Base Station LBT Failure Reporting for 5G Unlicensed Spectrum
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Solution Overview
Problem
In next-generation mobile communication systems, there is a challenge in distinguishing between service shadow areas and areas where the synchronization signal block (SSB) is not broadcast due to Listen-Before-Talk (LBT) failures, which complicates the optimization of service areas during minimization of drive tests (MDT) operations.
Innovation Solution
A method where a terminal performs listen-before-talk (LBT) for uplink transmission, detects LBT failures, and if the number exceeds a preconfigured threshold, it determines a radio link failure (RLF), reporting this to the base station, which then distinguishes between coverage holes and SSB transmission failures by reporting to a TCE server that the SSB has not been broadcast due to an LBT failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LBT procedures are implemented to share unlicensed frequency bands, then spectrum utilization efficiency is improved, but difficulty of detecting and measuring service availability deteriorates
Solution Approach 1:
The base station feeds back LBT failure information to the terminal through dedicated signaling (e.g., RRC messages). This feedback mechanism allows the terminal to distinguish between coverage holes and LBT-induced SSB transmission failures, resolving the measurement difficulty caused by LBT procedures
Solution Approach 2:
The base station acts as an intermediary that translates the internal LBT state into observable indicators for the terminal. By reporting LBT failure status, the base station mediates between the hidden channel access state and the terminal's service availability detection needs
2Measurement precision
If LBT failure reporting is implemented, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The failure detection is segmented into distinct types: coverage holes and LBT failures. By separating these failure modes and providing specific indicators for each, the system achieves precise measurement without requiring complex overall system changes
Solution Approach 2:
The system changes the parameter of failure indication by introducing specific cause values (e.g., 'lbtFailure') in RRC messages. This parameter-based differentiation enables precise measurement while maintaining standard message structures, avoiding excessive complexity
Data Source
AI summary
The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. Disclosed are a method and a device for a terminal to indicate whether LBT has failed or not and declare a detected LBT failure, in report mechanisms such as RLF, SCG failure, establishment failure, and MDT.