Two-Step RACH Message 2 Multiplexing for Lower Access Latency
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Solution Overview
Problem
Existing wireless communication systems face challenges in reducing latency and network inefficiencies in random access procedures, particularly in unlicensed spectra, due to the use of multiple messages and listen-before-talk procedures.
Innovation Solution
Implementing a two-step random access procedure that includes an uplink request message and a downlink response message, allowing for multiplexing of responses for multiple UEs in a single physical downlink shared channel, and omitting acknowledgement procedures to reduce latency and improve network efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a four-step random access procedure is used, then reliability of connection establishment is improved, but network latency increases and network efficiency deteriorates
Solution Approach 1:
The patent combines multiple random access procedures (two-step and four-step) into a unified framework where a single message 2 can serve multiple UEs. This merging reduces the number of separate message exchanges needed while maintaining reliable connection establishment through selective acknowledgment mechanisms.
Solution Approach 2:
The downlink message 2 is designed to serve multiple functions simultaneously: it can act as a random access response for two-step RACH UEs, provide scheduling assignments for four-step RACH UEs, and include acknowledgment information. This multi-functionality reduces overall latency by consolidating multiple control functions into a single message.
2Reliability
If multiple downlink response messages are sent to multiple UEs, then individual UE service quality is improved, but network overhead increases and network efficiency deteriorates
Solution Approach 1:
The patent merges multiple downlink response messages into a single multiplexed message 2 that serves multiple UEs simultaneously. This consolidation reduces network overhead and improves efficiency while maintaining individual UE service quality through UE-specific field identification.
Solution Approach 2:
The single message 2 is segmented into multiple UE-specific response fields, each containing dedicated information for a specific UE. This segmentation allows individualized service quality while maintaining the efficiency benefits of a single consolidated message structure.
3Reliability
If acknowledgement and NACK procedures are implemented, then retransmission reliability is improved, but message exchange complexity increases and latency increases
Solution Approach 1:
The patent extracts the acknowledgment function from a separate interactive procedure and embeds it directly within the downlink message 2 itself. UE-specific acknowledgment fields are embedded in the message, allowing reliability feedback without requiring additional uplink NACK messages or complex retransmission handshakes.
4Measurement precision
If separate downlink responses are sent to each UE, then individual UE decoding accuracy is improved, but network overhead increases and power consumption increases
Solution Approach 1:
The patent merges multiple individual downlink responses into a single multiplexed message 2, reducing the number of separate transmissions UEs must receive and process. This consolidation reduces power consumption while maintaining decoding accuracy through UE-specific field identification and targeted decoding approaches.
Data Source
AI summary
Methods, systems, and devices for wireless communications are described. The method includes identifying that the user equipment (UE) is to use a two-step random access channel (RACH) procedure that includes a first message (e.g., uplink request message) and a second message (e.g., downlink response). The methods include sending, as a first message of the two-step RACH procedure, the uplink request message to a base station, receiving, from the base station, a physical downlink control channel comprising an indication of resources of a broadcast or multicast physical downlink shared channel on which the downlink response is to be received, and receiving the downlink response from the base station on the broadcast or multicast physical downlink shared channel. The physical downlink shared channel may be configured to provide downlink responses for one or multiple UEs.