SSB-Linked Random Access Occasions for Low-Latency Two-Step RACH
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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 unsuitable preamble and payload occasions in existing four-step RACH configurations.
Innovation Solution
The system configures random access occasions by associating preamble and payload occasions with synchronization signal block (SSB) beams, ensuring threshold link quality and latency, and supports proximity-based multiplexing to optimize transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If four-step RACH configuration 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, where the first message combines preamble and payload transmissions. This segmentation reduces the number of round-trip exchanges while maintaining link quality through selective repetition opportunities in subsequent steps.
Solution Approach 2:
The payload is transmitted preliminarily in the first message along with the preamble, rather than waiting for separate subsequent messages. This preliminary action reduces overall transmission latency while the system maintains reliability through configured repetition mechanisms.
2Adaptability or versatility
If preamble and payload are transmitted in separate occasions, then transmission flexibility is improved, but overall procedure latency increases
Solution Approach 1:
The preamble and payload transmissions are merged into a single first message transmitted in one occasion, rather than being separated into multiple occasions. This merging reduces procedure latency while the system maintains flexibility through configurable repetition parameters and association with SSB beams.
3Reliability
If multiple random access occasions are configured for different SSB beams, then link quality is improved, but configuration complexity increases
Solution Approach 1:
A single random access occasion configuration serves multiple SSB beams universally, rather than requiring separate configurations for each beam. This multi-functionality approach maintains link quality through beam association while reducing configuration complexity by using shared parameters across multiple beams.
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.