Two-Level PUCCH HARQ Feedback for NR Multicast Users
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Solution Overview
Problem
Conventional approaches to multicast/broadcast systems in wireless communication face high signaling overhead and resource inefficiency due to numerous HARQ ACK/NACK feedback messages from multiple user equipment (UEs), especially when a large number of UEs are consuming the service, as they either lack feedback-triggered retransmissions or allocate dedicated physical uplink control channels (PUCCH) for each UE.
Innovation Solution
Implementing a two-level HARQ feedback mechanism using two distinct PUCCHs: a compact PUCCH #1 for periodic aggregate ACK/NACK feedback and a second PUCCH #2 for detailed feedback on demand, where PUCCH #2 is allocated only when necessary, reducing overhead and increasing resource efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dedicated PUCCH resources are allocated for each UE to transmit HARQ feedback, then feedback reliability is improved, but signaling overhead and resource consumption increase significantly
Solution Approach 1:
The feedback mechanism is segmented into two levels: a first PUCCH for transmitting aggregate ACK/NACK indicators and a second PUCCH for transmitting detailed per-packet feedback. This segmentation allows the system to reduce overall signaling overhead by using the compact first PUCCH for routine acknowledgments while reserving the second PUCCH for cases where detailed feedback is actually needed, thus resolving the contradiction between reliability and overhead.
Solution Approach 2:
The allocation of PUCCH resources is made dynamic rather than static. UEs are configured with both a first PUCCH (always available) and a second PUCCH (allocated on-demand). The gNB dynamically decides whether to allocate the second PUCCH based on whether detailed feedback is required. This dynamic approach allows the system to maintain reliability when needed while minimizing overhead during normal operation.
2Ease of operation
If dedicated PUCCH resources are allocated for each UE, then feedback transmission capability is improved, but resource efficiency deteriorates when many UEs are served
Solution Approach 1:
The first PUCCH serves as a universal resource that all UEs can use to transmit their HARQ feedback. This universal channel handles the majority of feedback transmissions efficiently. The second PUCCH serves as a supplementary resource allocated only when specific UEs need detailed feedback capability. This multi-functionality approach allows the system to maintain good feedback transmission capability while improving overall resource efficiency by avoiding dedicated resources for all UEs.
3Measurement precision
If comprehensive HARQ feedback is transmitted for all packets, then retransmission accuracy is improved, but signaling overhead increases
Solution Approach 1:
Instead of always transmitting complete per-packet HARQ feedback, the system uses partial action by transmitting only aggregate ACK/NACK information on the first PUCCH when detailed feedback is not needed. The second PUCCH is activated only when partial feedback is insufficient and comprehensive feedback is required for accurate retransmission. This approach achieves the right balance between retransmission accuracy and signaling overhead by applying the appropriate level of feedback detail in each situation.
Data Source
AI summary
Techniques of transmitting and receiving HARQ feedback for point to multipoint data packets include using two different PUCCHs for providing ACK/NACK feedback to a sequence of point-to-multipoint (PTM) data packets. For example, when a gNB sends PTM data packets (e.g., as part of a subscription) to subscriber UE's, each UE sends ACK/NACK messages in response over a first PUCCH which has a smaller bandwidth than a conventional PUCCH under which full uplink control information (UCI) may be sent. In some implementations, the ACK/NACK messages are a single bit. In response to a NACK message from a UE, the gNB allocates a second PUCCH to the UE. The UE then send additional details to explain the NACK message. In some implementations, the additional details include an identifier of a missing data (e.g., packet m of n).