Two-Step Random Access Using MsgA and HARQ-ACK for Lower Latency
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Solution Overview
Problem
Existing wireless communication systems face challenges in reducing latency and optimizing channel access in unlicensed spectrum through conventional 4-step random access procedures, particularly in scenarios requiring uplink synchronization and handovers.
Innovation Solution
A two-step random access procedure is introduced, involving MsgA transmission and MsgB reception, with power control mechanisms, HARQ-ACK feedback, and PUCCH resource management to enhance synchronization and reduce latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a 4-step random access procedure is used, then the procedure is more reliable and compatible with existing systems, but the latency for connection set-up, handover, and uplink synchronization increases
Solution Approach 1:
The patent segments the traditional 4-step random access procedure into a more efficient 2-step procedure by combining Message 2 and Message 3 into a single MsgB, and combining Message 1 and Message 2 transmission into a single MsgA transmission. This segmentation reduces the number of sequential steps from 4 to 2, directly reducing latency while maintaining reliability through enhanced power control and HARQ-ACK feedback mechanisms.
Solution Approach 2:
The patent implements preliminary power control adjustments before MsgA transmission and before MsgB transmission. By pre-calculating and applying appropriate power levels based on path loss measurements and received signal strength, the system ensures reliable reception from the outset, reducing the need for retransmissions and thereby reducing overall latency while maintaining high reliability.
2Loss of time
If a 2-step random access procedure is implemented, then latency is reduced and channel access efficiency is improved, but the complexity of power control and HARQ-ACK feedback management increases
Solution Approach 1:
The patent introduces HARQ-ACK feedback mechanisms where the receiving device sends acknowledgments for both MsgA and MsgB transmissions. This feedback enables the transmitting device to adjust power levels and retransmit if necessary, automating the power control process and reducing manual configuration complexity while maintaining low latency through rapid error correction.
Solution Approach 2:
The patent implements dynamic power control where transmission power is adjusted based on real-time channel conditions, previous transmission outcomes, and feedback received. This dynamic adaptation allows the system to optimize performance for each transmission attempt, reducing the need for complex static configurations and simplifying overall system management while maintaining low latency.
3Reliability
If power control is optimized for 2-step random access, then transmission reliability is improved, but the computational overhead and processing requirements increase
Solution Approach 1:
The patent performs preliminary power control calculations before MsgA and MsgB transmissions by measuring reference signal received power and calculating path loss. By pre-computing the required transmission power levels based on these measurements, the system ensures reliable transmission from the first attempt, reducing the need for complex real-time processing during actual data transmission and thereby reducing processing overhead while maintaining high reliability.
Solution Approach 2:
The patent enables devices to autonomously determine their transmission power levels by measuring downlink reference signals, calculating path loss, and applying pre-configured power control parameters. This self-service approach eliminates the need for complex network-controlled power adjustment and extensive signaling, reducing processing overhead while maintaining transmission reliability through autonomous adaptive power control.
Data Source
AI summary
At least one common PUCCH resource set configuration can be received (1310) for a 2-step random access procedure. At least one common PUCCH resource set can be determined (1320) based on the at least one common PUCCH resource set configuration. A PRACH and a corresponding MsgA PUSCH can be transmitted (1330). A MsgB PDSCH can be received (1340) in response to the transmitted PRACH and MsgA PUSCH. The received MsgB PDSCH can be decoded (1350). A successRAR intended to the UE can be identified (1360) from the decoded MsgB PDSCH. A common PUCCH resource set of the at least one common PUCCH resource set and a PUCCH resource of the common PUCCH resource set can be determined (1370) based on the successRAR. At least HARQ-ACK feedback information for the MsgB PDSCH can be transmitted (1380) on the PUCCH resource.