RACH-less Handover Synchronization in 5G Non-Terrestrial Networks
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Solution Overview
Problem
Current 5G/NR wireless communication systems face challenges in reducing handover delay and overhead during cell switching, particularly in non-terrestrial networks where large propagation distances and cell sizes necessitate efficient handover mechanisms without the use of random access channels (RACH).
Innovation Solution
Implementing a RACH-less handover process where user equipment (UE) performs autonomous DL and UL synchronization based on configurations received from the base station, followed by an initial UL transmission to notify arrival in the target cell, allowing for reduced handover delay and overhead by eliminating the need for RACH procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RACH procedures are used for handover, then reliability of connection establishment is improved, but handover delay and overhead increase
Solution Approach 1:
The patent extracts and removes the RACH procedure from the handover process, enabling direct UL transmission without the traditional RACH preamble exchange. This eliminates the time-consuming RACH steps while maintaining connection reliability through alternative mechanisms like configured grants and PDCCH monitoring.
Solution Approach 2:
The network pre-configures UL resources (configured grants) and synchronization parameters before handover execution. The UE performs autonomous DL/UL synchronization in advance using pre-provided reference signals and timing information, preparing everything needed for immediate UL transmission without waiting for RACH procedures.
2Reliability
If RACH procedures are used for handover, then uplink synchronization is achieved, but signaling overhead increases
Solution Approach 1:
The patent removes the RACH signaling exchange from the handover process. Instead of exchanging RACH preambles and receiving random access responses, the UE directly transmits UL data using pre-configured resources, eliminating the associated signaling overhead while achieving UL synchronization through autonomous procedures.
Solution Approach 2:
The UE performs autonomous UL synchronization using pre-configured reference signals and timing information provided by the network. The UE independently adjusts its UL timing based on downlink measurements and network configurations without requiring interactive synchronization protocols, thereby reducing signaling overhead.
3Speed
If autonomous DL and UL synchronization is performed, then handover speed is improved, but synchronization accuracy may deteriorate
Solution Approach 1:
The network pre-configures accurate synchronization parameters, reference signals, and timing information before handover. The UE uses these pre-provided high-precision references to perform autonomous synchronization, achieving both speed (immediate handover execution) and accuracy (precise timing alignment) simultaneously.
Solution Approach 2:
The system implements feedback mechanisms where the network monitors UL reception quality and provides correction information through PDCCH or RRC signaling. The UE adjusts its autonomous synchronization based on this feedback, maintaining high synchronization accuracy despite the speed of autonomous operation.
Data Source
AI summary
Methods and apparatuses for a MAC CE for multi-TRP operation in a wireless communication system. A method of a UE comprises: receiving, from a base station, a RACH-less switching command for a RACH-less switching operation to a target cell; determining whether a DRX is configured for the target cell; and retaining an active time during the RACH-less switching operation based on a determination that the DRX is configured for the target cell, monitoring a PDCCH to acquire a UL grant of an initial UL transmission, wherein the initial UL transmission for the RACH-less switching operation includes a transmission of a RRCReconfigurationComplete message to a target satellite or the target cell.