UE MAC PDU Rebuilding for Random Access Grant Alignment
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Solution Overview
Problem
In 5G NR wireless communication systems, user equipment (UE) faces challenges in efficiently selecting and managing random access (RA) resources during the RA procedure, particularly when switching between contention-based (CBRA) and contention-free (CFRA) resources, due to mismatches in uplink grant sizes and MAC PDU sizes, leading to inefficiencies in data transmission.
Innovation Solution
The method involves a UE's MAC entity and HARQ entity managing the Msg3 buffer and Multiplexing and Assembly (M&A) entity to rebuild and retransmit MAC PDUs based on the size of the uplink grant received, ensuring that the MAC PDU is adjusted to match the granted resources, allowing for efficient transmission by discarding or modifying subPDUs as necessary to align with the UL grant size, thereby optimizing the RA resource selection and transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE selects different RA resources each time during RA procedure, then the reliability of random access is improved, but the device complexity increases due to resource selection and management overhead
Solution Approach 1:
The network pre-configures multiple RA resources (preambles and time-frequency resources) for the UE before the random access procedure. The UE simply selects from these pre-configured options based on simple criteria rather than performing complex resource selection, reducing device complexity while maintaining reliability through diverse resource options
Solution Approach 2:
The network acts as an intermediary by providing RA resource configuration information to the UE. This configuration serves as a mediator that guides the UE's resource selection process, simplifying the UE's decision-making while ensuring reliable and coordinated resource usage across the network
2Productivity
If the MAC PDU size is adjusted to match the uplink grant size, then the productivity of data transmission is improved, but the device complexity increases due to MAC PDU rebuilding and subPDU management
Solution Approach 1:
The MAC PDU structure is made dynamic and adaptable. The UE can adjust the MAC PDU size and composition based on the received uplink grant size, building or removing subPDUs as needed. This dynamic adjustment enables efficient use of granted resources while the standardized procedures keep implementation complexity manageable
Solution Approach 2:
The MAC PDU is segmented into multiple subPDUs, each carrying specific data or control information. This segmentation allows flexible reconfiguration of the MAC PDU structure to match different uplink grant sizes by adding, removing, or adjusting individual subPDUs, improving transmission efficiency while maintaining structured organization
3Loss of substance
If the UE discards or modifies subPDUs to align with UL grant size, then the loss of substance is reduced, but the reliability decreases due to potential data loss from discarding subPDUs
Solution Approach 1:
The UE can discard certain subPDUs (such as padding subPDUs or low-priority data subPDUs) when the MAC PDU size needs to be reduced to match the uplink grant. This selective discarding minimizes waste of transmission resources while preserving important data, balancing efficiency and reliability through prioritization strategies
Data Source
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AI summary
A method for random access performed by a UE is provided. The method includes: receiving, by a MAC entity of the UE, a UL grant in an RAR from a base station during an ongoing random access procedure, wherein the MAC entity includes a Msg3 buffer, an M&A entity, and a HARQ entity; obtaining, by the HARQ entity, a first MAC PDU from the Msg3 buffer after determining that at least one MAC PDU is in the Msg3 buffer, wherein the first MAC PDU includes a first type of MAC subPDU carrying a MAC SDU and a second type of MAC subPDU carrying a MAC CE; and indicating to the M&A entity, by the HARQ entity, to discard a specific type of MAC subPDU from the first MAC PDU, when a size of the UL grant is different from a size of the first MAC PDU.