SRS Triggered by RACH Msg 2 for QCL Beam Refinement
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Solution Overview
Problem
In wireless communication systems, particularly at high carrier frequencies, the random access channel (RACH) procedure faces challenges due to high path loss, leading to suboptimal beamforming between user equipment (UE) and base stations, which hinders effective coverage and connection establishment.
Innovation Solution
The implementation of sounding reference signals (SRS) triggered by RACH message 2, allowing multiple SRS transmissions with different beams to refine both UE and base station beams, enabling the selection of the best beam and improving coverage by providing quasi co-location information for downlink signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high carrier frequencies are utilized, then bandwidth and data rate are improved, but path loss increases and coverage deteriorates
Solution Approach 1:
The patent segments the beamforming process into multiple stages: initial broad beam transmission for coverage, followed by SRS-triggered beam refinement using narrower beams. This segmentation allows the system to first ensure coverage at high frequencies, then progressively refine beam direction to maintain both coverage and data rate.
Solution Approach 2:
The patent implements preliminary beam refinement actions before actual data transmission. The SRS-triggered beam refinement procedure performs preliminary beam direction optimization using narrower beams, establishing optimal beamforming parameters in advance to overcome path loss before high-rate data transmission begins.
2Reliability
If beamforming is established during RACH procedure, then coverage is improved, but the RACH procedure complexity increases
Solution Approach 1:
The patent merges the beam refinement function into the existing RACH procedure by triggering SRS transmissions during the RACH message exchange. This combining approach integrates coverage improvement mechanisms into the standard access procedure without requiring separate beam training phases, thus improving coverage while limiting complexity increase.
Solution Approach 2:
The patent implements self-service beam refinement where the UE autonomously performs SRS transmissions triggered by RACH messages to enable its own beam direction optimization. The UE uses its own sounding reference signals to facilitate beam refinement, reducing the need for complex base station-controlled beam training procedures.
3Measurement precision
If multiple SRS transmissions with different beams are used, then beam refinement precision is improved, but signaling overhead increases
Solution Approach 1:
The patent applies partial action by transmitting multiple SRS signals only when beam refinement is needed during the RACH procedure, rather than continuously. The SRS-triggered mechanism activates multiple beam transmissions selectively based on RACH message reception, achieving precise beam refinement while limiting signaling overhead to only when necessary for coverage improvement.
Data Source
AI summary
Apparatus, methods, and computer-readable media for sounding reference signals (SRSs) triggered by random access channel (RACH) message 2 for RACH message 4 physical downlink shared channel quasi co-location (QCL) are disclosed herein. A user equipment (UE) may transmit, to a base station via a transmit beam over a random access channel, a random access preamble and receive a random access response based on the random access preamble. The UE may transmit, to the base station via a plurality of transmit sub-beams, a plurality of SRS transmissions triggered by the random access response. The UE can receive, from the base station, a downlink control signal that includes an SRS resource indicator (SRI) that indicates a selected transmit sub-beam for a corresponding SRS transmission. The UE can use the SRI as QCL information for improved reception of downlink signaling with a refined receive sub-beam corresponding to the selected transmit sub-beam.