Early UL Synchronization for Timing Advance Handover Latency
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Solution Overview
Problem
Traditional LTM in wireless communication systems suffer from long interruptions due to downlink and uplink synchronization and random access procedures during handover, leading to increased latency and data loss.
Innovation Solution
Implementing early uplink synchronization and pre-configuration for timing advance management in user equipment (UE) to reduce handover latency, including receiving PDCCH orders for UL synchronization procedures and performing PRACH transmissions before cell switch commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional LTM handover procedures are used with downlink and uplink synchronization and random access procedures, then handover reliability is maintained, but handover interruption time and latency increase
Solution Approach 1:
The patent applies preliminary action by performing uplink synchronization and random access procedures to the target cell before the actual handover execution. The UE transmits PRACH preambles and receives timing advance commands in advance, so that when handover is triggered, the UE is already synchronized with the target cell, eliminating the need for synchronization delays during the handover itself.
Solution Approach 2:
The handover process is segmented into distinct phases: a preparation phase where uplink synchronization and random access are performed in advance, and an execution phase where the handover is triggered immediately. This segmentation allows the time-consuming synchronization procedures to be decoupled from the critical handover execution path, reducing overall interruption time while maintaining reliability.
2Loss of time
If early uplink synchronization and pre-configuration procedures are implemented, then handover latency is reduced, but device complexity and signaling overhead increase
Solution Approach 1:
The PDCCH order structure is enhanced to serve multiple functions: it not only triggers random access but also carries timing advance commands and uplink grant information simultaneously. This multi-functionality allows the UE to complete synchronization, obtain uplink timing, and get transmission resources in a single signaling exchange, reducing the number of separate procedures needed.
Solution Approach 2:
The patent merges the timing advance command reception and uplink grant allocation into the same PDCCH order message that triggers the random access procedure. Instead of separate signaling for synchronization, timing adjustment, and resource allocation, all these functions are combined into one unified procedure, simplifying the overall process despite the advanced timing.
Data Source
AI summary
Apparatus and methods are provided for timing advance management for the UE in the LTM to reduce latency. In one novel aspect, early UL synchronization for timing advance management is provided. In one embodiment, the UE receives PDCCH order from the connected serving cell indicating an early UL synchronization procedure towards a candidate cell and receives a timing advance (TA) of the candidate cell in the cell switch command. In one embodiment, the PDCCH order indicates whether the PRACH is to be an initial transmission or a retransmission to the candidate cell and the UE increments a power ramping counter when the PDCCH order indicates a retransmission. In one embodiment, the PDCCH order includes a cell indicator of the candidate cell with one or more reserve bits of DCI 1_0 of the PDCCH order. In one embodiment, the PDCCH order indicates whether a RAR is expected.