Sidelink HARQ Feedback Reservation in Unlicensed Spectrum
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Solution Overview
Problem
Current cellular V2X communication designs face challenges in deploying sidelink HARQ feedback transmissions in unlicensed spectrum due to regulatory requirements like listen-before-talk (LBT) and channel availability, especially in groupcast communication scenarios, where feedback transmission is subject to channel sensing and may not be immediate.
Innovation Solution
A mechanism is introduced where a transmitter UE performs channel sensing to determine resource availability for HARQ feedback and sends a reservation signal to reserve the resource, allowing receiver UEs to transmit acknowledgment feedback only if the channel is clear, adhering to LBT regulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmitter UE transmits data in unlicensed spectrum, then sidelink communication is enabled, but the receiver UE cannot immediately transmit acknowledgment feedback due to LBT requirements and channel sensing
Solution Approach 1:
The transmitter UE performs channel sensing and transmits a reservation signal in advance to secure the feedback resource before the receiver UE needs to transmit. This preliminary action ensures the channel is reserved for feedback transmission, eliminating the need for the receiver to perform LBT at feedback time and reducing feedback delay while maintaining reliability
Solution Approach 2:
A reservation signal is introduced as an intermediary mechanism between data transmission and acknowledgment feedback. This reservation signal acts as a mediator that secures the channel resource in advance, allowing the feedback transmission to proceed without LBT delays while ensuring the channel is available when needed
2Adaptability or versatility
If the receiver UE performs LBT before transmitting acknowledgment feedback, then regulatory compliance is achieved, but feedback transmission efficiency is reduced
Solution Approach 1:
The transmitter UE performs the LBT-equivalent channel sensing and reservation action in advance by transmitting a reservation signal. This preliminary action pre-secures the channel for feedback, so the receiver UE does not need to perform LBT before feedback transmission, thereby maintaining regulatory compliance while improving feedback efficiency
Solution Approach 2:
The transmitter UE serves the dual purpose of both data transmission and feedback channel reservation. By including a reservation signal in its transmission, the transmitter self-services the feedback channel allocation, eliminating the need for the receiver to independently perform LBT and improving overall system efficiency
Data Source
AI summary
Certain aspects of the present disclosure provide a method for wireless communications by a transmitter UE. The method generally includes transmitting data to at least one receiver UE in an unlicensed spectrum used for sidelink communication, determining if a resource in a slot is available for the at least one receiver UE to provide acknowledgment feedback for the data transmission, and transmitting a reservation signal in the slot if the resource is determined to be available.