NR-U RACH Gap Scheduling for Listen-Before-Talk Access
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Solution Overview
Problem
Existing 5G NR systems face challenges in accessing unlicensed spectrum due to RACH transmission blockages, leading to increased latency and resource wastage in initial access procedures.
Innovation Solution
Implementing techniques to differentiate between licensed and unlicensed frequency bands through bitfield manipulation in MIB, CRC masking, GSCN differentiation, RRC signaling, DMRS sequence generation, and PRACH puncturing to create gaps for LBT, ensuring efficient RACH transmission in NR-U operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If RACH transmissions are performed in consecutive ROs without gaps in unlicensed bands, then access speed is improved, but transmission reliability deteriorates due to LBT failures
Solution Approach 1:
The patent segments the consecutive RACH occasions into groups with inserted gaps. Specifically, it divides ROs into multiple groups and inserts gaps between certain groups based on LBT outcomes, allowing independent handling of transmission opportunities while maintaining overall access efficiency.
Solution Approach 2:
The patent performs LBT procedures in advance before RACH transmissions in unlicensed bands. By conducting clear channel assessment beforehand and inserting gaps when LBT fails, the system prepares transmission conditions preliminarily, preventing blocked transmissions and improving reliability without significantly impacting access speed.
2Reliability
If gaps are inserted between RACH occasions to accommodate LBT procedures, then transmission reliability is improved, but access latency increases
Solution Approach 1:
The patent dynamically determines gap insertion based on LBT outcomes and frequency band type. Gaps are inserted only when necessary (when LBT fails in unlicensed bands), and the gap duration and positioning are dynamically adjusted based on timing advance values and uplink slot structures, optimizing the balance between reliability and latency.
Solution Approach 2:
The patent changes multiple parameters to minimize latency impact: it adjusts gap duration based on timing advance values, selects gap positions within uplink slots to align with existing structures, and modifies RACH configuration parameters (like prach-ConfigurationIndex and messageA-DMRS-SequenceInitialization) to accommodate gaps while maintaining access efficiency.
3Productivity
If RACH transmissions are performed without gap insertion, then resource utilization is improved, but transmission blockages increase
Solution Approach 1:
The patent introduces gap periods as intermediary elements between RACH transmissions in unlicensed bands. These gaps serve as mediators that allow LBT procedures to occur, enabling the system to sense the channel and determine transmission feasibility, thereby reducing blocked transmissions while maintaining reasonable resource utilization through efficient gap placement.
Solution Approach 2:
The system performs self-service by autonomously determining when to insert gaps based on LBT outcomes and current transmission conditions. The gNB configures appropriate gap patterns and the UE autonomously applies them during RACH procedures, allowing the system to adapt to channel conditions without external intervention while maintaining resource efficiency.
Data Source
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AI summary
Disclosed are techniques for reducing likelihood of Random Access Channel (RACH) transmission blockages and thereby facilitate an initial access procedure for new radio (NR) unlicensed spectrum (NR-U) operation in a fifth generation (5G) wireless communication system including an NR node. In some embodiments, a parameter generated by a gNB and received by a UE indicates that, from among a set of consecutive RACH Occasions (ROs), a gap is available for performing a listen-before-talk (LBT) procedure before commencing a RACH transmission.