LBT Failure Indication via DMRS for 5G NR Latency Reduction
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Solution Overview
Problem
In wireless communication systems, particularly in 5G NR, listen before talk (LBT) failures lead to significant delays and uncertainty in channel access, especially on unlicensed spectrum, as the gNB cannot determine if a UE missed an UL grant or if LBT blocked the transmission, affecting latency-sensitive CG-PUSCH operations.
Innovation Solution
A method where a UE transmits an indication of LBT failure on the physical uplink shared channel (PUSCH) resources, using a demodulation reference signal (DMRS) and/or UL-SCH resource elements, allowing the gNB to reschedule transmissions and reduce latency by distinguishing between missed grants and LBT failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT is performed before UL transmission on unlicensed spectrum, then channel access compliance is achieved, but transmission latency increases due to LBT failures
Solution Approach 1:
The patent implements a feedback mechanism where the UE transmits an LBT failure indication to the gNB when LBT fails. This feedback allows the network to recognize the LBT failure state and trigger appropriate rescheduling actions, transforming the silent failure into an actionable signal that enables timely recovery and reduces overall latency.
Solution Approach 2:
The patent performs preliminary LBT before the scheduled UL transmission to proactively detect channel availability. By conducting the LBT check in advance and preparing the LBT failure indication transmission, the system prevents wasted transmission attempts and enables faster response when channel access fails, thereby reducing overall latency.
2Loss of information
If LBT failure indication is transmitted using DMRS and UL-SCH resource elements, then scheduling uncertainty is reduced, but signal processing complexity increases
Solution Approach 1:
The patent makes the existing DMRS and UL-SCH resources multi-functional by enabling them to carry both normal data transmissions and LBT failure indications. This eliminates the need for separate dedicated resources for LBT failure signaling, reducing overall system complexity while maintaining clear indication capability through appropriate resource element patterns that the gNB can detect.
Data Source
AI summary
Systems, methods, apparatuses, and computer program products for handling a listen before talk (LBT) failure are provided. One method may include performing, by a user equipment, listen before talk (LBT). When the listen before talk (LBT) is successful, the method may include transmitting an intended transmission subsequent to the listen before talk (LBT). When the listen before talk (LBT) is not successful, the method may include transmitting an indication of listen before talk (LBT) failure by transmitting a portion of the intended transmission subsequent to the listen before talk (LBT).