NR-U Handover Management Using Inactivity Indicators
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Solution Overview
Problem
Handovers in New Radio-Unlicensed Standalone (NR-U SA) communication systems face challenges due to the lack of a reliable channel for control signaling in unlicensed frequency bands, leading to difficulties in determining whether signaling failures are caused by radio link issues or temporary channel occupancy, especially under mobility conditions.
Innovation Solution
Implementing handover procedures that include conditional handover commands with inactivity indicators, where the UE device transitions to an Inactive State upon handover failure due to an occupied unlicensed channel, allowing for quick reconnection when the channel becomes available, and using listen-before-talk (LBT) procedures to manage channel occupancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If handover procedures are implemented in NR-U SA systems using unlicensed frequency bands, then mobility management capability is improved, but handover failure rate increases due to channel occupancy by other systems
Solution Approach 1:
The patent implements conditional handover (CHO) where the UE is pre-configured with multiple potential target cells and their corresponding handover commands before actual handover is needed. When the serving cell experiences downlink failures, the UE can immediately execute the pre-prepared handover command to a suitable target cell without waiting for new command generation, thereby reducing handover failure rate while maintaining mobility management capability
Solution Approach 2:
The patent introduces a mechanism where the network pre-allocates and configures alternative target cells and backup handover commands in advance. This creates a cushion or safety buffer that prevents handover failures when unlicensed channels are occupied, as the UE has predetermined fallback options ready to execute immediately when failures occur
2Device complexity
If the UE transitions to IDLE state upon handover failure, then resource cleanup is simplified, but service reestablishment time increases
Solution Approach 1:
The patent pre-configures the UE with multiple potential target cells and their handover commands before handover failure occurs. This preliminary preparation allows the UE to quickly switch to a pre-identified suitable target cell using the pre-configured command, significantly reducing the time needed for service reestablishment compared to transitioning to IDLE and starting over
Solution Approach 2:
The patent introduces an intermediate state between connected and idle states. Instead of immediately transitioning to IDLE upon handover failure, the UE enters an intermediate state where it can rapidly select and execute handover to a pre-configured target cell. This intermediary mechanism bridges the gap between maintaining connection and allowing quick reconnection, reducing service interruption time
3Quantity of substance
If control signaling is performed over unlicensed bands in NR-U SA, then licensed band resources are freed, but signaling reliability deteriorates due to listen-before-talk requirements
Solution Approach 1:
The patent implements conditional handover where handover commands are pre-configured and prepared in advance while the channel conditions are still favorable. This preliminary action allows the handover execution to occur quickly when needed, reducing the impact of LBT delays and improving control signaling reliability even though signaling occurs over unlicensed bands
Solution Approach 2:
The patent introduces dynamic adaptation mechanisms where the UE can select from multiple pre-configured target cells based on real-time channel conditions. This dynamic selection capability allows the system to adapt to changing unlicensed band availability, maintaining signaling reliability by choosing the best available target when LBT succeeds, while still freeing licensed band resources
Data Source
AI summary
Handovers in a New Radio-Unlicensed Standalone (NR-U SA) communication system are managed by invoking one of a plurality of handover procedures based on conditions related to the communication device and channel status. One example of one of the plurality of handover procedures includes sending a handover command with an inactivity indicator to the UE device where the UE device transitions to an Inactive State (such as RRC_INACTIVE) in response to a handover failure (HOF) resulting from an occupied unlicensed channel. The UE device provides the I-RNTI allocated by the last serving gNB when resuming from the RRC_INACTIVE to the active state; thereby reducing the latency associated with a new connection from the idle mode. The target gNB uses the I-RNTI to retrieve the UE context from the last serving gNB.