Common NACK for Grant-Free Uplink Reliability
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Solution Overview
Problem
In 5G communication networks, especially for URLLC, existing feedback mechanisms face challenges in achieving extremely high reliability and low latency due to the inability to identify unsuccessful uplink transmissions using configured grant resources, leading to decreased reliability and increased latency when ACK signaling is used for all successful receptions.
Innovation Solution
Introducing a broadcasted common NACK message that indicates an uplink resource used for unsuccessful data packet transmission, allowing UEs to retransmit without explicit ACK signaling, thereby reducing overhead and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ACK based feedback is used for all successful receptions, then reliability is improved, but overhead and latency increase
Solution Approach 1:
The patent extracts the feedback mechanism from a universal ACK-based approach and implements a selective feedback approach where only NACK messages are sent when needed. This removes unnecessary ACK overhead while maintaining reliability through targeted NACK feedback for unsuccessful transmissions.
Solution Approach 2:
Instead of the conventional approach where ACK is sent for successful reception and NACK for unsuccessful reception, the patent inverts this by using only NACK for unsuccessful transmissions and silence for successful ones. This inversion reduces feedback overhead while maintaining the reliability needed for URLLC.
2Reliability
If individual NACK feedback is provided for each UE, then reliability is improved, but device complexity and signaling overhead increase
Solution Approach 1:
The patent merges individual NACK feedback messages into a single common NACK message that can be broadcast to multiple UEs simultaneously. This combining approach maintains the reliability of individual feedback while reducing the overall complexity and signaling overhead by handling multiple UEs in one message.
Solution Approach 2:
The common NACK message serves multiple functions: it provides feedback to multiple UEs simultaneously, indicates resource usage status, and triggers appropriate retransmission behavior. This multi-functionality reduces the need for separate feedback mechanisms for each UE, thereby reducing overall system complexity.
3Loss of time
If grant-free access is implemented, then latency is reduced, but reliability decreases due to inability to identify unsuccessful transmissions
Solution Approach 1:
The patent introduces a feedback mechanism specifically tailored for grant-free access where the gNB monitors uplink resources and sends common NACK messages when transmissions are unsuccessful. This feedback enables UEs to identify and retransmit failed packets, thereby improving reliability while maintaining the low latency benefits of grant-free access.
Solution Approach 2:
The system enables UEs to self-identify their transmissions through DMRS sequences and autonomously determine whether retransmission is needed based on the presence or absence of NACK messages. This self-service approach maintains the autonomy and low latency of grant-free access while adding the reliability feedback mechanism.
Data Source
AI summary
There is presented a method for operating a user equipment, UE (300) in a wireless communication network (10). The method comprises receiving (302) a message indicating an uplink radio resource, the uplink resource having occurred before receiving the message. The method further comprises transmitting (304) a second representation of a data packet based on determining that the indicated uplink radio resource has been used by the UE for transmitting a first representation of the data packet, prior to receiving the message. Additionally, a method for operating a network node (200) in a wireless communication network (10) is disclosed, the method comprises detecting (202) a signal on an uplink resource configured for grant free access and transmitting (204) a non-UE specific message based on the signal not being successfully received and wherein the non-UE specific message comprises information indicating the uplink resource configured for grant free access. Corresponding network node and user equipment are also presented.