MAC CE Cell Activation for FR2 Inter-Cell Mobility
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Solution Overview
Problem
Existing L1/L2 based mobility in intra-distributed unit (DU) and intra-frequency scenarios face limitations in frequency range 2 (FR2) deployments, particularly in managing inter-cell beam management and carrier aggregation, where the serving cell remains unchanged, and there is a need for efficient activation and deactivation of TCI states for PDCCH and PDSCH reception.
Innovation Solution
The implementation of medium access control (MAC) control elements (CE) for activating pre-configured cell configurations, enabling L1/L2 based inter-cell mobility, including downlink MAC CE for controlling simultaneous special cell (SpCell) and secondary cell (Scell) changes, with two-stage activation of serving cells, and network confirmation of WTRU determined cell sets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L1/L2 based mobility is used in intra-DU and intra-frequency scenarios, then beam management and carrier aggregation can be maintained with unchanged serving cell, but inter-cell mobility and TCI state management become complex and inefficient
Solution Approach 1:
The patent introduces MAC CE as an intermediary mechanism between L1/L2 beam management and RRC layer cell configuration. The MAC CE carries TCI state activation commands that enable efficient inter-cell mobility without requiring full RRC reconfiguration, thus simplifying the management complexity while maintaining reliability
Solution Approach 2:
The patent segments the cell reconfiguration process into two independent parts: (1) RRC layer pre-configuration of candidate cell parameters and (2) MAC CE-based activation of specific TCI states for actual cell switching. This segmentation allows beam management to operate independently from complex cell reconfiguration procedures
2Productivity
If carrier aggregation is used in FR2 deployments to aggregate multiple control channels, then bandwidth utilization improves, but the number of TCI states increases significantly (e.g., 64 states)
Solution Approach 1:
The patent applies partial action by activating only a subset of pre-configured TCI states (e.g., up to 8 states) via MAC CE commands rather than managing all 64 possible TCI states. This selective activation reduces the effective configuration complexity while maintaining the ability to utilize aggregated bandwidth when needed
Solution Approach 2:
The patent uses preliminary action by pre-configuring all candidate TCI states through RRC signaling before actual cell aggregation operations. The MAC CE then simply activates the required subset from this pre-prepared pool, eliminating the need for dynamic TCI state creation and reducing real-time management complexity
3Reliability
If traditional handover procedures are used for cell changes, then network control is maintained, but handover latency and signaling overhead increase
Solution Approach 1:
The patent implements preliminary action by having the network pre-configure candidate cell parameters and TCI states through RRC signaling before handover is needed. When handover is required, the network simply sends a MAC CE command to activate the pre-prepared configuration, reducing handover latency while maintaining network control over the candidate selection
Solution Approach 2:
The patent extracts the complex cell reconfiguration parameters from the handover execution phase and places them in the pre-configuration phase. The MAC CE command only needs to carry the essential activation trigger and candidate cell identification, separating the heavy configuration burden from the time-critical handover action
Data Source
AI summary
A wireless transmit/receive unit (WTRU) may receive a radio resource control (RRC) message comprising configuration information. The configuration information may include one or more preconfigured candidate cell configurations. Each of the preconfigured candidate cell configurations may include a special cell (SpCell) configuration, a secondary cell (SCell) configurations, and/or a candidate cell index. The WTRU may receive a medium access control (MAC) control element (CE). The MAC CE may indicate to apply a first preconfigured candidate cell configuration of the one or more preconfigured candidate cell configurations and an activation state for each SCell in the first preconfigured candidate cell configuration. The WTRU may initiate a handover to a SpCell in the first preconfigured candidate cell configuration based on the indication in the MAC CE. The WTRU may transmit data to the SCells activated by the MAC CE.