L1/L2-Triggered Mobility Cell Switch Bearer for 5G Inter-DU Beam Management
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Solution Overview
Problem
Current inter-DU inter-cell beam management in 5G NR networks experiences high latency, overhead, and data loss during user equipment (UE) mobility due to frequent user plane resets and ping-pong effects, leading to impaired user experience.
Innovation Solution
Implementing L1/L2-triggered mobility (LTM) with a cell switch (CS) bearer that configures multiple RLC entities and MAC entities across source and target cells, allowing seamless handovers with reduced latency and data loss by utilizing pre-configured candidate cells and maintaining a time alignment timer for efficient beam management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If legacy handover procedure with L3 measurements and RRC reconfiguration is used, then reliability of data transmission is improved, but handover latency and interruption time increase
Solution Approach 1:
The patent applies preliminary action by pre-configuring multiple candidate cells and their associated protocol stacks (MAC entities, RLC entities, PDCP entities) before handover is needed. When handover is triggered, the UE can immediately activate a pre-configured target cell without waiting for configuration setup, thus reducing handover latency while maintaining reliability through pre-validated configurations.
Solution Approach 2:
The patent segments the handover process by separating the configuration phase (where multiple candidate cells are pre-configured with full protocol stacks) from the execution phase (where handover is simply triggered by activating a pre-configured target). This segmentation allows the time-consuming configuration work to be done in advance, reducing actual handover latency.
2Productivity
If frequent handovers are performed to maintain optimal beam connection, then instantaneous throughput is improved, but ping-pong effects and signaling overhead increase
Solution Approach 1:
The patent pre-configures multiple candidate cells with complete protocol stacks in advance, so when beam quality degrades, the UE can switch to a pre-configured alternative without triggering a full handover procedure. This reduces ping-pong effects by providing stable pre-validated options rather than repeatedly executing complete handover sequences.
Solution Approach 2:
The patent enables dynamic selection among pre-configured candidate cells based on beam quality measurements. The UE can quickly switch between pre-configured cells when L3 measurements indicate beam degradation, maintaining optimal throughput without the overhead of repeated full handover procedures, thus reducing ping-pong effects while preserving productivity.
3Reliability
If user plane reset is performed during inter-DU handover, then data transmission reliability is maintained, but data loss and retransmission overhead increase
Solution Approach 1:
The patent pre-configures multiple PDCP entities along with their associated RLC and MAC entities for candidate cells before handover. During handover, the PDCP entity can be seamlessly switched to the target cell's PDCP entity without resetting the user plane, preventing data loss while maintaining reliability through pre-established data transmission paths.
Solution Approach 2:
The patent maintains continuity of useful action by keeping the user plane active and avoiding resets during handover. The pre-configured protocol stacks enable continuous data transmission from source to target cell without interruption or reset, eliminating data loss and retransmission overhead while preserving transmission reliability through the pre-validated handover path.
4Reliability
If complete L2 and L1 resets are performed during cell switch, then connection reliability is ensured, but handover overhead and interruption time increase
Solution Approach 1:
The patent pre-configures complete protocol stacks (MAC entities, RLC entities, PDCP entities) for multiple candidate cells before handover is needed. When handover is triggered, the UE simply activates a pre-configured target cell without performing complete L2/L1 resets, reducing handover overhead and complexity while maintaining connection reliability through pre-validated configurations.
Solution Approach 2:
The patent extracts the time-consuming L2/L1 reset operations from the handover execution phase and performs them in advance during the pre-configuration phase. By separating configuration from execution, the patent reduces handover overhead and complexity while ensuring connection reliability through pre-established protocol stacks.
Data Source
AI summary
Apparatus and methods are provided for L1/L2-triggered mobility (LTM) cell switch. In one novel aspect, the UE performs an LTM handover by selecting and using the best beam taking advantage of the ping-pong effect of frequent cell switches for intra-CU with inter-DU and intra-DU cell switches. In one embodiment, the UE receives pre-configuration for the LTM, configures a second protocol stack based on the pre-configuration, configures a cell switch (CS) bearer upon receiving a cell switch command, wherein the CS bearer is associated to the source cell and the target cell. The UE performs the LTM handover based on the CS bearer. In one embodiment, the pre-configuration included multiple candidate cells and the UE configures the second protocol stack with multiple RLC entities. The MAC entity of the second protocol stack is a master cell group (MAC) MAC entity, which can be associated to multiple cells and multiple RLC entities.