SRS Triggered in RACH Msg2 for Timing Alignment
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Solution Overview
Problem
Current wireless communication systems face challenges in improving coverage and efficiency for random access procedures, particularly in new radio (NR) and LTE technologies, due to issues with sounding reference signal (SRS) transmission triggered by downlink (DL) random access channel (RACH) messages.
Innovation Solution
The proposed solution involves a method for wireless communication where a user equipment (UE) receives a DL RACH message indicating the need to transmit an SRS, and subsequently transmits the SRS and an uplink (UL) RACH message, with the SRS being transmitted either before or after the UL RACH message.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SRS transmission is triggered by DL RACH message in random access procedure, then coverage enhancement is achieved, but device complexity increases due to additional signal transmission and timing coordination requirements
Solution Approach 1:
The network entity triggers SRS transmission in advance within the DL RACH message (Msg2) before the UE transmits the UL RACH message (Msg3). This preliminary action allows the network to obtain uplink channel quality information earlier in the random access procedure, enabling coverage enhancement while maintaining clear timing coordination through explicit triggering.
Solution Approach 2:
The SRS transmission acts as an intermediary signal between the DL RACH message and the UL RACH message. It provides the network with uplink channel sounding information without requiring the UE to transmit the full UL RACH message, thereby enhancing coverage while managing device complexity through a dedicated intermediate signaling step.
2Measurement precision
If SRS is transmitted before UL RACH message, then timing alignment is improved, but loss of time occurs due to additional transmission step
Solution Approach 1:
The SRS is transmitted before the UL RACH message as a preliminary timing alignment step. The network uses the SRS to determine uplink timing advance and provides this information in the UL grant, enabling the UE to transmit the UL RACH message with proper timing alignment. This preliminary action improves measurement precision for timing alignment.
3Productivity
If SRS transmission is indicated in DL RACH message, then resource allocation efficiency is improved, but device complexity increases due to additional monitoring and transmission requirements
Solution Approach 1:
The DL RACH message (Msg2) serves multiple functions: it provides random access response information, uplink grant, and simultaneously triggers SRS transmission. This multi-functionality improves resource allocation efficiency by consolidating multiple control functions into a single message, reducing the need for separate signaling resources.
Solution Approach 2:
The UE automatically transmits the SRS when triggered by the DL RACH message without requiring additional explicit scheduling commands. The UE uses its own resources and capabilities to fulfill the SRS transmission requirement, reducing network overhead and improving resource allocation efficiency while managing device complexity through self-service operation.
Data Source
AI summary
Certain aspects of the present disclosure provide techniques for transmitting sounding reference signals (SRSs) triggered by a downlink (DL) random access channel (RACH) message (e.g., msg2). A method that may be performed by a user equipment (UE) generally includes receiving a DL RACH message that indicates the UE is to transmit an SRS, transmitting the SRS, in accordance with the indication, and transmitting an uplink (UL) RACH message.