Two-Step Random Access Occasion Mapping for Low-Latency UE Access
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Solution Overview
Problem
Existing wireless communication systems face challenges in configuring random access occasions for two-step random access procedures, particularly in achieving low transmission latency and desirable link level quality, due to limitations in existing four-step RACH procedures.
Innovation Solution
Configuring random access occasions by associating preamble and payload transmissions with synchronization signal block (SSB) beams, ensuring threshold link quality and reducing latency through proximity-based multiplexing, and determining suitable occasions for transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If four-step RACH procedure is used, then link quality can be maintained, but transmission latency increases
Solution Approach 1:
The random access procedure is segmented into two steps instead of four: (1) UE transmits preamble and payload together in MsgA, and (2) gNB responds with MsgB containing acknowledgment and uplink grant. This segmentation reduces the number of round-trip exchanges while maintaining link quality through selective acknowledgment and retransmission mechanisms.
Solution Approach 2:
The preamble transmission and payload transmission are merged into a single MsgA transmission occasion. The UE transmits both the random access preamble and the uplink data payload simultaneously in the same time-frequency resource, eliminating the need for separate transmission steps and reducing overall latency.
2Adaptability or versatility
If multiple preamble and payload occasions are configured, then transmission flexibility improves, but system complexity increases
Solution Approach 1:
Different preamble occasions and payload occasions are configured with different properties (e.g., different time resources, frequency resources, or spatial beams) to suit different transmission scenarios. The gNB can select appropriate occasions based on channel conditions, UE capabilities, and traffic requirements, providing localized optimization without overwhelming system complexity.
Solution Approach 2:
The system dynamically selects which preamble occasions and payload occasions to use based on real-time conditions. The gNB can activate or deactivate specific occasions through RRC signaling or MAC CE commands, allowing the system to adapt to changing traffic patterns and channel conditions while maintaining a manageable configuration set.
Data Source
AI summary
Aspects described herein relate to configuring and selecting preamble and payload occasions for performing two-step random access procedures. Configurations on preamble occasions, payload occasions, association pattern between the occasions and synchronization signal block (SSB) beams, and the rules for selecting preamble and payload occasions for random access message transmission can be determined by the network and signaled to user equipment (UE). Based on the configurations and rules, UE can measure the link level quality and select possible preamble and payload occasions for one or more SSB beams achieving a threshold signal quality. Sets of one or more preamble occasions and one or more payload occasions can be further determined based on whether the preamble and payload occasion(s) can achieve a threshold transmission latency. The one or more preamble occasions and one or more payload occasions can be used to transmit random access messages in the two-step random access procedure.