scheduling grant from the NE; and sending the L1 CSI report to the NE based on the scheduling grant; and receiving an L1 based handover command from the NE.