UL Sync Recovery at Beam Change via Random Access
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Solution Overview
Problem
In high-speed train (HST) deployments using New Radio (NR) frequency range 2 (FR2), the synchronization between beams during handover from one cell to another in a cellular network is challenging, particularly for uplink (UL) synchronization recovery, due to changes in downlink propagation delay and beam colocation issues.
Innovation Solution
A method where user equipment (UE) initiates a random-access procedure for beam switching when specific conditions are met, such as excessive downlink propagation delay or non-colocation of beams, to ensure synchronization with the new beam, using pre-allocated resources and configuring UE to search for link recovery candidates in a specific direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If beam switching is performed without random-access procedure, then beam switch delay is reduced, but uplink synchronization accuracy deteriorates
Solution Approach 1:
The network pre-configures the UE with multiple candidate beams and their associated random-access resources before beam switching is needed. When beam switching is required, the UE can immediately initiate the random-access procedure on the pre-configured candidate beam without waiting for network signaling, thus reducing beam switch delay while maintaining synchronization accuracy through the pre-established random-access resources.
2Measurement precision
If random-access procedure is always initiated for beam switching, then uplink synchronization accuracy is improved, but connection interruption time increases
Solution Approach 1:
The patent applies different beam switching strategies based on local conditions: when the current beam quality deteriorates below a threshold or specific events occur (e.g., handover, cell reselection), the UE initiates beam switching with random-access procedure to ensure synchronization. When beam quality is adequate and no special events occur, the UE can perform faster beam switching without random-access. This localized application of random-access procedure optimizes the balance between synchronization accuracy and interruption time.
3Reliability
If multiple candidate beams are configured for link recovery, then reliability of beam switching is improved, but device complexity increases
Solution Approach 1:
The patent segments the beam management process into distinct phases: configuration phase where the network provides multiple candidate beams with associated random-access resources, evaluation phase where the UE monitors beam qualities, and execution phase where the UE switches to a pre-selected candidate beam. This segmentation allows the UE to maintain a manageable configuration by only actively processing candidate beams when needed, reducing overall device complexity while preserving reliability through multiple pre-evaluated options.
Data Source
AI summary
Disclosed in a mechanism for a user equipment connected to a base station via a first beam, to determine that a beam switch is to be performed from the first beam to a second beam, wherein the base station manages both the first and second beams and to perform the beam switch at least by a random-access procedure using the second beam to synchronize communications between the user equipment and the second beam.