Two-Step RACH HARQ Feedback for TA Command Failure
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Solution Overview
Problem
Wireless communication systems face challenges in efficiently handling a radio resource control (RRC) connected user equipment's failure to receive a timing advance (TA) command during the two-step random access procedure, leading to increased latency and resource utilization in synchronizing with the network.
Innovation Solution
Implementing a hybrid automatic repeat request (HARQ) procedure for the second RACH message, where if it fails, the user equipment (UE) can either start a new RACH procedure or trigger a radio link failure (RLF), thereby reducing latency and resource usage by allowing the UE to exit the HARQ loop and retry the preamble.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a two-step random access procedure is used for RRC connected UE, then access latency is reduced, but the complexity of handling TA command failure increases
Solution Approach 1:
The patent implements HARQ feedback mechanism where the UE sends acknowledgment signals for received TA commands. When the TA command is not received or feedback fails, the system triggers appropriate error handling procedures including RLF (Radio Link Failure) or retransmission, creating a closed-loop feedback system that manages complexity through structured response protocols
Solution Approach 2:
The patent pre-configures multiple handling scenarios for TA command failure before they occur. The UE is pre-programmed with decision trees that specify whether to initiate RLF, retry the random access procedure, or wait for retransmission based on the failure condition, eliminating the need for complex real-time decision-making during actual failure events
2Reliability
If HARQ procedure is implemented for second RACH message, then reliability of TA command delivery is improved, but resource consumption increases
Solution Approach 1:
The patent applies partial HARQ implementation where HARQ is enabled only for specific conditions (e.g., when TA command is not received within expected time window) rather than universally for all RACH messages. This selective approach provides reliability improvement where needed while avoiding unnecessary resource consumption in scenarios where the TA command is successfully received on the first attempt
3Loss of information
If the UE waits for HARQ retransmission of second RACH message, then data completeness is improved, but procedure duration increases
Solution Approach 1:
The patent implements periodic monitoring with timeout mechanisms where the UE monitors for HARQ retransmission of the second RACH message at predetermined intervals. When the timeout threshold is reached without receiving the retransmitted message, the UE stops waiting and initiates alternative procedures (RLF or random access retry), balancing data completeness with acceptable procedure duration through time-bound expectations
Data Source
AI summary
Wireless communication devices, systems, and methods related to handling user equipment's (UE's) failure to receive a timing advance (TA) command from a base station during in a two-step random access procedure are provided. For example, a method of wireless communication can include transmitting a first random access channel (RACH) message (e.g., msgA); monitoring for a second RACH message (e.g., msgB) from the BS including a timing advance (TA) command; performing a hybrid automatic repeat request (HARQ) procedure on the second RACH message; and performing, when the HARQ procedure on the second RACH message fails, at least one of: starting a new RACH procedure or triggering a radio link failure (RLF).