Serving Cell Change Signaling for Low-Latency Inter-Node Mobility
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Solution Overview
Problem
Existing L1/L2 based inter-cell mobility procedures in telecommunication networks face challenges in reducing latency, overhead, and interruption time during serving cell changes, particularly due to uncertainties in inter-node interface delays and reliance on RRC messages that cause MAC resets.
Innovation Solution
Implementing lower layer signaling, such as MAC CE or DCI, for UE and network nodes to manage serving cell changes, allowing immediate data transfer upon successful reception of downlink beams in the target cell, without requiring RRC reconfiguration and MAC resets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RRC reconfiguration is used for serving cell changes, then reliability of cell change procedure is improved, but latency and interruption time increase
Solution Approach 1:
The patent segments the cell change procedure into two parts: (1) L1/L2-based fast execution for actual cell switching, and (2) RRC reconfiguration for subsequent configuration updates. This segmentation allows the time-critical cell change to occur quickly via lower layer signaling, while RRC reconfiguration handles non-time-critical configuration updates, thereby reducing overall latency while maintaining reliability.
Solution Approach 2:
The patent applies preliminary action by having the UE prepare and execute the serving cell change at L1/L2 layer before RRC reconfiguration is completed. The UE monitors the target cell's downlink beam in advance and can switch cells immediately upon receiving the trigger, without waiting for RRC reconfiguration to finish, thus reducing interruption time while ensuring reliable handover.
2Manufacturing precision
If RRC messages are used for serving cell changes, then configuration accuracy is improved, but overhead increases
Solution Approach 1:
The patent segments configuration signaling into two categories: (1) Essential cell change parameters transmitted via compact L1/L2 signaling (e.g., TCI state indication, beam ID) that enable immediate cell switching, and (2) Detailed configuration parameters transmitted via RRC reconfiguration afterward. This segmentation reduces the overhead of the time-critical cell change signaling while maintaining configuration accuracy through subsequent RRC updates.
Solution Approach 2:
The patent extracts only the essential parameters needed for immediate cell execution (such as target cell ID, beam/TCI state) from the full RRC configuration and transmits them via compact L1/L2 signaling. The remaining detailed configuration parameters are transmitted separately via RRC reconfiguration, thereby reducing the overhead of the fast cell change procedure while preserving configuration accuracy.
3Loss of time
If L1/L2 signaling is used for serving cell changes, then latency is reduced, but uncertainty in inter-node interface delays increases
Solution Approach 1:
The patent implements feedback mechanisms where the UE confirms successful reception and execution of the L1/L2-based cell change trigger to the network. This feedback allows the network to verify that the cell change was successfully executed despite inter-node interface delays, thereby reducing uncertainty and maintaining reliability while keeping latency low.
Solution Approach 2:
The patent applies beforehand cushioning by incorporating timing margins and confirmation mechanisms in the L1/L2-based cell change procedure. The network accounts for potential inter-node interface delays by allowing sufficient time for the UE to execute the cell change and send confirmation, thereby cushioning against timing uncertainties while maintaining fast handover.
4Stability of the object's composition
If MAC reset is performed during serving cell changes, then configuration consistency is improved, but interruption time increases
Solution Approach 1:
The patent segments the configuration update process into two phases: (1) Immediate cell execution via L1/L2 signaling that maintains existing MAC configurations to avoid interruption, and (2) Subsequent configuration consistency updates via RRC reconfiguration. This segmentation allows the cell change to proceed without MAC reset, reducing interruption time, while configuration consistency is restored in the second phase.
Solution Approach 2:
The patent applies preliminary action by having the UE maintain its MAC configuration during the fast L1/L2-based cell change, avoiding MAC reset and associated interruptions. The configuration consistency is then preliminarily ensured by having the network send updated RRC reconfiguration messages after the cell change, rather than requiring MAC reset before the cell change itself.
Data Source
AI summary
A method performed by a user equipment, UE, the method comprising: executing (601) a serving cell change procedure from a source cell provided by a first network node to a target cell provided by a second network node, wherein the serving cell change procedure is performed using lower layer signalling; and in response to executing the serving cell change procedure, performing (602) one or more of: (i) transmitting a serving cell change indication to the second network node indicating that the serving cell change has been executed; (ii) monitoring a downlink control channel in the target cell for scheduling of user data in a downlink to the UE; and (iii) transmitting a scheduling request in the target cell for scheduling of user data in an uplink from the UE.