2-Step RA Back-off via MAC Subheader Segmentation
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Solution Overview
Problem
The 2-step random access procedure in wireless network communications faces issues such as incomplete detection of msgA by the gNB, leading to unnecessary back-off for both 2-step and 4-step UEs, and potential fallback to 4-step RA procedure without proper congestion management.
Innovation Solution
A mechanism is introduced using a MAC control element (CE) specific to the 2-step RA procedure, employing an E/T/R/R/BI MAC subheader or an E/T/RAPID MAC subheader to indicate back-off and/or fallback to a 4-step RA procedure for UEs performing a 2-step RA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gNB detects only the preamble from msgA (incomplete detection), then the gNB responds with a RAR causing UE to back-off, but this results in unnecessary back-off for both 2-step and 4-step UEs and potential unnecessary fallback to 4-step procedure
Solution Approach 1:
The patent segments the back-off mechanism into two distinct types: legacy back-off (E/T/R/R/BI MAC subheader) affecting all UEs, and 2-step specific back-off (using reserved RAPID values or new MAC CE) affecting only 2-step UEs. This segmentation allows the gNB to apply back-off selectively based on which part of msgA was detected, preventing unnecessary back-off for 4-step UEs while still managing 2-step RA congestion effectively.
2Reliability
If the gNB applies legacy back-off mechanism to 2-step RA, then congestion is managed, but 4-step UEs are also impacted with unnecessary back-off
Solution Approach 1:
The patent applies local quality by making the back-off mechanism specific to the RA type. The gNB uses different back-off indicators for different UE groups: legacy BI for general RA congestion and 2-step specific BI (via reserved RAPID or new MAC CE) for 2-step RA congestion. This allows congestion management to be applied locally to the affected UE group without impacting other UEs, thereby maintaining high resource utilization efficiency for 4-step procedures.
3Adaptability or versatility
If the network introduces 2-step specific back-off mechanism, then selective back-off is achieved, but the MAC protocol complexity increases
Solution Approach 1:
The patent achieves universality by making the existing MAC subheader structure multi-functional. The E/T/R/R/BI format can serve both legacy back-off (T=0) and 2-step specific back-off (T=1 with reserved RAPID or new MAC CE). This multi-functionality allows the MAC protocol to maintain a unified structure while providing differentiated back-off capabilities, minimizing the increase in protocol complexity while achieving selective back-off.
Data Source
AI summary
A wireless device configured to perform a 2-step random access, RA, procedure transmits (802) a message according to the 2-step RA procedure, the message comprising a first random access preamble. The wireless device receives (804), during a RA response window following the transmitting of the message, a Medium Access Control, MAC, subheader. Using one or more bits or fields included in the received subheader, the wireless device determines (806) that it should take action according to any one of the following: backing off, according to a back-off parameter, for a subsequent RA attempt according to the 2-step RA procedure; falling back to a 4-step RA procedure by transmitting a new RA preamble; and falling back to a 4-step RA procedure after backing off according to a back-off parameter, by transmitting a new random access preamble after the back-off.