Two-Step Random Access Channel Procedure in Unlicensed Bands
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Solution Overview
Problem
Current random access procedures in unlicensed bands for next-generation 5G systems face challenges in efficiently configuring a time point for signal reception and performing a two-step random access procedure, particularly in shared spectrum channel access scenarios.
Innovation Solution
A method and apparatus for performing a two-step random access procedure by transmitting a physical random access channel preamble and receiving a random access response, where a single PRACH occasion is mapped to a specific physical uplink shared channel occasion with a time gap, and the reception window for the response starts at least one symbol after the last symbol of the corresponding PUSCH occasion, regardless of successful or failed PUSCH transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single PRACH occasion is mapped to multiple PUSCH occasions in unlicensed band, then the random access procedure can be performed, but it becomes difficult to properly configure the time point for receiving the random access response signal
Solution Approach 1:
The patent segments the reception window configuration by associating each PUSCH occasion with its corresponding PRACH occasion. The reception window for Message B is configured separately for each PUSCH occasion based on the time gap from that specific PUSCH occasion, allowing independent optimization of reception timing for each transmission opportunity.
Solution Approach 2:
The patent performs preliminary configuration of the reception window parameters before the actual random access procedure. The time gap between PUSCH and Message B reception is pre-determined and configured, allowing the terminal to calculate the exact reception timing in advance without complex real-time adjustments.
2Speed
If the reception window for Message B starts immediately after PUSCH transmission, then the response can be received quickly, but the terminal cannot account for both successful and failed PUSCH transmission cases
Solution Approach 1:
The patent applies different reception window configurations based on the local condition of PUSCH transmission outcome. For successful PUSCH transmission, the reception window starts at a specific time gap after PUSCH. For failed transmission (e.g., LBT failure), a different reception window configuration is applied, ensuring reliable detection of Message B in both scenarios.
Solution Approach 2:
The reception window configuration is made dynamic rather than fixed. The terminal adjusts the Message B reception timing based on whether the PUSCH transmission was successful or failed. This dynamic adjustment allows the system to optimize reception timing for each specific transmission outcome while maintaining overall procedure reliability.
3Productivity
If multiple PUSCH occasions are configured without time separation, then resource utilization is high, but the terminal cannot properly distinguish and process responses for each PRACH occasion
Solution Approach 1:
The patent introduces the time gap as an intermediary parameter between PUSCH transmission and Message B reception. This time gap acts as a separator that allows the terminal to distinguish which PUSCH occasion corresponds to which Message B reception, even when multiple PUSCH occasions are configured. The time gap serves as a mediator that maintains the relationship between PRACH and PUSCH occasions.
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3
AI summary
The present disclosure discloses a method by which a terminal performs a random access channel (RACH) procedure in an unlicensed band. In particular, the method comprises: transmitting a first physical random access channel (PRACH) preamble through message A, and in response to the message A, receiving a random access response (RAR) through message B related to contention resolution, wherein the first PRACH preamble is a PRACH preamble mapped to a physical uplink shared channel (PUSCH) occasion for the message A, and the window for reception of the message B may start after at least one symbol from the last symbol of the PUSCH occasion.