Uplink Control Information Transmission in Unlicensed Spectrum
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Solution Overview
Problem
Current LTE technologies face challenges in transmitting uplink control information via unlicensed spectrum, particularly in scenarios with long backhaul latency or standalone LTE operation, where the unlicensed channel may be busy, leading to limited time for UE to prepare transmissions and potential drops in UCI/PUCCH transmission.
Innovation Solution
The proposed solution involves dynamic allocation of PUCCH resources for HARQ-ACK transmission in unlicensed spectrum, allowing multiple transmission opportunities across multiple UL subframes, with implicit resource allocation and opportunistic transmission strategies to ensure reliable UCI/PUCCH transmission, even after initial LBT-blocked opportunities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If UCI transmission is attempted in unlicensed spectrum with LBT procedure, then spectrum utilization is improved, but transmission reliability deteriorates when channel is busy
Solution Approach 1:
The network node performs LBT procedure in advance before allocating PUCCH resources, and prepares multiple alternative PUCCH resources beforehand. When the initial transmission opportunity is blocked, the UE can immediately switch to pre-configured alternative resources without waiting for new scheduling decisions, thus maintaining transmission reliability while utilizing unlicensed spectrum.
Solution Approach 2:
The system dynamically changes PUCCH resource parameters (time, frequency, resource block allocation) based on LBT outcomes. Multiple PUCCH resources with different temporal and spectral characteristics are allocated, allowing the system to adapt to channel conditions and find available transmission opportunities, thereby resolving the conflict between spectrum utilization and transmission reliability.
2Reliability
If multiple transmission opportunities are provided for HARQ-ACK, then transmission reliability is improved, but resource allocation complexity increases
Solution Approach 1:
The PUCCH resources are segmented into multiple distinct allocations across different time slots and frequency resources. Each segment corresponds to a specific transmission opportunity with clearly defined resource characteristics. This segmentation allows the network to provide multiple transmission opportunities while maintaining organized, manageable resource allocation structures that reduce overall system complexity.
Solution Approach 2:
The PUCCH resource allocation is made dynamic through implicit indexing mechanisms where the specific resource used is determined by the scheduling decision rather than being statically fixed. This dynamic approach allows flexible adaptation to channel conditions and traffic patterns while simplifying the allocation process through rule-based resource selection rather than complex manual configuration.
3Reliability
If PUCCH resources are guaranteed in multiple UL subframes, then UCI transmission reliability is improved, but time resources are consumed
Solution Approach 1:
PUCCH transmission opportunities are arranged periodically across multiple UL subframes with regular intervals. This periodic structure provides guaranteed transmission opportunities at predictable time points, allowing the system to maintain reliability while efficiently utilizing time resources. The periodic pattern enables better time resource management compared to ad-hoc allocation, reducing overall time consumption.
Solution Approach 2:
The system allows the UE to skip blocked transmission opportunities and rush to the next available PUCCH resource without waiting for re-scheduling. When LBT blocks an initial transmission opportunity, the UE can immediately proceed to alternative pre-configured resources in subsequent subframes, reducing the time loss by eliminating idle waiting periods and maintaining continuous transmission flow.
Data Source
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AI summary
Systems, methods, apparatuses, and computer program products for the transmission of uplink (UL) control information via unlicensed spectrum are provided. One method includes dynamically allocating, by a network node, control channel resources for transmitting of uplink control information (UCI). The method may also include scheduling a user equipment with multiple transmission opportunities for each hybrid automatic repeat request (HARQ) acknowledgement/non-acknowledgement (A/N) on the control channel in multiple uplink subframes.