Conditional HARQ Acknowledgement for NTN Stalling Reduction
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Solution Overview
Problem
In 5G wireless systems, particularly in non-terrestrial networks (NTN), the poor link budget and long round-trip time (RTT) lead to stalling issues due to the need for repeated transmissions and limited HARQ processes, resulting in reduced efficiency, increased power consumption, and lower throughput for IoT devices.
Innovation Solution
Implementing conditional HARQ acknowledgement, where the user equipment (UE) estimates the quantity of remaining repetitions needed for successful reception and sends a conditional feedback to the network, allowing the network to adjust transmissions and assume successful decoding, thereby reducing stalling and conserving resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If repeated transmissions are used to ensure reliable reception in NTN, then reliability is improved, but stalling occurs due to long RTT and limited HARQ processes
Solution Approach 1:
The network performs preliminary action by transmitting a plurality of repetitions of the transport block before receiving any acknowledgement from the UE. The network schedules and transmits all required repetitions in advance based on the estimated channel conditions and UE capability, rather than waiting for feedback after each transmission attempt. This eliminates the stalling problem caused by long RTT in NTN while ensuring reliable reception through multiple pre-scheduled repetitions.
2Reliability
If the network waits for explicit acknowledgments before transmitting next transport block, then reliability is improved, but throughput is reduced due to stalling
Solution Approach 1:
The invention extracts the acknowledgement feedback mechanism from the transmission control loop in NTN scenarios. Instead of requiring explicit ACK/NACK feedback before transmitting the next transport block, the network independently determines transmission reliability based on pre-configured repetition counts and channel conditions. This removes the feedback waiting step that causes stalling and reduces throughput, while maintaining reliability through the pre-scheduled multiple repetitions.
3Productivity
If multiple HARQ processes are used to reduce stalling, then productivity is improved, but device complexity and power consumption increase
Solution Approach 1:
The invention makes the repetition transmission mechanism universal by designing it to work effectively with a single HARQ process. The network configures the UE with a predetermined number of repetitions for each transport block, and the UE processes all repetitions within the same HARQ process context. This eliminates the need for multiple parallel HARQ processes while achieving the same throughput improvement, thereby reducing device complexity and power consumption.
Data Source
AI summary
Systems, methods, apparatuses, and computer program products for conditional hybrid automatic repeat request (HARQ) acknowledgement (ACK). For instance, a user equipment (UE) may estimate, during reception of a downlink transmission with x repetitions, an amount of extra energy that may be needed to help ensure successful decoding. The UE may then express this estimate as a quantity of repetitions (y) needed for successful reception, and may inform the radio access network (RAN) of this quantity (e.g., at least one round-trip time (RTT) before the last repetition of the x repetitions is sent). The RAN may handle this message as a conditional positive ACK. The RAN may send the quantity of repetitions y, and may implicitly assume an ACK for that TBS after sending the y repetitions. The RAN may send the next transport blocks (TBS) for that HARQ process after completing transmission of they repetitions.