MsgB Multiplexing and HARQ in Two-Step RACH
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Solution Overview
Problem
The two-step random access channel (RACH) in mobile communications faces challenges regarding the multiplexing, addressing, and hybrid automatic repeat request (HARQ) for MsgB, including whether MsgB should contain information for a single UE or multiple UEs, its addressing to RA-RNTI or C-RNTI, and the support and feedback mechanisms for HARQ.
Innovation Solution
A method and apparatus for a user equipment (UE) to transmit a first message with a preamble index and data, receiving a second message containing a random access response and contention resolution information, where MsgB is addressed to either a cell radio network temporary identifier (C-RNTI) or a random access radio network temporary identifier (RA-RNTI), with options for HARQ support and partitioning of MsgB for multiple UEs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MsgB contains information for multiple UEs, then the efficiency of random access procedure is improved, but the complexity of message structure and addressing increases
Solution Approach 1:
The MsgB is segmented into multiple parts or fields, where different fields serve different functions (RAR field for random access response, CR field for contention resolution). This segmentation allows the message to efficiently serve multiple UEs while maintaining a structured format that manages complexity through clear field delimitation and interpretation rules.
2Adaptability or versatility
If MsgB is addressed to RA-RNTI, then the capability to address multiple UEs is improved, but the precision of UE identification decreases
Solution Approach 1:
The RA-RNTI serves as an intermediary address that allows the network to send a single MsgB to multiple UEs simultaneously. The message includes both the RA-RNTI for initial addressing and additional fields (such as preamble ID, UE identity) that enable each UE to identify whether the message is intended for them, thus maintaining precise identification while enabling multi-UE addressing.
3Reliability
If HARQ is supported for MsgB, then the reliability of message delivery is improved, but the complexity of feedback mechanisms increases
Solution Approach 1:
The patent implements HARQ feedback mechanisms where UEs send acknowledgments (ACK/NACK) for received MsgB. The feedback complexity is managed by defining clear feedback triggers (e.g., successful contention resolution), standardized feedback formats, and timing relationships between MsgB transmission and expected feedback, thereby achieving high reliability while controlling system complexity.
Data Source
AI summary
Various examples and schemes pertaining to multiplexing, addressing and HARQ for MsgB in two-step RACH in mobile communications are described. An apparatus implemented in a user equipment (UE) transmits to a network node of a wireless network a first message containing a preamble index and data. In response, the apparatus receives from the network node a second message containing a random access response (RAR) and contention resolution information. The second message is addressed to either a cell radio network temporary identifier (C-RNTI) of the UE or a random access radio network temporary identifier (RA-RNTI).