Secondary Cell Beam Failure Recovery Through Primary Cell BFR Signaling
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Solution Overview
Problem
In wireless communication networks utilizing the millimeter wave spectrum, beam failures can occur due to factors like UE orientation and environmental obstructions, disrupting communication links between user equipment and secondary cells, necessitating effective beam failure recovery mechanisms.
Innovation Solution
The user equipment initiates a beam failure recovery operation by transmitting a BFR Medium Access Control (MAC) Control Element to the primary cell, utilizing various methods such as dedicated scheduling requests, contention-based random access, and timer/counter-controlled retransmissions to ensure successful beam recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE transmits BFR MAC CE to the primary cell using traditional grant requests, then the beam failure recovery can be initiated, but the recovery process fails when grant requests are unavailable
Solution Approach 1:
The patent introduces the primary cell as an intermediary mediator when the SCell beam fails. Instead of directly recovering the SCell beam, the UE transmits BFR MAC CE through the primary cell, which then coordinates the recovery process. This intermediary approach ensures recovery can proceed even when direct grant requests to the SCell are unavailable.
Solution Approach 2:
The primary cell is given multiple functions: it serves as both the default communication path and the recovery coordination point. The BFR MAC CE transmission mechanism is designed to work universally across different scenarios (available grants, unavailable grants, different cell configurations), making the recovery process adaptable to various network conditions.
2Reliability
If the UE waits for grant requests to transmit BFR MAC CE, then transmission resources are properly allocated, but recovery is delayed when grants are not available
Solution Approach 1:
The UE is configured with pre-established uplink resources and BFR MAC CE templates in advance. When beam failure is detected, the UE can immediately transmit using pre-allocated resources without waiting for dynamic grant requests. This preliminary preparation eliminates the time delay associated with grant acquisition while maintaining proper resource allocation.
Solution Approach 2:
The patent allows the UE to skip the traditional grant request waiting step by using configured uplink resources directly. The BFR MAC CE transmission rushes through the critical recovery phase without the usual scheduling delay, prioritizing rapid recovery over strict resource allocation procedures in time-critical scenarios.
3Reliability
If the UE uses multiple recovery methods (dedicated requests, random access, retransmissions), then recovery success rate increases, but the system complexity increases
Solution Approach 1:
The patent implements a dynamic recovery mechanism where the UE adapts its transmission strategy based on network responses and timing conditions. The system transitions between different recovery approaches (initial transmission, retransmission, alternative methods) based on real-time feedback, optimizing success rates while managing complexity through conditional logic rather than permanent multi-path infrastructure.
Solution Approach 2:
The recovery process incorporates feedback loops where the UE monitors for acknowledgments, timing expiration, and network responses. Based on this feedback, the UE dynamically adjusts its behavior (retransmit BFR MAC CE, try alternative methods, or declare recovery failed). This feedback-driven approach achieves high reliability through iterative refinement rather than complex pre-planned multi-path systems.
Data Source
AI summary
A user equipment (UE) is connected to a wireless network and operates in a carrier aggregation (CA) state that includes a first connection to a primary cell and a second connection to a secondary cell. The UE determines a beam failure has occurred for one of the first connection or the second connection and initiates a beam failure recovery (BFR) operation. The BFR operation includes transmitting, to the primary cell, a BFR Medium Access Control (MAC) Control Element (CE).