Uplink Scheduling for NR-U LBT Blocking
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Solution Overview
Problem
In New Radio (NR) unlicensed spectrum operations, there is an issue with uplink transmissions blocking each other due to unknown propagation delays between user equipment (UE) and network nodes, leading to inefficient resource allocation and potential blocking of physical random access channel (PRACH) transmissions by physical uplink control channel (PUCCH) or PUSCH transmissions.
Innovation Solution
Implementing a listen-before-talk (LBT) procedure and configuring multiple starting slots for UL transmissions, where UEs perform UL transmissions based on LBT results and use preambles to indicate transmission durations and cell associations, and applying orthogonal covering codes for multiplexing in PUCCH formats to support efficient UE multiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PUSCH or PUCCH transmission is performed by a UE, then uplink control information can be transmitted, but the transmission may block the PRACH preamble transmission from another UE due to unknown propagation delays
Solution Approach 1:
The network node schedules multiple starting slots for UL transmissions in advance before the actual transmission occurs. This preliminary configuration allows UEs to have pre-defined alternative transmission opportunities, enabling them to switch slots if blocking is detected, thereby preventing PRACH blocking while maintaining uplink efficiency
Solution Approach 2:
The system dynamically selects which starting slot to use for UL transmission based on real-time channel conditions and LBT results. Instead of using a fixed starting slot, the UE can adaptively choose from multiple scheduled slots, making the system flexible enough to avoid blocking PRACH transmissions while maintaining high uplink productivity
2Reliability
If LBT procedure is performed before UL transmission, then channel access can be achieved, but transmission delay increases due to the additional procedure
Solution Approach 1:
The network node schedules multiple starting slots in advance, performing the channel access planning beforehand. This allows the UE to have pre-configured transmission opportunities ready, reducing the need for repeated LBT procedures and minimizing transmission delays while ensuring reliable channel access
Solution Approach 2:
The UE autonomously selects which scheduled starting slot to use based on its own LBT results and channel conditions, without requiring additional network coordination. This self-service approach eliminates unnecessary signaling delays and allows the UE to quickly adapt to channel conditions using the pre-scheduled slots
3Reliability
If multiple starting slots are configured for UL transmission, then blocking of PRACH can be prevented, but resource allocation complexity increases
Solution Approach 1:
The uplink transmission resources are segmented into multiple discrete starting slots, each independently scheduled and controllable. This segmentation allows the system to distribute UEs across different slots, preventing blocking while maintaining manageable complexity through structured resource division rather than complex dynamic allocation
Data Source
AI summary
Various examples and schemes pertaining to uplink (UL) designs for New Radio (NR) unlicensed spectrum (NR-U) operation in mobile communications are described. An apparatus as a user equipment (UE) receives, from a network node, a scheduling of a plurality of starting slots for an UL transmission by the apparatus. The apparatus performs a listen-before-talk (LBT) procedure and, based on a result of the LBT procedure, the apparatus performs the UL transmission with an initial slot of the UL transmission in one of the plurality of starting slots.