PDSCH Reception Switching via Layer 2 Mobility in 5G Handover
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Solution Overview
Problem
Existing 5G communication systems face high latency and overhead during cell handovers due to L3-based serving cell changes, which involve complete L2 and L1 resets, leading to significant interruption times.
Innovation Solution
Implementing layer 2 mobility by using RRC messages and MAC CEs to manage data scrambling identities and TCI state lists for seamless PDSCH reception, allowing L1 to switch between cells while L2 continues, thereby reducing interruption times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L3-based serving cell change is performed with complete L2 and L1 resets, then cell handover reliability is improved, but handover latency and interruption time increase significantly
Solution Approach 1:
The patent segments the handover process into separate L1 (physical layer) and L2 (MAC layer) operations. L1 beam switching is performed independently without requiring complete L2 reset, while L2 maintains connectivity through persistent MAC CEs. This segmentation allows faster handover by eliminating the need for synchronized L1-L2 reset while maintaining reliability through coordinated layer operations.
Solution Approach 2:
The patent applies preliminary action by pre-configuring TCI state lists and data scrambling identities at L2 before actual cell switching occurs. MAC CEs are prepared in advance with identifiers that will be used during handover, allowing the terminal to quickly switch beams at L1 without waiting for complete L2 reconfiguration, thus reducing handover latency while ensuring reliable connection establishment.
2Reliability
If complete L2 reset is performed during serving cell change, then connection reliability is improved, but overhead and processing complexity increase
Solution Approach 1:
The patent divides the handover management into distinct L1 and L2 responsibilities. L2 handles high-level connection maintenance through pre-configured MAC CEs and TCI state lists, while L1 executes specific beam switching operations. This segmentation reduces overall processing complexity by allowing each layer to operate independently within its scope while maintaining connection reliability through their coordinated interaction.
Solution Approach 2:
The patent uses copying by maintaining persistent MAC CE configurations that can be reused across cell switches. Instead of creating entirely new L2 configurations for each handover, the system copies and reuses pre-configured MAC CE templates with updated identifiers, significantly reducing processing complexity while ensuring reliable connection establishment through proven configuration patterns.
3Speed
If L1 switches between adjacent cells while L2 continues, then handover speed is improved, but coordination complexity between layers increases
Solution Approach 1:
The patent introduces MAC CEs as intermediaries between L1 and L2 layers during handover. These MAC CEs carry identifiers for data scrambling identities and TCI state lists that L2 prepares in advance and passes to L1 for execution. This intermediary mechanism enables fast L1 beam switching while maintaining L2 connectivity, reducing layer coordination complexity by providing a standardized interface for information exchange.
Solution Approach 2:
The patent applies preliminary action by pre-configuring all necessary L2 parameters (MAC CEs, TCI state lists, data scrambling identities) before L1 switching occurs. This advance preparation eliminates the need for complex real-time coordination during actual handover, as L1 simply executes pre-approved switching based on pre-configured L2 parameters, thereby increasing handover speed while managing coordination complexity.
4Device complexity
If traditional L3-based handover with RRC signaling is used, then mobility management is simplified, but interruption time and service continuity are degraded
Solution Approach 1:
The patent extracts the time-critical handover functions from L3 RRC signaling and relocates them to L2 MAC layer operations. MAC CEs handle the urgent tasks of beam switching coordination and connection maintenance during handover, while L3 RRC signaling continues to handle higher-level mobility management. This extraction eliminates L3 involvement from the time-sensitive handover execution path, dramatically reducing interruption time while keeping overall mobility management relatively simple.
Solution Approach 2:
The patent enables self-service by allowing L2 MAC layer to autonomously manage handover execution using pre-configured MAC CEs and TCI state lists without requiring L3 RRC intervention during the actual cell switch. The MAC layer independently coordinates beam switching and maintains connectivity through persistent configurations, reducing interruption time by eliminating L3 signaling delays while keeping mobility management simple through automated layer-2 operations.
Data Source
AI summary
A method and apparatus for layer 2 mobility is provided. Method for lower layer mobility includes receiving from a base station a first RRC message, receiving from the base station a first MAC CE, the first MAC CE comprises an identifier related to the first data scrambling identity and the first TCI state list, performing PDSCH reception based on the first data scrambling identity and the first TCI state list, receiving from the base station a second MAC CE, the second MAC CE comprises an identifier related to the second data scrambling identity and the second TCI state list, and performing PDSCH reception based on the second data scrambling identity and the second TCI state list, The second MAC CE comprises an identifier related to the second data scrambling identity and a second TCI state list.