HARQ-ACK Timing in NR-U via LBT Segmentation
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Solution Overview
Problem
The challenge in expanding 5G NR networks to unlicensed spectrum is maintaining fair coexistence with incumbent technologies, particularly in bands like the 5 GHz, where the HARQ feedback mechanism needs to be enhanced to accommodate listen before talk (LBT) procedures, ensuring efficient operation and spectrum utilization.
Innovation Solution
The enhancement of HARQ timing and scheduling procedures in NR systems to allow efficient operation in unlicensed spectrum, including assigning set indices to PDSCHs, determining HARQ-ACKs, and using downlink control information (DCI) to manage HARQ-ACK transmissions and retransmissions based on LBT outcomes, ensuring proper timing and resource allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If NR operates on unlicensed spectrum with LBT procedure, then spectrum availability is expanded, but HARQ feedback timing and reliability are compromised
Solution Approach 1:
The patent divides HARQ feedback into two independent types: Type-1 feedback sent immediately after LBT success (within same COT) and Type-2 feedback sent in subsequent COT. This segmentation allows the system to maintain reliability through multiple feedback opportunities while operating flexibly on unlicensed spectrum, resolving the contradiction between spectrum availability and feedback reliability.
Solution Approach 2:
The patent implements preliminary HARQ feedback transmission (Type-1) immediately after LBT success before the actual data transmission completes. This preliminary action ensures that at least one feedback opportunity is captured, improving reliability while allowing the system to adapt to unlicensed spectrum constraints.
2Loss of time
If HARQ feedback is transmitted immediately in same COT, then latency is reduced, but LBT failure risk increases
Solution Approach 1:
The patent segments the feedback transmission into two stages: immediate feedback (Type-1) within the same COT to minimize latency, and deferred feedback (Type-2) in subsequent COT to ensure delivery. This segmentation resolves the contradiction by providing both low-latency and reliable transmission opportunities.
Solution Approach 2:
The patent implements a feedback mechanism where the access node receives both Type-1 and Type-2 HARQ feedback and uses this information to determine retransmission needs. The feedback loop ensures that even if immediate feedback fails, the system can still achieve reliable communication through the second feedback opportunity.
3Reliability
If multiple HARQ-ACK sets are transmitted, then data reliability is improved, but scheduling complexity increases
Solution Approach 1:
The patent segments HARQ-ACK feedback into distinct sets (Type-1 and Type-2) with different transmission timing and conditions. This segmentation organizes the complexity by creating clear rules for when each set is transmitted, making the scheduling process more manageable while improving reliability through multiple feedback opportunities.
Solution Approach 2:
The patent uses preliminary configuration of feedback timing and conditions before actual transmission occurs. By pre-defining when Type-1 and Type-2 feedback should be sent based on LBT outcomes and COT boundaries, the system reduces real-time scheduling complexity while maintaining high reliability.
Data Source
AI summary
Methods, systems, and computer programs for enhancing HARQ-ACK timing procedure. In one aspect, a method can include encoding, by a next generation NodeB (gNB), one or more sets of physical downlink shared channels (PDSCHs) with respect to a listen before talk (LBT) operation on an unlicensed spectrum, transmitting, by the gNB, the encoded one or more sets of PDSCHs to the UE, and determining, by the gNB, scheduling for receiving a HARQ-ACK from the UE corresponding to the one or more sets of PDSCHs based on the LBT operation.