Early Random Access for Low-Latency LTM Cell Switching
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Solution Overview
Problem
Existing wireless communication systems face challenges in minimizing service interruption and latency during cell switching, particularly in 5G systems, due to reliance on L3 measurements and RRC signaling for serving cell changes, which incur long delays and increased overhead.
Innovation Solution
Implementing L1/L2 Triggered Mobility (LTM) with early random access for cell switch, utilizing DCI and MAC PDU messages to facilitate seamless transitions between cells, reducing the need for complete L2 resets and minimizing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L3 measurements and RRC signaling are used for serving cell change, then reliable cell switching is achieved, but service interruption time and latency increase
Solution Approach 1:
The patent performs downlink synchronization and receives RRC reconfiguration messages in advance during the LTM procedure, preparing the UE for cell switching before the actual handover executes. This preliminary preparation reduces the time required during the actual cell switch while maintaining reliability through pre-configured parameters and identifiers.
Solution Approach 2:
The cell switching process is divided into distinct phases: LTM indication reception, downlink synchronization, RRC reconfiguration message reception, and final cell switch execution. By segmenting the process, the patent enables parallel processing of synchronization and message reception, reducing overall service interruption time while maintaining reliable switching through structured procedure completion.
2Reliability
If L3 measurements and RRC signaling are used for serving cell change, then complete handover control is achieved, but overhead and processing complexity increase
Solution Approach 1:
Downlink synchronization is performed in advance before the actual cell switch, and RRC reconfiguration messages are received and processed beforehand. This preliminary action allows the network to prepare all necessary configuration parameters, identifiers, and synchronization information in advance, reducing the complexity and overhead during the actual handover execution phase.
3Speed
If early random access is implemented in LTM, then cell switching speed is improved, but uplink transmission timing complexity increases
Solution Approach 1:
The patent implements early random access procedure where the UE transmits random access preamble to the target cell and receives random access response containing timing advance commands. This feedback mechanism provides the UE with precise timing alignment information from the target cell, enabling fast cell switching while automatically adjusting uplink timing to maintain synchronization and reduce complexity through closed-loop control.
Data Source
AI summary
A technique for random access in conjunction with LTM operations is provided. The technique comprises performing an early random access procedure in a specific LTM candidate cell based on PDCCH order. Based on the early random access procedure, shorter cell switch delay is achieved. The specific LTM candidate cell is identified based on an implicit identifier determined from an explicit identifier indicated by the base station.