HARQ-ACK Retransmission Control in Unlicensed NR Bands
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Solution Overview
Problem
In unlicensed bands, the transmission of Hybrid Automatic Repeat Request (HARQ-ACK) in the 5G New Radio (NR) system is unreliable due to interference from Wi-Fi and limitations imposed by Listen Before Talk (LBT), leading to inefficient resource utilization and retransmission failures.
Innovation Solution
A base station and terminal system that includes a transmitter to send control information for HARQ-ACK retransmission requests, using a granularity-based indication bit to manage the number of retransmissions, and a receiver to handle the retransmitted signals, ensuring efficient communication in unlicensed bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HARQ-ACK is transmitted in unlicensed bands, then communication coverage is expanded, but transmission reliability deteriorates due to Wi-Fi interference and LBT limitations
Solution Approach 1:
The base station performs preliminary actions by transmitting control information that indicates the number of HARQ-ACKs to be retransmitted before the actual retransmission occurs. This allows the terminal to prepare and execute retransmission efficiently, improving reliability in the challenging unlicensed band environment while maintaining expanded coverage
2Reliability
If the number of HARQ-ACK retransmissions is increased, then communication reliability is improved, but resource utilization efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts the number of HARQ-ACK retransmissions based on actual transmission conditions. The base station transmits control information indicating the specific number of HARQ-ACKs to be retransmitted, allowing flexible adaptation to channel conditions rather than using fixed retransmission schemes, thus balancing reliability improvement with resource efficiency
Solution Approach 2:
The invention changes the parameter of retransmission quantity from a fixed value to a dynamically indicated value. By transmitting control information that specifies the number of HARQ-ACKs to retransmit, the system can adjust this parameter according to actual transmission success rates and channel conditions, optimizing both reliability and resource utilization
3Productivity
If granular control of HARQ-ACK retransmission is implemented, then resource utilization efficiency is improved, but control information complexity increases
Solution Approach 1:
The control information is segmented into specific fields that indicate the number of HARQ-ACKs to be retransmitted. Rather than complex overall control mechanisms, the invention segments the control information into manageable indicators that can be processed efficiently by both base station and terminal, achieving granular control with minimal complexity increase
Data Source
AI summary
A terminal apparatus includes a receiver and a transmitter. The receiver receives, from a base station, a downlink assignment index (DAI) that is transmitted by means of a downlink control information (DCI) format. The DAI indicates an accumulative number of a transmitted physical downlink shared channel (PDSCH) included in a group of PDSCHs. A range of the accumulative number of which the DAI is indicative is variably configured. The transmitter, in operation, transmits, to the base station, hybrid automatic repeat request acknowledgement (HARQ-ACK) information based on the DAI.