NR-PRACH Multiple Msg1 Transmission for Access Latency Reduction
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Solution Overview
Problem
Current wireless communication systems, particularly in 5G networks, face challenges in reducing access latency during the random-access channel (RACH) procedure, which affects the efficiency of user equipment (UE) in communicating with base stations.
Innovation Solution
The method involves transmitting multiple physical random-access channel (PRACH) preambles (Msg1) by user equipment (UE) on multiple RACH transmission occasions before the end of a random-access response (RAR) window, and determining which preambles are detected based on explicit signals in RARs or associated signatures, such as RA-RNTI values, RAR windows, and control regions for PDCCH, to optimize antenna usage for uplink transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If multiple PRACH preambles are transmitted on multiple RACH transmission occasions, then access latency is reduced and beam-matching is accelerated, but the complexity of determining which preambles are detected increases
Solution Approach 1:
The patent segments the RACH procedure by transmitting multiple preambles on different RACH transmission occasions (time slots), allowing the UE to test multiple beams in parallel. Each preamble transmission is separated in time, enabling the network to process and respond to each one individually while reducing overall access latency through parallel beam testing.
Solution Approach 2:
The patent implements feedback mechanisms where the network provides explicit signals in RARs (Random Access Responses) indicating which preambles were detected. This feedback allows the UE to identify successfully detected preambles and determine which beams should be used for subsequent uplink transmissions, resolving the complexity of determining detected preambles through structured network responses.
2Productivity
If multiple PRACH preambles are transmitted simultaneously on different beams, then beam-matching is accelerated, but the signaling overhead to indicate detected preambles increases
Solution Approach 1:
The patent merges multiple RAR messages into a single RAR containing indications for multiple detected preambles. Instead of sending separate responses for each preamble, the network combines the detection results for all transmitted preambles into one consolidated response message, reducing signaling overhead while maintaining beam-matching acceleration.
Solution Approach 2:
The RAR message structure is designed to serve multiple functions simultaneously: it acknowledges multiple detected preambles, provides uplink scheduling information, and indicates which beams should be used for subsequent transmissions. This multi-functional approach reduces the need for additional signaling messages.
Data Source
AI summary
Methods and apparatus are provided to reduce access latency in a random-access channel (RACH) procedure. A user equipment (UE) can transmit multiple Msg1 on multiple RACH transmission occasions before the end of a random-access response (RAR) window. The UE receives one or more RARs in response to the multiple transmitted Msg1. The one or more RARs can be carried in a single RAR window or multiple RAR windows. The UE determines the detected Msg1 based on explicit signals, implicit indications, or both. The explicit signals can be carried in the one or more RARs received by the UE. The implicit indications can be one or more signatures being associated with the multiple RACH transmission occasions. The one or more signatures comprise at least one of physical random-access channel (PRACH) preambles or preamble indices, random-access radio-network temporary identifier (RA-RNTI) values, RAR windows, and control regions for physical downlink control channel (PDCCH).