2-Step RACH HARQ Retransmission Timing for Lower Access Latency
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Solution Overview
Problem
The 2-step RACH procedure in wireless communication systems experiences significant latency due to undefined retransmission timelines, leading to inefficiencies in message exchange between UEs and base stations, particularly when decoding failures occur.
Innovation Solution
Implementing defined timeline arrangements for retransmission schemes in the 2-step RACH procedure, including specific time gaps and window monitoring for messages, allowing UEs and base stations to determine appropriate retransmission or acknowledgement based on decoding success or failure of received payloads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If retransmission is implemented when RAR is not received within the RAR window, then reliability of message delivery is improved, but system latency increases significantly due to waiting time
Solution Approach 1:
The patent applies preliminary action by defining retransmission timelines in advance before retransmission is actually needed. The network configures the UE with specific time gaps (e.g., msgA-TransmissionTimeIndicator, msgB-TransmissionTimeIndicator) that specify exactly when retransmission should occur, eliminating the need to wait for the RAR window to expire before initiating retransmission procedures.
2Stability of the object's composition
If the UE waits for the RAR window to expire before retrying the RACH procedure, then the system maintains proper timing synchronization, but significant latency is introduced
Solution Approach 1:
The patent applies dynamics by making the retransmission timing flexible and configurable rather than fixed. The network can dynamically adjust time gaps for retransmission based on current system conditions, allowing the UE to retransmit at optimized times that balance timing synchronization requirements with latency reduction goals.
3Reliability
If the RAR window is extended to allow more time for RAR reception, then reliability of RAR delivery is improved, but the overall access procedure latency increases
Solution Approach 1:
The patent applies feedback by implementing a mechanism where the UE monitors for RAR within the configured window and provides implicit feedback through its retransmission behavior. If RAR is not received by the deadline, the UE automatically retransmits according to the pre-configured timeline, creating a feedback loop that ensures delivery without requiring an excessively long initial window.
Data Source
AI summary
Wireless communications systems and methods related to the timing arrangements and the transmission gap configurations in 2-step random access channel (RACH) procedures to improve system latency and reliability of a RACH HARQ process are provided. The UE transmits a first message including a random access preamble and a payload, and then monitors for a second message in response to the first message during a random access response (RAR) window. In response to determining that no second message is received by the UE from the BS or a back off indicator is received within the RAR window, the UE re-transmits the preamble and payload of the first message after the RAR window lapses. In response to determining if the second message received within the RAR window carries a FallbackRAR or SuccessRAR, the UE then determines to re-transmit the payload of the first message based on the FallbackRAR, or to transmit an acknowledgement message based on the SuccessRAR.