Unlicensed RACH Response Reception via Timing and RA-RNTI
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Solution Overview
Problem
In wireless communications, particularly in unlicensed radio frequency spectrum bands, delays in the random access channel (RACH) procedure can occur due to failures in the listen-before-talk (LBT) procedure, leading to latency in communications.
Innovation Solution
The implementation of an apparatus and method that includes transmitting a RACH preamble associated with a RA-RNTI in a first PRACH occasion and obtaining a RACH response (RAR) message within a RAR window, which includes the RA-RNTI and timing information indicating a set of PRACH occasions, to determine if the RAR message is in response to the RACH preamble.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a base station uses listen-before-talk (LBT) procedure in unlicensed spectrum, then channel access is controlled to avoid collisions, but delays occur when LBT fails to identify available transmission opportunities
Solution Approach 1:
The base station performs LBT procedure in advance before transmitting the RAR message. By preparing the channel status beforehand and having multiple LBT opportunities within the RAR window, the system reduces delays caused by last-minute channel access failures while maintaining collision avoidance reliability.
Solution Approach 2:
The system dynamically adjusts the RAR window duration based on LBT success. When LBT fails, the window can be extended or repositioned to provide additional transmission opportunities. This dynamic adaptation allows the base station to respond flexibly to channel conditions, reducing overall delay while maintaining reliable channel access control.
2Reliability
If the RAR window is extended to provide more LBT opportunities, then the likelihood of successful RAR transmission increases, but the time for RACH procedure completion increases
Solution Approach 1:
Multiple LBT opportunities are prepared within the RAR window in advance, allowing the base station to attempt channel access multiple times without extending the overall procedure time significantly. This preliminary preparation of transmission opportunities increases success rate while keeping the window duration manageable.
Solution Approach 2:
The base station performs LBT procedure periodically at different opportunities within the RAR window rather than continuously. This periodic approach provides multiple discrete chances for successful transmission while maintaining a controlled overall time duration, balancing reliability and efficiency.
3Measurement precision
If timing information indicating PRACH occasions is included in the RAR message, then the UE can accurately identify the correct RAR response, but the RAR message structure becomes more complex
Solution Approach 1:
The timing information field in the RAR message serves multiple functions: it identifies the correct PRACH occasion, validates the RAR response, and provides synchronization cues. By making this single field multi-functional, the system achieves accurate RAR identification without proportionally increasing message structure complexity.
Solution Approach 2:
The timing information acts as an intermediary element that bridges the RAR message and the PRACH occasion. Instead of directly complexifying the message structure, the patent uses timing information as a mediator to provide the necessary identification and synchronization functions, keeping the overall structure relatively simple while achieving precise RAR matching.
Data Source
AI summary
This disclosure provides systems, methods, and apparatuses to enable a user equipment (UE) and a base station to improve reception of a random access response (RAR) by the UE in an unlicensed spectrum. A network may define a procedure for calculating a random access radio network temporary identifier (RA-RNTI) specific to unlicensed spectrum based on an extended RAR window. The calculation procedure may allow UEs transmitting in the window to calculate a unique RA-RNTI and identify a RAR addressed to the UE using the unique RA-RNTI. Additionally, or alternatively, a base station may transmit a RAR including timing information associated with a corresponding random access request. Accordingly, a UE may receive the RAR and compare the timing information with its own random access request in order to determine whether the RAR is addressed to the UE. Additionally, a UE may monitor a secondary cell or a sub-band for the RAR.