NR-U Random Access with Autonomous BWP Switching

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Solution Overview

Problem

The existing random access procedures in NR-U Serving Cells face challenges due to Listen-Before-Talk (LBT) failures, which cause delays and failures in the random access process, especially when performing UL transmissions with LAA SCells, and require enhancements to mitigate these issues for efficient channel access and reduced latency.

Innovation Solution

The proposed solution involves multiple models for random access in NR-U Serving Cells, including enhancements to the Random Access Resource Selection procedure, enabling selection of PRACHs associated with multiple BWPs or sub-bands, autonomous BWP switching, and LBT prioritization, to address LBT failures and optimize channel access. These models inform the MAC layer of LBT failures, allowing for corrective actions and efficient preamble transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If LBT is applied before transmission on LAA SCell, then channel access safety is improved, but transmission delay increases

Engineering Contradiction:

Improvechannel access safetyVSAvoidtransmission delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by performing LBT in advance before the actual transmission occurs. The UE performs LBT procedure before transmitting the random access preamble on the PRACH, ensuring the channel is clear beforehand. This prevents transmission conflicts and ensures safe channel access while managing the delay through proper timing advance mechanisms.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If random access procedure is performed with LBT failures, then channel access opportunity is maintained, but access success rate decreases

Engineering Contradiction:

Improvechannel access opportunityVSAvoidaccess success rate

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements dynamics by allowing the UE to adapt its behavior based on LBT outcomes. When LBT fails, the UE can dynamically adjust its random access strategy, such as selecting alternative PRACH occasions, adjusting transmission power, or waiting for a later opportunity. This dynamic adaptation maintains access opportunities while improving success rates through intelligent response to LBT failures.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent employs feedback mechanisms where the UE receives information about LBT outcomes and uses this feedback to adjust its random access procedure. The network provides feedback about channel conditions and LBT results, allowing the UE to modify its transmission parameters and strategies accordingly, thereby improving access success rate while maintaining channel access opportunities.

Inventive Principle:

Principle #23Feedback

3Adaptability or versatility

If multiple BWPs are configured for random access, then resource selection flexibility is improved, but procedure complexity increases

Engineering Contradiction:

Improveresource selection flexibilityVSAvoidprocedure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the bandwidth into multiple BWPs (Bandwidth Parts), each with its own PRACH configuration. This allows the UE to segment the random access resource selection process into manageable parts, choosing from multiple predefined BWPs based on channel conditions and requirements. The segmentation provides flexibility while keeping each individual BWP configuration simple and manageable.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11800563B2Random access with new radio unlicensed cells

Publication Date: 2023.10.24 IPLA HLDG INC

AI summary

A method may perform random access subject to Listen-Before-Talk (LBT) in an NR-U Serving Cell with multiple models. Enhancements may be to the Random Access Preamble Transmission procedure to enable autonomous BWP Switching or sub-band in the event the channel is busy for the active UL BWP.