UE Fallback from 2-Step to 4-Step Random Access
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Solution Overview
Problem
The existing technologies face challenges in efficiently handling 2-step and 4-step Random Access (RA) procedures, particularly in fallback scenarios from 2-step to 4-step RA procedures, due to issues like inaccurate Time Advance (TA) values and interference, which affect random access performance and resource utilization.
Innovation Solution
A method is introduced where a User Equipment (UE) transmits a msgA comprising a preamble and a message, and based on specific criteria such as a maximum number of msgA transmissions exceeded or receipt of an indicator, the UE determines to fallback from the 2-step RA procedure to the 4-step RA procedure, optimizing latency and resource management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a 2-step RA procedure is used to reduce latency, then access speed is improved, but reliability deteriorates due to LBT failures and interference
Solution Approach 1:
The patent implements dynamic procedure selection where the UE can switch between 2-step and 4-step RA procedures based on current channel conditions and LBT outcomes. The system dynamically adapts the access method rather than using a fixed procedure, allowing optimization of both speed and reliability according to real-time conditions.
Solution Approach 2:
The patent changes the procedural parameter from fixed 2-step to conditional fallback to 4-step based on LBT failure detection. By monitoring channel access success and modifying the RA procedure type accordingly, the system adjusts its behavior to maintain reliability while preserving fast access when conditions permit.
2Reliability
If fallback from 2-step to 4-step RA procedure is implemented to improve reliability, then access success rate is improved, but latency increases
Solution Approach 1:
The patent performs preliminary LBT channel access attempts before initiating the RA procedure. By checking channel availability in advance and preparing both 2-step and 4-step procedures, the system can quickly switch to the appropriate method without extensive reconfiguration, minimizing the time penalty of fallback.
Solution Approach 2:
When LBT fails or channel conditions are poor, the patent enables the UE to skip the lengthy 2-step procedure and directly initiate the 4-step RA procedure. This skipping mechanism avoids wasting time on a procedure likely to fail, thereby reducing overall access latency despite using the longer 4-step method.
3Reliability
If msgA transmissions are repeated to overcome LBT failures, then reliability is improved, but resource utilization deteriorates
Solution Approach 1:
The patent implements dynamic resource allocation where msgA transmission resources are allocated adaptively based on LBT success and channel conditions. Rather than continuously repeating msgA transmissions regardless of conditions, the system dynamically adjusts transmission attempts and resource usage to improve reliability while preventing resource waste.
Solution Approach 2:
The UE autonomously monitors its own msgA transmission status and LBT outcomes, making decisions about whether to retry or switch procedures without continuous network intervention. This self-service approach optimizes resource utilization by avoiding unnecessary retransmissions while maintaining reliability through intelligent retry logic.
Data Source
AI summary
The present disclosure relates to a method performed by a UE (101) for handling 2-step and 4-step RA procedures in a communications system (100). The UE (101) transmits a msgA comprising a preamble and a msg3 to a network node (103). The UE (101) applies a 2-step RA procedure when transmitting msgA. Based on a criterion, the UE (101) determines to fallback from the 2-step RA procedure to a 4-step RA, procedure. The criterion is that a maximum number of msgA transmissions has been exceeded or receipt of an indicator indicating that the UE (101) should fallback from the 2-step RA procedure to the 4-step RA procedure.