Default Spatial Relation for PUCCH Beam Failure Recovery
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Solution Overview
Problem
In 5G networks, during beam failure recovery, the spatial relation configuration for PUCCH and PUSCH becomes invalid, making it difficult for UE to perform transmission without a valid spatial relation, and existing contention-based PRACH methods fail to differentiate beam failure recovery requests from normal access, leading to challenges in channel state information and beam reporting.
Innovation Solution
Implementing a default spatial relation for PUCCH and PUSCH transmissions using CSI-RS or SS/PBCH beams identified during beam failure recovery, and modifying PRACH procedures to include a dedicated resource or RRC message for beam failure recovery requests, allowing the gNB to distinguish between normal and beam failure recovery access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If contention-based PRACH is used for beam failure recovery, then the procedure can be simplified, but the gNB cannot differentiate beam failure recovery requests from normal access
Solution Approach 1:
A dedicated PRACH resource (specific preamble or time-frequency resource) is introduced as an intermediary to indicate beam failure recovery requests. This dedicated resource acts as a mediator between the UE's beam failure recovery need and the gNB's ability to recognize and handle such requests differently from normal random access procedures.
2Reliability
If spatial relation configuration is cleared during beam failure, then the system reflects the beam failure state, but the UE cannot perform PUCCH/PUSCH transmission without valid spatial relation
Solution Approach 1:
The network pre-configures default spatial relations for PUCCH and PUSCH before beam failure occurs. When beam failure is detected and spatial relation is cleared, the UE can immediately use these pre-configured default spatial relations to maintain transmission capability without needing to re-establish spatial relations from scratch, thus ensuring continuous operation during recovery.
3Ease of operation
If default spatial relation is applied for PUCCH/PUSCH, then UE can transmit during recovery, but the transmission may not optimize for the new beam
Solution Approach 1:
The spatial relation configuration is made dynamic, transitioning from the original beam-specific configuration to a default spatial relation during recovery, and then back to an optimized spatial relation after recovery. This dynamic adaptation allows the system to maintain transmission capability during beam failure while preserving the ability to optimize for the new beam once recovery is complete.
Data Source
AI summary
An apparatus of a user equipment (UE) comprises one or more baseband processors to generate a beam failure recovery request to be transmitted to a Fifth Generation (5G) NodeB (gNB) over a physical random access channel (PRACH), to process a response from the gNB, and to generate a physical uplink control channel (PUCCH) transmission to be transmitted to the gNB using a default spatial relation comprising a same spatial filter as used for the beam failure recovery request transmission over the PRACH. A beam failure recovery request is to be transmitted to a gNB after a random access response from the gNB, wherein the beam failure recovery request is to be transmitted via Message 1 or Message 3 to the gNB, and a response is to be received from the gNB via Message 2 or Message 4.