Optimized Asymmetric Feedback Detection for Rate-adaptive HARQ with Unreliable Feedback

This work considers downlink incremental redundancy Hybrid Automatic Repeat Request (IR-HARQ) over unreliable feedback channels. Since the impact of positive feedback (i.e., ACK) error is smaller than that of negative feedback (i.e., NACK) error, an asymmetric feedback detection scheme is proposed to protect NACK and further reduce the outage probability. We formulate the HARQ process as a Markov Decision Process (MDP) model to adapt to the transmission rate of each transmission attempt without enriched feedback and additional feedback cost. We aim to optimize the performance of HARQ process under certain outage probability requirements by finding optimal asymmetric detection thresholds. Numerical results obtained on the downlink Rayleigh fading channel and 5G new radio (NR) PUCCH feedback channel show that by applying asymmetric feedback detection and adaptive rate allocation, higher throughput can be achieved under outage probability limitations.Comment: arXiv admin note: text overlap with arXiv:2305.0294

Performance Analysis of Early-HARQ for Finite Block-Length Packet Transmission

Traditional retransmission protocols require the receiver to decode the entire packet before sending feedback signals, which may not be a viable solution for ultra-reliable and low-latency communications (URLLC) as it may cause a significant delay. To address this issue, early hybrid automatic repeat request (E-HARQ) has been proposed as an alternative to reduce the processing time at the receiver and send the feedback signal as quickly as possible. In this work, we present a framework for analyzing the performance of ARQ protocols considering URLLC requirements for finite block-length packet transmission and use it to evaluate the performance of E-HARQ from an information theory perspective, comparing it to simple ARQ. The results show that this new class of retransmission protocols can significantly improve the performance of URLLC systems

Asymmetric ACK/NACK Detection for Ultra-Reliable Low-Latency Communications

The fifth generation wireless systems are expected to encounter new services in order to provide connectivity for a wide range of applications. One of the considered services is ultra-reliable low-latency communications (URLLC), which has stringent requirements on availability, reliability, and latency. The communication efficiency of URLLC can be improved by employing error control protocols, such as automatic repeat request (ARQ) and hybrid ARQ (HARQ). However, this requires a reliable feedback channel to carry acknowledgement (ACK) and negative ACK (NACK) signals. Improving the detection reliability of ACK and NACK signals simultaneously entails allocating more resources for the feedback channel. Instead, we propose employing an asymmetric signal detection to provide a better protection for NACK signals compared to the ACK signals, without assigning more resources to the feedback channel. The simulation results show that the asymmetric signal detection can achieve a better resource utilization for URLLC.Peer reviewe