HARQ ACK Feedback Time Window for Sidelink LBT Latency
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Solution Overview
Problem
In sidelink communications over unlicensed spectrum, the transmission and reception of HARQ ACK feedback are hindered by the Listen-Before-Talk (LBT) procedure, leading to potential resource waste and latency due to the uncertainty of HARQ ACK feedback via the Physical Sidelink Feedback Channel (PSFCH).
Innovation Solution
A scheme where a first device determines a time window for a second device to transmit HARQ ACK feedback, allowing the second device to transmit within this window on the PSFCH, PSCCH, or PSSCH, thereby providing an additional opportunity for feedback transmission and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ ACK feedback is transmitted via the Physical Sidelink Feedback Channel (PSFCH) at a predetermined occasion, then the feedback mechanism is simple and standardized, but the transmission is blocked by LBT procedure causing uncertainty and potential resource waste
Solution Approach 1:
The patent segments the feedback transmission opportunity into multiple possibilities: the original PSFCH predetermined occasion and additional time window opportunities. This segmentation allows the receiving device to attempt feedback transmission at multiple different times, increasing reliability while managing latency through structured time-based attempts.
Solution Approach 2:
The patent introduces dynamic feedback transmission opportunities where the time window for HARQ ACK feedback is determined based on actual transmission conditions. The first device dynamically determines whether to provide additional feedback opportunities based on the second device's transmission characteristics, making the system adaptable rather than fixed.
2Productivity
If the transmitting device performs LBT operation prior to transmission, then spectrum access fairness is ensured, but the HARQ ACK feedback transmission is blocked causing resource waste
Solution Approach 1:
The patent applies preliminary action by having the first device determine and signal the time window for HARQ ACK feedback transmission before the actual feedback is needed. This advance preparation allows the second device to prepare its feedback transmission, and the first device to monitor for the feedback in the predetermined time window, reducing wasted energy from blocked transmissions.
Solution Approach 2:
The patent implements a feedback mechanism where the first device monitors for HARQ ACK feedback from the second device within the determined time window. This feedback loop allows the system to adapt to transmission conditions and ensure that energy is not wasted on feedback attempts that are likely to be blocked by LBT.
3Reliability
If a time window is determined and signaled for HARQ ACK feedback transmission, then feedback reliability is improved through additional transmission opportunities, but device complexity increases
Solution Approach 1:
The patent makes the time window determination mechanism universal by having the first device use the same determination logic for all second devices, based on transmission parameters such as modulation and coding scheme. This multi-functional approach allows the system to handle different feedback scenarios through a single standardized process, reducing actual implementation complexity.
Solution Approach 2:
The patent changes parameters such as the size and positioning of the time window based on transmission conditions like modulation and coding scheme. This parameter adaptation allows the system to optimize feedback reliability for different transmission scenarios without requiring complex device architecture, as the same basic mechanism adapts to different conditions through parameter adjustment.
Data Source
AI summary
Example embodiments of the present disclosure relate to devices, methods, apparatuses and computer readable stor-age media for hybrid automatic repeat request acknowledgement (HARQ ACK) feedback for sidelink communications. In example embodiments, a first device determines a time window to be used by a second device to transmit HARQ ACK feedback for sidelink transmission from the first device to the second device. Then, the first device transmits an indication of the time window to the second device. Further, the first device monitors the HARQ ACK feedback from the second device within the time window.