RACH Resource Allocation in NR-U via SSB to Beam Index Mapping
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Solution Overview
Problem
Current Random Access Channel (RACH) resource allocation in New Radio (NR) systems faces challenges in supporting repetition transmission modes and associating with Synchronization Signal and PBCH blocks, particularly in NR-Unlicensed operation, where beamforming and Listen-Before-Talk (LBT) failures complicate the mapping of SSB indices to beam indices and resource allocation.
Innovation Solution
A PRACH transmission resource selection scheme is introduced, where an SSB index is transformed into a beam index based on knowledge of cycled beams for LBT failures, and the beam index is used to select the ROG association index, allowing for efficient preamble selection across cloned ROs within an ROG, enabling half or full subband PRACH transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SSB index mapping to beam index is implemented in conventional RACH resource allocation, then beamforming support is provided, but the mapping fails under LBT failures in NR-Unlicensed operation
Solution Approach 1:
The patent introduces dynamic adaptation of RACH resource allocation by detecting LBT failure conditions and adjusting the mapping between SSB indices and beam indices accordingly. When LBT failure is detected, the system dynamically switches to an alternative mapping strategy that maintains RACH functionality despite the failed beam, making the system adaptive to changing channel conditions in NR-U environments.
Solution Approach 2:
The patent changes the mapping parameters (SSB index to beam index correspondence) based on LBT failure detection. When a beam fails LBT, the system modifies the parameter mapping to associate SSB indices with alternative available beams, thereby maintaining reliable RACH resource allocation under varying channel access conditions without requiring system reconfiguration.
2Reliability
If repetition transmission mode is supported in RACH, then transmission reliability is improved, but resource allocation complexity increases
Solution Approach 1:
The patent segments the RACH resource allocation into multiple occasions (ROs) within a RACH occasion group, where each RO can be independently configured for repetition transmissions. By dividing the resource allocation into manageable segments with clear association rules to SSB indices and beam indices, the system supports repetition modes while maintaining organized and tractable resource management despite the increased complexity.
3Reliability
If beam cycling is implemented to handle LBT failures, then system robustness is improved, but the association between SSB indices and beam indices becomes complex
Solution Approach 1:
The patent establishes preliminary association rules between SSB indices and beam indices that are pre-configured and documented before beam cycling begins. These predetermined mapping relationships allow the system to cycle through multiple beams robustly while maintaining clear, pre-defined association logic, reducing the operational complexity of managing dynamic beam switching and SSB index mappings during LBT failure recovery.
Data Source
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AI summary
In accordance with an example embodiment of the present invention, a method comprising: receiving, by a user equipment of a communication network, information comprising a random access channel configuration and a number of cycled beams; determining a number of random access channel occasions for a random access channel occasion group; transforming synchronization signal blocks to a beam index given the number of cycled beams and associating beams with the number of random access channel occasions of the random access channel occasion group; identifying a random access channel occasion group associated with the beam index; selecting at least one preamble associated with the beam index in the random access channel occasion group; and transmitting the at least one preamble within each of the number of random access channel occasions of the random access channel occasion group to perform a random access channel procedure.