2-Step Random Access Retransmission After PUSCH Decode Failure
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Solution Overview
Problem
The 2-step Random Access (2-step RACH) process in wireless communication systems faces issues where a preamble is detected but the data signal on the PUSCH is not correctly decoded, leading to inefficiencies in the 4-step RACH conversion mechanism, especially for UEs that only support the 2-step RACH mode.
Innovation Solution
Implementing a dual type Msg B response mechanism, where a Msg B of type I is sent when the preamble and data on PUSCH are correctly decoded, and a Msg B of type II is sent when the data is not correctly decoded, allowing for retransmission of Msg A with adjusted transmission parameters based on previous information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If 2-step RACH is used to shorten random access latency and reduce signaling overhead, then access efficiency is improved, but the reliability of data signal decoding deteriorates
Solution Approach 1:
The Msg B response is segmented into multiple types (first type for successful decoding, second type for unsuccessful decoding), allowing the system to provide differentiated responses based on decoding outcomes. This segmentation enables the 2-step RACH to handle decoding failures independently without falling back to 4-step RACH, thus maintaining low latency while improving reliability.
Solution Approach 2:
The base station provides feedback through different Msg B types indicating whether the data signal was successfully decoded. When decoding fails, the second type Msg B triggers a retransmission of Msg A with adjusted parameters. This feedback mechanism ensures reliable data transmission while maintaining the fast access benefits of 2-step RACH.
2Reliability
If 4-step RACH conversion mechanism is used when preamble is detected but data signal is not correctly decoded, then decoding reliability is improved, but access latency increases and signaling overhead increases
Solution Approach 1:
The system performs preliminary action by sending the second type Msg B immediately when decoding fails, which pre-triggers the retransmission process. This eliminates the need to wait for the UE to initiate a full 4-step RACH procedure, thereby maintaining low latency while ensuring reliable decoding through controlled retransmissions with adjusted parameters.
3Ease of operation
If Msg A retransmission is performed without adjusting transmission parameters, then retransmission simplicity is maintained, but access success rate deteriorates
Solution Approach 1:
The transmission parameters of Msg A are made dynamic and adjustable based on previous decoding attempts. The UE adjusts parameters such as transmit power, modulation scheme, or coding rate when performing retransmissions triggered by second type Msg B. This dynamic adaptation improves access success rate while maintaining relatively simple operation through automated parameter adjustment.
Data Source
AI summary
A method and a device in a node used for wireless communication are disclosed in the present disclosure. A first node transmits a first Random-Access (RA) Preamble and a first radio signal, the first RA Preamble being associated with the first radio signal, the first RA Preamble being transmitted on a Physical Uplink Shared Channel (PUSCH), and a first bit block being used for generating the first radio signal; receives Physical Downlink Control Channel PDCCH, the PDCCH comprising a first information block; and transmits a second RA Preamble and a second radio signal, the second RA Preamble being associated with the second radio signal, and the second RA Preamble being transmitted on a PUSCH, the first bit block being used for generating the second radio signal; the RA channels being Physical Random Access Channel (PRACH) occasions.