UE Cell Reselection in Unlicensed 5G NR via Missing Reference Signal Monitoring
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Solution Overview
Problem
In 5G NR communication systems, the existing cell reselection and random access procedures are inefficient in unlicensed frequency scenarios due to congestion issues, leading to repeated preamble transmission failures and increased latency, as they do not adequately account for the congestion level of unlicensed radio channels.
Innovation Solution
The proposed solution involves a user equipment (UE) that monitors the number of continuously missing reference signals and performs cell reselection to a different frequency radio cell when the threshold is exceeded, and implements an improved random access procedure with LBT failure notification and multiple RAR reception windows to quickly retransmit the preamble, allowing for earlier cell reselection and reduced latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE performs cell reselection in unlicensed frequency bands using existing procedures, then the UE can access the network, but repeated preamble transmission failures occur due to channel congestion
Solution Approach 1:
The UE performs LBT (Listen-Before-Talk) procedure before transmitting the random access preamble to check if the unlicensed channel is available. This preliminary action prevents transmission attempts on congested channels, avoiding repeated failures and reducing latency by only transmitting when the channel is clear.
Solution Approach 2:
The system implements feedback mechanisms where the UE monitors channel occupancy and congestion levels on unlicensed frequencies. Based on this feedback, the UE adjusts its random access behavior, including selecting alternative frequencies or delaying transmissions until channel conditions improve, thereby increasing success rate and reducing latency.
2Loss of time
If the UE monitors reference signals continuously to detect missing signals for cell reselection, then cell reselection can be triggered earlier, but the complexity of the UE increases
Solution Approach 1:
Instead of monitoring all reference signals continuously, the UE focuses on monitoring a subset of critical reference signals (such as synchronization signals and physical broadcast channel signals) that are sufficient to detect cell reselection opportunities. This partial monitoring approach reduces processing complexity while still enabling timely cell reselection.
3Reliability
If the UE stays on the congested unlicensed frequency, then it maintains connection to the current cell, but repeated preamble transmission failures occur
Solution Approach 1:
The UE dynamically adapts its frequency selection based on real-time channel conditions. When congestion is detected on the current unlicensed frequency through LBT failures or reference signal monitoring, the UE switches to alternative frequencies (licensed or other unlicensed bands). This dynamic adaptation ensures maintained connectivity while avoiding congested channels, improving random access success rate.
Data Source
AI summary
The present disclosure relates to a user equipment (UE) comprises a receiver, which receives reference signals from a serving base station on which the UE is camping, the serving base station controlling an unlicensed serving radio cell in which the UE is located. Processing circuitry of the UE monitors the reception of reference signals to determine a number of reference signals that are continuously missing. The processing circuitry determines to perform cell re-selection from the unlicensed serving radio cell on which the UE is camping to another radio cell that has a different frequency than the unlicensed serving radio cell, in case the determined number of reference signals that are continuously missing is above a threshold.