Unlicensed 5G Handover LBT for Source and Target Cells
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Solution Overview
Problem
Existing mobility enhancements for unlicensed carriers in 5G networks face challenges such as LBT failures during handovers, leading to service interruptions, latency, and inefficient resource usage due to reestablishing connections.
Innovation Solution
Implementing Listen Before Talk (LBT) procedures during handovers for both source and target cells, allowing UEs to determine channel availability before establishing connections, thereby preventing handovers to potentially failing cells and maintaining uninterrupted service.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If shared radio frequency spectrum access is implemented between LTE and Wi-Fi systems, then spectrum utilization efficiency is improved, but interference between systems increases and reliability deteriorates
Solution Approach 1:
A Wi-Fi spectrum coordinator is introduced as an intermediary entity that manages spectrum access between Wi-Fi and LTE systems. The coordinator receives interference indicators from the eNodeB, determines appropriate backoff periods, and controls Wi-Fi transmission timing to avoid LTE uplink slots, thereby mediating the conflict between shared spectrum access and interference avoidance
Solution Approach 2:
The system implements a feedback mechanism where the eNodeB sends interference indicators to the Wi-Fi spectrum coordinator based on measured interference levels. The coordinator uses this feedback to dynamically adjust Wi-Fi transmission behavior, including setting backoff periods and modifying transmission schedules, creating a closed-loop control system that responds to actual interference conditions
2Productivity
If Wi-Fi transmissions are allowed during LTE uplink slots, then spectrum productivity is improved, but uplink interference increases and connection reliability worsens
Solution Approach 1:
The Wi-Fi spectrum coordinator proactively schedules Wi-Fi transmissions to occur during LTE downlink slots rather than uplink slots, before interference problems occur. By pre-coordinating transmission timing based on LTE TDD patterns, the system prevents uplink interference from Wi-Fi before it can affect LTE communications
Solution Approach 2:
The system dynamically adjusts Wi-Fi transmission schedules based on varying LTE TDD configurations and traffic conditions. The coordinator can modify backoff periods, transmission timing, and spectrum access parameters in real-time to adapt to changing network conditions, making the spectrum sharing arrangement flexible rather than static
3Reliability
If strict interference avoidance is implemented for Wi-Fi transmissions, then LTE uplink reliability is improved, but Wi-Fi spectrum access efficiency deteriorates
Solution Approach 1:
The system applies different transmission quality requirements to different time slots. Wi-Fi transmissions are restricted during LTE uplink slots where interference must be avoided, but are permitted during LTE downlink slots where interference is less critical. This localized application of quality constraints allows Wi-Fi to access spectrum efficiently in appropriate time windows while protecting LTE uplink reliability
Data Source
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AI summary
This disclosure provides systems, methods and apparatuses for a user equipment (UE) performing Listen Before Talk (LBT) procedures during a handover, such as during a dual active protocol stack (DAPS) handover or a conditional handover. During the handover, the UE may have a source connection with a source cell. If the source cell is unlicensed, the UE may perform LBT for a channel of the source cell. The UE may establish a target connection with a target cell before releasing the source connection with the source cell. If the target cell is unlicensed, the UE may perform LBT for a channel of the target cell.