Unlicensed-Band Preamble Opportunities After LBT Failures
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Solution Overview
Problem
Existing communication systems face challenges in unlicensed bands due to long latency and failure in random access procedures caused by listen before talk failures, leading to uplink radio link failure and handover issues, especially when beams allocated with contention free random access resources experience ongoing LBT failures.
Innovation Solution
User equipment selects and prioritizes both contention based and contention free random access resources based on network-configured rules, detecting listen before talk failures to switch to contention based resources when a predetermined number is reached, thereby providing additional preamble transmission opportunities and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If user equipment prioritizes beams associated with contention free random access resources, then beam selection is simplified and prioritization is achieved, but listen before talk failures occur frequently causing long latency and uplink radio link failure
Solution Approach 1:
The patent implements dynamic switching between contention-free and contention-based random access procedures based on real-time LBT failure detection. The user equipment monitors LBT outcomes and dynamically adjusts its random access strategy, transitioning from prioritizing CFRA beams to using CBRA resources when LBT failures are detected, thereby resolving the contradiction between ease of beam selection and random access reliability
Solution Approach 2:
The patent changes the random access procedure parameter from static CFRA prioritization to dynamic selection based on LBT failure conditions. By monitoring LBT failure counts and comparing them against thresholds, the system adjusts its beam and resource selection parameters, switching between different random access modes to maintain reliability while preserving operational simplicity
2Ease of operation
If user equipment continues to use contention free random access resources despite LBT failures, then beam prioritization is maintained, but latency increases and handover failure occurs
Solution Approach 1:
The patent implements a feedback mechanism where the user equipment monitors LBT failure outcomes and uses this information to adjust its random access strategy. The feedback from LBT results triggers a switch to contention-based random access when failures exceed a threshold, thereby reducing latency and preventing handover failure while maintaining beam prioritization logic
3Reliability
If user equipment switches to contention based random access resources, then listen before talk failures are avoided, but additional transmission opportunities are required increasing procedure complexity
Solution Approach 1:
The patent segments the random access procedure into distinct CFRA and CBRA modes with clear switching criteria. By dividing the procedure into manageable segments and defining specific trigger conditions for switching, the system maintains reliability through LBT failure avoidance while limiting procedure complexity through structured decision logic
Data Source
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AI summary
In accordance with some embodiments, a method may include selecting, by a user equipment, at least one random access occasion associated with at least one contention based random access resource and at least one random access occasion associated with at least one contention free random access resource. The method may further include detecting, by the user equipment, a predetermined number of listen before talk failures associated with one or more of the at least one random access occasion associated with at least one contention free random access resource. The method may further include transmitting, by the user equipment, in response to detecting a predetermined number of listen before talk failures, according to the selected at least one random access occasion associated with at least one contention based random access resource.