Multi-Level ACK/NACK Feedback for URLLC Link Adaptation
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Solution Overview
Problem
In wireless communication networks, especially in Ultra-Reliable Low-Latency Communication (URLLC) scenarios, maintaining a low Block Error Rate (BLER) is challenging due to the scarcity of NACK events, which hampers the effectiveness of traditional outer-loop link adaptation methods that rely on NACK/ACK ratios.
Innovation Solution
Implementing a multi-level ACK/NACK mechanism where the UE reports a decoding margin-based ACK or NACK, configured by the radio network node with settings such as target BLER, outer loop target rate, and SINR offset, allowing for earlier capacity adjustment and reducing retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional outer-loop link adaptation methods are used, then they can adjust capacity based on NACK/ACK ratios, but they become ineffective in URLLC scenarios where NACK events are scarce
Solution Approach 1:
The patent introduces multi-level ACK/NACK feedback where the UE reports not only whether decoding succeeded or failed, but also the decoding margin (how much margin was achieved). This enhanced feedback allows the network to perform outer-loop link adaptation based on decoding margin statistics rather than relying solely on NACK/ACK ratios, making it effective even when NACK events are scarce in URLLC scenarios.
Solution Approach 2:
The patent changes the parameter used for link adaptation from binary ACK/NACK status to decoding margin values. By configuring the UE to report decoding margins and using these continuous parameters for capacity adjustment, the system can achieve effective link adaptation in URLLC where traditional binary feedback fails due to lack of NACK events.
2Reliability
If multi-level ACK/NACK is implemented, then decoding margin information can be reported for earlier capacity adjustment, but the feedback message complexity increases
Solution Approach 1:
Instead of using complex multi-bit feedback codes, the patent uses parameter changes - specifically, the UE reports decoding margin as a numerical value (e.g., in dB). This single parameter carries rich information about decoding quality, enabling the network to perform link adaptation without requiring complex feedback encoding schemes.
Solution Approach 2:
The decoding margin acts as an intermediary parameter that bridges the gap between simple ACK/NACK feedback and detailed channel quality information. By introducing this intermediate parameter, the system achieves enhanced link adaptation capability without directly implementing complex feedback mechanisms.
3Productivity
If decoding margin-based feedback is used, then retransmissions can be reduced through earlier capacity adjustment, but the UE processing complexity increases
Solution Approach 1:
The UE performs self-service by internally calculating its own decoding margin based on the received signal quality and decoding performance. The UE autonomously determines whether to report a high or low decoding margin value without external intervention, reducing the need for complex network-controlled feedback mechanisms while still achieving enhanced link adaptation.
Data Source
AI summary
A method performed by a UE for handling communication in a wireless communication network. The method includes receiving, from a radio network node, a configuration data comprising one or more settings used to determine a decoding margin for determining a type of an ACK or NACK message from multi-level ACK or NACK messages. The one or more settings include one or more of: a target BLER, an outer loop target rate, a difference between the target BLER and the outer loop target rate, and a SINR offset. The method also includes transmitting, to the radio network node, the ACK or NACK message of the type for a received transport block, wherein the ACK or NACK message is of the type determined based on the received configuration data.